Effects of cryogenic blocking of pulvinar upon visually evoked responses in the cortex of the cat

EXPERIMENTAL

Effects

NEUROLOCY39,

112-122

(1973)

of Cryogenic Blocking of Pulvinar upon Visually Evoked Responses in the Cortex of the Cat

LEO M. CHALUPA,

HARVEYANCHELANDDONALD

Departments of Psychology, Institute, Urriversity

Physiology of Califonzia, Received

and Psychiatry, Los Angeles,

October

B.

LINDSLEY'

alad Brain Research California 90024

30,1972

Visually evoked responses on the suprasylvian and marginal gyri were markedly diminished in amplitude by cooling of the pulvinar. Both the early and late components of the evoked response on the suprasylvian gyrus were affected but only the afterdischarge or late components on the marginal gyrus were reduced. The latter effect was shown to be mediated by the suprasylvian gyrus. Cooling of the B layer of the lateral geniculate, which we have previously shown to be a source of visual input to the pulvinar, reduced both the early and late components of the responses on the suprasylvian and marginal gyri, whereas cooling of the A layer caused a reduction of only the primary response components on the marginal gyrus. These results are interpreted as demonstrating two visual input systems to the cortex, one via direct geniculostriate pathways and another from the B layer of the lateral geniculate via the pulvinar to the suprasylvian gyrus. The former is mainly responsible for the primary response components of the marginal gyrus and the latter for the afterdischarge or late components.

INTRODUCTION Widespread responsesto visual, auditory, and somatosensory stimulation have been observed in the pulvinar and related posterolateral association nuclei of the thalamus of the cat, indicating that this region is a polysensory convergence center (1, 2, 9, 10). Evoked potential mapping, recovery cycle, and intermodality experiments demonstrated that in the pulvinar visual responseswere more prominent and that the visual modality was dominant in sensory interreaction tests (9). Chalupa, Anchel and Lindsley (3) have demonstrated that the pulvinar receives visual input from 1 This work was supported by USPHS Grant NS-8552. Assistance was also provided by the Mental Health Training Program (USPHS Grant MH-6415). Dr. Anchel’s address is : Department of Psychiatry, McMaster University, Hamilton, Ontario, Canada. 112

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the B-layer of the lateral geniculate body, the suprasylvian gyrus and the dorsal portion of the superior colliculus. The principal purpose of the present study was to investigate the cuiitributioii ol the pulvinar to visually evoked cortical responses. METHODS Data were obtained from 20 adult cats. After induction of anesthesia with halothane (IFluothane), the animal was placed in a stereotaxic instrument, the skull and dura mater overlying the marginal and suprasylvian gyri were removed, and the saphenous vein was cannulated for subsequent infusion of gallamine triethiodide (Flaxedil) . Homatropine hydrobromide was used to insure pupillary dilation and translucent, white, plastic contact lenses were placed on the cornea to diffuse the light and to prevent drying. A heating pad kept the animal at normal body temperature. After surgery, halothane was discontinued and the animal was maintained on a mixture of 80% NzO and 20% 02. In some animals a comparison was made of responses obtained under NZO, barbiturate anesthesia, and from unanesthetized brain. In all cases a paralyzing level of gallamine triethiodide (,Flasedil) was infused and the animals were artificially respirated. All incisions and pressure points were thoroughly infiltrated with lidocaine hyclrochloride (Xylocaine) to insure local anesthesia in the case of the unanesthetized brain. Following observations in the locally anesthetized animal, sodium pentobarbital (Nembutal) was intravenously administered to a level of 35 mg/kg. Light flashes were delivered by a Grass PS-2 photostimulator set at maximum intensity (appros 4 log units above dark-adapted electrophysiological threshold) and passed through an optical system which focused a spot of light over the entire contact lens. A period of dark adaptation was allowed before recording was begun. The eye contralateral to the recording electrodes was stimulated and a felt-black partition was placed between the eyes to eliminate light spread to the opposite eye. Monopolar responses were recorded from cortical and subcortical structures by means of flush-cut stainless steel electrodes with the indifferent electrode embedded in neck muscle. Cortical recordings were made with the electrode tip on the surface of the pia over the marginal gyrus (A2, L4) and over the posterior medial suprasylvian gyrus (AZ, LlO). Evoked responses were amplified by Grass P5 preamplifiers, displayed on a dual-beam 565 Tektronix oscilloscope and stored on magnetic tape for later analysis. The cryogenic blocking system has been described in detail (13). Briefly, it consisted of ethyl alcohol cooled in a dry ice and alcohol bath and circulated under pressure (loo-200 psi) through polyethelyene tubes connected to a cryoprobe located in, or on, the surface of the animal’s

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brain. For subcortical cooling, the cryoprobe was constructed from fine hypodermic needle tubing soldered together to form a double cnnnula system. Fine heater wire \vrappetl around the shaft of the probe kept it at normal temperature and cooling was limited to the exposed tip (3 mm for pulvinar cooling and 0.3 mm for geniculate cooling). Microthermocouples mounted on the shaft and tip permitted constant monitoring of the tern.perature. The tip temperature could be effectively controlled by varying the flow rate of the alcohol and in the present experiment a temperature of 5 C to 15 C was employed. For surface cortical cooling a 3 x 4 mm U-shaped foot-plate was used. It consisted of hypodermic tubing with a thin layer of solder connecting the two sides of the U. The experimental procedure consisted of recording cortical and subcortical responses to contralateral eye stimulation before, during, and after cooling of a specified brain structure. For each condition ten consecutive responses were “averaged” by a Mnemotron Computer of Average Transients with an analysis time of 500 msec. The averaged response was subsequently graphed by a Mosely X-Y plotter. The cooling period generally lasted for 3-5 min and in most cases changes in evoked potentials were obtained 2-3 min after the onset of the cooling period. Total reversibility of the cooling effect was obtained usually within 5 min following termination of cooling. If the changes in evoked responses obtained during the cooling period did not revert to the precook levels during the postcool period, the data were not utilized. Subcortical electrode and cryoprobe sites were identified and confirmed histologically after each experiment. RESULTS Figure 1 shows visually evoked responses recorded from the marginal gyrus (A2, L4) in the unanesthetized brain (A), under nitrous oxide (B), and under barbiturate anesthesia (C). Under nitrous oxide the evoked responses were very similar in pattern and waveform to those obtained in the unanesthetized brain, differing mainly in amplitude; in both cases there were prominent positive and negative initial or early components and also longer duration positive and negative late afterdischarge components. In contrast, under barbiturate anesthesia (35 “g/kg) amplitude of both the early and late components of the response were reduced and there was a marked change in the overall configuration of the response. In particular, the slow, positive-negative, late components were entirely absent and in their place was a second response similar to that of the initial or primary response. Thus it was evident that preparations under nitrous oxide (80% N20, 20% 0,) could be used without significantly modifying the cortical evoked potentials from those obtained in the unanesthetized brain, whereas

FIG. 1. Visual evoked responses from the marginal gyrus oi a cat under three conditions : (A) unanesthetized brain ; (B) nitrous oxide ; (C) sodium pentobarbitaf. Each record shows three superimposed traces. Calibrations : 100 mscc; 100 pv.

barbiturate anesthesia greatly depressedand changed the configuration of the response. in order to determine the effect of the pulvinar upon visually evoked responses over the marginal and suprasylvian gyri the activity of the pulvinar was blocked reversibly by cooling. In six experiments, a cryoprobe was introduced into the yuivinar at A 6.5, L 6.0 H +4 and responseswere recorded on the marginal and suprasylvian gyri before, during and after cooling, Results from a typical experiment are shown in Fig. 2. During cooiing of the pulvinar the initial positive and negative components of the response on the marginal gyrus remained essentially unchanged in amplitude but the late positive and negative components were reduced to 40% of the precool level. The mean for all animals was 4S5%,with a range from 25 to 70%. (All amplitude measures are based on peak to peak values of initial positive and negative waves for early components and on the late major positive and negative waves for late components.) In the case of the suprasylvian gyrus, cooling of the pulvinar markedly reduced the amplitude of the overall response,including the initial components as well as the late afterdischarge components. For all animals the initial or early com-

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ANCHEL,

AND

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COOL

FIG. 2. Average evoked potentials from the marginal sylvian gyrus (SSG) elicited by photic stimulation before, the pulvinar. Calibration : 50 msec ; 50 pv.

gyrus during

(MG) and

and supraafter cooling

ponents of the response on the suprasylvian gyrus were reduced to 600J0 (range 54-68s) while the late components of the afterdischarge were reduced to 44% (range 3542%) of the precool level. After recovery from cooling the responses of both the marginal and suprasylvian gyri returned to the normal precool level. In all experiments involving pulvinar cooling, responses were also recorded in the optic radiations 1-2 mm dorsal to the lateral geniculate body. There was no change in the response of the optic radiations during pulvinar cooling indicating that the changes observed over the visual cortex were not due to spread of cooling to the lateral geniculate body. Chalupa, An&e1 and Lindsley (3) 1lave shown that visually evoked cortical responses to ipsilateral and contralateral eye stimulation could be affected differentially by selective cooling of layers A, A1 and B of the dorsal nucleus of the lateral geniculate body. Cooling layers A or B reduced the response of the marginal gyrus to contralateral eye stimulation and cooling of layer A1 reduced the response to ipsilateral eye stimulation. Only the cooling of layer B reduced the long-duration negative component of the pulvinar response to photic stimulation. In view of these results it seemed important to compare the effect of cooling layers A and B of the geniculate on the responses of the marginal and suprasylvian gyri to photic stimulation of the contralateral eye. Figure 3 presents results which are typical of three such experiments. The top row shows the effect of cooling layer A of the geniculate upon the visually evoked response of the marginal gyrus. As expected, the initial positive-negative response was reduced, however, the longer duration

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positive-negative waves comprising the afterdischarge were not affected. Cooling layer B (second row) greatly reduced the positive component of the afterdischarge on the marginal gyrus but did not affect the late, longduration, negative component. It also reduced the initial positive-negative complex, but to a lesser extent than when layer A was cooled. In the bottom two rows, it may be seen that cooling of layer A had no appreciable effect upon the response of the suprasylvian gyrus, whereas the cooling of layer B modified the afterdischarge and reduced the amplitude of the overall response. Summarizing the results thus far it may be pointed out that cooling of the pulvinar had no effect upon the amplitude of the primary components of the visually evoked response on the marginal gyrus but significantly reduced the afterdischarge or late components. Cooling of the pulvinar affected both the early and late components of the response on the posterior suprasylvian gyrus (Fig. 2). Selective cooling of the layers in the lateral geniculate nucleus demonstrated that cooling of the A layer affected mainly the primary response on the marginal gyrus, whereas cooling of the B layer, which has previously been shown to reduce the response of the pulvinar (3), markedly reduced the amplitude of the positive component of the afterdischarge on the marginal gyrus and reduced the amplitude of both the initial and late components of the response on the suprasylvian (Fig. 3). COOL

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SSG-B

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FIG.

sylvian lateral

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3. Average evoked potentials from the marginal gyrus (MG) and gyrus (SSG) before, during and after cooling of the A or B layers geniculate body. Calibrations : 50 msec; 100 q.

supraof the

11%

CHALUPA,

ANCHEL,

AND

LINDSLEY

Anatomical studies have demonstrated projections from the pulvinar to the suprasylvian gyrus (4-6, 8, 17,) but to our knowledge no projections from the pulvinar to the marginal gyrus have been reported. Therefore, it was thought that the effect of pulvinar cooling on the afterdischarge recorded on the marginal gyrus might be mediated via the suprasylvian gyrus. To test this hypothesis, the suprasylvian gyrus was cooled and visually evoked responses were recorded from the marginal gyrus. The region cooled extended from A0 to A4 and from L9 to L12 and included a portion of area 19, as defined by Heath and Jones (S), and also overlapped the PMSA region of Thompson, Johnson and Hoopes (16). Figure 4A shows typical results of cooling the suprasylvian gyrus upon the response of the marginal gyrus to photic stimulation. There was a significant decrease in the amplitude of the late positive and negative components of the afterdischarge (mean value in all experiments 46% of precool level ; range 28-64s). The fact that there was no appreciable change in the primary response on the marginal gyrus suggests that the change in the afterdischarge was not due to spread of cooling from the suprasylvian gyrus. However, to further control for this possibility a microthermocouple

A

6

PRE-COOL

COOL ,/ “’

-~. ~,‘\J”\./J-

WA h

POST

COOL

FIG. 4. Average evoked potentials from marginal gyrus before, during and after cooling of the suprasylvian gyrus: (A) under nitrous oxide, (B) under sodium pentobarbital. Calibrations : 50 msec ; 100 pv.

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was placed on the marginal gyrus in two experiments. The temperature on the marginal gyrus, during the cooling period remained within +2 C. of that of the precool period. The preceding changes in the afterdischarge on the marginal gyrus brought about by cooling of the pulvinar, or of the suprasylvian gyrus, were obtained in animals maintained on a mixture of SO% N,O and 20% Oz. In three additional experiments the effects obtained under nitrous oxide were compared with those under sodium pentobarbital, (35 mg/kg) since it was observed (Fig. 1) that the late components of the response of the marginal gyrus under sodium pentobarbital were very different from those under nitrous oxide. *Figure 4B shows the results obtained under sodium pentobarbital. Cooling of the suprasylvian gyrus resulted in no significant change of the response on the marginal gyrus, either of its primary or secondary components. This result was obtained in two other cats. Similarly, in three cats under sodium pentobarbital anesthesia, cooling of the pulvinar resulted in no significant modification of the primary or secondary response recorded on the marginal gyrus. These results under barbiturate anesthesia contrast markedly with those obtained under nitrous oxide in which cooling of either the pulvinar or the suprasylvian gyrus affected the afterdischarge or late components of the visually evoked response on the marginal gyrus.

DISCUSSION The foregoing results have demonstrated that cooling of the pulvinar reduced the amplitude of both the early and late components of the visually evoked response on the suprasylvian gyrus but reduced the amplitude of only the afterdischage or late components on the marginal gyrus. This suggested that the effect of the pulvinar upon the response of the marginal gyrus was mediated via the suprasylvian gyrus. A test of this hypothesis was provided by cooling the suprasylvian gyrus which, like cooling of the pulvinar, also reduced the afterdischarge on the marginal gyrus, but did not affect its early or primary components. The implication of these results is that there is visual input from the pulvinar to the suprasylvian gyrus and that suprasylvian input to the marginal gyrus is responsible for an appreciable part of the afterdischarge recorded on the marginal gyrus. In accord with the first part of this view are the findings of Buser, Borenstein and Bruner (2), who showed that stimulation of the pulvinar-lateral posterior complex evoked short latency responses on the suprasylvian gyrus, and the results obtained by Bruner (1)) who found that KC1 applied in the posterolateral region of the thalamus suppressed photically induced responses on the suprasylvian gyrus. In addition, neuroanatomical studies have revealed projections from the pulvinar to the suprasylvian gyrus (4-6, 8, 17). With

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respect to the second part of the abovementioned view, namely, that the sul~rasylvian gyrus provides input to the marginal gyrus which is resl)ousible for some of the late coml~nents of its response to photic stimulation, there are known anatomical connections from the suprasylvian gyrus to the marginal gyrus (S), although their functional significance has not heretofore been reported. We have previously shown that cooling of the B layer of the lateral geniculate nucleus caused a decrease in the negative component of the pulvinar response to contralateral eye photic stimulation. In contrast, cooling of layer A of the geniculate did not affect the amplitude of the pulvinar response. These results were interpreted as showing that the B layer provides visual input to the pulvinar. In the present study, cooling of the A layer of the geniculate reduced the primary but not the late components of the response on the marginal gyrus and had no effect upon either the early or late components of the response on the suprasylvian gyrus. In contrast, cooling of the B layer of the geniculate reduced the amplitude of the early and late components of the responses on both the marginal and suprasylvian gyri. Our interpretation of these results is as follows: Although the A and Al layers supply input to the marginal gyrus (areas 17 and 18) which is responsible for the primary components of the visually evoked response on the marginal gyrus, these specific projections have no appreciable effect upon early or late components of the response of the suprasylvian gyrus or the late components of the marginal gyrus response. Also they do not affect the pulvinar response. On the other hand cooling of the B layer of the geniculate affects the pulvinar response, the late components of the responses of the suprasylvian and the marginal gyrus, as well as the primary or early components on both the marginal and suprasylvian gyri. Thus it appears that the B layer of the lateral geniculate has two modes of influence on the visual cortex, one, by direct projection to the marginal gyrus and the other, via the pulvinar to the suprasylvian gyrus. Its effect upon the afterdischarge or late components of the response of the marginal gyrus appear to be by this latter route. Narikashvili, Kajaia and Timchenko (12) found that low intensity electrical stimulation of the B layer of the geniculate evoked the largest response on the suprasylvian gyrus, while stimulation of A and A1 layers did not evoke responses on the suprasylvian gyrus. In view of our results, we are inclined to believe that the effects of B layer stimulation were mediated via the pulvinar to the suprasylvian gyrus. The visual input system which involves the B layer of the lateral geniculate, the pulvinar, the suprasylvian gyrus, and the marginal gyrus, seems to be a route supplementary to the direct pathway from layers A and A1 of the lateral geniculate nucleus to the marginal gyrus (areas 17 and 18).

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The input mediated by this pnlvinar-suprasylvian route seems to have its major effect upon the afterdischarge or the late components of the response of the marginal gyrus. The late components of visually evoked responses in humans have often been noted to manifest amplitude changes related to attention or vigilance (11, p. 3’2). Steriade (14) has suggested that the afterdischarge may be correlated with perceptual integrative processes. In the cat, afterdischarge has been associated with arousal (15) and with the presentation of reward during instrumental conditioning (7). If the afterdischarge or late components of the visually evoked response are related to states of arousal and attention then the results presented here suggest that the pulvinar may play an important role in these processes. REFERENCES J. 1965. AffCrence visulles non-primaires vers le cortex &r&bra1 chez le chat. J. Physiol. (Payis), 57 : Suppl. 12, l-120. BUSER, P., P. BORENSTEIN, and J. BRUNER. 1959. Etude des syst&mes “associatifs” visuels et auditifs chez le chat anesth& au chloralose. Elcctroencrpl~nlogr. Clin. Nmrophysiol. 11 : 305-324. CHALUPA, L. M., H. AN~HEL, and D. B. LINDSLEY. 1972. Effects of cryogenic blocking of the lateral geniculate, suprasylvian gyrus, superior colliculus and optic tract on flash-evoked responses in the pulvinar of the cat. Exfi. Ncwol.

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