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C G Gross

Publications and source records attributed to C G Gross.

At least 19 recordsLinked to original sources
PubMed1992

Intrinsic signal optical imaging in the forepaw area of rat somatosensory cortex.

The responses of somatosensory cortex (S-I) to tactile stimulation of the forepaw were assessed by intrinsic signal optical imaging. The tips of digits two or five were alternately touched with mechanical tappers while video photographs were taken of S-I illuminated by an 800-nm light source. The resulting images showed two highlighted areas about 300 microns in diameter and 500 microns apart. Generation of these images required less than 1 hr. Electrode penetrations placed in the areas highlighted during stimulation provided multiunit recordings with receptive fields appropriate for the stimulated digit and not the other digit. Penetrations between the high-lighted areas yielded receptive fields on intervening digits. These results demonstrate that intrinsic signal optical images are obtainable in S-I and confirm the functional somatotopy previously reported using electrical recording. Furthermore, the short time required to produce the images and the obtainable spatial resolution suggest that optical recording could be employed for the study of cortical reorganization in this brain region.

Animals↗
PubMed1992

Representation of visual stimuli in inferior temporal cortex.

In primates, inferior temporal (IT) cortex is crucial for the processing and storage of visual information about form and colour. This article reviews the properties of IT neurons and considers how these properties may underlie the perceptual and mnemonic functions of IT cortex. The available evidence suggests that the processing of the facial image by IT cortex is similar to its processing of other visual patterns. Faces and other complex visual stimuli appear to be represented by the pattern of responses over a population of IT neurons rather than by the responses of specific 'feature detectors' or 'grandmother' cells. IT neurons with adult-like stimulus properties are present in monkeys as young as six weeks old.

Afferent Pathways↗
PubMed1992

Face recognition.

The study of face-selective neurons in the monkey temporal lobe, and face recognition deficits in humans after brain damage have both become very active fields of investigation. Face-selective neurons appear to be members of ensembles for coding faces rather than individual face detectors or grandmother cells. They reflect the more general role of temporal cortex in pattern recognition. In humans there are a variety of face-processing impairments that result from damage to different areas, and which reflect interference at different levels of processing of the facial image.

Animals↗
PubMed1991

Stimulus selectivity and state dependence of activity in inferior temporal cortex of infant monkeys.

Inferior temporal cortex is necessary for visual object recognition in adult primates but is less critical in infants. Nonetheless, in macaques as young as 6 weeks old, inferior temporal neurons showed adult-like visual response properties, including form selectivity and bilateral receptive fields, indicating that extended maturation and visual experience may not be necessary for adult-like encoding of complex objects. However, before the animals were 4 months old, visual responsiveness was found in inferior temporal cortex only in awake monkeys performing a behavioral task and not in anesthetized ones, suggesting that extraretinal factors profoundly influence function in "association" cortex in developing as well as mature animals.

Aging↗
PubMed1991

Functional interactions among neurons in inferior temporal cortex of the awake macaque.

Functional interactions among inferior temporal cortex (IT) neurons were studied in the awake, fixating macaque monkey during the presentation of visual stimuli. Extracellular recordings were obtained simultaneously from several microelectrodes, and in many cases, spike trains from more than one neuron were extracted from each electrode by the use of spike shape sorting technology. Functional interactions between pairs of neurons were measured using cross-correlation. Discharge patterns of single neurons were evaluated using auto-correlation and PST histograms. Neurons recorded on the same electrode (within about 100 microns) had more similar stimulus selectivity and were more likely to show functional interactions than those recorded on different electrodes spaced about 250 to 500 microns apart. Most neurons tended to fire in bursts tens to hundreds of milliseconds in duration, and asynchronously from the stimulus induced rate changes. Correlated neuronal firing indicative of shared inputs and direct interactions was observed. Occurrence of shared input was significantly lower for neuron pairs recorded on different electrodes than for neurons recorded on the same electrode. Direct connections occurred about as often for neurons on different electrodes as for neurons on the same electrode. These results suggest that input projections are usually restricted to less than 500 micron patches and are then distributed over greater distances by intrinsic connections. Measurements of synaptic contribution suggest that typically more than 5 near-simultaneous inputs are required to cause an IT neuron to discharge.

Animals↗
PubMed1991

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

Animals↗
PubMed1991

Habituation-like decrease in the responses of neurons in inferior temporal cortex of the macaque.

In both anesthetized and behaving macaques, we examined the responses of neurons in the inferior temporal cortex (IT) to repeated presentation of a visual stimulus. In anesthetized animals, the responsiveness of IT neurons decreased with repeated stimulus presentation at interstimulus intervals (ISIs) of 2-12 s but not at 20 s. Responsiveness recovered after a 5-min period of no stimulus presentation. The response decrement was similar in anesthetized and awake animals at a 2-s ISI, but at a 6-s ISI, response decrement in the awake animal was much less.

Anesthesia↗
PubMed1990

Auditory association cortex lesions impair auditory short-term memory in monkeys.

Monkeys that were trained to perform auditory and visual short-term memory tasks (delayed matching-to-sample) received lesions of the auditory association cortex in the superior temporal gyrus. Although visual memory was completely unaffected by the lesions, auditory memory was severely impaired. Despite this impairment, all monkeys could discriminate sounds closer in frequency than those used in the auditory memory task. This result suggests that the superior temporal cortex plays a role in auditory processing and retention similar to the role the inferior temporal cortex plays in visual processing and retention.

Animals↗
PubMed1990

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.

Animals↗
PubMed1989

Afferent basis of visual response properties in area MT of the macaque. I. Effects of striate cortex removal.

The middle temporal area (MT) of the macaque monkey is a region of extrastriate cortex involved in the analysis of visual motion. MT receives strong projections from striate cortex and from area V2, which is dependent on striate for visual responsiveness. Accordingly, the visual properties of MT neurons have been thought to reflect the further processing of its input from striate cortex. We examined the dependence of MT activity on pathways deriving from striate cortex by recording from MT neurons following removal of their striate input. Repeated recordings in area MT were made in 4 hemispheres of anesthetized macaques following either partial or total ablations of striate cortex. Cells in MT were tested for responsiveness, selectivity for direction of motion and direction tuning, and ocular dominance. Receptive fields were also plotted. In an additional animal, we recorded from MT neurons during reversible cooling of the central representation in striate cortex. We found that striate cortex removal or inactivation did not abolish the visual responsiveness of the majority of MT cells. Although the residual responses were generally much weaker than in the intact animal, direction selectivity and binocularity were still present. Moreover, receptive field size and overall topography appeared unaltered.

Afferent Pathways↗
PubMed1988

Topographical organization of cortical afferents to extrastriate visual area PO in the macaque: a dual tracer study.

We have examined the origin and topography of cortical projections to area PO, an extrastriate visual area located in the parieto-occipital sulcus of the macaque. Distinguishable retrograde fluorescent tracers were injected into area PO at separate retinotopic loci identified by single-neuron recording. The results indicate that area PO receives retinotopically organized inputs from visual areas V1, V2, V3, V4, and MT. In each of these areas the projection to PO arises from the representation of the periphery of the visual field. This finding is consistent with neurophysiological data indicating that the representation of the periphery is emphasized in PO. Additional projections arise from area MST, the frontal eye fields, and several divisions of parietal cortex, including four zones within the intraparietal sulcus and a region on the medial dorsal surface of the hemisphere (MDP). On the basis of the laminar distribution of labeled cells we conclude that area PO receives an ascending input from V1, V2, and V3 and receives descending or lateral inputs from all other areas. Thus, area PO is at approximately the same level in the hierarchy of visual areas as areas V4 and MT. Area PO is connected both directly and indirectly, via MT and MST, to parietal cortex. Within parietal cortex, area PO is linked to particular regions of the intraparietal sulcus including VIP and LIP and two newly recognized zones termed here MIP and PIP. The wealth of connections with parietal cortex suggests that area PO provides a relatively direct route over which information concerning the visual field periphery can be transmitted from striate and prestriate cortex to parietal cortex. In contrast, area PO has few links with areas projecting to inferior temporal cortex. The pattern of connections revealed in this study is consistent with the view that area PO is primarily involved in visuospatial functioning.

Animals↗
PubMed1979

Visual areas in the temporal cortex of the macaque.

Visual receptive fields and responsiveness of neurons to somesthetic and auditory stimuli were studied in the inferior temporal cortex and adjacent regions of immobilized macaques. Neurons throughout cytoarchitectonic area TE were responsive only to visual stimuli and had large receptive fields that almost always included the center of gaze and usually extended into both visual half-fields. There was no indication of any visuotopic organization within area TE. Neurons in an anterior and in a dorsal portion of TE tended to have larger receptive fields. By contrast, dorsal, ventral and anterior to area TE, units often responded to somesthetic and auditory as well as to visual stimuli. In these regions visual receptive fields were even larger than in TE and often included the entire visual field. Posterior to TE the neurons were exclusively visual and had much smaller receptive fields that were confined to the contralateral visual field and were topographically organized.

Animals↗
PubMed1979

Role of inferior temporal cortex in interhemispheric transfer.

Neurons in inferior temporal cortex of the rhesus monkey usually have large receptive fields that extend well across the midline into both visual half-fields. The responsiveness of these neurons to stimuli in the ipsilateral visual half-field depends on the splenium and anterior commissure, the same pathways necessary for interhemispheric transfer of visual habits. Since inferior temporal neurons have the same trigger features in both half-fields and are usually binocular, they may be the site of the interhemispheric neural convergence that underlies interhemispheric transfer. If so, bilateral removal of inferior temporal cortex should interfere with interhemispheric transfer even when the commissures are intact. To test this, monkeys were trained on pattern discriminations with one eye and then tested for transfer with the other eye. Five experimental monkeys received bilateral inferior temporal lesions and, to restrict input from each eye to one hemisphere, section of the optic chiasm. Ten controls received either bilateral temporal lesions alone, chiasm section alone or remained unoperated. Only the experimental animals showed impaired transfer. These results suggest that inferior temporal neurons mediate interhemispheric transfer by providing perceptual equivalence for patterns in the left and right visual fields, and, by implication, perhaps also for patterns in different parts of the same field.

Animals↗
PubMed1979

Color categories in macaques.

This experiment investigated whether macaque monkeys partition the photic spectrum into the same four basic hue categories that humans do, i.e., blue, green, yellow, and red. Monkeys were trained to respond in the presence of one chromatic stimulus and were tested, in extinction, for generalization to others. In extinction, the monkeys responded at similar and high levels to stimuli that fell in the same basic human hue category as the training stimulus and at similar and much lower levels to stimuli that fell in a different human hue category from the training stimulus. It was concluded that macaques and humans categorize the spectrum in a similar fashion.

Animals↗
PubMed1978

Localization and detection of visual stimuli following superior colliculus lesions in rhesus monkeys.

Rhesus monkeys were trained to fixate a central stimulus and to detect and localize a 50 msec light flash presented 6-80 degrees on either side of the central stimulus. Following large lesions of the superior colliculus, they showed persistent deficits in localizing flashes presented 43-80 degrees from the fixation stimulus. However, they were not consistently impaired when the flashes were presented more centrally, and their performance with peripheral stimuli improved when the stimulus duration was 1 sec. Thus, the superior colliculus appears to be necessary for the localization of brief visual stimuli in the far periphery.

Animals↗
PubMed1978

Inferior temporal lesions do not impair discrimination of rotated patterns in monkeys.

Ablation of inferior temporal cortex in the rhesus monkey produces a visual discrimination learning deficit. The severity of this deficit has often been found to be a function of task difficulty. This report concerns a type of visual discrimination problem that, although difficult, is not sensitive to inferior temporal lesions. Monkeys with anterior, posterior, and complete inferior temporal lesions were repeatedly unimpaired or only slightly impaired in learning to discriminate a pattern from the same pattern rotated 90 degrees or 180 degrees; yet they were very severely impaired in learning equally or more difficult discriminations of two different patterns. This demonstration that discrimination of orientation of patterns is relatively spared after inferior temporal lesions helps specify the pattern-recognition processes that require inferior temporal cortex.

Animals↗