Brain stimulation and species-typical behaviour: Activities evoked by electrical stimulation of the brains of chickens (Gallus gallus)

Anita.Behav.,1971,19, 757-779 BRAIN

STIMULATION

ACTIVITIES

EVOKED

BRAINS

AND

SPECIES-TYPICAL

BY ELECTRICAL

OF CHICKENS

BEHAVIOUR:

STIMULATION

OF THE

(GALLUS GALLUS)

BY RICHARD E. PHILLIPS & ORLAN M. Y O U N G R E N

University of Minnesota, Department of Animal Science, St Paul, Minnesota 55101 Abstract. Responses to electrical stimulation of 1500 brain loci in eighty-seven birds were analysed for: types of motor patterns elicited, ability of single loci to evoke more than one pattern, dependence of evoked responses on external stimuli, and anatomical location of points yielding various motor patterns. Frequencies of occurrence of motor responses are tabulated and the points plotted on drawings of frontal sections. Frequencies of joint occurrence of two patterns at the same site are analysed. The archistriatum and its efferent tract were frequent sites for several components of agonistic behaviour. Complex sequences other than fighting and threat were not elicited, but many elements of such sequences were readily elicited. These were markedly influenced by external cues. The apparent stereotypy of species-typical behaviour in animals suggests that the behaviour may be organized by the connectivity and dynamic properties of brain circuits that are common to all members of a species. The pioneering work of W. R. Hess (1954) suggested a means to explore this idea. A huge literature on electrical stimulation of the brain (ESB) indicates that a variety of activities such as eating, drinking, fighting, escape and mating can be elicited, and that their activation is accompanied by motivational effects (Roberts & Kiess 1964; Roberts & Carey 1965; Roberts, Steinberg & Means 1967; Doty 1969). Roberts et al. (1967) especially, used the technique to provide evidence that complex behaviours are 'represented' in the brains of mammals by hierarchical 'centres' in which complete sequences are more probable near the centre of the distribution (of points that elicit elements of the behaviour) and isolated elements more common nearer the outer limits of the distribution. They draw the parallel between their findings and the hierarchical scheme of behaviour proposed by Tinbergen (1951). Von Holst & yon Saint Paul modified Hess's techniques and used movable electrodes to study behaviour evoked by electrical stimulation of the brains of chickens. They reported (Holtst & St Paul 1963) spectacular ability to evoke all kinds of natural behaviours including appropriate vocalizations, but they reported no information on anatomical localization and presented only 'typical' results. More recently Akerman et al. (1960) and Akerman (1966a, b) elicited feeding, fighting, escape and courtship

with brain stimulation in pigeons; Harwood & Vowles (1966) produced feeding in doves (Streptopelia risoria), and Goodman & Brown (1966) found both positive and negative reinforcing effects from some sites in pigeons (Columba livia) and also presented localization data for several classes of evoked behaviour. Putkonen (1966a, b; 1967) concentrated primarily on behaviour evoked from the archistriatum of chickens: he reported mostly simple motor patterns such as myosis and feather movements; he did evoke more complex fighting and escape sequences, but these were variable in detail and most responses were much less complex. Putkonen, and Goodman & Brown are the only authors to show negative as well as positive points, very useful data for comparison. The present series of experiments was begun in 1964 to replicate the work of Hoist and St Paul and to extend their results by localization of the active sites. One of the aims of this report is to present sufficient behavioural-anatomical evidence to enable other investigators to concentrate on specific problems without having to make the extensive search for active areas that we faced. A preliminary report was given by Phillips (1965), and Maley (1969) reported some of the results of similar studies carried out in this laboratory on mallard ducks. The present paper ~s the first extensive report of our results with chickens. In addition to the results reported in detail here, we have stimulated 440 pre-optie and anterior hypothalamic sites in both cocks and hens (Phillips, in preparation) and approxim757

758

ANIMAL

BEHAVIOUR,

ately 800 sites in mallard ducks of both sexes (Maley 1969; Phillips, in preparation).

Methods Birds For the early experiments, any birds that came to hand were used. After the first year, however, we used only F1 crosses between two inbred lines of Red Plymouth Rocks (maintained as part o f Dr R. N. Shoffner's genetics research) between the ages of 6 to 12 months. This minimized individual variation in skull and brain dimensions. The breed was chosen because the birds were docile and easy to handle.

Electrodes and Implantation Our electrode connectors have been o f two types: one, modelled after those of Hoist with four movable electrodes, and the other with fixed electrodes composed of small groups of permanently implanted wires. Most of our work has been with the latter. They are made of 0.13-mm nichrome or stainless steel wire that is insulated with enamel except for the tips which are scraped bare for 0.25 to 0.5 mm. Two to five of these cemented together with successive tips spaced 0.5 to 1.0 mm apart vertically, were stereotaxically implanted (Kopf stereotaxic instrument with bird head-holder) under sodium pentobarbital anaesthesia. Stereotaxic co-ordinates from the brain atlas of Tienhoven & Juhasz (1962) were modified for our birds. Up to four (usually three) electrode bundles were implanted in each bird. A 10-cm bare stainless steel wire sewn through the connective tissue between scalp and skull served as our indifferent electrode. Electrodes were soldered to a variety of connectors, the best being the female contacts of sections of amphenol micro-miniature strip connectors. The electrodes and contacts were assembled before implantation and were cemented to the skull with cold-cure dental acrylic. The acrylic was anchored by moulding it around three stainless steel screws set in the bone. These connectors were quite small and interfered very little with the activities of the birds. We taped the leads to the head-connectors with 5 • 10-ram strips of surgical tape to maintain good contact. After implantation birds were allowed at least a week to recover before testing. Several birds were tested for as much as a year, but most were tested for a month or less.

Testing The bulk of our testing was done in plywood

19,

4

observation boxes approximately 1.75 m 3, set with their bottoms approximately 70 cm above the floor of the room. The walls were painted white and the floor of each pen, covered 4 to 5-cm deep with wood shavings, was lighted by a bare 75- to 100-W bulb and ventilated with a 20cm fan; both light and fan were controlled by switches outside the box. The birds could be viewed through one-way plastic mirrors. Cine records were taken through a large plate glass window from the darkened room; for sound recording a microphone was placed inside the box. Monophasic, rectangular stimulating pulses (0.5-ms duration, 100 pps) were produced by a Grass S-4 or S-8 stimulator coupled through Grass SIU-4 stimulus-isolation units. Current was monitored on a cathode-ray oscilloscope connected across a 100-ohm resistor in series with the bird. A switching system on the outside of each test box permitted stimulation through any one of ten electrodes singly or any two of ten simultaneously without handling the bird. This reduced disturbances from handling during testing. Usually we turned the stimulus on at a very low current then turned it up slowly until an effect was noted. Details of variations in procedure will be given in the pertinent sections. Currents over 500 IxA were rarely tried, and behaviours with thresholds over 200 I~A are interpreted with caution. Floor litter (wood shavings), a nest and eggs, a roost, food and water were available during all tests. Most birds were also tested with living, female conspecifics, a stuffed squirrel, soft plastic models of worms, insects and reptiles, and in the presence of the experimenter. Responses were recorded in narrative form at the time of testing. Once sufficient experience had been gained, sixtytwo categories of responses of varying complexity were devised and key-sort cards made for each electrode. Electrode coordinates and behaviour classes evoked were punched in the edges to facilitate sorting.

Histological Localization At the termination of testing birds were killed with sodium pentobarbital; 5 s of 0.5 gA positive direct current from the top and bottom electrodes of each bundle electroplated off enough iron to give a blue spot when the brain was perfused with 1 per cent potassium ferrocyanide in 10 per cent formalin. After fixing and washing, the brains were exposed in the skull, the head replaced in the stereotaxic instrument, and the brain sliced in three pieces parallel to the

PHILLIPS & YOUNGREN: BRAIN STIMULATION IN CHICKENS electrode tracks (frontal section) with a thinbladed knife held in the electrode carrier. They were then removed, imbedded in egg albumin, cut at 35 to 50 gm, and routinely stained with cresyl violet. Various fibre stains and some unstained material mounted in glycerol (viewed with crossed polarizing filters) were occasionally used to supplement the Nissi material. All locations for electrodes given in this paper were determined histologically unless explicitly stated otherwise. Head plugs were much harder to keep on cocks than on hens, thus in many males localization was not precise. Such sites are not included in any tabulations although the behavioural data from them are included in some of the discussions of results. The data reported here resulted from stimulating 1482 brain electrode sites of eighty-seven free-moving chickens. Of these, 913 sites in seventy-five birds were tested with chronically implanted electrodes and 569 sites in twelve birds were tested with movable electrodes patterned after those of Hoist (Holst & St Paul 1963). The detailed analyses are based on 724 electrodes where testing was repeated on 2 or more days and where the electrodes could be located accurately in histological sections (for roving electrodes criteria were present on at least three out o f four trials and good localization). These criteria eliminated all but seventeen of the sites with movable electrodes and also a number of our earlier implants in which head-plugs loosened before we finished testing. In order to analyse the questions of how behaviour is organized and where the controlling structures might lie in the brain, we looked at our data in three ways: by classifying and counting simple motor patterns, by looking at co-occurrences of motor patterns, and by analysing the brain locations from which various motor patterns and combinations of them were elicited. T o test for deviations from random association between pairs of behaviours that were elicited, a two-way matrix of the categories was constructed and the joint occurrences tabulated. An expected value for each joint occurrence presuming strictly random association was calculated by casting each pair of categories as a 2 • 2 contingency table, using the number of occurrences of each category and the total sample (724 electrodes) for the marginal and the grand totals (the number of joint occurrences being a cell in the body of the table). Probabilities for the

759

deviation between observed joint occurrences and expected numbers were computed from the chi-square distribution or the normal approximation to the deviation between two proportions. Some expected numbers are quite small, but corresponding marginal totals are quite large so that in these cases the deviations of the approximation that form the exact probabilities are not large enough to seriously affect the validity to significance statements. For the sake of getting on with it the exact probability was not computed but conservative error levels were used. Results Table I summarizes the types and frequencies of occurrence of motor patterns that were elicited with ESB at 724 electrode sites in seventy-six chickens. Each category was tabulated once for each site as either occurring or not occurring in response to ESB at that site. The table reveals that most of the categories are of small motor acts rather than of complex behaviour. Response categories were developed gradually, as experience with ESB developed, based primarily on the impression that possible subdivisions of the responses assigned to a category tended to vary together; responses assigned to different categories tended to vary more (though not completely) independently. Thus these categories reflect what can be expected from ESB in birds; finer divisions may be found by further study, but more complex responses are unlikely to result from stimulation of single points. A similar amount of data for mallard ducks (Phillips, in preparation) gives much the same result: complex, 'natural' units of behaviour are scarce and fragments thereof are much more frequent. Sites yielding only one motor pattern were rare, despite widespread distribution of points yielding very similar behaviour, and behaviour fitting several categories was often produced at one electrode. Observed and 'expected' joint frequencies for various behaviours elicited from single sites are compiled in Table II. Threat and Attack Under the heading of 'Attack' (Table I) are included several types of vigorous responses with bill or feet directed toward objects in the environment. Most of the points yielded pecking at other birds, often at otherwise dominant individuals. Occasionally these attacks were quite specifically directed either at birds or at the stuffed squirrel that was present in the pen. For example, stimulation through an electrode

760

ANIMAL

BEHAVIOUR,

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Table L Frequencies of Behaviours Assignable to Various Classes Evoked from 724 Sites with Accurately-Determined Anatomical Locations

Vocalize*

357

Lift wrists

30

Circle

342

Directed escape

30

Half crouch

128

Lower wing tips

28

Full crouch

122

Attack

28

Nervous

164

Hide

24

Panic

116

Scratch face or head

22

Headshake

94

Freeze

21

No response

93

Preen

21

Fluff or ruffle plumage

87

Standing tall

21

Peck

71

Spread tail

21

Fly

57

Body shake

20

Bill wipe or taste

44

Gape

11

Raise hackles

37

Fan tail

9

Backing

36

Scratch in litter

5

Eat

32

Waltz

1

Raise tail

31

*The categories in Table I are defined as: vocalization--any syringeal sound; circle--locomote in a circle smaller than the test pen; half crouch--flex the tibio-tarsal joint; full crouch--flex tibio-tarsal joint so that body rests on substrate; nervous--quick, darting head movements often with very hesitant, slow walking; panic--wild running and/or flying, often running into walls and objects; headshake--quick lateral head rotation like that in response to irritation of the head region; no response--no observable effect of stimulus; fluff or ruffle plumage---erection of plumage of part or all of the body; peck--striking objects (except other birds or the stuffed squirrel) with the bill; fly--flight; bill wipe or taste-lateral wiping or rapid partial opening and closing of the bill; raise hackles---erection of the hackle feathers; backing-locomotion tail first; eat--pecking at and appearing to swallow objects; raise tail---elevate tail feathers from their prestimulus position; lift wrists--lifting the carpal joints out from their (at res0 covering of body feathers; directed escape-repeated attempts to fly up or fly through the windows of the test box; lower wing tips----extendthe carpal joint, bringing tips of primaries close to substrate; attack--peck, bite, wing-beat or spur a companion, another animal or model, or the observer; hide--movement to a more or less concealed position and remaining there motionless; scratch face---scratch face with toe; freeze--to remain immobile; preen--to take feathers in bill one at a time, and to run them through it; standing tall--head and neck extended upward, tibio-tarsal joint near 180; spread tall--spread tail but keeping it folded in its normal inverted 'V' position; body shake---rapid, partial back-and-forth rotation around the long axis of the body serving to settle disarrayed plumage; gape--open mouth wide; fan tail--spread tail in a single plane, not in its normal inverted 'V'; scratch in litter--scratch substrate with feet; waltz--short curving walks with the outside (of the curve) wing drooped, the body tilted, and the outside foot stepping through the primaries. Each category was tabulated as occurring or not occurring at a given site regardless of the number of tests made at that site. The categories are not mutually exclusive. Responses were tabulated if they occurred on at least two out of three trials with latencies less than 60 s, on each of two or more test days with thresholds less than 200 ~tA for fixed electrodes (for roving electrodes only if at least three out of four trials on the single test day). i n one h e n caused her to attack 100 times out o f 119 trials. I n eighty-nine o f these she pecked a n d kicked at the squirrel ferociously b u t only in eleven did she attack a c o m p a n i o n . II1 contrast, sites in several birds produced pecking a n d vigorous chasing of other birds, with or without a c c o m p a n y i n g threat gestures, b u t the

birds treated the squirrel as p a r t of the floor; walking over it as if it were n o t there. Still other points elicited non-specific attacks on almost a n y t h i n g i n sight; a hen, a shoe, the experimenter's hand, a cork. Stimulation t h r o u g h one such electrode caused a h e n to peck hard at a n y t h i n g seen by the left eye, b u t objects

PHILLIPS & YOUNGREN: BRAIN STIMULATION IN CHICKENS seen only by the right eye were not attacked. She bit large pieces out of a cork with each peck. This response remained stable for 5 months (January to May, as long as she was tested). At least one electrode produced bitingtossing pecks at lifelike plastic worms, small reptiles and arthropods, These pecks were vigorous and were followed by very rapid lateral headshakes that usually threw the object a foot or more. They looked very much like the behaviour used to subdue large prey before eating it, but no attempt was made to swallow the objects. The same sites, however, sometimes produced pecking and eating grains of maize. In some of the attacks produced by ESB the stimulated animal moved about the test chamber almost as if alone and attacked only sporadically when it, so to speak, 'stumbled upon' the stimulus object. Brief attacks might be interspersed with fairly extensive bouts of running, circling or 'random' walking. One can certainly see hints of such behaviour in intact animals, but it was striking in some of the ESB-activated subjects. The specificity of the responses at different electrodes to various environmental cues and the many sites that produced no attack despite strong activation seemed to rule out non-specific pain (Ulrich, Hutchinson & Azrin 1965; Barfield & Sachs 1968) or fright effects as the elicitor of these attacks. So did control experiments in three hens in which stimulation via subcutaneous electrodes never produced attack or non-fear behaviour. In these birds currents strong enough to cause local muscle twitches or jerks usually produced freezing and only occasionally running or flight; lower currents mostly resulted in immobility. Maley (1969) found the same effects in similar control experiments with mallards. In addition to actual attack, ESB at many electrodes produced varied feather and body postures and movements that suggested imminent attack without attacks actually occurring. Thus a bird that drew itself tall, raised its hackles, lifted its carpals from its sides and raised and spread its tail looked very much like a hen about to attack another (see Putkonen 1967; Baeumer 1955; Kruijt 1964 for illustrations of this posture). This interpretation received some support from the birds themselves. For example, one hen would attack and fight a dominant when stimulated strongly, but with weaker stimulation she would behave as described above. The first hints of this behaviour

761

would immediately elicit an attack from the dominant bird, who otherwise was not overtly aggressive. This suggests that the companion responded to the behaviour of :the stimulated bird as to a threat by a subordinate. Analyses of joint occurrences of pairs of the movements and postures of the 'threat' described above revealed that all possible pairs of them: standing tall, raising the tail, spreading the tail, lifting the wrists and/or drooping their tips, fluffing or ruffling the plumage, and raising the hackles, were elicited from the same electrodes far more often than would be expected by chance ( P < 0 . 0 I , Table II). Of these only tail spreading and lifting the wrists had greater than chance-level joint frequencies with attack. Attacks themselves also occurred frequently at sites that produced pecking and lift wrists (e
Escape and Fear-Like Behaviour Joint frequencies of directed escape and fly, panic, hide and nervous were all significantly higher (P
12 1 '2**

4 0'8**

8 4'6

14 4.8**

18 1'6'*

11 1'9"*

5 1'3"*

9 7'4

20 %8**

2 0"8

1 0-9

1 0.6

0 3"5*

3 3-7

1 3"5

2 4-0

6 2"7*

9 15-8"

2 16.6"*

0 1'6

1 I "9

3 1 "3

4 7.4

0 7.8**

Bill wipe. taste

19 3'2**

14 3"7**

8 2-5**

27 14'7"*

20 15.4

Fluff or tutTI 9

4 1'0'*

t I '2

1 0'8

4 4.7

5 5.0

Attack

3 2'6

8 3-0**

4 2"1

I1 12"0

12 12.6

Peck

1 1 "1

I 1.3

2 0'9

6 5"0

4 5-2

26 20-5

Panic

4 5-0

3 3"4

3 2'1

Bill wipe, taste Observed Expected

Head-shake Observed F,xpected

Preen Observed Expected

Lift wrists or lower wing tips (total 44 sites) Observed Expected 2 1 "3 4 2.7

3 5 "7

23 5-7**

2 1-3

2 2-7

2 5.3

6 11.3

3 2.5

26 5.3**

0 1.7

0 3.6*

1 0.8

6 1.7"*

4 4.3

4 9"2

7 2-1"*

I0 4.3**

0 I'8

1 3.9

0 0-9

4 1-8

1 3.5

6 7.4

1 1-7

! 7.0*

6 15'0"*

0 3.3*

8 10 3.6** 7.0

5 4"3

37 9"1'*

11 19 2"4** 4-8**

2 2.4

2 1"6

15 34 9'6* 19.5"*

11 10-I

Directed escape Fly

2 1"9

4 1"0"*

0 1"0

0 0"7

13 4"0**

3 4'2

Hide

I 1.5

0 3"1

0 0-7

3 1.5

2 0'9

5 0'9**

7 5'2

13 5-5**

Preen

Headshake

Tail spread or fanned (tolal 27 sites) Observed Expected

6 3'5

3 3.7

Raise tail

9 3'8**

31 21.6"

Standing tall

Lift wrists or lower wing tips

Panic Observed Expected

Fly Observed Expected

Directed escape Observed Expected

Raise tall Observed Expected

Standing tall Observed Expected

Full crouch Observed Expected

H a l f crouch Observed Expected

Full crouch

Tail spread or fanned

1 10.0"*

9 21"3"*

3 4.8

14 10.0

10 6"I

46 26"3**

32 12"9"*

13 6'8**

5 7.0

3 4.8

30 27.6

40 29-0*

12 1-3"*

19 2.9**

1 0.5

0 1.3

0 0"8

0 3.5*

0 1-7

0 0.9

0 0-9

1 0.6

4 3-7

0 3-9*

Head N e r v o u s scratch

Table H . Joint-Freqmmeiea of Pairs of Behavinur Categories with Expected Values Calculated on the Basis ol Their Individual Frequencies

1 2.2

6 4.8

2 1"1

' 21 9 2.2**

15 1"4"*

6 5"9

5 2"9

2 1-5

I1 1-6"*

4 1"1"*

7 6'2

19 6'5**

Raise hackles

2 1-9

3 4-1

1 0-9

5 1.9"

0 1 '2

5 5"1

1 2'5

1 1-3

2 1 '4

3 0'9*

5 5-4

6 5-6

Eat

0 0.3

0 0-6

0 0-1

0 0-3

1 0'2

0 0"8

0 0"4

0 0"2

1 0"2

0 0'I

0 0.8

1 0-9

Scratch in litter

:>

to

*P.~0"$.

* * P <0"01.

Eat Observed Expected

Raise hackles Observed Expected

H e a d scratch Observed Expected

Nervous Observed Expected

Hide Observed Expected

Peck Observed Expected

Attack Observed Expected

Fluff or ruffle Observed Expected 7 3.4* 8 2-7**

13 8"5

4 2.9

1 1'2

2 3"6

3 5-6

4 2-2

9 6-8

9 11'4

5 4-5

14 13'9

2 2"4

2 0"9

6 2.9*

13 5.4"*

12 16.1

10 6.3

24 19'7

1 5.0*

0 0-7

2 2-2

0 0.9

0 2-6

2 1-I

11 8.4

I l "2

5 3.6

2 1-4

20 4.4**

0.2

0'2

o.1

1-o

1'6

0

0 1 -I

0 0-2

2 0'4*

1 0-2

0 0-6

0

7 7.2

I 1-0

20 3'1"*

4 1-2"

3 3-8

t')

Z

o~

C~

O

~P ~'~

*0

~'O

764

ANIMAL

BEHAVIOUR,

through the bill of normal preening. At one of the two 'good' sites the bird always first made several incomplete preening movements and also fluffed its feathers and scratched its face, then began to preen. It repeated twelve times in twelve tests, with no preening in the inter-trial intervals. In fact, it slept during seven of the eleven 2-rain intervals. It preened for as long as 2 rain when the stimulus was inadvertently left on. Threshold for this response was 45 IxA. The other bird with a 'good' preen site would preen every time the current was slowly raised to threshold (90 I~A) but would peck and eat corn from the floor when the current was raised quickly to the same level. Both responses were elicited many times and were quite consistent effects. This bird, too, dozed between stimulus periods. At this site higher currents (200 ~tA) led to circling and pecking at the bird's own feathers, actions quite distinct from the relaxed preening produced with lower currents. At both sides latencies for preening were long and variable and the movements were not precisely predictable from moment to moment. Seven of the sites that produced tentative looking and pecking at the plumage ('preening') also gave pecking at the wails or floor (P<0.01), suggesting that the responses have at least some closely contiguous anatomical representation.

Feeding and Drinking At thirty-two loci ESB caused birds to peck at the litter as if tentatively feeding, and at three they actually ate corn that had been thrown onto the pen floor. No bird ever consistently went to the dish of mash (the normal diet of these birds all their lives) and fed. Voracious post-stimulus feeding occurred at two sites in our study; at both, attacks occurred during stimulation. Drinking was not elicited in this study nor in that of Putkonen (1967). Akerman et al. (1960) described it in pigeons, but Goodman & Brown (1966) could not replicate their results; Hoist & St Paul (1963) reported drinking elicited in chickens, but no details were given.

Co-Occurrences of Multiple Responses at Single Electrodes Figure 11 is a diagram of the response pairs that occurred (or failed to occur) together much more often (P<0.01) than would be expected from chance association, based on their individual frequencies. Three clusters of responses are discernible; one of attack-associated re-

19,

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sponses, a second of behaviour associated with escape, and a third of behaviour involving the appearance of discomfort in the head region. The first two groups are linked primarily by full crouch which was strongly associated with one element in each. The third group, those involving the head, is negatively associated (co-occurrences less than expected by chance) with elements of either of the other two clusters. (Only those different from 'expected' with P<0.01 are included in the diagram; inclusion of those 0.01 < P < 0 . 0 5 would increase its complexity but would not alter the basic configuration.)

Anatomical Localization Figure 1 shows all the points for which satisfactory anatomical information is available. We sampled the brain stem widely, but the distribution of points reflects our extra attention to coordinates where vocalizations were readily evoked. This resulted in a bias of the sample toward tractus occipito mesencephalicus and its projections; this bias stemmed from attempts to replicate responses, not from especial effort to sample particular structures. One point is clear; the points for every response plotted are too scattered to be equated with single, gross anatomical structures. This may well reflect the imperfect choice of categories to be plotted, but we hope that the plots provide a useful reference both for comparison with other species and for workers who might want to improve upon them.

Attack, Threat and Pecking (Figs 2 and 3) Attacks were elicited from forebrain and as far caudally as the posterior hypothalamus (Fig. 2). The lack of attack sites farther caudally is striking, especially in view of the larger number of test points in caudal than in rostral areas. In the forebrain, basal and medial placements were the only ones to yield attack. Most of these seem to be in or close to the medial archistriatum and its projections. Six (all in augmentatum) of the forty-two points tested from the paleostriatum also produced attacks or pecking at another bird. At several points low currents produced attacks or pecking at other birds, yet higher currents resulted in threat (ruffled feathers, raised hackles, wrists out from body slightly). Still higher currents sometimes resulted in panic, but we did not systematically test for this

PHILLIPS & YOUNGREN: BRAIN STIMULATION IN CHICKENS

/

.:: oil

765

9

Fig l~Loeations of all points stimulated in this study plotted on tracings of our stereotaxic atlas. The anterior coordinates of the sections are given below each figure, and the hash-mark ( -- ) at the left of each indicatesboth vertical 5 and 1 mm scale. since most (not all) points will yield panic if current is raised to 300 to 500 ixA. Although attack behaviour was elicited only from more rostral areas, feather erection that looked very much like parts of threat could be elicited readily from mid-brain structures (Fig. 3), especially the region of the oceipito-mesencephalie tract and the lateral reticular formation. Pecking at feathers (Fig. 4) tended to be elicited from points more rostal than those for attack, whereas pecking at a mirror (weak attack?) closely overlapped overt attack (Fig. 2). Pecking at the litter (Fig. 4) was primarily a mid-brain response, although a 'few points occurred throughout the rostral range of attack and peck sites. Tail raising and tail spreading, ruffling of the plumage and lifting or drooping the wings (Fig. 3) showed the same distribution as litter pecking in mid-brain but were much more frequently evoked from hypothalamic regions. Waltzing was clearly elicited at only the one site (Fig. 3) in ventral neostriatum or extreme caudal archistriatum, but components (uni, lateral feather erection, wing abduction and

wing drooping) were elicited severa! times. Ten of these sites were striatal, one was diencephalic (probably in tr. occipito mesencephalieus) and two were in mid-brain. Eight of the ten striate electrodes, including the one yielding the most complete waltzing, also produced pecking at feathers or attack.

Feeding and Preening (Figs 4 and 5) The best preening and feeding sites in chickens were located far rostrally in paleostriatum or nucleus basalis near (but mostly ventral to) the general area from which Harwood & Vowles (1966) produced increased feeding and preening, and near the pre-optic region where Akerman et al. (1960) elicited hyperphagia in pigeons~ No stimulus-bound eating was elicited from the pre-optic area despite more than fifty points tested (nor have any of the 440 pre-optic sites in an ongoing study yielded feeding; these birds are still alive so no histology is available, but the implants are in the pre-optie region), The site (Fig. 4) from which both preening and eating corn were elicited was in anterior

766

ANIMAL

BEHAVIOUR,

19, 4

~r [] A

9 41h

Attack A t t a c k squirrel Pick other bird Spur other bird Throw objects Threaten Waltz

Fig. 2. Attack and related behaviours. In this and subsequent figures the small numbers are current thresholds in microamperes. In this and subsequent figures smaller categories are used than for the analyses in Tables I and II, but the legend for Table I describes what has been lumped in each category there. medial paleostriatum quite close to where Goodman & Brown (personal communication) showed a weak feeding point. This same area also yielded several litter-pecking and ownfeather pecking responses (Fig. 4). In two birds voracious feeding followed immediately after the cessation of stimulation in medial rostral hypothalamus (Fig. 5), close to the pre-optic area. One of these sites produced attack, both on companions and on the stuffed squirrel, the other yielded pecking at a variety of objects although not overt attack. A third, less intense, post-stimulus eating site was located in ventrocaudal neostriatum. Feeding often occurred after stimulation and during inter-trial periods, but only at these three sites did it appear clearly and reliably at stimulus offset.

Crouching (Fig. 5) So many sites (319) produced some crouching that we believe most of it consisted of poorly oriented responses to a sudden, new, "nonspecific sensation. Some sites produced much more striking effects, i.e. strong, persistent and repeatable crouching as the principal re-

sponse, and only those included in Fig. 5. Putkonen (1967) described and illustrated what he called a 'trophotrope syndrome': the birds squatted down, ruffled their plumage and appeared relaxed. We replicated his results in four birds with electrodes in the same region, the rostro-lateral tip of nucleus geniculatus lateralis. This was the closest to sleep that we saw during ESB, but the birds did not tuck the head under the wing as in full sleep.

Head Shake, Face Stretch, Bill Wipe (Fig. 6) Head shaking, face scratching and bill wiping are considered together because they all seem to be responses to irritation of the head region. Their close relationships are reflected in their high joint frequencies with one another (Table II, Fig. 11) and also in their lack of or negative association with almost all other responses. In males 13/128 sites yielded face scratching, 13/128 bill wiping or tasting, and 18/128 head shaking. In females these responses were relatively much less common (13/651, 21/651, 76/651 respectively). The most obvious difference between the sexes is the much larger area of

PHILLIPS & YOUNGREN: BRAIN STIMULATION IN CHICKENS

~kWings out ,!, Taildown [~Wings dropped ,L Tai.Iup 9 Ruffled or fluffed (raised) 0 Sleeked --Tail spread

i

Fig. 3. Locations of points evoking feather, wing, and tail movements.

N ~

.~

~ f"

~ f

~

r~, ~ ) ~

J

~

, ~ ~

PICKING 9 Mirror Li,te; * Squirrel 4, Own feathers Feathersof companion

Fig. 4. Points that yielded picking or pecking directed at various objects.

767

768

ANIMAL

BEHAVIOUR,

19,

4

t /~'~-~--

l

/

ulus

/f

Fig. 5. Points yielding crouching (as a primary part of the response), eating (of corn or wood shavings, never of normal food), and post-stimulus eating (real eating of normal diet of mash).

Fig. 6. Points yielding head scratch, face scratch and bill wipe.

PHILLIPS & YOUNGREN: BRAIN STIMULATION IN CHICKENS comb and wattle in the cocks. This skin is very sensitive compared to other cutaneous areas, and the large area of it might be expected to be related to a larger brain representation in cocks than in hens. The points follow the course of tr. quinto frontalis closely enough to suggest that it is involved in most of these responses. Escape (Figs 7 and 8) Evoked fear and escape behaviour was extremely variable between birds and electrodes, but surprisingly consistent at individual sites. ESB at some loci regularly produced flying up, preceded at lower intensities by looking up and intention movements to fly; others consistently yielded flight oriented to the windows in the test boxes, while still others elicited crouching, hiding, blind scrambling (Panic, Fig. 8) or merely jerky, 'nervous' walking. Often (112/160) vocalizations were elicited from the same sites that produced escape. The specificity of responses at paticular sites, and the variability between sites, suggests that at least some of the fear-like behaviour resulted from more or less direct activation of central coordinating mechanisms. The absence of fear

769

reactions at many sites where other effects, including forced postures and rapid circling, were found reinforces this interpretation. Panic (frantic scrambling), directed escape, hiding and flight all seem to be evoked from very much the same brain regions. The low thresholds for various escape (except crouching) responses plot very well on the course of tr. occipito mesencephalicus (Karten & Hodos 1967; Tienhoven & Juhasz 1962; Phillips 1966 and unpublished degeneration studies of archistriate projections). Thresholds for panic averaged 46 I~A for the twelve points in the tract, 89 ~tA for the sixty-one points within 0.5 mm of it (or in the area lateral and caudal to n. ovoidalis where many of its fibres seem to terminate), and 162 IxA for the thirty-five points farther from the tract (mostly in archistriatum). Only 7-3 per cent of the 480 points outside the tract and its midbrain projection area evoked panic compared to 19.0 per cent of those in the tract and 33.7 per cent of those points near it. These structures are homologous with the amygdala-hypothalamus-midbrain circuits which produce similar behaviour in mammals (Gloor, Murphy & Dreifuss 1969; Morgane

Fig. 7. Thresholds for running responses.The restricted distributionof lowthreshold points indicatesa specific,local effectratl~erman a general one to any stimulation.

770

ANIMAL

BEHAVIOUR,

19,

4

9

Panic

Fig. 8. Points yielding panic (wild, undirected running and flapping including.collisions with walls and other obstacles).

1969; Molina & Hunsperger 1959). The points for so many elements of expressive behaviour fell within the projection field of the archistriatum, including tr. occipito mesencephalicus and the extensive area lateral to n. ovoidalis and surrounding, but not including, MLD, where electrical stimulation of the ipsilateral arehistriatum produces large, short-latency evoked potentials (Phillips 1966) and where small lesions in the archistriatum produce extensive fibre degeneration (Phillips unpublished) that we compared the locations of 'no response' (Figs 5, 6 and 9), 'crouching', "headshake', 'bill wipe', and 'head scratch' to these structures for comparison. None of the plots of these five categories is primarily in archistriate projections, and most points for attack lie outside tr. occipito mesencephalicus. Points for escape, pecking, feather and tail postures, and vocalizations (Phillips, Youngren & Peek, in preparation) all follow it closely down into the mid-brain. Thresholds for peck and for tail movements were like those for panic; average thresholds in tr. occipito mesencephalicus were 53 and 45 lxA, respectively, while those for points near it were 57 and 54 IIA, and those for points farther from

it average 92 IxA. For plumage movements (fluff, ruffle, raise hackles), however, threshold values were reversed with those in the tract higher (average 96 IxA) than those near it (average 56 tIA), but, like points for panic, pecking, and tail movements, points farther away had the highest thresholds (average 144 lxA). Thus all of these behaviours seem to be most readily evoked from the regions that receive archistriate projections, but threshold data indicate that various behaviours are differentially affected by stimulation in tr. oceipito mesencephalicus and stimulation in its synaptie fields. Possible contributions from paleostriatum are not ruled out, but tr. occipito mesencephalicus diverges from ansa lenticularis, which runs lateral to most of the responsive areas in the thalamus and ventral to them in mid-brain (Karten & Hodos 1967), so it would appear not to be involved, at least at the caudal sites. The anatomical distributions of fear-like and attack-related responses appear to overlap completely, but within this our evidence indicates that they are separate. This is shown most clearly in Fig. 11 where the two groups of responses form highly interconnected clusters

77t

PHILLIPS & YOUNGREN: BRAIN STIMULATION IN CHICKENS

.

No

response

Fig. 9. Points from whichno responseswere obtained. This figureis intended primarily to emphasize the relationship between affective behaviours and tr. occipito mesencephalieusby demonstratingthe lack of correlation of 'no response" points with this tract. with but a single connecting pair of jointly occurring responses (full crouch). Whether this diagram describes anatomical localization or functional organization (without necessarily reflecting localization) is an open question. We strongly favour an anatomical interpretation because many of the responses (all of those reported here) are quite site-specific and repeatable. Also they often appear to be only fragments of normal sequences.

Vocalizations Vocalizations were produced at more sites than any other category of behaviour, except fear-like actions, and 'they form the basis for a separate paper (in preparation). The most striking aspect of elicited vocalizations is the very short latency and very high degree of stimulus control that can be obtained. The lowest thresholds were obtained from the torus semieircularis just ventral and medial (to but not in) the large celled portion that Boord (1968) has shown to be a main auditory nucleus. This is the same region where Brown (1965a) elicited alarm calls in red-winged blackbirds

with ESB and muted them (Brown 1965b)with lesions.

Response Repeatability In the present study many sites showed considerable variability, but at most sites the behaviour elicited was stable from trial t o trial, and these are the sites on which this paper is based. Of 123 different sites repeatedly tested over periods ranging up to a year, ninety-six showed little or no change, twenty-two deteriorated (higher thresholds or lower probability of the response) to some degree, and five got better (lower thresholds or higher probability of the response). Another measure of repeatability is shown in Tables III and IV. Thresholds for a response were determined repeatedly for each of four birds (one site in each) on 11 days between 8 and 22 November 1965. Table III shows results of repeated trials on a single day. Table IV those o f tests repeated on different days. It can readily be seen, not only that the behaviour was consistently elicited, but also that its threshold remained relatively stable over this 2-week

ANIMAL

772

BEHAVIOUR,

Table HI. Bird No. P 163 (E3). Effects of Repeated Trials and of Drowsiness on Thresholds for a Vocal Response (15 min between tests, 2 rain between trials)

Drowsy, tends to sleep

No

Test 3 current (~A)

Test 4 current (t-tA)

Test 5 current (~A)

160

130

135

135

185

140

110

125

150

165

140

125

135

160

170

140

140

135

145

170

130

130

125

155

185

40

140

125

125

175

190

"o 30 o

140

125

125

175

190

125

175

160

Table IV. Thresholds (~tA) for Vocal Responses Showing Variation between Birds and between Days for individual Birds

Date (Novembe0 P 163

response

at

.05

rnser

i~110

Test 2 current (~A)

Tests used 300 ms trains of pulses at 100 pps. Threshold was that current that gave one call for each train.

4

WIpA) ,~Q120

Test 1 current (~A)

140

19,

OCI00 ~. ~o

d~

.~

20

.C I,-

.,~L,,

,~2,

Single-Pulse

,15, W i d t h (,o.t] . . . . . .

,~, ~. . . . tlmulatlon~l

Fig. 10. Graph of threshold in microamperes versus pulse-width for three different pulse-repetition rates demonstrating marked non-linearity with short pulse durations.

P 145

P 161

P 162

Stimulus Parameters

Pulse duration and pulse repetition rate are frequently considered to be interchangeable so long as the total current delivered remains constant. To test this we stimulated single sites repeatedly with different frequencies and pulse durationS. The results of one such experiment are plotted in Fig. 10. We used clucking as the response and measured thresholds for response to constant-current pulses (results are similar but more variable with constant-voltage pulses). Clearly the generalization above holds only for a very limited range of pulse-widths and repetition rates. This emphasizes the importance o f stimulu s p a r a m e t e r s and the difficulties of making detailed comparisons of the results of different workers, each using slightly different stimulus parameters as well as different test procedures and even different species, a point that has been made by Brown (1969) and by Kramer, St Paul & Heineke (1964).

8

142

89

67

130

9

149

90

67

129

10

131

86

59

96

11

122

66

54

106

14

130

75

67

116

15

132

80

71

125

16

135

70

65

125

17

127

65

63

110

18

121

66

67

114

31

144

77

63

115

22

130

57

63

119

period. Another example is an electrode that yielded attacks in 100 of 119 trials: eighty-nine of these attacks were specifically directed at a stuffed squirrel despite the presence of other objects. We have not tabulated all of our results this way, but these examples give a good indication of the fact that, although responses to stimulation at a site m a y vary at times, many quite stable responses are obtained.

L o c a l i z a t i o n and S t i m u l u s Spread

Von Holst argued against the value of localization studies partly on the assumption that non-uniformities in brain electrical impedance prevented determination of where a given stimulus was actually producing its effects,

PHILLIPS & YOUNGI~EN: BRAIN STIMULATIONIN CHICKENS Subsequent studies such as that of Cohen & Pitts (1967) have shown that the actual field stimulated is that in the region of the tip and is quite restricted. Thus lesions only 0.5-mm diameter raised thresholds to five times what they were prior to lesioning. In our experiments movements of as little as 0-1 mm sometimes radically altered the response that could be evoked, and it was unusual for electrodes as much as 1-0 mm apart not to differ appreciably in their effects. Discussion

Attacks were among the most complex behaviour elicited by ESB in this study, and our data confirm and extend the reports of attack produced by ESB in birds by Hoist & St Paul (1963), Goodman & Brown (1966), Akerman (1966b), Putkonen (1966a, 1967) and Maley (1969). None of the points yielding coordinated attack were caudal to dicencephalic levels, although components were produced by mesencephalic placements. Similarly Maley (1969) concluded that in mallards attacks could not be evoked from mid-brain; so did Goodman & Brown (1966). The two mid-brain points that evoked jabbing pecks at companions in mallards (Phillips 1964) are difficult to reconcile with other results. The electrodes were in mesencephalic projections for ascending spinal afferents (Karten 1963); they may have triggered pain responses and thus aggression of the sort reported by Ulrich et al. (1965). The birds that Phillips used then were much wilder than those used by any other workers, including Maley (1969), and may have been more reactive than those in which mid-brain stimulation failed to elicit attacks (for example, they would not eat in his presence until they had been starved for 2 or 3 days, and then they would do so only furtively and very briefly). Also these 'attacks' were very brief pecks at another bird, not the sustained fighting that can be elicited more rostrally. Our Nots differ slightly from those of Putkonen (1967) primarily in that he never produced attack from paleostriatum whereas several of our electrodes inventral paleostriatum augmentation did. Our points, however, were very close to the region where he got attacks from the archistriatum. Barfield (1965), using testosterone implants in this area in cockerels, increased attack behaviour as did Goodman & Brown (1966) and Akerman (1966b) with electrical stimulation in pigeons.

773

Phillips (1964) elicited escape behaviour from the archistriatum and tractus occipito mesencephalicus in mallards, and Akerman (1966b) described escape behaviour from two sites in the archistriatum. In the present study with chickens several archistriate sites yielded marked escape. This result differed from Maley's (1969) but not from Phillips' earlier mallard work. In addition several electrodes, both in our chickens and in those of Putkonen, evoked very marked 'excitement' and mild signs of alarm. These included rapid pacing, occasional runs or jumps, and slight crouching which would surely have been expressed as panic in the wild mallards with which Phillips worked. Maley's sample of medial archistriate points was relatively small, and his mallards were much less flighty and much less prone to panic under any circumstances than the stock that Phillips used. Activation of the archistriatum itself may only occasionally activate escape behaviours, but stimulation almost anywhere along its primary output, tr. occipito mesencephalicus, has been very effective in all studies reported (Goodman & Brown 1966; Putkonen 1967; Akerman 1966b, Maley 1969; Brown, personal communication). The effectiveness of the lesions in this tract reported by Phillips (1964, 1968) in reducing escape might thus result from reducing or eliminating archistriate excitation of cells receiving inputs from its major downstream projection. The failure of many brain electrodes (including those inducing gross motor disturbances) and of subcutaneous electrodes to elicit escape behaviour indicates that only restricted regions of the brain yield escape behaviours when stimulated by localized electric currents. Maley (1969) has discussed this in detail for mallard ducks. Although escape and attack responses formed two almost independent clusters when analysed for their co-occurrence with stimulation by the same electrode (Table II, Fig. 11) their gross anatomical distributions seem to overlap completely with no evidence for the medial-lateral differentiation described by Akerman (1966b) for defensive threat and escape. Mechanisms controlling food and water intake in birds remain poorly understood. Results of lesion studies of the importance of the rostral diencephalon and basal telencephalon in the control of feeding are equivocal and fail to provide consistent localization. Feldman et al. (1957) reported aphagia in chickens following vaguely-described hypothalamic lesions. Kuenzel & Helms (1967) produced obesity in white-

774

ANIMAL

BEHAVIOUR,

19,

4

ft

/:\, i

t

, FULL

',

I CROUCH

~

,

Fig. 1I. Diagram of the pairs of behaviour categories in Table I that cooccurred at the same sites with greater (or less than) random frequency. All pairs whose joint frequencies differed with a probability.of P<0.01 are connected by lines. Solid lines indicate observed frequenems higher than chance level; broken lines, those occurring together at less than chance level. This diagram is a statement of apparent anatomical relationships (pairs of structures so related that both members are activated by a single electrode) and does not represent temporal sequences as many similarlooking diagrams do. throated sparrows with lesions just above the dorsal supra-optic commissure in the plane of the anterior commissure, and Lepkovsky & Yasuda (1966) claim to have produced hyperphagia with hypothalamic lesions but they provided no useable anatomical data. Smith (1969) found aphagia after lateral anterior hypothalamic lesions that appear to be in very much the same region where Akerman et al. (1960) produced feeding by ESB. The ease with which non-specific effects might produce aphagia, the small numbers of experimental animals involved, and the lack of anatomical details limit the value of several of these studies. Despite a special search for it, we found no ESB-evoked feeding in chickens or ducks. Likewise Maley (personal communication) never evoked it in his mallards and Putkonen (1967)

did not report it from his chickens. Only Holst & St Paul (1963) and Akerman et al. (1960) have reported compulsive eating or drinking in birds. Goodman & Brown (1966) were unable to replicate the results of the latter workers, and they are open to another interpretation. The Swedish workers offered their birds peas, which may have high peck-releasing value in themselves, and the eating elicited may have been more akin to our pecking-at-the-litter than to true feeding. Thus, although we never produced true feeding (i.e. on mash), three of our birds that pecked at the litter ate corn that was scattered in it. In studies in progress in this laboratory, Mrs J. Tweeton has clearly increased the frequency of feeding during bouts of ESB with pre-optie electrodes in fowl, but the behaviour is not time-

PHILLIPS & YOUNGREN: BRAIN STIMULATIONIN CHICKENS locked to pulse trains. Her technique is to stimulate for 15 s out of each minute for 5 min, and to compare the number of 30-s periods in which feeding occurs in this period with counts in comparable periods before and after the test period with counts in comparable periods before and after the test period, and with complete replicate experiments in which the leads from the stimulator are disconnected. The increase in feeding differs sharply from vocalizations evoked from the same electrodes in that the calls occur during the 15-s 'on' periods and not during the 45-s 'off' periods, whereas, the feeding shows no relationship to individual trains and cannot be elicited by single trains. Similarly, Harwood & Vowles .(1966) reported increased feeding behaviour m Streptopelia risoria with ESB, but it came with long and variable latencies and would not sustain pecking on partial reinforcement schedules. Preening was not readily elicited in this study and other workers have likewise reported little of it. Putkonen (1967) did not describe preening from his Chickens. Akerman (1966b) reported no normal preening but he did evoke 'displacement preening' from a number of electrodes in pigeons. His description suggests that the bill did not touch the feathers. Goodman & Brown (1966) elicited 'occasional preening' from one site in pigeons but gave no details. Harwood & Vowles (1966) reported increased preening from striatal sites in Streptopelia, but the responses showed quite long and variable latencies; Delius (1967) also dealt with very long latency responses. One problem with testing for preening is that once it starts it tends to persist, so that long-latency, weakly stimulusbound preening requires a large sample of widely spaced trials and control periods to distinguish it from spontaneous or 'operant level' activity. Full preening and oiling sequences have been reliably elicited from several mallard ducks (Phillips, in preparation). Apparently species differ in the ease with which preening can be evoked by ESB; this is probably related to the importance and frequency of preening in their normal behaviour. The unexpectedly frequent concurrence of preening with peeking-like responses (Table II, P<0.01) and the co-occurrence of preening and of pecking corn at the same electrode in one hen suggest that the coordinating mechanisms for peeking for a variety of end results (feeding, preening, fighting) are at least partially shared. Similar reports of combined pecking and

775

preening in pigeons (Goodman & Brown 1966; /kkerman 1966b) and doves (Harwood & Vowles 1966) support this suggestion. Furthermore, the response that is produced by ESB seems to depend largely on cues from the environment (i.e. a bird might peck at wood shavings on the floor, corn, a nail in the wall or feathers according to what was available). Behavioural studies of pecking by Red Jungle Fowl in conflict situations also suggest this relationship (F. Feekes, personal communication). Our first expectation based on the reports of Hoist & St Paul (1963) and of Akerman (1966a, b) was that ESB in appropriate loci would evoke complex sequences of courtship, parental, alimentary, agonistic and defensive behaviour. In fact Hoist & St Paul (1963, p. 2) said ' . . . nearly all known movements can be elicited, serving orientation and the needs of the body, directed towards enemies, rivals, the sex partner and the young, with all the associated calls.' We found, however, despite a sample of more than 2600 brain points in chickens and ducks, that the only complex, natural sequences evoked were agonistic ones (fighting, threat and fleeing). By far the most frequent results of ESB were simple motor patterns like turning the head or moving a feather tract. Putkonen (1967) in chickens and Maley (1969) in ducks obtained similar results. Some of the most complex behaviour to have been described in detail was reported for mammals by Roberts and his coworkers (1962, 1964, 1965, 1967). Even their concentration on limited hypothalamic regions yielded more fragments than complete sequences. They stressed that the complex sequences they elicited were highly dependent on appropriate environmental stimuli, a conclusion which fits our findings well. Several explanations for our failure to elicit stereotyped sequences of behaviour with brain stimulation in chickens may be offered: (1) that behaviours occurred but that we were unable to detect them; (2) that the experimental situation was inadequate for their elicitation; (3) that we failed to sample adequately; (4) that the technique itself is inadequate for the elicitation of such behaviours; and (5) that fixedaction-patterns are not rigidly sequentially programmed in the central nervous system. (1-2) The first two explanations can be discounted. Our test situation was such that, in the absence of stimulation, our birds would crow, preen, dust, court, copulate, threaten, fight, sleep, drink, eat, scratch out nests and lay

776

ANIMAL B E H A V I O U R ,

eggs, and explore. Thus, these behaviours occurred and we recognized them, yet they were not observed as short-latency, stimulus-bound responses to stimulation of the same birds in the same test chambers. (3--4) The third and fourth arguments, that the sample or technique was inadequate, are harder to refute. The stereotyped nature of crowing (Siegel, Phillips & Folsom 1965), its frequency, and its apparently 'spontaneous' nature seem to fit Lorenz's (1950) concept of fixed action-patterns. It further fits inasmuch as once crowing has been initiated it cannot be stopped by external stimuli (i.e. prodding, pulling the cock's tail, electric shock, ESB in brain areas yielding a wide variety of behaviours). Similarly courtship displays in ducks are so unvarying (Dane, Walcott & Drury 1959; McKinney, personal communication) that they seem to be fixed action patterns; indeed, they seem to have been part of the stimulus for Lorenz's development of the concept. Our failure to find sites where ESB would evoke crowing and social courtship indicates either that the technique is inadequate or that, despite testing nearly 2000 sites in chickens and over 900 in ducks, we have failed to sample sufficiently to find potential command neurons for crowing and similar behaviours. Inadequate sampling is always a possibility: a count of points on a 0-5-mm grid of the chicken brain atlas of van Tienhoven & Juhasz (1962) yielded approximately 7000 points. A 0.1-mm grid would thus consist of q-875 000 points, clearly a hopeless number to sample exhaustively. Further analysis however, suggests a smaller number since over 4000 of the 7000 points counted were in the forebrain where evoked behaviours are scarce in all vertebrates that have been studied. The possibility that shifts of a few microns in electrode position can make crucial differences cannot be ruled out; our attempts to improve precision by using smaller electrodes, however, resulted in higher threshold currents and more forced circling and grotesque postures but less natural-looking behaviour. Miller (1965) similarly found that smaller electrodes resulted in little or no behaviour rather than in improved response resolution. Our experience with closelyspaced, fixed electrodes and with movable electrodes indicates that changes of 0.5 mm or more in electrode location are usually necessary to produce major changes in the evoked response. The differences between the results of Hoist

119, 4

& St Paul and our own may be those of criteria. Ours were that the behaviour could be elicited repeatedly with currents of 200 ~tA or less (at 100 pps), usually on more than one test day and with latencies less than 60 s. Hoist & St Paul did not state their criteria nor did they publish details of results. Viewing their films suggests that the responses they evoked were similar to what we have seen but that we have interpreted them differently. Thus they reported evoking crowing whereas we do not; Putkonen (1967) did but only after such long latencies that other effects of the stimulus had already faded. He, therefore, considered it to be a post-stimulus effect (personal communication). We have seen post-stimulus crowing, and crowing often follows a wide variety of disturbances. We, therefore, believe that post-stimulus crowing is most likely a response to the end of disturbing ESB. Another possible explanation for our failure to elicit crowing and other stereotyped natural patterns was pointed out in a review by Dory (1969). He suggested that stimulation may activate only one of the symmetrical pair of structures (one on each side of the brain) that normally interact to produce a behaviour pattern, and that the output from the unstimulated side might inhibit that from the stimulated side. He cited evidence from animals as different as toads and monkeys to support his idea. We are currently testing it, but the difficulty of getting two electrodes in corresponding sites in the right and left sides of the brain will make only positive results meaningful. The results of Bergquist (1970) in opossums and from pilot experiments in chickens makes us doubtful that bilateral stimulation will give responses very different from those reported here; so does the failure of unilateral lesions to abolish escape responding (Phillips 1964, 1968) and alarm vocalizations (unpublished) whereas bilateral destruction of the same structures is effective. One uncertainty with ESB is that electrodes large enough to evoke observable complex be, haviour are probably large enough tO stimulate hundreds if not thousands of cells simultaneously (but see Stoney, Thompson & Asanuma 1968). This is not likely the way these cells would normally fire in intact animals. Doty (1969) emphasized as almost axiomatic that such simultaneous activation of many adjacent cells can produce only disruption of complex behaviour organized by these cells, and that

PHILLIPS & YOUNGREN: BRAIN STIMULATIONIN CHICKENS integrated responses must result from activities of neurons post-synaptic to those directly fired by the stimulus. This need not necessarily be true: if the brain were organized with cells akin to the command interneurons that Kennedy, Evoy & Fields (1966) and Willows (1967) have described in invertebrates, and if clusters of these neurons, all serving the same function, were anatomically localized (not necessarily in homogeneous clusters), ESB could trigger complex sequences directly by firing these cells. To the best of our knowledge no such command neurons have been identified in vertebrates, but the short latencies and rigid stimulus control of alarm vocalizations (Brown 1965a; Murphy & Phillips 1967) are suggestive. Most responses, however, even the fragments of 'natural' sequences elicited in the present study (pecking, bill wiping, head and face scratching, ruffling body plumage, preening) are much less rigidly stimulus-bound and stereoptyped. (5) The most likely explanation of our negative results is that fixed-action-patterns may not be rigidly programmed in the central nervous system in chickens. ESB in particular brain regions does increase the probability of occurrence of quite complex and specific dusters of responses such as those involved in attack and escape, sequences that occur naturally in the species studied. The occurrence of various components, such as raising the hackles, jumping, kicking with the spurs, and pecking, however, seems to fluctuate appreciably from trial to trial and individual to individual, and some do not appear at all if appropriate external stimuli are absent. Holst & St Paul (1963) and Roberts et al. (1967) have also emphasized this point. This same lack of consistency has been found in normal behaviour and led to the development of terms such as 'acts' (Russell, Mead & Hayes 1954) for behaviour of complexity similar to what we have called simple motor patterns. Stokes' (1962) beautifully quantitative study of agonistic displays of blue tits provides an excellent example of how even strongly correlated components of complex behaviour vary in different ways rather than as a unit; Barlow (1968) has suggested that this may be the norm and that rigid sequences may be fairly rare. Much of the thrust of the current emphasis on the ontogeny of behaviour, for example Hailman's (1967) study of pecking in the laughing gull chick, carries the same implication. I f rigidly programmed sequences are in fact, rare in nature, and the common situation

777

is one of variable relationships between simpler motor patterns (each of which itself is likely to be greatly modifiable by the set of inputs to it at any given moment), two superimposed types of central organization of motOr output are suggested. The first is of the nature of command neurons or networks (Willows & Hoyle 1969) which need only be activated to trigger a fairly stereotyped output. More complex behaviour such as attack, escape, courtship and preening seem better to fit the scheme emphasized by Roberts et al. (1967). They propose that complex behaviour evoked by ESB results from activation of anatomically neighbouring neurons whose output effects facilitation of sets of reflexes which depend on cues from the environment for their actual triggering. Thus ESB would raise the probability of occurrence of sets of responses provided that appropriate sensory cues were present. Much of the organization of the sequences observed (which may be similar or identical to those observed in intact animals) would depend on the organization of the environment. This scheme of Roberts' accounts for both the stereotypy and the variability of sequences of behaviour whether they are evoked by natural stimuli or by ESB. Glickman & Schiff (1967) have proposed a similar organizational scheme. Presumably responses such as alarm calls are sub-units available for activation by the facilitatory circuits. This paper has been primarily an attempt to provide a description of the responses that can be evoked by ESB and sufficient anatomical data to enable interested workers to build from it. The most promising directions for further work suggested by these experiments are: (1) more precise studies on the variability in latency, sequence and form of such responses as feathertract movements, attack, directed escape, pecking, and preening-like movements; (2) detailed analyses of anatomical distribution and cooccurrence with other behaviour (especially with various vocalizations) of pecking, preening, and body and plumage movements; (3) interactions of readily-elicited behaviour such as vocalizations, pecking, attack o r escape with external cues and with past experience of the individual; and (4) a detailed study of afferent and efferent connections of and the timing mechanism for the rhythmic calling that has been elicited in several species. Thorough search in the vicinity of points that yielded . poststimulus crowing or eating, or of those that yielded components of waltzing, will:pr0bably

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show t h a t frequency o f occurrence o f these b e h a v i o u r s can be increased by s t i m u l a t i o n o f very restricted b r a i n regions. I f so, this w o u l d p r o v i d e a tool for study o f central a n d peripheral integration. Acknowledgments This w o r k was s u p p o r t e d b y the M i n n e s o t a Agricultural Experiment S t a t i o n a n d b y a U n i t e d States Public Health Service grant, N a t i o n a l Institutes o f H e a l t h G r a n t no. N B 06981. W e wish to t h a n k especially D r F r a n k M a r t i n for his advice o n the statistical analysis o f joint-occurrences, a n d M r s Aileen N y g a r d w h o m a d e all o f the histological p r e p a r a t i o n s . W e also w a n t to t h a n k M. J. M a l e y for m a n y stimulating discussions a n d for criticizing the manuscript. W e are especially grateful to F. W. Peek, R. F. L o c k n e r , a n d G . M. Speers for their very helpful criticism a n d suggestions for the manuscript. P a p e r no. 7232, Scientific J o u r n a l Series, M i n n e s o t a A g r i c u l t u r a l Experim e n t Station, St Paul. REFERENCES Akerman, B. (1966a). Behavioural effects of electrical stimulation in the forebrain of the pigeon. I. Reproductive behaviour. Behaviour, 26, 323-338.. A,kerman, B. (1966b). Behavioural effects of electrical stimulation in the forebrain of the pigeon. II. Protective behaviour. Behaviour, 26, 339-350. Akerman, B., Andersson, B., Fabricius, E. & Svensson, L. (1960). Observations on central regulation of body temperature and of food and water intake in the pigeon (Columbia livia). Acta physiol. Seand., 50, 328-336. Baeumer, E. (1955). Lebensart des Haushuhns. Z. TierpsychoL, 12, 387--401. Barfield, R. J. (1965). Induction of aggressive and courtship behavior by intracerebral implants of androgen in capons. Am. Zool., 5, 203. Bartield, R. J. & Sachs, B. D. (1968). Sexual behavior: stimulation by painful electric shock to skin in male rats. Science, N. Y., 161, 392-395. Barlow, G. W. (1968). Ethological units of behavior. In: The Central Nervous System and Fish Behavior (Ed. by D. Ingle). University of Chicago Press. Bergquist, E. H. (1970). Output pathways of hypothalamic mechanisms for sexual, aggressive, and other motivated behaviors in opossum. J. comp. physioL PsychoL, 70, 389-398. Boord, R. L. (1968). Ascending projections of the primary cochlear nuclei and nucleus laminaris in the pigeon. J. comp. NeuroL, 133, 523-542. Brown, J. L. (1965a). Vocalization evoked from the optic lobe of a songbird. Science, N.Y., 149, 1002-1003. Brown, J. L. (1965b). Loss of vocalization caused by lesions in the Nucleus mesencephalicus lateralis of the Red winged Blackbird. Am. Zool., 5e693. Brown, J. L. (1969). The control of avian vocalization by the central nervous system. In: Bird Vocalization (Ed. by R. A. I--Iinde).Cambridge University Press.

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(Received 28 April 1970; revised 19 January 1971; second revision 8 May 1971; MS. number: A990)