Role of the telencephalon in color vision of fish

EXPERIMENTAL

Role

NEUROLOGY

of the

6, 173-185

Telencephalon JERALD

Laboratory Diseases

(1962)

of Neuroanatomical and Blindness, National

Received

in Color J.

Vision

of

Fish

BERNSTEIN~

Sciences, National Institute of Neurological Institutes of Health, Bethesda, Maryland April

18, 1962

The role of the telencephalon in hue discrimination and interocular transfer of hue discrimination has been studied. Cardiac deceleration, a conditioned autonomic response, was used as the measure of discrimination in goldfish. Electric shock was the unconditioned stimulus. After occluding one eye, normal fish were trained to a red and a green stimulus selected to be of equal brightness. The naive or transfer eye was then tested on red and green stimuli of known brightness as perceived by these experimental animals. Normal fish and fish with the forebrain contralateral to the trained eye ablated demonstrated interocular transfer of a hue discrimination. Following ablation of the forebrain homolateral to the trained eye or bilateral forebrain ablation, operated fish demonstrated a loss in ability to make an interocular transfer to generalizations of hue. However, the ability to make an interocular transfer of a hue discrimination returns if a suitable period is allowed postoperatively. It was concluded that the telencephalon is not essential for color vision or for the interocular transfer of color vision in fish. Introduction

The effect of forebrain ablation on hue discrimination of fish was studied previously (5, 15), and it was found that the forebrain had no role in the color vision of fish. However, the results are subject to doubt because of inadequate control for brightness cues during tests for hue discrimination. When brightness cues are properly controlled, fish trained subsequent to bilateral forebrain extirpation demonstrate a loss in ability to make a hue discrimination (1). These operated animals only respond to the brightness differences of stimuli differing in both brightness and color. The identical operation and training procedure using stimuli that differ only in relative brightness does not result in any loss in ability to make a brightness discrimination (2). In mammals, incomplete decussation of the optic nerve leads to a 1 The gratefully

author is indebted to Mary E. Bernstein for reading acknowledges her aid in all phases of this work. 173

the EKG

records

and

174

BERNSTEIN

bilateral projection of the retinal image on the visual cortex. To delineate the pathways subserving interocular transfer, an operation has to be carried out to obtain a unilateral projection of the visual image in the visual cortex. Myers (12) transected the decussating fibers of the optic nerve and found that there was excellent interocular transfer when cats were trained to do relatively easy tasks, but interocular transfer was poor on more difficult discriminations. The corpus callosum was found to play a major role in the transfer of visual information between the hemispheres of the cortex (13). After sectioning the corpus callosum and the decussating fibers of the optic nerve, interocular transfer does not occur (21) ; one cerebral hemisphere does not benefit from the experience of the other half (13, 14) and the two hemispheres can function independently of one another (18, 19). Both eyes can learn contradictory color visual tasks simultaneously if the midbrain commissures are also sectioned; however, this extensive surgery does not prevent transfer of simple brightness discriminations (22). The optic nerve of the bird is completely decussated; consequently this animal displays a unilateral projection of optic fibers to the visual cortex. Chickens and pigeons (6, 7) demonstrate complete interocular transfer; however, chickens do not demonstrate any ability to react to distortions of the original training stimuli ( 11) . In the fish there is not only complete decussation of the optic nerve, but no cortex or corpus callosum. In fact, the main visual correlating center may be the optic tectum of the mesencephalon. There is interocular transfer of a pattern discrimination in the fish (8, 10, 20), but like the chicken the transfer eye does not show any ability to react to distortions of the patterns used during training ( 17). If an autonomic response is used as the criterion for learning, the fish demonstrates complete interocular transfer when they are trained to discriminate between a pair of stimuli differing in three parameters, pattern, brightness, and color. However, when the fish are trained in a maze the transfer or untrained eye must have the visual experience of swimming through the maze in order for interocular transfer to occur (8). The present study was undertaken to determine the role of the forebrain in the color vision of fish. Interocular transfer was used as the behavioral index of brain function and heart rate, a simple autonomic criterion, was used as the criterion of learning. After it was found that normal fish demonstrated interocular transfer of hue, the effect of forebrain ablation (subsequent to training) on the ability of fish to make such a discrimination was studied.

TELENCEPHALON

AND

COLOR

VISION

175

Methods Cardiac electrodes were bilaterally implanted (9) in the anterior portion of the visceral gavity of 6- to g-inch goldfish (Carassius auratus L.) . An electrocardiogram was recorded on a Sanborn recorder using a Sanborn high-gain preamplifier. The fish was suspended in a 30-gallon aquarium and isolated from outside distraction by a white plastic hood. The aquarium was illuminated by a 100-w Mazda lamp and lined with Coloraid Gray #5 art paper mounted in plastic ( 1) . The stimulus patches used in this experiment were l-inch clear plastic squares containing Color-aid art papers alone or in combination with Kodak Wratten filters. These squares were mounted on plastic rods for the purpose of presenting the stimuli to the test animal. The composition, brightness, and color characteristics of the stimuli have been described (1). The designation of “dark,” “light,” and “medium” in Table 1 means that stimuli were, as perceived by normal fish (1, 2, 9), respectively lighter than, darker than, or of the same brightness as the gray background lining the aquarium. These stimuli were also distinctly red and green as designated in Table 1. The brain case was opened and the various portions of the forebrain removed by aspiration. The cranial cavity was then closed with a metal cap. The cranial cap and operation have been described ( 1) . Three types of ablation were performed: the forebrain contralateral to the trained eye; the forebrain homolateral to the trained eye; and bilateral forebrain ablation. After training, operation, and testing, the brains of all forebrain-ablated fish were perfused with Bodian’s No. 3 fixative, sectioned (10 p), and stained by a modification of Bodian’s technique (3), with Protargol-S (Winthrop Laboratories) and no copper or mercuric salts added. A summary of the training and testing stimuli are given in sequence of stimulus presentation in Table 1. The procedure involved conditioning of the heart rate, using electric shock as the unconditioned stimulus and the various stimulus patches as the conditioned stimulus. In this procedure, learning can be demonstrated by showing that presentation of a stimulus previously associated with shock results in a greater cardiac deceleration than does presentation of a stimulus not previously associated with shock (1, 2, 9). Prior to the training series for each fish, the right eye, which will be referred to as the “transfer eye,” was always covered with an opaque black vinyl plastic contact lens. This lens fitted tightly into the bony orbit of the eye and eliminated the possibility of the right eye perceiving the

interocular transfer or hue generalization

Trained

M. g. M. r.

M. g. M. r.

Neut.

L. g. L. r.

L. g. L. r.

Neut.

D. r. D.g.

D. r. D. g.

Pos.

Test

1

Transfer

L. r. L. g.

L. r. L. g.

Pos.

eye

sequence. normal during

D. g. D. r.

D. g. D. r.

Neut.

training.

M.g. M. r.

Neut.

as presented

STIMULI~

in sequence

AND TESTING

stimuli

TABLE OF TRAINING

each in an ABBA counterbalanced before testing; the animals were D., dark ; r., red; g., green.

M. r. M. g.

M. r. M. g.

Pos.

eye

stimuli0

0 All stimuli were presented twice b All extirpations were performed POX, positive; L., light; M., medium;

No

Interocular transfer and hue generalization

Discrimination

Training

SUMMARY

Abbreviations:

M.r. ‘M. g.

Pos.

Trained

Neut.,

M. g. M. r.

Neut.

neutral;

M. r. M. g.

Pos.

eye

TELENCEPHALON

AND

COLOR

VISION

177

reflection of the stimuli used during training. The left eye, which was always the eye that received the training, wilI be referred to as the “trained eye.” During training, a pair of stimuli, designated as medium red and medium green, were employed. One stimulus of the pair was presented with electric shock (the positive stimulus) during the last 2 set of a S-set presentation. The other member of the pair was never paired with electric shock (the neutral stimulus) during 10 set of presentation, These stimuli were randomly presented at 1-min intervals against the gray background. After twenty-five training trials, an ABBA counterbalanced (neutral, positive, positive, neutral) presentation of the training stimuli was carried out. While testing for cardiac conditioning both training stimuli were presented in an identical manner, for 10 set each, and no electric shock was given during the counterbalanced series of presentations. The heart rate was recorded for 10 set prior to stimulus presentation and 10 set during stimulus presentation. The conditioned cardiac responsewas one of deceleration of heart rate upon presentation of the stimulus associatedwith shock. If the animal had learned this hue discrimination (9), five additional training trials were given before testing. If the animal was to be operated upon it was removed from the training apparatus and the appropriate ablation performed. The opaque plastic eye cup was removed from the right or transfer eye and placed on the left or trained eye. Ten minutes or 4 hours postoperatively (according to operated group) the test fish was presented a counterbalanced series of two pair of test stimuli. These stimuli were light green, dark red; and dark green, light red; and were perceived by normal fish to be lighter than and darker than the gray background against which they were presented (9). When trained to the medium red and medium green stimuli, normal fish react to test stimuli on the basis of hue and not on the basis of the brightness (9). However, if the forebrain of the fish is bilaterally ablated lo-min prior to training the test animals respond to the brightness characteristics of the test stimuli ( 1). One group of animals underwent a bilateral forebrain ablation 6 weeks prior to training and testing. These animals were trained to the medium red and medium green stimuli, and after a lo-min lapse the transfer eye was tested with the light and dark, red and green testing stimuli. Additional tests were performed on animals that did not demonstrate interocular transfer of the test stimuli. The medium red and medium green training stimuli were presented to the transfer eye in counterbalanced order. The eye-cup was then removed from the left eye and placed on

178

BERNSTEIN

the right eye. Ten minutes later the left or training eye was tested with the medium red and medium green training stimuli in counterbalanced sequence to determine if the test animals were capable of responding appropriately to any stimuli following forebrain ablation. Results

The averaged data for the animals used in these experiments are summarized in Tables 2 and 3. The figures represent the heart rate before and during stimulus presentation. The test stimulus designatedas positive is the stimulus of the samecolor as the stimulus paired with shock during training (the positive training stimulus). These data for all counterbalanced sequenceshave been reduced to an average response to the neutral stimulus and an average responseto the positive stimulus. Interocular Transfer of a Hue Discrimination in Normal Unoperated Fish and in Fish Following Unilateral Forebrain Ablation. The ‘mean results of the five normal unoperated control fish are shown in Table 2. MEAN

TABLE 2 DECELERATION IN HEART RATE IN BEATS PER MIN IN NORMAL CONTROLS AND AFTER UNILATERAL FOREBRAIN ABLATION Normal unoperated controls

Stimuli

Forebrain contralateral to trained eye ablated preoperative

Medium red and training stimuli (trained eye) Light red, dark green, and dark light green test stimuli (transfer eye)

green

red,

neutral positive p<

39.23 0.01

neutral positive p<

17.67 29.94 0.05

Medium red and green training stimuli (transfer eye)

neutral positive p<

Medium red and training stimuli (trained eye)

neutral positive p<

green

17.85

UNOPERATED Forebrain homolateral to trained eye ablated training

17.21 32.70 0.01 IO-min nostonerative

14.68 36.03 0.02 testing

14.26 25.66

19.29 20.60 0.40

0.01

1.41

7.63 0.20 11.40 29.37 0.01

TELENCEPHALON

AND

COLOR

VISION

179

These animals as well as all the animals used in this series of experiments learned the original training problem within an average of twenty-five training trials. After learning the original problem the transfer eye of the normal control animals was tested with the dark and light, red and green test stimuli. As can be seen in Table 2, there was complete interocular transfer and generalization of hue. The cardiac responses to the positive test stimuli were significantly greater than the responses to the neutral test stimuli. Another group of five animals was trained. After these animals had learned the original problem, the forebrain contralateral to the trained eye was ablated and 10 min later the transfer eye was tested. There was complete interocular transfer and generalization of hue by the animals in this operated group (Table 2 ) . The mean results of the test sequences for the five animals that were trained and then had the forebrain homolateral to the trained eye ablated are given in Table 2. Ten minutes after extirpation of the forebrain, interocular transfer of a hue discrimination could not be demonstrated for this group of operated animals during the generalization tests or when the transfer eye was tested with the original stimuli used during training. There were no consistent responses to the color or brightness of the test or training stimuli. The trained eye was then tested with the medium red and medium green training stimuli. The cardiac responses to the stimulus formerly associated with electric shock were significantly greater than the responses to the neutral stimulus. Interocular Transfer of a Hue Discrimination Following Bilateral Forebrain Ablation. Five animals were trained and then the forebrain was extirpated bilaterally. Ten minutes postoperatively the transfer eye was tested with the light and dark, red and green test stimuli. There was no consistent response to the color or brightness of the test stimuli (Table 3). The transfer eye was then tested with the medium red and medium green training stimuli. The operated animals may have discriminated these stimuli (P < 0.10) as indicated by the low probability value obtained from a t-test of these data. However, when the trained eye was presented the training stimuli the operated animals responded appropriately to the stimuli and showed no demonstrable loss in magnitude of response between pre- and postoperative condition of the animal. Seven animals were trained and then the forebrain was bilaterally extirpated. Four hours postoperatively the animals were tested on the light and dark, red and green stimuli. There was complete interocular transfer

180

BERNSTEIN

and generalization (Table 3) to the color of the test stimuli by these operated animals. These animals also responded appropriately to the training stimuli as would be expected of animals that demonstrated interocular transfer and generalization of a hue discrimination. In both cases the cardiac responses to the positive stimuli were significantly greater than the responses to the neutral stimuli. TABLE

MEAN

3

DECELERATION IN HEART RATE IN BEATS PER MIN BILATERAL FOREBRAIN ABLATION

Stimuli

AFTER

Training 6 weeks postoperative

preoperative Medium red and green training stimuli (trained eye)

neutral positive p<

12.00

6.56

13.15

32.39 0.02

37.36 0.01

35.98

0.01

Testing 10 min postoperative Light red, dark green, and dark light green test stimuli (transfer eye)

4 hours

postoperative

10 min after training

neutral positive p<

13.92

29.13

14.90

17.32

47.11

27.50

0.30

0.02

Medium red and green training stimuli (transfer eye)

neutral positive

4.39 a.79

17.06 37.52

p<

0.10

0.02

Medium red and green training stimuli (trained eye)

neutral positive p<

red,

0.02

17.41 29.62 0.02

Six weeks after bilateral forebrain ablation, five animals were trained to the medium red and green stimuli. After a lo-min lapse, these animals were tested on the light and dark, red and green test stimuli. These. animals demonstrated complete interocular transfer and generalization of hue (Table 3). Hue Discrimination in Operated Fish When Testing the Trained Eye After Bilateral Forebrain Ablation. Five animals were trained to the medium red, medium green training stimuli and the trained eye was tested 10 min after bilateral forebrain ablation. The results from this

TELENCEPHALON

AND

COLOR

VISION

181

group would determine whether the operated animals were making a hue or brightness discrimination when using the trained eye postoperatively. These animals learned the original training problem with an average neutral response of 5.92 beats per min and an average positive response of 26.40 beats per min (P < 0.01). Postoperatively the test animals responded to the color differences of the dark and light, red and green test stimuli. The average neutral response was 5.83, and the average positive response, 15.56 beats per min (P < 0.05). It may be concluded that forebrain ablation subsequent to training has no effect on generalization of a learned hue discrimination if the same eye is trained and tested. Histological Results. Serial cross sections of all the operated brains were examined. All unilateral lesions were alike in extent. For this reason, the two groups of unilaterally ablated animals will be treated simultaneously. The following nomenclature is based on the work of Herrick (4)) and the nucleus preopticus will be considered the most rostra1 area of the diencephalon. As can be seen in Fig. 1, the telencephalon sheared at an oblique angle along the endorhinal fissure. This fissure is the ventral border of the area olfactoria dorsalis and the dorsal border of the area olfactoria medialis of the telencephalon. The sections Fig. 1A and B, respectively, represent the approximate rostra1 and caudal site of the lesion. Rostrally the nucleus olfactorius anterior had been ablated and only the ventral portion of the area olfactoria medialis is present. The pars lateralis, dorsalis, and medialis of the area olfactoria dorsalis had been totally extirpated. By following the sections caudad (Fig. IB) it was evident that the area olfactoria posterior has been totally extirpated. After bilateral forebrain ablation it was evident that telencephalon had been completely ablated. Rostrally (Fig. 1C) the nucleus preopticus of the diencephalon is evident. A section more caudad (Fig. ID) shows that the area olfactoria posterior of the telencephalon had been extirpated. The area somatica seen in Fig. 1B and D receives ascending fibers from the dorsal portion of the thalamus; these fibers are in continuity with the area rostra1 to this site which is designated as the area olfactosomatica (4). The area olfacto-somatica had been ablated following unilateral or bilateral extirpation of the telencephalon. There might have been damage to the area somatica as well, because of edema of the areas caudad to the lesion and the loss of fibers passing through the areas that project rostrally into the telencephalon.

182

BERNSTEIN

FIG. 1. Photomicrographs of cross sections of fish brain following forebrain 18.5 X. A, approximate rostra1 site of the ablation, modified Bodian technique, lesion following unilateral extirpation of the right hemisphere of the telencephalon. B, approximate caudal site of the lesion following unilateral extirpation of the right hemisphere of the telencephalon. C, approximate rostra1 site of the lesion following bilateral extirpation of the telencephalon. D, approximate caudal site of the lesion following bilateral extirpation of the telencephalon. Abbreviations: A. D. p. d., pars dorsalis of the area olfactoria dorsalis; A. D. p. l., pars lateralis of the area olfactoria dorsalis; A. D. p. m., pars medialis of the area olfactoria dorsalis; A. 0. M., area olfactoria medialis; A. 0. P., area olfactoria posterior; A. S., area somatica; F. E., fissura endorhinalis; Hab., habenula; Hyp., hypothalamus; M., midline; N. O., nervous opticus; N. PO., nucleus preopticus, T. O., tectum opticum.

TELENCEPHALON

AND

COLOR

VISION

183

Discussion

The experiments show that the telencephalon of the goldfish is not essential for color vision or for interocular transfer of a hue discrimination. Furthermore, the goldfish can demonstrate interocular transfer and generalization of a hue discrimination. These animals respond appropriately to the color differences of the test stimuli despite the proven brightness differences in the stimuli. Although normal fish do not demonstrate interocular transfer to distortions of the original patterns used during training (17), the present work shows that they respond well to distortions of colored stimuli (i.e., distortions of brightness and saturation). Forebrain extirpation results in a selective suppression of the color visual system of the fish. If goldfish are trained 10 min after bilateral forebrain ablation and then tested with the same stimuli used in the present paper, they respond only to the brightness differences of the test stimuli (1). When the animals are trained and then the forebrain is bilaterally ablated, the test animal will make an interocular transfer and generalization of a hue discrimination if it is tested after sufficient time has elapsed for postoperative recovery. If the forebrain homolateral to the trained eye is ablated and that half of the brain receiving the sensory input from the naive eye does not have a forebrain present, there is no interocular transfer of generalizations of hue. The same phenomenon occurs if the animal is tested 10 min after bilateral forebrain ablation. It appears that color vision is suppressed immediately after forebrain ablation and brightness becomes more apparent to the test animal (2). It is not surprising to find that these animals did not respond to the color differences in the stimuli differing in color and brightness. There appears to be a great difference in the ability of fish to demonstrate interocular transfer. These differences seem to be based not only on the type of stimuli used (pattern vs. color), but also on the type of response that is trained (complex motor acts vs. autonomic response). Perhaps the fish trained in mazes with one eye occluded did not receive sufficient training trials for interocular transfer to be manifested. The possibility would seem to deserve further investigation. What is the anatomical location of the area in which transfer of visual information occurs? This experiment has shown that the telencephalon is not essential for interocular transfer. There is also some negative evidence to narrow the area in which interocular transfer of visual information is taking place. Evoked potentials could not be recorded from the com-

184

BERNSTEIN

missural system of the optic tectum of the goldfish upon photic stimulation of the eye (16). This leaves two other areas, the medulla oblongata or the diencephalon. There does not seemto be any reason for the supposition that the medulla is directly involved with the transfer of visual information between the halves of the brain. However, the diencephalon is known to carry fibers directly involved with vision (4). For this reason it would not be surprising to find the commissural system of the diencephalon involved in the interhemispheric transfer of visual information in the fish. References I. 2. 3. 4. 5.

6. 7. 8. 9. 10. 11. 12. 13.

J. J. 1961a. Loss of hue discrimination in forebrain ablated fish. Exptl. Neurol. 3: 1-17. BERNSTEIN, J. J. 1961b. Brightness discrimination following forebrain ablation in fish. Exptl. Neural. 3: 297-306. BODIAN, D. 1936. A new method for staining nerve fibers and nerve endings in mounted paraffin sections. Anet. Record. 66: 89-97. HERRICX, C. J. 1922. Functional factors in the morphology of the forebrain of fishes, In “Libra en honor de S. Ramon y Cajal.” 1: 143-204. JANZEN, W. 1933. Untersuchungen iiber Grosshirnfunktionen des Goldfisches (Carassius aura&). 2001. Jahrb. Abt. allgem. Zool. Psysiol. Tiere 62: 592-628. LEVINE, J. 1945a. Studies in the interrelations of central nervous structures in binocular vision: I. The lack of bilateral transfer of visual discriminative habits acquired monocularly by the pigeon. 1. Genet. Psychol. 67: 105-129. LEVINE, J. 194513. Studies in the interrelations of central nervous structures in binocular vision: II. The conditions under which interocular transfer of discrimination habits takes place in the pigeon. J. Genet. Psychol. 67: 131-142. MCCLEARY, R. A. 1960. Type of response as a factor in interocular transfer in the fish. J. Comp. Physiol. Psych. 63: 311-321. MCCLEARY, R. A., and J. J. BERNSTEIN. 1959. A unique method for control of brightness cues in study of color vision in fish. Physiol. Zool. 32: 284-292. MCCLEARY, R. A., and L. A. LONGFELLOW. 1961. Interocular transfer of pattern discrimination without prior binocular experience. Science 134: 141% 1419. MENKHAUS, VON, I. 1957. Versuche iiber einaugiges Lernen und Transponieren beim Haushuhn. Z. f. Tierpsyckol. 14: 210-230. MYERS, R. E. 1955a. Interocular transfer of pattern discrimination in cats following section of crossed optic fibers. J. Comp. Physiol. Psych. 46: 470-473. MYERS, R. E. 195513. Function of corpus callosum in interocular transfer. BERNSTEIN,

Brain

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358-363.

14. MYERS, R. E. 1959. Interhemispheric communication through corpus callosum: Limitations under conditions of conflict. J. Comp. Physiol. Psych. 62: 6-9. 15. NOLTE, W. 1933. Experimentelle Untersuchungen zum Problem der Localization des Assoziations vermogens in Fischgehirn. Z. vergleich. Physiol. 18: 255-279.

TELENCEPHALON

16. 17. 18. 19. 20. 21.

22.

AND

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VISION

185

1959. Electroenecephalographic patterns of J. P., and I. J. WEILER. the goldfish (Carussius aurutus L.). J. Exptl. Biol. 36: 435-452. SCHULTE, A. 1957. Transfer and Transposition versuche mit monokular Dressierten Fischen. 2. vergleich. Physiol. 99: 432-476. SPERRY, R. W. 1961a. Cerebral organization and behavior. Science. 133: 17491757. SPERRY, R. W. 1961b. Some developments in brain lesion studies of learning. Federation Proc. 20: 609-616. 1949. Interocular transfer of visual discriminaSPERRY, R. W., and E. CLARK. tion habits in a teleost fish. Physiol. 2002. 29: 372-378. SPERRY, R. W., J. S. STAMM, and N. MIN~.x. 1956. Relearning tests for interocular transfer following division of optic chiasma and corpus callosum in cats. J. Camp. Physiol. Psych. 49: 529-533. TREVARTHEN, C. B. 1962. Double visual learning in split-brain monkeys. Science. 136: 258-259. SCRADE,