Lesions Of Striate Cortex Research Articles

Visual responses of neurones in the second visual area of flying foxes (Pteropus poliocephalus) after lesions of striate cortex.

1. The first (V1) and second (V2) cortical visual areas exist in all mammals. However, the functional relationship between these areas varies between species. While in monkeys the responses of V2 cells depend on inputs from V1, in all non-primates studied so far V2 cells largely retain responsiveness to photic stimuli after destruction of V1. 2. We studied the visual responsiveness of neurones in V2 of flying foxes after total or partial lesions of the primary visual cortex (V1). The main finding was that visual responses can be evoked in the region of V2 corresponding, in visuotopic co-ordinates, to the lesioned portion of V1 ('lesion projection zone'; LPZ). 3. The visuotopic organization of V2 was not altered by V1 lesions. 4. The proportion of neurones with strong visual responses was significantly lower within the LPZs (31.5 %) than outside these zones, or in non-lesioned control hemispheres ( > 70 %). LPZ cells showed weak direction and orientation bias, and responded consistently only at low spatial and temporal frequencies. 5. The data demonstrate that the functional relationship between V1 and V2 of flying foxes resembles that observed in non-primate mammals. This observation contrasts with the 'primate-like' characteristics of the flying fox visual system reported by previous studies.

Greater residual vision in monkeys after striate cortex damage in infancy.

1. Monkeys with large unilateral surgical ablations of striate cortex, sustained either in adulthood or at 5-6 wk of age, were trained on an oculomotor detection and localization task and tested with visual stimuli in the hemifields ipsilateral and contralateral to the lesion 2-5 yr after surgery. 2. Monkeys with lesions sustained in adulthood were largely unable to detect stimuli in the hemifield contralateral to the lesion, with only one monkey showing recovery toward the end of testing. Monkeys with lesions of striate cortex made in infancy, however, each showed residual detection capacity at the beginning of testing and improved to near normal by the end of testing. 3. Each of the monkeys showing a residual ability to detect within the contralateral hemifield was also able to localize visual targets with eye movements. 4. These findings demonstrate that the vision surviving striate cortex damage in primates is more robust after early damage as has been shown to be the case for primary somatosensory, motor, and association cortex.

Towards the neuronal correlate of visual awareness

Several encouraging developments towards identifying the neuronal correlate of visual awareness have emerged recently. Increasingly sophisticated behavioral paradigms permit the study of visual awareness in human as well as in non-human primates. In patients with anatomically restricted lesions in striate and extrastriate cortex, highly informative deficits of visual awareness are observed. Similar deficits can be obtained in normal obgservers with a novel class of psychophysical displays. Taken together, these results suggest that the contents of visual awareness of reflect neuronal activity in certain extrastriate, but not in striate, visual cortical areas.

Localization of visual stimuli after striate cortex damage in monkeys: parallels with human blindsight.

Blindsight is a phenomenon in which human patients with damage to striate cortex deny any visual sensation in the resultant visual field defect but can nonetheless detect and localize stimuli when persuaded to guess. Although monkeys with striate lesions have also been shown to exhibit some residual vision, it is not yet clear to what extent the residual capacities in monkeys parallel the phenomenon of human blindsight. To clarify this issue, we trained two monkeys with unilateral lesions of striate cortex to make saccadic eye movements to visual targets in both hemifields under two conditions. In the condition analogous to clinical perimetry, they failed to initiate saccades to targets presented in the contralateral hemifield and thus appeared "blind." Only in the condition where the fixation point was turned off simultaneously with the onset of the target--signaling the animal to respond at the appropriate time--were monkeys able to localize targets contralateral to the striate lesion. These results indicate that the conditions under which residual vision is demonstrable are similar for monkeys with striate cortex damage and humans with blindsight.

Discrimination of motion direction in perimetrically blind fields

Three patients with bilateral and two with unilateral striate cortex lesions have been tested for their ability to discriminate motion direction within their perimetrically blind field. No optokinetic nystagmus could be recorded in any of the three cases of cortical blindness, but all the patients could discriminate with a high level of success between two opposite directions of movement (at least along the horizontal plane) in a forced-choice indication task. In contrast, the two hemispherectomized patients remained at chance level in the same task. This indicates that the residual capacities observed in the patients with occipital lesions depend upon cortical structures. According to neurophysiological findings, the most likely substrate would be the homologue of area MT of the monkey.

Contribution of striate cortex and the superior colliculus to visual function in area MT, the superior temporal polysensory area and inferior temporal cortex

We studied the visual responses of single neurons in three extra-striate visual areas of the macaque following lesions of striate cortex, lesions of the tecto-pulvinar system or both. After striate lesions, there was (a) considerable specific activity remaining in area MT including direction selectivity, (b) only non-specific activity in the superior temporal polysensory area (STP), and (c) no visual responsiveness at all in inferior temporal cortex (IT). In animals with striate lesions, interruption of the tecto-pulvinar pathway eliminated the residual visual activity in MT and STP that survived the striate lesions. Interruption of the tecto-pulvinar pathway alone had little or no effect on visual evoked activity in any of the three areas. These results are related to the relative dependence of visual responsiveness in MT, STP and IT on striate cortex and the superior colliculus, to differences between the dorsal and ventral cortical processing streams, and to neural mechanisms underlying blind sight.

Afferent basis of visual response properties in area MT of the macaque. II. Effects of superior colliculus removal

In a previous study (Rodman et al., 1989), we found that many neurons in the middle temporal area (MT) of the macaque monkey remain visually responsive and directionally selective after striate cortex lesions or cooling. In the present study, we examined the effects of superior colliculus (SC) lesions and combined lesions of striate cortex and the SC on the visual properties of MT neurons. Removal of the SC alone had no effect on the proportion of visually responsive cells, strength of direction selectivity and direction tuning, orientation tuning, receptive field size, or binocularity in MT. There was, however, a slight increase in response strength to both stationary and moving slit stimuli. In contrast to the minor effects of SC lesions alone, addition of an SC lesion to striate cortex damage abolished all visual responsiveness in area MT. The results indicate that pathways damaged by the SC lesion are not necessary for most of the properties of MT neurons found in the intact animal, although these pathways are capable of sustaining considerable visual responsiveness and direction selectivity when striate input is removed.

Parameters affecting the loss of ganglion cells of the retina following ablations of striate cortex in primates

Partial lesions of striate cortex were made in newborn and adolescent or young adult macaque monkeys, one newborn squirrel monkey, and adult squirrel and owl monkeys. After survival times ranging from 3 1/2 weeks to 8 years, the retinas were examined for transneuronal retrograde ganglion cell loss and retinal projections to the dorsal lateral geniculate nucleus, and other targets were examined for changes. After lesions in infant macaque monkeys and long postoperative survivals, nearly 80% of the ganglion cells were lost in the altered portions of the retinas. The degeneration appeared to be exclusively of ganglion cells projecting to the parvocellular layers of the lateral geniculate nucleus, and the loss of this class of cell appeared to be complete or nearly complete for the affected portions of the retina. Cases with shorter survivals showed that nine-tenths of the potential loss occurred within 6 months, and about half of the potential loss took place within one month. In cases where lesions were placed in adolescent and young adult macaque monkeys, the loss also was of ganglion cells projecting to the parvocellular layers. However, the rate of cell loss was slower so that little or no cell loss was apparent after six months, and only one-third to three-fourths of the potential loss occurred within 12-14 months. A cell loss of 22% was measured in the altered portions of the retina of a squirrel monkey lesioned as an infant and surviving for 6 months, but no regions of ganglion cell loss were apparent in the retinas of owl and squirrel monkeys lesioned as adults and surviving as long as two or more years. We conclude that nearly 80% of the ganglion cells project to the parvocellular layers in macaque monkeys, and that the ultimate survival of these ganglion cells depends on the presence of target neurons in the parvocellular layers. Age is important in that the loss of ganglion cells proceeds rapidly in infant macaque monkeys, but slowly in older animals. Infant New World monkeys, judging from one squirrel monkey, are also susceptible to ganglion cell loss, although apparently at a rate comparable to older macaque monkeys. Finally, adult New World monkeys do not appear to be susceptible to ganglion cell loss. These age and species differences in rates of loss and susceptibility to loss challenge a "sustaining collateral" hypothesis proposed earlier (Weller et al., 1979), and suggest alternatives and modifications.

Projection patterns of surviving neurons in the dorsal lateral geniculate nucleus following discrete lesions of striate cortex: implications for residual vision.

In four monkeys with long-standing partial ablation of the striate cortex pellets of horseradish peroxidase were placed in either the striate cortex immediately adjacent to the ablation, or in the extrastriate cortex of the ventral prelunate gyrus, i.e. in visual area V4. We examined the dorsal lateral geniculate nucleus to see whether surviving neurons, within the region that shows retrograde degeneration as a result of the cortical lesion, project to remaining striate cortex and/or to extrastriate cortex. Neurons labelled from extrastriate cortex were found throughout the degenerated region, whereas neurons labelled from striate cortex were confined to the border between the normal and degenerated region of the nucleus. This shows that isolated neurons found within the degenerated region survive striate cortex damage because they project to an extrastriate visual area, and not because their terminals depart from the otherwise strict topographic representation of the lateral geniculate nucleus on to striate cortex.

The effects of repeated intense hypoxia on learning and memory in the guinea pig

A lesion of striate cortex, area V1, produces blindness in the retinotopically corresponding part of the visual field, although in some cases visual abilities in the blind field remain that are paradoxically devoid of conscious visual percepts (“blindsight”). Here we demonstrate that the blindsight subject GY can experience visual sensations of phosphenes in his blind field induced by transcranial magnetic stimulation (TMS). Such blind field percepts could only be induced when stimulation was applied bilaterally, i.e. over GY's area V5/MT in both hemispheres. Consistent with an earlier report [Cowey, A., & Walsh, V. (2000). Magnetically induced phosphenes in sighted, blind and blindsighted observers. Neuroreport, 11, 3269–3273], GY never experienced phosphenes when stimulation was restricted to his ipsilesional V5/MT. To the best of our knowledge this is the first time GY has experienced visual qualia in his blind hemifield. The present report characterizes the necessary conditions for such conscious experience in his hemianopic visual field and interprets them as demonstrating that only via a contribution from GY's intact hemisphere can activation in the damaged hemisphere reach visual awareness.

Detection of visual stimuli in far periphery by rats: possible role of superior colliculus.

Previous work has been shown that rats with lesions of the superior colliculus fail to respond to distracting visual stimuli presented in the peripheral field while the animals are running towards a central stimulus. To assess how far this peripheral neglect is due to an attentional deficit, rats were trained before operation to obtain reward by running towards either peripheral or central lights that were presented when the animals' heads were stationary in a known position. Response to stimuli presented 120 deg from the midline was severely impaired after removal of the superior colliculus: the animals behaved as if they had difficulty in detecting the onset of the light. In contrast, response to stimuli 40 deg from midline was unaffected. Control lesions of striate cortex did not significantly impair performance at any position. The finding that collicular animals were impaired at responding to stimuli in the far periphery, that were not irrelevant distractors but instead predicted reward, suggests that one component of the visual neglect produced by damage to the superior colliculus in rats may be a sensory deficit in the far peripheral field. In addition, comparison with previous results indicates that training to attend to visual stimuli in more central regions does improve performance, as would be expected if the deficit were an attentional one. It is therefore argued that collicular neglect in rats should be regarded as a multicomponent impairment.

Punctate chemical lesions of striate cortex in the macaque monkey: effect on visually guided saccades.

Chemical agents which reversibly or irreversibly disrupt neural processing offer several advantages over traditional techniques for behavioral studies of the central nervous system. In order to evaluate the utility of chemical agents for a behavioral analysis of visual cortical function in primates, we have tested the effects of muscimol and ibotenic acid on the function of striate cortex in awake, behaving monkeys. We studied the monkey's ability to generate saccadic eye movements to visual targets at various locations in the visual field following an injection of one or the other chemical solution into a topographically identified location in striate cortex. Our results show that deficits in the generation of visually guided saccades following such injections are similar to those that result from surgical ablation of striate cortex, although recovery is more rapid following the injections. The experiments indicate that, with certain restrictions, chemical inactivation is a useful technique for behavioral analysis of visual cortical function.

Spatial contrast sensitivity of dark-reared cats with striate cortex lesions

We measured the spatial contrast sensitivity of two dark-reared cats before and after bilateral ablations of area 17 and parts of area 18. These lesions produced large deficits in the contrast sensitivity of both cats at intermediate and high spatial frequencies. This postoperative reduction in contrast sensitivity in dark-reared cats is relatively similar to the sensitivity deficits produced by the same cortical lesions in normally reared cats. However, both pre- and postoperatively, the normally reared cats exhibited contrast sensitivity that is clearly superior to that of the dark-reared cats. The results demonstrate both that striate cortex is significantly involved in the spatial contrast sensitivity of dark-reared cats and that dark rearing produces widespread deficits, independent of those in striate cortex, through much of the visual system.

Effects of inferior temporal lesions on visual discrimination performance in monkeys with complete and incomplete striate cortex ablations.

In order to determine whether inferior temporal cortex participates in the relearning of visual discriminations following striatectomy, monkeys were retrained to perform two preoperatively acquired discriminations (brightness-flux and brightness-area) after receiving bilateral striate cortex lesions and then retested in the same tasks after bilateral inferior temporal surgery. After inferior temporal surgery, the monkeys with histologically verified total ablation of striate cortex showed little or no impairment in relearning the discriminations, whereas the monkeys with remnants of intact striate cortex were severely impaired. These findings suggest that inferior temporal cortex is, at most, of minor importance in relearning brightness-flux and brightness-area discriminations in the absence of striate cortex. This interpretation is consistent with the view that the contribution of inferior temporal cortex to visual discrimination performance depends on input from striate cortex.

Visual activation of neurons in the primate pulvinar depends on cortex but not colliculus

Superior colliculus lesions had little effect on the visual response of neurons in the monkey inferior pulvinar. By contrast, striate cortex lesions eliminated the visual response of all inferior pulvinar neurons for a period of 3 weeks after the lesion. At longer survival times, a few pulvinar neurons responded to small light spots, but sensitivity to orientation and direction of movement never returned. Thus striate cortex, rather than the colliculus, appears to be responsible for the visual properties of pulvinar cells.

Contribution of striate inputs to the visuospatial functions of parieto-preoccipital cortex in monkeys

In Experiments 1 and 2, monkeys received 3-stage operations intended to serially disconnect parieto-preoccipital from striate cortex. At each stage (unilateral parieto-preoccipital removal, contralateral striate removal and posterior callosal transection) the monkeys were tested for retention of the landmark task, a visuospatial discrimination sensitive to the effects of bilateral parieto-preoccipital damage. To check the effectiveness of the disconnection, the monkeys were also tested after removal of the remaining parieto-preoccipital cortex. The results demonstrated that corticocortical inputs from striate cortex are crucial for the visuospatial functions of parieto-preoccipital cortex, just as they had been shown earlier to be crucial for the pattern discrimination functions of inferior temporal cortex. Relative to inferior temporal cortex, however, parieto-preoccipital cortex was found to be especially dependent on ipsilateral (as compared with contralateral) striate inputs. In Experiment 3, monkeys received bilateral lesions of either lateral or medial striate cortex and were tested on both a pattern discrimination task, to assess residual inferior temporal function, and the landmark task, to assess residual parieto-preoccipital function. The results indicated that the pattern discrimination functions of inferior temporal cortex are especially dependent on inputs from lateral striate cortex, whereas the visuospatial functions of parieto-preoccipital cortex are equally dependent on inputs from lateral and medial striate cortex. The relatively greater contribution to parieto-preoccipital than to inferior temporal cortex made by ipsilateral and medial striate inputs (representing contralateral and peripheral visual fields, respectively) can also be seen in the receptive field properties of parieto-preoccipital and inferior temporal neurons. The differences in the organization of striate inputs to these two cortical association areas presumably reflect differences in the processing required for spatial vs object vision.

Spatial and temporal sensitivity of normal and amblyopic cats.

1. We used the behavioral technique of conditioned suppression to measure spatial and temporal contrast sensitivity to counterphased, sine-wave gratings in eight cats. These included two normally reared cats before and after bilateral ablations of cortical area 17 and part of area 18, two cats raised in total darkness, two cats raised with binocular lid suture, and two cats raised with monocular lid suture, Visual deficits induced by cortical lesions or visual deprivation were evaluated with respect to the preoperative data of the normally reared cats. 2. The cortical lesions had virtually no qualitative effect on the cat’s visual capacities. Contrast sensitivity was reduced at higher but not lower spatial frequencies, and this can be described succinctly as a loss of spatial acuity. 3. Dark-reared and binocularly sutured cats qualitatively exhibited poorer visual capacity than that of the cortically ablated animals. The contrast sensitivity resultant from these two forms of binocular deprivation was basically similar and consisted of significant sensitivity losses at all spatial and temporal frequencies. Much more than high spatial frequencies was affected, and this amblyopia cannot be characterized simply as a spatial acuity loss. 4. Monocularly sutured cats had normal vision and contrast sensitivity with the nondeprived eye, but with the deprived eye they displayed the most severe amblyopia and poorest contrast sensitivity of any of the cats. Again, sensitivity losses were evident for all spatial and temporal frequencies, and this amblyopia is more severe than a loss of spatial acuity. 5. These psychophysical data are related to the status of W-, X-, and Y-cell pathways in these cats. Sensitivity to low spatial frequencies and integrity of the Y-cell pathway is correlated with good visual capacity. Since Y-cells are uniquely sensitive to low spatial frequencies, then the Y-cell pathway seems sufficient and perhaps necessary for reasonable visual performance. 6. Finally, because the amblyopia of normally reared cats with lesions of striate cortex is far less severe than that of the lidsutured and dark-reared cats, it follows that the constellation of deficits reported for striate cortex in these visually deprived cats cannot provide an adequate neural explanation for their amblyopia. Attempts to relate deprivation amblyopia to striate cortex abnormalities should thus be reconsidered.

Hypertrophy of neurons in dorsal lateral geniculate nucleus following striate cortex lesions in infant monkeys

Monkeys whose left striate cortex had been removed in infancy received bilateral injections of horseradish peroxidase (HRP) into the prelunate gyrus (PLG) prestriate cortex. Scattered large neurons in the dorsal lateral geniculate nucleus were retrogradely labeled in both hemispheres. On the lesioned side, the HRP-labeled cell bodies were 58% larger in area, showing an overall increase in soma size and complexity of dendritic field, suggesting a hypertrophy of the geniculate-PLG pathway following a neonatal striate cortex lesion.

Grating detection and visual acuity after lesions of striate cortex in hooded rats.

The ability of rats to detect high-contrast square-wave gratings over a range of spatial frequencies was measured before and after ablation of striate cortex. The animals relearnt to detect low-frequency gratings very quickly after operation, and their acuity was reduced from 1.0 c/deg to about 0.7 c/deg. These effects were in striking contrast to those produced by larger posterior cortical ablations, which included both striate and prestriate cortex (Dean 1978); after the larger lesions, rats required many weeks of retraining to detect even low-frequency gratings and their acuity was reduced to 0.3 c/deg. The difference in the effects of the two lesions suggested that the rats with striate ablation were using information about spatial contrast that was relayed either by spared remnants of the geniculo-cortical pathway, or by the pathway from superior colliculus to prestriate cortex via the lateral posterior nucleus. To try and distinguish between these possibilities, the destriate rats were given a further lesion of the superior colliculus. This second lesion severely disrupted contrast detection: the animals made about as many errors as rats with large posterior cortical removal in relearning to detect a low-frequency grating, which is about 20 to 30 times as many as after either striate cortex or superior colliculus lesions alone. This result suggests that rats, like other mammals, can use spatial information conveyed in the tectocortical path when striate cortex has been destroyed.

The striate projection zone in the superior temporal sulcus of Macaca mulatta: location and topographic organization.

In the rhesus monkey, the caudal portion of the superior temporal sulcus (STS) receives a direct projection from lateral striate cortex, the striate are representing central vision. The present study was undertaken to determine whether STS also receives a direct projection from areas of striate cortex representing peripheral vision, with the intent of defining the entire striate projection zone in STS as well as providing information regarding a possible topographic organization within this secondary visual area. A series of five rhesus monkeys was prepared with unilateral lesions of lateral, posterior, or medial striate cortex, such that, collectively, the lesions in the series included all of striate cortex with little or no invasion of prestriate cortex. The monkeys were sacrificed seven days after surgery and their brains were processed by the Fink-Heimer procedure. An analysis of the distribution of terminal degeneration within STS indicated: (1) All areas of striate cortex project to a restricted region along the caudal portion of STS. The ventral limit of this region can be demarcated by an imaginary line connecting the ventral tips of the lunate and intraparietal sulci; from this limit the region extends dorsocaudally for approximately 12 mm to the point at which STS frequently bifurcates, sending one spur forward into the inferior parietal lobule. (2) Within this portion of STS there is an orderly mapping of the visual field; progression from central vision to the far periphery is represented by a progression down the posterior bank of STS and continuing along the entire floor, or insula-like portion, of the sulcus. (3) Projections from striate cortex to STS terminate predominantly in layer IV and the deep part of layer III. (4) There is a distinctive pattern of myelination contained within the striate projection zone of STS. These anatomical findings concerning the striate projection zone of STS in the rhesus monkey are remarkably similar to those that have been described for the middle temporal visual area (MT) in New World monkeys, and thus support earlier proposals that the two areas are homologous.