Posteromedial Lateral Suprasylvian Research Articles

Neural Processing of Second-Order Motion in the Suprasylvian Cortex of the Cat

Neuronal responses to second-order motion, that is, to spatiotemporal variations of texture or contrast, have been reported in several cortical areas of mammals, including the middle-temporal (MT) area in primates. In this study, we investigated whether second-order responses are present in the cat posteromedial lateral suprasylvian (PMLS) cortex, a possible homolog of the primate area MT. The stimuli used were luminance-based sine-wave gratings (first-order) and contrast-modulated carrier stimuli (second-order), which consisted of a high-spatial-frequency static grating (carrier) whose contrast was modulated by a low-spatial-frequency drifting grating (envelope). Results indicate that most PMLS neurons responded to second-order motion and for the vast majority of cells, first- and second-order preferred directions were conserved. However, responses to second-order stimuli were significantly reduced when compared to those evoked by first-order gratings. Circular variance was increased for second-order stimuli, indicating that PMLS direction selectivity was weaker for this type of stimulus. Finally, carrier orientation selectivity was either absent or very broad and had no influence on the envelope's orientation selectivity. In conclusion, our data show that PMLS neurons exhibit similar first- and second-order response profiles and that, akin primate area MT cells, they perform a form-cue invariant analysis of motion signals.

Effects of Feedback Projection From Cortical Area PMLS on Response Properties of Striate Neurons*

In the nervous system,numerous feedforward and feedback circuits are formed by descending projections together with ascending inputs.It has been shown that the transmission and processing of neural signals are modulated by these extremely complicated pathways,but little is known about the functional roles of feedback projections in the cortex.Area posteromedial lateral suprasylvian(PMLS) in the extrastriate cortex of the cat was inactivated locally and reversibly by microinjection of inhibitory neurotransmitter GABA,and extracellular recording was performed to investigate the changes in visual response properties of neurons in the striate cortex.The PMLS inactivation resulted in an overall reduction in the responses of striate neurons to moving stimuli,accompanied by little change in the relative stability of responsiveness and a decline in the ratio of maximal firing rate to spontaneous activity level.In the meanwhile,the direction selectivity index decreased,but the change of orientation tuning strength was insignificant,the preferred direction kept unvaried except for a few bi-directional cells.Further analysis revealed that the neuronal responses were reduced in all the stimulus directions,but most largely in the preferred direction,which might serve as the key factor to weaken the direction selectivity.These findings indicate that the feedback projection from PMLS can enhance the direction selectivity of striate neurons but exert little effect on the orientation tuning.It appears that the feedback modulation is characterized by the important role of PMLS in visual motion processing in the cerebral cortex.

Posteromedial lateral suprasylvian motion area modulates direction but not orientation preference in area 17 of cats

In visual cortices of cats there are two major, largely parallel, feedforward processing streams which conduct visual information from the primary visual cortices to the parietal and temporal visual cortices, processing motion and form information, respectively. In addition to the feedforward streams, there exist many feedback projections from higher-order visual cortices to lower-order visual cortices. Using the intrinsic signal optical imaging, this study has examined the influence of feedback signals originating from area posteromedial lateral suprasylvian (PMLS), the dominant motion-processing region of the parietal cortex, on responses of neurons, orientational maps, and directional maps in cats’ area 17 (striate cortex). The inactivation of area PMLS by local application of GABA resulted in the reduction of the magnitude of responses of area 17 cells though area 17 of the cat is mainly involved in form information processing rather than motion. Furthermore, inactivation of area PMLS abolished the global layout of direction maps in area 17 but did not affect the basic structure of the orientation maps in area 17. Thus, it appears that higher-order cortical areas along one information processing stream may exert cross-stream modulatory effects on fundamental properties of neurons located in the lower-order areas along distinct information processing streams.

Simple and complex visual motion response properties in the anterior medial bank of the lateral suprasylvian cortex

The cortical regions surrounding the suprasylvian sulcus have previously been associated with motion processing. Of the six areas originally described by Palmer et al. [J Comp Neurol 177 (1978) 237], the posteromedial lateral suprasylvian (PMLS) cortex has attracted the greatest attention. Very little physiological information is available concerning other suprasylvian visual areas, and in particular, the anteromedial lateral suprasylvian cortex (AMLS). Based on its cortical and sub-cortical connectivity patterns, the AMLS cortex is a likely candidate for higher-order motion processing in cat visual cortex. We have investigated this possibility by studying the receptive field sensitivity of AMLS neurons to complex motion stimuli. Neurons in AMLS cortex exhibited large (mean of 354° 2) and complex-like receptive fields, and most of them (74%) were classified as direction selective on the basis of their responses to sinusoidal drifting gratings. Most importantly, direction selectivity was present for complex motion stimuli. A subset of the neurons sampled (eight of 38 cells; 21%) exhibited pattern-motion selectivity in response to moving plaid patterns. The capacity of AMLS neurons to signal higher-order stimuli was further supported by their selectivity to moving complex random-dot kinematograms. Finally, 45% of 20 neurons were direction selective to a radial optic flow stimulus. Overall, these results suggest that AMLS cortex is involved in higher-order analyses of visual motion. It is possible that the AMLS cortex represents a region between PMLS and the anterior ectosylvian visual area in a functional hierarchy of areas involved in motion integration.

Functional plasticity in extrastriate visual cortex following neonatal visual cortex damage and monocular enucleation

Neonatal lesions of primary visual cortex (areas 17, 18 and 19; VC) in cats lead to significant changes in the organization of visual pathways, including severe retrograde degeneration of retinal ganglion cells of the X/β class. Cells in posteromedial lateral suprasylvian (PMLS) cortex display plasticity in that they develop normal receptive-field properties despite these changes, but they do not acquire the response properties of striate neurons that were damaged (e.g., high spatial-frequency tuning, low contrast threshold). One possibility is that the loss of X-pathway information, which is thought to underlie striate cortical properties in normal animals, precludes the acquisition of these responses by cells in remaining brain areas following neonatal VC damage. Previously, we have shown that monocular enucleation at the time of VC lesion prevents the X-/β-cell loss in the remaining eye. The purpose of the present study was to determine whether this sparing of retinal X-cells leads to the development of striate-like response properties in PMLS cortex. We recorded the responses of PMLS neurons to visual stimuli to assess spatial-frequency tuning, spatial resolution, and contrast threshold. Results indicated that some PMLS cells in animals with a neonatal VC lesion and monocular enucleation displayed a preference for higher spatial frequencies, had higher spatial resolution, and had lower contrast thresholds than PMLS cells in cats with VC lesion alone. Taken together, these results suggest that preserving X-pathway input during this critical period leads to the addition of some X-like properties to PMLS visual responses.

Long-term neurochemical changes after visual cortical lesions in the adult cat

Peripheral deafferentation alters cortical function and such alterations have been shown to affect the cortical expression of the calcium-binding proteins calbindin and parvalbumin and of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA). To determine whether cortical deafferentation produces similar effects, we examined the long-term consequences of cortical lesions on the neurochemistry of interconnected cortical areas. We studied the reciprocal effects of localized damage to either visual cortical areas 17 and 18, or posteromedial lateral suprasylvian (PMLS) cortex in the adult cat. These areas are strongly interconnected and play an important role in the processing of visual information. Combined lesions of areas 17 and 18 caused a marked, topographically specific decrease in the proportion of neurons expressing calbindin in supragranular layers of PMLS cortex. Similarly, lesions of PMLS cortex caused topographically restricted decreases in calbindin expression within supragranular layers of areas 17 and 18, but not in other cortical areas with which PMLS is interconnected. To categorize the calbindin-positive neurons affected by such lesions, we carried out double-labeling experiments for the inhibitory neurotransmitter GABA. This investigation showed lesions of areas 17 and 18 to affect calbindin-positive excitatory and inhibitory neurons equally, but PMLS lesions had stronger effects on inhibitory, calbindin-positive neurons. This finding may represent differential damage to feed-forward vs. feed-back projections in the two types of lesions. Finally, the expression of parvalbumin and GABA was unchanged, even in zones of decreased calbindin immunoreactivity. Our results suggest that damage to adult visual cortical areas, whether striate or extrastriate, induces neurochemical changes in the supragranular corticocortical network to which these areas belong. That changes were restricted to calbindin expression suggests cell-specific and/or biochemical pathway-specific alterations in calcium homeostasis.

Neuronal responsiveness to three-dimensional motion in cat posteromedial lateral suprasylvian cortex.

The neuronal responsiveness to three-dimensional (3D) motion in cat posteromedial lateral suprasylvian (PMLS) cortex was studied using a computer-controlled, stereoscopic 3D graphic display capable of reproducing the major visual cues for natural 3D motion, including motion disparity, size, texture, and shading changes. The animals were anesthetized with nitrous oxide supplemented with alphaxalone, and paralysis prevented eye movement. Systematic investigation of neuronal responsiveness to 3D motions in 26 different directions revealed that more than half of the PMLS cells were selectively responsive to approaching (AP cells, 112 of 271) or recessive motion (RC cells, 64 of 271). The remaining cells were selectively responsive to frontoparallel motion (FP cells, 49 of 271) or nonselectively responsive to motion in multiple directions (NS cells, 46 of 271). The dependency on these visual cues was investigated as a reduction in the response amplitude or the response selectivity for the removal of a single cue from the motion stimuli containing the full visual cues. The AP and RC cells showed a strong dependency on the motion disparity cue, moderate dependency on the size cue, and weak dependency on the texture and shading cues. The FP cells showed no dependency on those visual cues. The cue dependency analysis indicated the existence of nonlinear interactions between those visual cues. Comparison of the responses to a combination of the motion disparity and size cues with the summed responses to each of the individual cues revealed that the responses to the combined cues are roughly predicted as a linear sum between the preferred responses. This comparison also showed nonlinear summation between the nonpreferred responses, i.e., responses to the combined cues were smaller than the summed responses. A similar quasilinear summation of the preferred responses between the two eyes and a nonlinear summation of the nonpreferred responses were found in the AP and RC cells for the motion disparity stimulus. All of these observations indicate that quasilinear and nonlinear interactions of the responses to various stimulus elements underlie the 3D motion responsiveness of the PMLS cells.

Correlation analysis of corticotectal interactions in the cat visual system.

We have studied the temporal relationship between visual responses in various visual cortical areas [17, 18, postero medial lateral suprasylvian (PMLS), postero lateral lateral suprasylvian (PLLS), 21a]) and the superficial layers of the cat superior colliculus (SC). To this end, simultaneous recordings were performed in one or several visual cortical areas and the SC of anesthetized paralyzed cats, and visually evoked multiunit responses were subjected to correlation analysis. Significant correlations occurred in 117 (24%) of 489 cortex-SC pairs and were found for all cortical areas recorded. About half of the significant correlograms showed an oscillatory modulation. In these cases, oscillation frequencies covered a broad range, the majority being in the alpha- and beta-band. On average, significant center peaks in cross-correlograms had a modulation amplitude of 0.34. Our analysis revealed a considerable intertrial variability of correlation patterns with respect to both correlation strength and oscillation frequency. Furthermore, cortical areas differed in their corticotectal correlation patterns. The percentage of cells involved a corticotectal correlation, as well as the percentage of significantly modulated correlograms in such cases, was low for areas 17 and PMLS but high for areas 18 and PLLS. Analysis of the cortical layers involved in these interactions showed that consistent temporal relationships between cortical and collicular responses were not restricted to layer V. Our data demonstrate a close relationship between corticotectal interactions and intracortical or intracollicular synchronization. Trial-by-trial analysis from these sites revealed a clear covariance of corticotectal correlations with intracortical synchronization. The probability of observing corticotectal interactions increased with enhanced local cortical and collicular synchronization and, in particular, with interareal cortical correlations. Corticotectal correlation patterns resemble in many ways those described among areas of the visual cortex. However, the correlations observed are weaker than those between nearby cortical sites, exhibit usually broader peaks and for some cortical areas show consistent phase-shifts. Corticotectal correlations represent population phenomena that reflect both the local and global temporal organization of activity in the cortical and collicular network and do not arise from purely monosynaptic interactions. Our findings show that both striate and extrastriate inputs affect the superficial SC in a cooperative manner and, thus, do not support the view that responses in the superficial SC depend exclusively on input from the primary visual areas as implied by the concept of "two corticotectal systems." We conclude that the corticotectal projections convey temporal activation patterns with high reliability, thus allowing the SC evaluation of information encoded in the temporal relations between responses of spatially disseminated cortical neurons. As a consequence, information distributed across multiple cortical areas can affect the SC neurons in a coherent way.

Cortical projections of the parvocellular laminae C of the dorsal lateral geniculate nucleus in the cat: an anterograde wheat germ agglutinin conjugated to horseradish peroxidase study.

The areal and laminar distributions of the projection from the parvocellular part of laminae C of the dorsal lateral geniculate nucleus (Cparv) were studied in visual cortical areas of the cat with the anterograde tracing method by using wheat germ agglutinin conjugated to horseradish peroxidase. A particular objective of this study was to examine the central visual pathways of the W-cell system, the precise organization of which is still unknown. Because the Cparv in the cat is said to receive W-cell information exclusively from the retina and the superior colliculus, the results obtained would provide an anatomical substrate for the W-cell system organization in mammals. The results show that the cortical targets of the Cparv are areas 17, 18, 19, 20a, and 21a and the posteromedial lateral suprasylvian (PMLS) and ventral lateral suprasylvian(VLS) areas. In area 17, the projection fibers terminate in the superficial half of layer I; the lower two-thirds of layer III, extending to the superficial part of layer IV; and the deep part of layer IV, involving layer Va. These terminations form triple bands in area 17. The projection terminals in layer I are continuous, whereas those in layers III, IV, and Va distribute periodically, exhibiting a patchy appearance. In areas 18 and 19, the projection fibers terminate in the superficial half of layer I and in the full portions of layers III and IV, forming double bands. In these areas, the terminals in layer I are continuous, whereas those in layers III and IV distribute periodically, exhibiting a patchy appearance. In area 20a, area 21a, PMLS, and VLS, projection fibers terminate in the superficial part of layer I, in part of layer III, and in the full portion of layer IV, although they are far fewer in number than those seen in areas 17, 18, and 19. The present results demonstrate that the Cparv fibers terminate in a localized fashion in both the striate and the extrastriate cortical areas and that these W-cell projections are quite unique in their areal and laminar organization compared with the X- and Y-cell systems.

Excitatory convergence of Y and non-Y information channels on single neurons in the PMLS area, a motion area of the cat visual cortex.

We analysed the receptive field properties of neurons in the posteromedial lateral suprasylvian (PMLS) visual cortical area of anaesthetized cats in which there was selective conduction block of the largest (Y-type) fibres in one optic nerve. As in normal cats, in cats with selective block of one optic nerve the great majority of PMLS cells could be activated by photic stimulation through either eye. However, the responses evoked by stimulation via the eye with the selectively pressure-blocked optic nerve ('Y-blocked eye') were significantly weaker than those of the same cells evoked by the stimulation via the normal eye. Accordingly, eye dominance histograms were shifted markedly in favour of the normal eye. Furthermore, there was a significant shift towards lower preferred velocities when PMLS cells were photically stimulated via the Y-blocked eye. Finally, when stimulated via the Y-blocked eye, PMLS cells responded poorly or not at all to high stimulus velocities (> or = 100 degrees/s). On the other hand, a number of receptive field properties, such as the spatial organization of receptive fields, the size of the discharge fields, orientation tuning and direction selectivity indices, were not significantly affected by the removal of the Y input. We conclude that virtually all neurons in the PMLS area of the cat receive excitatory input from both Y and non-Y information channels, although the Y channel provides the dominant input and makes the principal contribution to the detection of high-velocity motion.

Limits of parallel processing: excitatory convergence of different information channels on single neurons in striate and extrastriate visual cortices.

1. It has been postulated that the distinct parallel retino-geniculo-cortical information channels characterizing visual pathways of virtually all mammals are selectively linked to parallel motion, colour and/or form information processing 'streams' distinguishable within the primary visual cortices, extrastriate cortical areas of occipital lobes and the temporal and parietal visual cortices. 2. Using selective pressure-blocking of the large-fibre channel (the so-called Y-channel) in the optic nerve of the cat, we have experimentally examined the 'selective excitatory parallel links' hypothesis. We conclude that the majority of neurons in the primary visual cortices (areas 17, 18) as well as in the two 'higher order' visual areas, area 21a and posteromedial lateral suprasylvian (PMLS) area, constituting, respectively, part of the 'form' and part of the 'motion' processing streams, receive their excitatory inputs from both Y- and non-Y-information channels. In areas 17, 18 and 21a (but not in PMLS area), there are, however, subpopulations of cells that apparently receive excitatory inputs from only one information channel. 3. Review of the relevant work on the macaque monkey suggests that the situation is similar in the primate: that is, there is a substantial degree of excitatory convergence of different retino-geniculo-cortical information channels on single neurons in the primary visual cortices and the extrastriate cortices constituting parts of the form/colour or the motion processing streams. 4. Despite this high degree of excitatory convergence of different information channels, the large-fibre channels (the Y-channel in the cat and the magnocellular or Y-like channel in macaque), are in both carnivores and primates the principal contributors to the motion processing cortical streams.

Lateral suprasylvian visual cortex is activated earlier than or synchronously with primary visual cortex in the cat

To explore functional connectivity between area 17 and posteromedial lateral suprasylvian (PMLS) area of the cat cerebral cortex, we carried out cross-correlation analysis of spike trains of neurons recorded simultaneously from both areas of anesthetized, paralyzed cat. Most of correlated pairs had peaks which indicate that PMLS cells were activated earlier than or simultaneously with their partners in area 17, suggesting that ‘backward’ as well as synchronous activation operates between these cortical areas.

Chapter 16 Afferent and developmentally inherent mechanisms of form and motion processing in cat extrastriate cortex

Publisher Summary This chapter focuses on afferent and developmentally inherent mechanisms of form and motion processing in cat extrastriate cortex and presents the studies of the mechanisms of compensation for visual cortex damage in adult cats and newborn kittens. As part of these studies, it is investigated that the effects of both acute and long-term removal of inputs from different areas on the receptive- field properties of neurons in the posteromedial lateral suprasylvian (PMLS) extrastriate the visual area of cortex. This has allowed determining the role of various inputs in the elaboration of PMLS receptive fields in normal adult animals. In addition, it has provided evidence that the development of certain receptive field properties depends upon intrinsic characteristics of the PMLS neurons, not simply upon the particular inputs to the neurons. In normal adult cats, PMLS neurons respond selectively to stimulus motion (MS), direction (DS), orientation (OS), and spatial frequency content (SF). The orientation tuning is broad, and spatial resolution and optimal spatial frequency are low.

Chapter 27 Neural plasticity after brain damage

Publisher Summary The greater recovery following neonatal damage also is partly because the neonatal brain can resist deleterious changes that occur following brain damage in adults. For example, posteromedial lateral suprasylvian (PMLS) cortical binocularity that is lost following adult visual cortex (VC) damage is sustained following neonatal damage. The greater recovery in neonates is partly because the neonatal brain can develop new projections or physiological properties, whereas the adult brain cannot. For example, cortical direction selectivity is lost following both neonatal and adult VC damage, but young kittens can re-develop this property whereas adults cannot. This greater capacity for anatomical and physiological compensation in neonates occurs despite the fact that some consequences of the damage are more severe in neonates than adults. For example, the retrograde degeneration in the lateral geniculate nucleus (LGN) and retina are more severe following VC damage in newborn kittens than in adult cats, but the remaining retinal and LGN cells are able to compensate better in newborn kittens than in adults. Brain damage has anatomical and physiological effects that extend well beyond the damaged tissue. In the visual system, for example, VC damage produces anterograde changes in structures that normally receive VC inputs and retrograde changes in structures that normally send projections to VC. The retrograde changes, as well as anterograde change can even be transneuronal. Despite these deleterious effects of brain damage, some recovery is possible. The recovery that occurs in adults does not depend on neural plasticity or reorganization in remaining brain tissue. Rather, remaining areas of the brain, including those that are abnormal as a result of the damage, appear to serve functions for which they were not critical before the damage.

Are neurons in cat posteromedial lateral suprasylvian visual cortex orientation sensitive? Tests with bars and gratings.

There is controversy in the literature concerning whether or not neurons in the cat's posteromedial lateral suprasylvian (PMLS) visual cortex are orientation selective. Previous studies that have tested cells with simple bar stimuli have found that few, if any, PMLS cells are orientation selective. Conversely, studies that have used repetitive stimuli such as gratings have found that most or all PMLS cells are orientation selective. It is not known whether this difference in results is due to the stimuli used or the laboratories using them. The present experiments were designed to answer this question by testing individual PMLS neurons for orientation sensitivity with both bar and grating stimuli. Using quantitative response measures, we found that most PMLS neurons respond well enough to stationary flashed stimuli to use such stimuli to test for orientation sensitivity. On the basis of these tests, we found that about 85% of the cells with well-defined receptive fields are orientation sensitive to flashed gratings, and a similar percentage are orientation sensitive to flashed bars. About 80% of the cells were orientation sensitive to both types of stimuli. The preferred orientations typically were similar for the two tests, and they were orthogonal to the preferred direction of movement. The strength of the orientation sensitivity (measured as the ratio of discharge to the preferred and nonpreferred orientations) was similar to both types of stimuli. However, the width of the orientation tuning curves was systematically broader to bars than to gratings. Several hypotheses are considered as to why previous studies using bars failed to find evidence for orientation sensitivity. In addition, a mechanism for the difference in orientation tuning to bars and gratings is suggested.

Morphology of visual callosal neurons with different locations, contralateral targets or patterns of development.

In kittens, callosally projecting neurons were labeled by retrograde transport of FITC- (fluorescein isothiocyanate)- and TRITC- (tetramethylrhodamine isothiocyanate)-conjugated latex microspheres injected in two different visual areas (17, 17/18, 19, or postero-medial lateral suprasylvian; PMLS) at postnatal day 3. At postnatal day 57 more than 1200 labeled neurons in visual cortical areas were intracellularly injected with 3% lucifer yellow (LY) in perfusion-fixed slices of the contralateral hemisphere. The distribution of labeled neurons was charted, and LY-filled neurons were classified on the basis of their area and layer of location, and dendritic pattern. The dendritic arbors of 120 neurons were computer reconstructed. For the basal dendrites of supragranular pyramidal neurons a statistical analysis of number of nodes, internodal and terminal segment lengths, and total dendritic length was run relative to the area of location and axonal projection. Connections were stronger between homotopic than between heterotopic areas. Overall tangential and laminar distributions depended on the area injected. Qualitative morphological differences were found among callosally projecting neurons, related to the area of location, not to that of projection. In all projections from areas 17 and 18, pyramidal and spinous stellate neurons were found in supragranular layers. In contrast, spinous stellate neurons lacked in projections from area 19, 21a, PMLS and postero-lateral lateral suprasylvian (PLLS). In all areas, the infragranular neurons showed heterogeneous typology, but in PMLS no fusiform cells were found. Quantitative analysis of basal dendrites did not reveal significant differences in total dendritic length, terminal, or intermediate segment length among neurons in area 17 or 18, and this was related to whether they projected to contralateral areas 17-18 or PMLS. All injections produced exuberant labeling in area 17. No differences could be found between neurons in area 17 (with transient axons through the corpus callosum) and neurons near the 17/18 border (which maintain projections to the corpus callosum). In conclusion, morphology of callosally projecting neurons seems to relate more to intrinsic specificities in the cellular composition of each area than to the area of contralateral axonal projection or the fate of callosal axons.

The development of somatostatin immunoreactive neurons in cat visual cortical areas

The development of somatostatin immunoreactive (SOM-ir) neurons in cat striate and extrastriate cortex was studied to determine whether temporal changes in the morphology, distribution and density of SOM-ir neurons during development would provide clues to the emergence of specific cortical areas. The visual cortical areas examined included areas 17–19 and 7, posteromedial lateral suprasylvian, posterolateral lateral suprasylvian cortex and splenial visual area. We observed that the pattern of SOM-ir neurons in the cortical plate reflects the maturation of the cortical plate. At 1 week of age, SOM-ir neurons were only found in layers V and VI of the developing cortex; by 2 weeks of age, SOM-ir neurons were found in layer IV; and by 3 weeks of age, SOM-ir neurons were located in all layers of the cortex except layer I. SOM-ir neurons in the subplate were much more numerous under lateral cortical areas than under medial areas. This difference decreased over the first 2 postnatal weeks and by the 14th day after birth (P14), the distribution and numbers of SOM-ir neurons in the subplate/white matter had reached the adult pattern. The timing of exuberant SOM expression in the subplate suggests a function in the formation of visual corticocortical connections which begin to develop during the first postnatal week in the kitten.

How complete is physiological compensation in extrastriate cortex after visual cortex damage in kittens?

Previous studies indicate that neurons in the cat's posteromedial lateral suprasylvian (PMLS) visual area of cortex show physiological compensation after neonatal but not adult damage to areas 17, 18, and 19 of the visual cortex (collectively, VC). Thus, VC damage in adults produces a loss of direction selectivity and a decrease in response to the ipsilateral eye among PMLS cells, but these changes are not seen in adult cats that received VC damage as kittens. This represents compensation for early VC damage in the sense that PMLS neurons develop properties they would have had if there had been no brain damage. However, this is only a partial compensation for the effects of VC damage. A full compensation would involve development of properties of the VC cells that were removed in the damage. The present study investigated whether this type of compensation occurs for detailed spatial- and temporal-frequency processing. Single-cell recordings were made in PMLS cortex of adult cats that had received a VC lesion on the day of birth or at 8 weeks of age. Responses to sine-wave gratings that varied in spatial frequency, contrast, and temporal frequency were assessed quantitatively. We found that the spatial- and temporal-frequency processing of PMLS cells in adult cats that had neonatal VC damage were not significantly different from PMLS cells in normal cats. Therefore, there was no evidence that PMLS cells can compensate for VC damage by developing properties that are better than normal and like those of the striate cortex cells that were damaged. We also assessed the effects of long-term VC damage in adult cats to determine whether the normal properties seen in cats with neonatal VC damage represent a compensation for abnormalities in PMLS cortex present after adult damage. In a previous study, we found that acute VC damage in adult cats has small but reliable effects on maximal response amplitude, maximal contrast sensitivity, and spatial resolution (Guido et al. 1990b). In the present study, we found that long-term VC damage in adult cats does not increase these abnormalities as a result of secondary degenerative changes. In fact, the minor abnormalities that were present after an acute VC lesion were virtually absent following a long-term adult lesion, perhaps because they were due to transient traumatic effects. Therefore, there was little evidence for abnormalities in spatial- or temporal-frequency processing following long-term adult VC damage for which PMLS cells might show compensation following long-term neonatal damage.(ABSTRACT TRUNCATED AT 400 WORDS)

Thalamic projections to the lateral suprasylvian visual area in cats with neonatal or adult visual cortex damage

Previous transneuronal anterograde tracing studies have shown that the retino-thalamic pathway to the posteromedial lateral suprasylvian (PMLS) visual area of cortex is heavier than normal in adult cats that received neonatal damage to visual cortical areas 17, 18, and 19. In contrast, the strength of this projection does not appear to differ from that in normal animals in cats that experienced visual cortex damage as adults. In the present study, we used retrograde tracing methods to identify the thalamic cells that project to the PMLS cortex in adult cats that had received a lesion of visual cortex during infancy or adulthood. In five kittens, a unilateral visual cortex lesion was made on the day of birth, and horseradish peroxidase (HRP) was injected into the PMLS cortex of both hemispheres when the animals were 10.5 to 13 months old. For comparison, HRP was injected bilaterally into the PMLS cortex of three cats 6.5 to 13.5 months after they received a similar unilateral visual cortex lesion as adults. In cats with a neonatal lesion, retrograde labeling was found in the large neurons that survive in the otherwise degenerated layers A and A1 of the lateral geniculate nucleus (LGN) ipsilateral to the lesion. Retrograde labeling of A-layer neurons was not seen in the undamaged hemisphere of these animals or in either hemisphere of animals that had received a lesion as adults. As in normal adult cats, retrograde labeling also was present in the C layers of the LGN, the medial interlaminar nucleus, the posterior nucleus of Rioch, the lateral posterior nucleus, and the pulvinar nucleus ipsilateral to a neonatal or adult lesion. Quantitative estimates indicate that the number of labeled cells is much larger than normal in the C layers of the LGN ipsilateral to a neonatal visual cortex lesion. Thus the results indicate that the heavier than normal projection from the thalamus to PMLS cortex that exists in adult cats after neonatal visual cortex damage arises, at least in part, from surviving LGN neurons in the A and C layers of the LGN. Although several thalamic nuclei, as well as the C layers of the LGN, continue to project to PMLS cortex after an adult visual cortex lesion, these projections appear not to be affected significantly by the lesion.

Development of the projections from the dorsal lateral geniculate nucleus to the lateral suprasylvian visual area of cortex in the cat

In the study reported in the preceding paper, we used retrograde labeling methods to show that the enhanced projection from the thalamus to the posteromedial lateral suprasylvian (PMLS) visual area of cortex that is present in adult cats following neonatal visual cortex damage arises at least partly from surviving neurons in the dorsal lateral geniculate nucleus (LGN). In the C layers of the LGN, many more cells than normal are retrogradely labeled by horseradish peroxidase (HRP) injected into PMLS cortex ipsilateral to a visual cortex lesion. In addition, retrogradely labeled cells are found in the A layers, which normally have no projection to PMLS cortex in adult cats. The purpose of the present study was to investigate the mechanisms of this enhanced projection by examining the normal development of projections from the thalamus, especially the LGN, to PMLS cortex. Injections of HRP were made into PMLS cortex on the day of birth or at 1, 2, 4, or 8 weeks of age. Retrogradely labeled neurons were present in the lateral posterior nucleus, posterior nucleus of Rioch, pulvinar, and medial interlaminar nucleus, as well as in the LGN, at all ages studied. Within the LGN of the youngest kittens, a small number of retrogradely labeled cells was present in the interlaminar zones and among the cells in the A layers that border these zones. Such labeled cells were virtually absent by 8 weeks of age, and they are not found in normal adult cats. Sparse retrograde labeling of C-layer neurons also was present in newborn kittens.(ABSTRACT TRUNCATED AT 250 WORDS)