Facilitation of active avoidance behavior by reinforcing septal stimulation in the rat

Phvvioloffy and Beharior. Vol. l, pp. 335-339. Pergamon Press Ltd., 1966 Printed in Great Britain

Facilitation of Active Avoidance Behavior by Reinforcing Septal Stimulation in the Rat ROBERT GOLDSTEIN

Washington University School o f Medicine, St. Louis, Missouri (Received 4 F e b r u a r y 1966) GOt.DSTEIN, R. Facilitation of acth)e avoidance behaviour by reinforcing septal stimulation in the rat. PHYSIOL.BEHAV. I (4) 335-339, 1966.--Rats with chronically implanted electrodes in the septal area were trained to bar press for brain stimulation. Following this, experimental animals were stimulated noncontingentlywith reinforcing stimulation while learning an active avoidance task. Results showed a significantly greater improvement of stimulated over nonstimulated animals in avoidance learning and intertrial activity. It was hypothesized that septal stimulation reduces the motivational level and thus permits the animals to perform adaptively in the active avoidance situation. The prediction was made that if this level could be reduced by procedural modifications, the facilitatory effects of stimulation would be reversed. Septal stimulation and avoidance

Septal area

Avoidance learning

RECENT STUDIES INDICATE THAT shock-motivated behavior is affected similarly by both stimulation and ablation of septal nuclei. Avoidance of shock by response inhibition ("passive avoidance") is disrupted by septai lesions in cats [2, 13] and rats [5]. Corroborating Kaada's [5] observations, Harvey and his group [4] have shown, in addition, that the disruptive effect of septal ablation is manifested not only in passive avoidance but, in parallel fashion, also in the establishment of conditioned suppression. In contrast to McCleary's interpretation of this phenomenon which attributes it to a deficiency in response inhibition, presumably a normal function of the septal area, Harvey et al. view it as a direct result of the increased thirst attendant upon septal lesions, an effect which they explored in their work. In either case it has been demonstrated in the studies by Kasper [6] and Goldstein [3] that medial septal stimulation had the same effects as lesions on passive avoidance and conditioned suppression, respectively. In avoidance tasks which involve movement of the animal for their solution ("active avoidance"), cats [2, 13] and rats [7, 8] with septal lesions were superior to controls in the post-operative acquisition of this habit. The present study represents an attempt to assess the effects of noncontingent reinforcing septal stimulation in an active avoidance task. Following McCleary's hypothesis as to the function of the septal region and considering the similar effects of lesions and stimulation of this area on passive avoidance it was predicted that stimulated animals would achieve a higher level of avoidance performance than controls. Rats chronically implanted with electrodes in the medial

Brain

Brain stimulation

septal area were trained to bar press for brain stimulation. Following this, an experimental group was stimulated noncontingently during avoidance training. METHOD

Subjects and apparatus Thirty-one male albino rats (Holtzman) 90-100 days old at the time of implantation served as subjects. The self-stimulation box was 8 in. :< 8 in. × 20 in. high with a grid floor of t in. brass rods mounted ½ in. apart. A plexiglas bar, ~ in. wide, projected 1~ in. into the box about I i in. above the grids. The box was enclosed in an aluminium cooling chest ventilated by a small exhaust fan 'and placed so that the rats could be observed through a plexiglas window in the chest cover. A white masking noise was piped into the chest at all times through a 4 in. speaker mounted on the box wall. The stimulation circuit (60 c/s AC) was interrupted by the contacts of a Hunter timer such that the pulse duration as well as the intensity was under the experimenter's control. For noncontingent stimulation, in the avoidance phase, a repeat cycle timer was arranged to drive the Hunter timer. The shuttle box dimensions were 24.5 in. "< 6 in. "< 23 in. high. The grid floor was composed of ~ in. brass rods spaced | in. apart, alternate rods wired together. The power, supplied by a 650 V step-up transformer, was fed through a 650 Kohm current limiting resistor and interrupted by an isolation transformer. This box was placed in an otherwise dark room illuminated with a 60 W incandescent

)This research was conducted at the Malcolm Bliss Mental Health Center and was supported in part by USPHS grant MH 07140 from tim National Institute of Mental Health. st would like to express my appreciation to Mrs. Janet Asdourian and to Dr. Hans Schmidt. Jr. for critical reading of preliminary drafts of this manuscript. 335

336 bulb located behind and slightly above the level of the grids. A 4 in. speaker attached to the outside top of the box provided white noise at all times during conditioning trials. The experimenter sat directly in front of and about 2 ft away from the apparatus. The stimulus control panel was below the table on which the box stoo-] so that the experimenter's manipulations were not visible to the animal. In both the Skinner box and shuttle box the brain stimuli were delivered through a coiled retractable cable plugged into an overhead s~,ivel arrangement mounted on the center top of the chambers. /~'roccdllrc

Surgery. Under ether anesthesia a bipolar electrode was implanted in each rat stereotaxically. The electrode was constructed of two twisted 0.005 in. nichrome wires each ~riply insulated except at the tip and directed at a target in the midline of the septai area. Three jeweler's screws were inserted partially through the dorsal skull surface and secured to the electrode with dental cement. Serf-stimulation training. Animals were operated over a period of I 1 days. Four days after the last rat was operated, self-stimulation began. This was administered in 10-20 rain sessions rotating animals so that about 3-4 days elapsed bctweer~ sessions for each rat. Training continued until stable rates of response were emitted, a period extending for approximately 30 days. Since relatively consistent rates within and across days were obtained for each subject using 0.3 sec, 90 I.tA pulses, the duration and intensity remained tixed at these values for all animals in the avoidance phase. However, since the rates of bar pressing across animals at these parameters did vary somewhat, the rate of nonconlingent pulsing for each one in the following avoidance training was determined by the mean number of responses in the animal's last two self-stimulation sessions (each 10 rain in duration). Ten animals with a relatively low incidence of seizures were selected as experimental animals, The remaining 21 were assigned to the control group. Conditioned avoidance (CAR) training. Stimulating leads were connected, the animal was placed into one side of the shuttle box, the door was closed and, for the experimental subjects, stimulus pulses began. This stimulation constituted the only difference in conditions between the two groups. One rain and 15 sec later the first trial started. The CS (a doorbell buzzer supplied by 3 VDC) was turned on, followed in 5 scc by concurrent electrification of the appropriate grid. An escape or avoidance response (terminating the CS and, in the former case, shock) was defined as a crossing of the animal exclusive of tail over the midline of the box. If, after 35 sec of CS ~ shock the rat did not escape, the trial was terminated. The interval between the onset of successive trials was I rain. Ten trials were run daily for 9 consecutive days. Under two conditions the 1 rain intertrial interval was modified. First, if the animal was within 2 in. of the midline and immobile at the time of CS onset, he was prodded from below until hc went to either side. After a 5 sec delay the tri,d began. The necessity for invoking this criterion was infrequent and then only later in training when some animals occasionally would freeze in the area of the midline. The second condition required more drastic modification. It was noted in a preliminary study that stimulated animals made more spontaneous (interlrial) crossings than did the controls. This difference in activity demanded a procedural change to minimize its effects. Thus, if a spontaneous crossing (SC)

GOLDSTEIN

appeared imminent at the time a trial would normally begin, the CS would be delayed until immediately after the response was made. By preventing the fortuitous reinforcement of a spontaneous crossing, indeed punishing such a response, this contingency could be expected to complicate the task for the more active (experimental) animals and thus bias tl',e results against the hypothesis. Though stringent, it was judged necessary in order to preclude the confounding of this source of activity with true avoidance responses. Histology. Shortly after the final training day the animals were etherized and perfused successively with isotonic saline and 10~, formalin. The brains were removed, sliced by frozen section procedure and examined microscopically. The sections of six experimental rats were then stained with cresyl violet and re-examined by blind procedure for placement. Pre- and poststain estimates of electrode locus were in almost exact agreement. RESULTS

The mean number of avoidance responses as well as the median number of spontaneous crossings across trial blocks are plotted in Fig. I. Though reciprocal latencies were calculated as well, they were found to produce redundant information and ~ill not be considered further. As can be seen in Fig. !, the two groups were virtually identical in both SCs and CARs in the first trial block, thus supporting the assumption that the procedures used to assign animals did not bias the results.

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T R I ALS { Block of I0) FIG. I. Mean number of CARs (left ordinate) and median number of SCs (right ordinate) across all trials for stimulated and control animals. Applying the U approximation to the normal curve [15], the increase in number of avoidance responses from blocks I to 9 (thus adjusting for the small initial difference) was significantly greater for the experimental group (Z ----- 1.87; Zoos :~ 1.64, I tailed). Although there was a significant differcnc~ between the controls and experimentais in total SCs (Z = 3.51, p < 0.01, two tailed), the correlation between total SC and increase in

AVOIDANCE BEHAVIOR AND SEPTAL STIMULATION

337 improvement in C A R are plotted in Fig. 2. Several instances among these suggest that SC variation might account for a significant portion of the C A R variance: (Animal 33). However, there exists abundant evidence in these data to refute this conclusion; consistently few SCs coupled with great CA R improvement in animal 8, apparently random SC-CAR relationships in animals 41 and 52, and block to

C A R from blocks 1 to 9 was significant only for the control animals: Experimentals, rho -~ 0.28 (p > 0.05)~ controls, rho ~ 0.63 (p < 0.01). A more detailed picture of the relationship between SC and CA R can be obtained by examining the block by block sequence of these variable in individual animals. For this purpose, the data for the 5 animals who showed the greatest

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FIG. 2. CAR and SC performance as a function of trials for the 5 experimental animals showing the greatest improvement in number of CARs.

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FIG. 3. Electrode localization of available experimental animals (one missing) on De Groot schematics. Indicated next to the animals' identifying number is the correction to be added to De Groot's AP coordinate (given on the upper right of each section) for more exact AP localization of that electrode.

338

GOLDSTEIN

block SC-CAR discrepancies in these and the remaining animals (as well as animal 33) all argue against this position. The electrode placements for all experimental animals except 35 (lost in histology) are presented on De Groot [1] schematics in Fig. 3. In Table 1, the bar pressing rate, total CARs and SCs are given for all experimental animals. No obvious relationship existed between locus and performance, nor was there a significant correlation between noncontingent stimulation rate (which was also the rate of self-stimulation) and either C A R or SC.

TABLE 1 BAg PRESSING RATE (PRESS/MIN),TOTAL CARs AND TOTAL SOs FOR ALL EXPERIMENTALANIMALS

No.

Bar press rate (press/rain)

Total CAR

Total SC

4

8 19 33 35 41 44 45 48 52

31.3

57

34.4 24.9 27.4 22.5 13.5 20.8 14.6 33.4 22.2

42 21 49 31 23 26 40 36 49

184 66 72 313 126 111 98 308 188 161

DISCUSSION

The results of this study support the hypothesis that reinforcing septal stimulation as well as septal lesions can facilitate the learning and/or performance of an active avoid, ance response. This effect is consonant with the observation that septal stimulation [3] and lesions [13] have similar effects on passive avoidance behavior. The data submitted by McCleary [13] were in agreement with his hypothesis that the intact septal area plays an inhibitory role. The adverse effects of septal lesions on passive avoidance were accordingly effected by removing the inhibition which normally prevents the animals from approaching the shock source. In contrast to the inactivity called for in a passive avoidance task the successful performance of an active avoidance response involves movement and since inhibition of behavior in the active task is incompatible with the criterion response, he argued, septal lesions would be expected to potentiate learning. The data from the present stimulation experiment seem to accord well with this view. Though the stimulated rats maintained a significantly higher level of activity than controls throughout training, an effect which might easily be confounded with avoidance responses, a closer examination of the SC-CAR relationship in 5 experimental animals revealed little basis for this interpretation. Several points m u s t be considered however, before the statement can be accepted unqualifiedly that septal stimulation or indeed lesions enhance C A R learning and if so, whether McCleary's [13] interpretation is the only one that fits this phenomenon. The level of asymptotic performance achieved by the control group (2-3 CARs in 10 trials) is

quite low compared to most standards of avoidance behavior. Observing these animals it became quite obvious that an extremely dominant and progressively more frequent freezing response characterized their behavior, an effect absent in the experimental group. It is assumed that the high shock intensity produced a motivational level sufficiently disorganizing that the shuttle response, which under the present conditions is a difficult discrimination, represented an impossible task; freezing, typical of rats in a situation where shock is unavoidable (CER), ensued. Both Thomas and Slotnick [16] and Lubar [11, 12] have involved the freezing response as critical in attempts to account for alterations in C A R by cingulate lesion. Although the reduction of freezing and the improvement of shock avoidance by d-amphetamine [8] is consistent with the relationship observed in the present study, the emphasis implied above alters the hypothesized order of events. That is, it seems at least equally logical to assume that the freezing response becomes prepotent as a result of the animals' inability to cope with the avoidance task. This stands in contrast to the more common view of this phenomenon, e.g. Krieckhaus et al. [8] which suggests the reverse sequence: that the freezing response accounts for or causes the learning deficit in control animals. In both cases the appearance of the freezing response would be correlated with inadequate performance. According to the former position, however, the effect of septal lesions (or stimulation) on avoidance behavior is not by way of reducing the freezing response directly but by attenuating the mediating process (CER) to a level at which the problem becomes soluble (and thus precludes freezing). Although both interpretations yield the same prediction when the animals are freezing, they diverge in predicting the outcome when the task can be solved and freezing is apparently absent. This could be accomplished by reducing the complexity of the task, lowering the shock level or perhaps gradually increasing the shock level over trials to ! ma from a lower more optimal intensity. The present argument would hold that if these parameters were chosen carefully, the effects of septal stimulation would produce a decremental rather than a facilitatory effect on C A R learning. A second point, mentioned earlier, involves a secondary mechanism provided by Harvey et al. [4] to mediate the effects of septal lesions on shock avoidance behavior. It is their hypothesis that the increased thirst induced by septal lesions underlies the passive avoidance deficits observed in these animals. Kaada et al. [5], who explored this possibility previously, found no increase in water ingestion of their lesioned animals in a 24 hr intake test following 48 hr of deprivation, the level at which the adverse effects of their lesions were established. Although indirect, evidence submitted b y L u b a r and Wolfe [12] might also have some bearing on this issue since they found that rats with anterior cingulate lesions also increased their water intake. Selected rats with extensive cingulate lesions invading anterior areas in Kaada's experiment and cats with lesions here [13], performed as normals in passive avoidance tests contrary to what would be expected in intake is to be considered a critical variable. As for the effects of increased drive on active avoidance behavior, McCleary's cats with anterior cingulate lesions and King's operated control rats with anterior lesions were also not differentiable from normais. The data on the effects of cingulate lesions should be accepted with caution of course since these lesions might have effects other than on water intake which could conceivably cancel the effects on passive

AVOIDANCE BEHAVIOR AND SEPTAL STIMULATION avoidance of the increased thirst observed by Lubar. Nevertheless, it cannot be said definitively that the results of septal manipulation on passive avoidance are ascribable to either a change in drive level, reduction of the physiological state which we call "fear", specific attenuation of the freezing response, or some interaction of these variables. Whatever this mechanism(s) might be, the current data indicate, somewhat paradoxically, that both septal stimulation and lesions alter behavior in the same direction. With respect to C A R behavior the effects of extraneous

339 drive alterations, shock intensity, apparatus differences and other procedural variables must be controlled before it can be categorically accepted that either septal lesions or stimulation facilitate C A R learning or that their effects are similar. What can be stated at present is that both manipulations can improve active avoidance performance. Recent data submitted by McNew and Thompson [14] suggest, in addition, that lesions can have a deleterious effect on both passive and active avoidance a finding which underlines the necessity for procedural controls in this area.

REFERENCF~ Verh. K. Ned. Akad. Wet., Natuurkunden. 52: 1--40, 1959. 2. Fox, S. S., D. P. Kimble and M. E. Lickey. Comparison of caudate nucleus and septal-area lesions on two types of avoidance behavior. J. Comp. Physiol. Psychol. 58: 380-386, 1964. 3. Goldstein, R. Effects of noncontingent septal stimulation on the CER in the rat. J. Comp. Physiol. Psychol. 61: 132-135, 1966. 4. Harvey, J. A., C. E. Lints, L. E. Jacobson and H. F. Hunt. Effects of lesions in the septal area on conditioned fear and discriminated instrumental punishment in the albino rat. J. Comp. Physiol. Psychol. 59: 37-48, 1965. 5. Kaada, B. R., E. W. Rasmussen and O. Kveim. Impaired acquisition of passive avoidance behavior by subcallosal, septal, hypothalamic and insular lesions in rats. J. Comp. Physiol. Psychol. 55: 661-670, 1962. 6. Kasper, P. Attenuation of passive avoidance by continuous septal stimulation. Psyehon. Sci. 1: 219-220, 1964. 7. King, F. A. Effects of septal and amygdaloid lesions on emotional behavior and conditioned avoidance responses in the rat. J. Nerv. Ment. Dis. 126: 57-63, 1958. 8. Krieckhaus, E. E., N. E. Miller and P. Zimmerman. Reduction of freezing behavior and improvement of shock avoidance by d-amphetamine. J. Comp. Physiol. Psychol. 60: 36-40, 1965. 1. De Groot, J. The rat brain in stereotaxic coordinates.

9. Krieckhaus, E.E.,H.J. Simmons, G.J. Thomas and J. Kenyon. Septal lesions enhance shock avoidance behavior in the rat. E.xpl Neurol. 9: 107-113, 1964. 10. Lubar, J. F. Effect of medial cortical lesion* on the avoidance behavior of the cat. Y. Comp. Physiol. Psyehoi. fl~: 38-.46, 1964. 11. Lubar, J. F. and A. A. Perachio. One-way and two-way learning and transfer of an active avoidance respon~ in normal and cinffalectomJzed cats. J. Comp. Physiol. Psyehol. 60: 46--52, 1965. 12. Lubar, J. F. and J..W. Wolfe. Incr~__=_~edbasal water and food ingestion in cingulectomiz~ rats. Psychon. Sei. I: 289-290, 1964. 13. McCleary, R. A. Response specificity in the behavioral effects of limbic system lesions in the cat. Y. Comp. Physiol. P~,hol. ~1: 605--613, 1961. 14. McNew, J. J. and R. Thompson. Role of the limbic system in active and passive avoidance in the rat. J. Comp. Physiol. Psychol. 61: 173-180, 1966. i 5. Siegel, S. Nonparametrle Statistics for the Behavioral Sciences. New York: McGraw-Hill, 1956. 16. Thomas, G. J. and B. Slotnick. Effects of lesions in the cingulum on maze learning and avoidance conditioning in the rat. J. Comp. Physiol. Psychol. $$: 1085-1091, 1962.