Detection performance of normal cats and those lacking areas 17 and 18: a behavioral approach to analyse pattern recognition deficits

Summary The ability of cats to discriminate between two geometrical outline patterns in the presence of superimposed Gaussian visual noise was tested before and after bilateral removal of cortical area 17 and parts of area 18. The detection probability P_D was measured as a function of the signal-to-noise ratio for the parameters: noise bandwidth, spatial frequency content and rate of movement of patterns. In both normal and lesioned cats a broadband noise was found to be most effective in masking the large patterns while two other types of noise, a medium frequency noise and a high frequency noise had little or no masking effect. For recognition of the smaller patterns in normal cats the medium frequency noise was found to be more effective than the broadband noise. The performance of the lesional cats was disturbed severely at low signal-to-noise ratios and was significantly inferior to that of normal cats — especially for small patterns. However, at high S/N ratios and for large patterns the performance of the lesioned cats was comparable to that of normals while for the small patterns they reached P_D values inferior to those of normal cats. It is concluded that although pattern recognition can be performed successfully by cats lacking areas 17 and 18, these cortical areas probably make an essential contribuion to this function under natural conditions in two ways: a) because of the X-type input of area 17, they increase the acuity of the system by making it more sensitive to higher spatial frequencies, and b) they permit detection of patterns at much lower S/N ratios i.e. they lower the signal-to-noise ratio at which the system is able to detect the presence of a pattern in a background of statistical visual noise. The latter effect is not limited to the higher spatial frequencies but also affects the very low spatial frequencies which are normally used for pattern detection. Previous failures to demonstrate clear deficits in pattern discrimination after 17/18 lesions in cats may be attributed to the fact that the patterns presented for discrimination were not masked by visual noise. Movement of patterns led to a slight, but not significant improvement of the performance in both normal and lesioned cats, but the deficits found for stationary and moving patterns were more or less equal.     

Considerable deficits in the detection performance of the cat after lesion of the suprasylvian visual cortex

Summary The ability of two cats to discriminate between two geometrical outline patterns in the presence of superimposed structured background was tested before and after bilateral removal of the lateral suprasylvian visual areas (PMLS, PLLS, AMLS, ALLS, part of area 7). There were mild deficits when patterns and background were kept stationary; these deficits may be due to a partial undercutting of areas 17, 18 and 19. However, there was a severe impairment in performance when the patterns were moving on a stationary background which may be due to loss of the suprasylvian visual areas. Movement of the background relative to the figure resulted in an intermediate detection deficit.The paper is part of this author's doctoral thesis     

Lesions of visual cortex impair discrimination of hidden figures by cats

Cats lacking cortical visual areas 17, 18 and 19 can discriminate between patterns equal in luminous flux. The present experiment investigated the extent to which this ability varies with differences in the amount of contour and complexity of the patterns. To test this, cats were required to discriminate between patterns that were made progressively more alike in contour and complexity by increasing the number of masking stripes superimposed on each of a pair of stimuli. A mild deficit in shape discrimination among cats with lesions of areas 17, 18 and 19 was greatly exacerbated by masking the stimuli with superimposed stripes, and the severity of the deficit for each operated cat was correlated with the size of the contour and complexity difference between the stimuli. Finally, the severity of the deficit was related to the amount of geniculocortical damage. The results suggest that lesions largely confined to areas 17, 18 and 19 cause profound deficits on masked pattern discrimination even though performance with unmasked stimuli is relatively unimpaired. Indirect evidence suggests that this effect is not due solely to a reduction in visual acuity.     

The role of the lateral suprasylvian visual cortex of the cat in object-background interactions: Permanent deficits following lesions

The contribution of the lateral suprasylvian cortex to pattern recognition was studied by behavioural detection experiments in combination with bilateral lesions of different parts of the lateral suprasylvian areas (LSA) and area 7 in seven cats. In a two-alternatives forced choice task the cats had to discriminate simple outline patterns which were additively superimposed on a structured visual background made up of broadband Gaussian noise. For various stimulus conditions (moving or stationary patterns and/or background) the detection probability (P _D) of the cats was measured as a function of the signal to noise ratio (S/N). Each cat was tested before and after the lesion. Four different types of lesion could be distinguished depending on their extent: (1) lesion of parts of the (LSA); (2) lesion of parts of the LSA with undercutting of areas 17, 18 and 19; (3) lesion of area 7; (4) lesion of area 7 and parts of the LSA.

Effects of visual cortex lesions following recovery from monocular deprivation in the cat

Six monocularly deprived (MD) and four normal cats were trained monocularly on two-choice form and pattern discriminations. MD cats trained through the initially deprived eye were able to learn the discriminations; however, they required many more trials than normals. Retention tests showed that MD cats have nearly perfect retention of the discriminations over periods of up to 4 months. With retention intervals of 6 months or longer, there is a tendency for the MD cats to show an initial drop in performance, particularly on more difficult discriminations. However, criterion performance typically was attained with considerable savings, indicating good retention even over these extended intervals. Following the preoperative training and retention testing, the cats received one of the three types of visual cortex lesions. Two MD cats received total visual cortex removal (areas 17, 18, and 19). This produced a complete postoperative loss of the discriminations with continued chance performance over 800--1000 trials. Two MD cats and two normal cats received removal of the monocular segment of area 17, with the central visual field projection region of area 17 and all of areas 18 and 19 remaining intact. This produced no loss of the discriminations in either normal or MD cats beyond what is expected on the basis of normal forgetting. Two MD cats and two normal cats received removal of areas 18, 19, and the central 5--10 deg. of the visual field projection in area 17. Postoperative retention was somewhat variable for both normal and MD cats. However, subsequent acquisition of the discriminations by both normal and MD cats was in sharp contrast to the prolonged deficits produced by total visual cortex lesions. These results indicate that one or more of visual cortical areas 17, 18, and 19 are involved in the recovery of visual discrimination capacities in MD cats. However, the monocular segment of striate cortex does not appear to be specially involved in this ability, as has been suggested by previous investigations. Possible mechanisms for the recovered visual capacities in MD cats are considered.     

Critical periods for functional and anatomical compensation in lateral suprasylvian visual area following removal of visual cortex in cats

Previous experiments have found that neurons in the cat's lateral suprasylvian (LS) visual area of cortex show functional compensation following removal of visual cortical areas 17, 18, and 19 on the day of birth. Correspondingly, an enhanced retino-thalamic pathway to LS cortex develops in these cats. The present experiments investigated the critical periods for these changes. Unilateral lesions of areas 17, 18, and 19 were made in cats ranging in age from 1 day postnatal to 26 wk. When the cats were adult, single-cell recordings were made from LS cortex ipsilateral to the lesion. In addition, transneuronal autoradiographic methods were used to trace the retino-thalamic projections to LS cortex in many of the same animals. Following lesions in 18- and 26-wk-old cats, there is a marked reduction in direction-selective LS cortex cells and an increase in cells that respond best to stationary flashing stimuli. These results are similar to those following visual cortex lesions in adult cats. In contrast, the percentages of cells with these properties are normal following lesions made from 1 day to 12 wk of age. Thus the critical period for development of direction selectivity and greater responses to moving than to stationary flashing stimuli in LS cortex following a visual cortex lesion ends between 12 and 18 wk of age. Following lesions in 26-wk-old cats, there is a decrease in the percentage of cells that respond to the ipsilateral eye, which is similar to results following visual cortex lesions in adult cats. However, ocular dominance is normal following lesions made from 1 day to 18 wk of age. Thus the critical period for development of responses to the ipsilateral eye following a lesion ends between 18 and 26 wk of age. Following visual cortex lesions in 2-, 4-, or 8-wk-old cats, about 30% of the LS cortex cells display orientation selectivity to elongated slits of light. In contrast, few or no cells display this property in normal adult cats, cats with lesions made on the day of birth, or cats with lesions made at 12 wk of age or later. Thus an anomalous property develops for many LS cells, and the critical period for this property begins later (between 1 day and 2 wk) and ends earlier (between 8 and 12 wk) than those for other properties.(ABSTRACT TRUNCATED AT 400 WORDS)     

Effects of lesions of areas 17, 18 and 19 on interocular transfer of pattern discriminations in split-chiasm cats

Summary Split-chiasm cats with unilateral or bilateral lesions largely removing the commissurally connected portions of visual cortical areas 17, 18 and 19 showed good interocular transfer of monocularly learned pattern discriminations. The capacity for interocular transfer in these cats was in fact little or not different from that of split-chiasm cats with an intact cortex. Split-chiasm cats with an additional section of the forebrain commissures, as well as two split-chiasm cats with 17–18 lesions also submitted to forebrain commissurotomy after having shown good interocular transfer, were generally incapable of transferring pattern discriminations between the eyes. It is concluded that interocular transfer of pattern discriminations, in split-chiasm cats does not require areas 17, 18 and 19 and must therefore depend on other cortical areas.     

Patterns of cytochrome oxidase activity in areas 17, 18 and 19 of the visual cortex of cats and kittens

Summary The laminar pattern of cytochrome oxidase activity was studied in visual cortical areas 17,18 and 19 in adult cats and kittens, following electrophysiological determination of the boundaries of these areas in all but the youngest animals. The patterns of cytochrome oxidase staining and the cytoarchitectonic appearances of areas 17, 18 and 19 were compared. At all ages activity was especially high in the region of layers IV and VI in areas 17 and 18, and was low in all laminae in area 19. The results suggest that the degree of cytochrome oxidase activity in these regions of the visual cortex may be related to the strength and type of projection that they receive from the lateral geniculate nucleus. The cytochrome oxidase technique is a useful means of defining the 18/19 border, and may help locate the boundary between areas 17 and 18, in both adult cats and kittens.     

Interhemispheric influences on area 19 of the cat

Summary Anatomical studies have shown an extensive network of homotopic and heterotopic interhemispheric connections in area 19 of the cat visual cortex (Segraves and Rosenquist 1982a; 1982b). We have investigated their functional organization by recording visual responses in area 19 of cats following a midsagittal section of the optic chiasm. This operation interrupts all crossed optic fibers coming both from the nasal and the temporal retinae; as a result, each hemisphere receives optic fibers only from the lateral hemiretina of the ipsilateral eye which conveys information from the contralateral visual field. Visual information transmitted to the same hemisphere from the contralateral retina and the ipsilateral visual field must be attributed to an indirect, interhemispheric pathway. We found that a rather high proportion of neurons (31.8%) in area 19 of seven split-chiasm cats responded to visual stimuli presented to the contralateral eye. 1 — All neurons receiving this interhemispheric activation were also driven by the ipsilateral eye via an intrahemispheric pathway. 2 — The property of binocularity was significantly related to the visuotopic map in that both receptive fields of each binocular neuron adjoined or were in the immediate vicinity of the vertical meridian. 3 — Due to the small size of receptive fields in area 19, the contribution of the interhemispheric pathway to the representation of the visual field is rather limited and it is certainly less extensive than that predicted by anatomical studies. The representation of the ipsilateral visual field in area 19 of intact cats, as assessed electrophy-siologically, was comparable to that found in split-chiasm cats. Recordings in areas 17–18 of split-chiasm cats showed that the visual field represented through the corpus callosum in these visual areas is certainly not less and probably more, extensive than that found in area 19. The results support the conclusion that the relation to the vertical meridian and the receptive field size can explain the organization of the interhemispheric connections in the visual areas studied so far.     

Neurophysiological mechanisms of recovery from visual cortex damage in cats: Properties of lateral suprasylvian visual area neurons following behavioral recovery

Summary Damage to visual cortical areas 17, 18, and 19 in the cat produces severe and long-lasting deficits in performance of form and pattern discriminations. However, with extensive retraining the animals are able to recover their ability to discriminate form and pattern stimuli. Recent behavioral experiments from this laboratory have shown that a nearby region of cortex, the lateral suprasylvian visual area (LS area), plays an important role in this recovery (Wood et al., 1974; Baumann and Spear, 1977b). The present experiment investigated the underlying neurophysiological mechanisms of the recovery by recording from single neurons in the LS area of cats which had recovered from long-term visual cortex damage.Five adult cats received bilateral removal of areas 17, 18, and 19. They were then trained to criterion on two-choice brightness, form, and pattern discriminations. Recording from LS area neurons was carried out after the behavioral training, from 3 to 7 months after the visual cortex lesions. The properties of these neurons were compared to those of LS area neurons in normal cats (Spear and Baumann, 1975) and in cats with acute or short-term visual cortex damage and no behavioral recovery (Spear and Baumann, 1979). The results showed that all of the changes from normal which were produced by acute visual cortex damage were also present after the behavioral recovery. Moreover, all of the response properties of LS area neurons which remain after acute visual cortex damage were present in similar form after the behavioral recovery. There was no evidence for any functional reorganization in the LS area concomitant with its role in the behavioral recovery.These results suggest that functional reorganization plays little or no role in recovery from visual cortex damage in adult cats. Rather, the recovery of form and pattern discrimination ability appears to be based upon the functioning of residual neural processes in the LS area which remain after the visual cortex damage.     

Selective sparing after lesions of visual cortex in newborn kittens

Previous findings are discordant regarding the effects of perinatal lesions of Cortical Areas 17 and 18 on visual discrimination learning in cats. Three potential determinants of such sparing were investigated: age at lesion (4 or 181 days), age at testing (3 or 9 months), and stimulus complexity. Age at testing was not significant, but performance varied with stimulus complexity and cortical damage, and there was an interaction between stimulus complexity and age at lesion. Both operated groups were transiently impaired in discriminating objects and subsequently learned to discriminate simple 2-dimensional patterns as well as done by controls, but the lesion groups were permanently impaired in discriminating similar patterns circumscribed by irrelevant lines. The age-at-lesion groups differed, however, in discriminating patterns masked by superimposed lines. The group lesioned at 181 days was severely impaired at both acquisition and subsequent intercurrent performance; the group lesioned at 4 days was impaired only at intercurrent performance. This study suggests that sparing after early postnatal damage of Areas 17 and 18 occurs only under limited circumstances.     

Cortical mechanisms for local and global analysis of visual space in the cat

Summary The effects of lesions in the striate or extra-striate visual cortex of cats were evaluated using visual discrimination problems which required either local or global pattern processing. The results indicate that damage to areas 17 and 18 preferentially impairs local processes, while in addition they suggest that damage to the extra-striate cortex preferentially affects global processing. These findings may be related to the observations that cats with large lesions in the extra-striate cortex demonstrate deficits in form perception without reductions in visual acuity and those with lesions in areas 17–18 show elevations of acuity thresholds while maintaining excellent pattern and form vision.     

Longterm impairment of cat optokinetic nystagmus following visual cortical lesions

Summary Binocular and monocular gain of optokinetic nystagmus (OKN), OKN dynamics, vestibulo-ocular reflex (VOR) and VOR adaptation were measured in 5 normal cats and in 5 cats which underwent bilateral visual cortical lesions involving the 17–18 complex at least 4 months before testing. We observed longterm deficits after bilateral lesions involving area 17 and variable parts of area 18 but failed to observe deficits after 18–19 lesions. These deficits were limited to the OKN gain and the build-up time constant of OKN; the VOR and the optokinetic after-nystagmus (OKAN) time constant were within normal limits. Our results suggest that areas 17–18 operate in parallel to control the encoding of retinal slip velocity at the level of the nucleus of the optic tract (NOT) and the accessory optic system (AOS), which are known to represent the initial stage of the optokinetic pathways.     

Neuroplasticity in the cat’s visual system: test of the role of the expanded retino-geniculo-parietal pathway in behavioral sparing following early lesions of visual cortex

Sparing of the ability to redirect head and eyes to new stimuli and expansion of the retino-geniculo-parietal pathway are both robust aspects of the repercussions of early lesions of occipital visual areas in cats. The purpose of the present work was to test the proposition that the pathway expansions and spared behaviors are causally linked. The proposition was tested by deactivating either the dorsal lateral geniculate nucleus (dLGN) and thereby uncoupling the primary and secondary limbs of the retino-geniculo-parietal pathway, or silencing the terminus of the pathway, and then testing the ability of cats to detect and orient head and eyes to visual targets. Six cats sustained experimental unilateral lesions of occipital areas 17 and 18 and variable amounts of area 19 on postnatal days 1-2 or 26-30 to induce rewiring and expansion of visual pathways from retina through the dLGN onto a critical region of visuoparietal (VP) cortex. Unilateral lesions ensured that we could use the orienting performance of the intact hemisphere as a fiduciary marker of performance against which performance of the experimental hemisphere could be gauged. When the cats were adult, a secondary test lesion was made on the damaged side by injecting, under electrophysiological guidance, ibotenic acid into either dLGN of four cats or into VP cortex of two cats. Prior to injection of ibotenic acid, all cats oriented head and eyes with high proficiency throughout the contralesional field, and performance was indistinguishable from orienting to stimuli presented in the ipsilesional field; sparing of the orienting behavior was complete. Ibotenic acid lesions of both dLGN and VP cortex induced a profound neglect of stimuli introduced into the contralesional hemifield. Orienting into the ipsilesional field remained high throughout. Subsequently, there was restoration of orienting behavior over the next 4-6 (dLGN deactivation) and 9-12 (VP deactivation) days. The test results demonstrate the essential contribution made by the retino-geniculo-parietal pathway to the ability to detect and redirect head and eyes to look at visual stimuli following early lesions of occipital visual cortices. The subsequent post-test lesion restoration of high orienting proficiency shows that in the absence of dLGN, or the critical region of VP cortex, other regions of cerebral cortex, or other structures such as the superior colliculus, can emerge and make important contributions to orienting behavior. These results reveal a maintained residual, beneficial adaptive plasticity of mature neural circuits even in brains compromised by early lesions of occipital visual areas.     

Transgeniculate signal transmission to middle suprasylvian cortex in intact cats and following early removal of areas 17 and 18: a morphological study

 Removal of cat areas 17 and 18 early, but not late, in postnatal development results in the sparing of certain reflexive and nonreflexive visually guided behaviors. These spared behaviors are accompanied by an expansion of geniculocortical projections to middle suprasylvian (MS) cortex. However, little is known about the types of visual signals relayed along these pathways. The purpose of our study was to reveal the morphologies of the neurons participating in the rewired circuits and, by relating them to the morphologies of functionally characterized neurons described by others, infer the types of visual signals transmitted via the lateral geniculate nucleus (LGN) to MS cortex. To do this, we retrogradely labeled LGN neurons from MS cortex with fluorescent microspheres, and subsequently intracellularly filled them with Lucifer Yellow. We then classified well-filled neurons according to a battery of morphological parameters (such as soma size and shape, and dendritic field-form and specializations), and compared them with already defined structure/function relationships. By doing this, we found that the large majority of visual thalamic relay neurons to MS cortex of both normal cats and cats that incurred removal of areas 17 and 18 were types I and IV. These results indicate that visual Y and W signals, respectively, are relayed directly from LGN to MS cortex in both types of cats. Following the early lesions, some of the MS-projecting type I neurons were found in layers A and A1, where they are never found in intact cats. Thus, some layer A and A1 type I neurons redirect axons to MS cortex following early removal of areas 17 and 18. For the type IV MS-projecting neurons in early lesioned cats, the somas were hypertrophied and they had more profuse and broader dendritic arbors than equivalent neurons in intact cats. These results suggest that dynamic interactions take place between inputs and outputs of LGN neurons during development that influence final LGN neuron morphology. Moreover, they suggest that signals transferred to MS cortex by type IV neurons may be modified by early lesions of areas 17 and 18. Overall, these results contribute to our understanding of the types of behaviors that may be spared by early lesions of areas 17 and 18. Received: 22 May 1996 / Accepted: 3 September 1996     

Binocular neuronal responsiveness in Clare-Bishop cortex of Siamese cats

Summary Retinotopy and binocular responsiveness were studied extracellularly in a total of 278, 61, 110 and 275 cells sampled in areas 17, 18, 19 and Clare-Bishop (CB) of Siamese cats. The misalignment of the visual axes of the two eyes was determined by the pupil reflex method in the behaving animal. The recording sessions were conducted under N₂O anesthesia, supplemented with continuous infusion of short-lasting anesthetics (Saffan, Glaxo) and muscle relaxants (Gallamine triethiodide) using two types of visual stimulators presenting two-dimensional (2D) motion stimuli and the visual cues for three-dimensional (3D) motion. All of the nine Siamese cats demonstrated Boston type retinotopic abnormalities in all of cortical areas 17–19 and CB. Very few binocular cells were present in areas 17–19 and the posterior (A1-P2) CB but they were numerous in most of CB (A9-4). A significant fraction (36/78) of binocular cells in the major CB of the Siamese cats demonstrated similar response selectivity to that reported in normal CB cortex for stimulation with the 3D motion cues under both null disparity and strabismic conditions (binocular receptive fields for two eyes were optically superposed or separated by the strabismic angles estimated in the individual animals). These findings indicate that the binocular signals converging to the CB cells through different pathways (signals coming from the contralateral eye via the ipsilateral hemisphere including the interlaminar nucleus and areas 17–19, and commissural signals from the ipsilateral eye via the contralateral areas 17–19 and CB) were integrated to yield useful information for the recognition of 3D motion, and that the major CB is an actual site of binocular integration at least in Siamese cats, rather than being merely a reflection of the information processing before the CB cortex.     

Behavioral thermosensitivity after lesions of thalamic target areas of a thermosensory spinothalamic pathway in the cat.

The ability of 17 cats to discriminate floor temperatures 2-4 degrees C below the ambient temperature was tested before and after unilateral electrolytic thalamic lesions. The lesions were made contralateral to the paws showing better performance in the temperature discrimination task. They were aimed at one or more of the three main target areas of thermoreceptive-specific lamina I spinothalamic neurons [i.e., the nucleus submedius, the dorsomedial aspect of the ventral posterior medial nucleus, and the ventral aspect of the basal ventral medial nucleus (vVMb)], following microelectrode mapping of somatosensory thalamus. The thermosensory consequences of each lesion were measured in postoperative testing, beginning 6-8 days after the final preoperative test session. A mild but definite thermosensory deficiency was found in five cats, in which the response behavior on the contralateral side was reduced below the 69% criterion level for several sessions. Histological analysis indicated that these cats differed only by the inclusion in the lesion of all or part of vVMb. Consequently this area appears to be important for cats' thermosensory behavior. Nevertheless even large lesions of virtually all of the thermoreceptive lamina I spinothalamic projection areas produced only this mild thermosensory deficit in stark contrast with the massive defect observed previously after spinal lesions of the middle of the lateral funiculus, where lamina I axons ascend. Accordingly such spinal lesions were added at the C(4) level, on the same side as the thalamic lesions, in six cats 3 mo after the thalamic surgery. These lesions caused severe contralateral defects (i.e., chance level performance). Thus the present findings are taken to indicate that contralateral ascending projections to vVMb in the thalamus participate in cats' thermosensory discrimination but that ascending projections to the brain stem must play an important role in their behavioral thermosensitivity.     

Learning and interhemispheric transfer of visual pattern discriminations following unilateral suprasylvian lesions in split-chiasm cats

Summary A suprasylvian lesion removing cortical areas 7 and 21 and portions of area 19 and of the lateral suprasylvian area was placed in one hemisphere of split-chiasm cats. By comparison with the normal side and with cortically intact split-chiasm and split-brain cats, form discrimination learning with the eye on the injured side was severely retarded. This deficit could not be attributed to an unintentional undercutting of areas 17 and 18, since in three cases the laminae of the lateral geniculate nucleus showed little retrograde atrophy; marked degeneration was found in the medial interlaminar nucleus and the pulvinar complex. In addition, interocular transfer of form discriminations to the eye on the injured side was absent or poor, while transfer in the opposite direction was normal. A cat with a suprasylvian lesion undercutting areas 17 and 18 was unable to learn pattern discriminations with the eye on the injured side, in spite of prolonged training with that eye and normal learning with the other eye. Another cat with a suprasylvian lesion selectively removing the anteromedial and posteromedial portions of the lateral suprasylvian area showed no learning deficit on the injured side, but poor transfer to that side. A learning deficit on the side of the lesion emerged in this cat after forebrain commissurotomy.The results support the hypothesis of a major involvement of cortical areas outside of 17 and 18 in the processes of abstraction and generalization of visual information necessary for learning and interhemispheric transfer of form discrimination in the cat.     

Neuroplasticity in the cat’s visual system Origin, termination, expansion, and increased coupling of the retino-geniculo-middle suprasylvian visual pathway following early ablations of areas 17 and 18

We used anterograde and retrograde transsynaptic pathway tracing techniques to reveal the retinal origin and the cortical termination of the expanded retino-geniculo-middle suprasylvian (MS) cortex pathway in adult cats which sustained lesions of areas 17 and 18 on the day of birth (P1) or at 1 month of age (P28). Following anterograde transsynaptic transport of tritiated amino acids from the eye, four major results were obtained: (1) a strong and specific pathway from retina through dorsal lateral geniculate nucleus (dLGN) to the posterior half of MS cortex was identified; this pathway is a substantial expansion of an insignificant pathway present in intact cats; (2) the terminus of the pathway was lower layer III and layer IV; (3) contralateral projections were stronger than ipsilateral projections; (4) projections in P28 cats were stronger than those in P1 cats. Following retrograde transsynaptic transport of WGA-HRP from posterior MS cortex, four additional results were obtained: (1) the pathway was enlarged and visuotopically organized; (2) the pathway arose primarily from α- and γ-retinal ganglion cells; (3) a small number of β-cells in P1 cats and a modest number in P28 cats also contribute to the pathway; (4) the combined numbers of γ- and β-cells relative to α-cells was greater in temporal retina than in nasal retina. The combined demonstration of both origin and terminus of the pathway with transsynaptic tracers argued strongly for high levels of coupling between primary and secondary pathway limbs in both P1 and P28 cats. This level of coupling, as well as other features of the pathway, have much in common with the retino-geniculo-17/18 pathway of intact cats. However, the retino-geniculo-MS system in P1 cats transmits primarily Y and W signals, in P28 cats X, Y, and W signals; whereas the retino-geniculo-17/18 pathway transmits primarily X and Y signals. These results have implications for understanding the repercussions of early visual cortex lesions in monkeys and humans. Received: 17 November 1997 / Accepted: 10 February 1998     

Visual discrimination by cats given lesions of visual cortex in one or two stages in infancy or in one stage in adulthood

Sparing of visual function was studied in cats with bilateral cortical damage to Areas 17 and 18 and most of Area 19. Cats with lesions made in 2 stages, on Postnatal (P) Days 3 and 6, in 1 stage on P6, or in 1 stage in adulthood were compared with sham-operated controls on 10 visual discrimination tasks. On some tasks, both groups of cats that underwent surgery as infants showed considerable sparing of function compared with cats that had surgery as adults; the latter group showed a marked impairment. However, on several of the discriminations, 2-stage lesions permitted almost total sparing of pattern vision, whereas 1-stage lesions made neonatally were almost as debilitating as those incurred in adulthood. The findings suggest that differential behavioral consequences can follow physiological or anatomical changes, or both, that occur within a 4-day neonatal interoperative period.