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R Desimone

Publications and source records attributed to R Desimone.

69 records · Page 4Linked to original sources
PubMed1986

Both striate cortex and superior colliculus contribute to visual properties of neurons in superior temporal polysensory area of macaque monkey.

Although the tectofugal system projects to the primate cerebral cortex by way of the pulvinar, previous studies have failed to find any physiological evidence that the superior colliculus influences visual activity in the cortex. We studied the relative contributions of the tectofugal and geniculostriate systems to the visual properties of neurons in the superior temporal polysensory area (STP) by comparing the effects of unilateral removal of striate cortex, the superior colliculus, or of both structures. In the intact monkey, STP neurons have large, bilateral receptive fields. Complete unilateral removal of striate cortex did not eliminate visual responses of STP neurons in the contralateral visual hemifield; rather, nearly half the cells still responded to visual stimuli in the hemifield contralateral to the lesion. Thus the visual properties of STP neurons are not completely dependent on the geniculostriate system. Unilateral striate lesions did affect the response properties of STP neurons in three ways. Whereas most STP neurons in the intact monkey respond similarly to stimuli in the two visual hemifields, responses to stimuli in the hemifield contralateral to the striate lesion were usually weaker than responses in the ipsilateral hemifield. Whereas the responses of many STP neurons in the intact monkey were selective for the direction of stimulus motion or for stimulus form, responses in the hemifield contralateral to the striate lesion were not selective for either motion or form. Whereas the median receptive field in the intact monkey extended 80 degrees into the contralateral visual field, the receptive fields of cells with responses in the contralateral field that survived the striate lesions had a median border that extended only 50 degrees into the contralateral visual field. Removal of both striate cortex and the superior colliculus in the same hemisphere abolished the responses of STP neurons to visual stimuli in the hemifield contralateral to the combined lesion. Nearly 80% of the cells still responded to visual stimuli in the hemifield ipsilateral to the lesion. Unilateral removal of the superior colliculus alone had only small effects on visual responses in STP. Receptive-field size and visual response strength were slightly reduced in the hemifield contralateral to the collicular lesion. As in the intact monkey, selectivity for stimulus motion or form were similar in the two visual hemifields. We conclude that both striate cortex and the superior colliculus contribute to the visual responses of STP neurons. Striate cortex is crucial for the movement and stimulus specificity of neurons in STP.(ABSTRACT TRUNCATED AT 400 WORDS)

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PubMed1985

Selective attention gates visual processing in the extrastriate cortex.

Single cells were recorded in the visual cortex of monkeys trained to attend to stimuli at one location in the visual field and ignore stimuli at another. When both locations were within the receptive field of a cell in prestriate area V4 or the inferior temporal cortex, the response to the unattended stimulus was dramatically reduced. Cells in the striate cortex were unaffected by attention. The filtering of irrelevant information from the receptive fields of extrastriate neurons may underlie the ability to identify and remember the properties of a particular object out of the many that may be represented on the retina.

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PubMed1985

Contour, color and shape analysis beyond the striate cortex.

The corticocortical pathway from striate cortex into the temporal lobe plays a crucial role in the visual recognition of objects. Anatomical studies indicate that this pathway is mainly organized as a serial hierarchy of multiple visual areas, including V1, V2, V3, V4, and inferior temporal cortex (IT). As expected from the anatomy, we have found that neurons in V4 and IT, like those in V1 and V2, are sensitive to many kinds of information relevant to object recognition. In the spatial domain, many V4 cells exhibit length, width, orientation, direction of motion and spatial frequency selectivity. In the spectral domain, many V4 cells are also tuned to wavelength. Thus, V4 is not specialized to analyze one particular attribute of a visual stimulus; rather, V4 appears to process both spatial and spectral information in parallel. A special contribution of V4 neurons to visual processing may lie in specific spatial and spectral interactions between their small excitatory receptive fields and large silent suppressive surrounds. Thus, although the excitatory receptive fields of V4 neurons are small, the responses of V4 neurons are influenced by stimuli throughout a much larger portion of the visual field. In IT, neurons also appear to process both spatial and spectral information throughout a large portion of the visual field. However, unlike V4 neurons, the excitatory receptive fields of IT neurons are very large. Many IT neurons, for example, are selective for the overall shape, color, or texture of a stimulus, anywhere within the central visual field. Together, these results suggest that within the areas of the occipito-temporal pathway, many different stimulus qualities are processed in parallel, but the type of analysis may become more global at each stage of processing.

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PubMed1984

Subcortical projections of area MT in the macaque.

Area MT is a visuotopically organized area in extrastriate cortex of primates that appears to be specialized for the analysis of visual motion. To examine the full extent and topographic organization of the subcortical projections of MT in the macaque, we injected tritiated amino acids in five cynomolgus monkeys and processed the brains for autoradiography. The injection sites, which we identified electrophysiologically, ranged from the representation of central through peripheral vision in both the upper and lower visual fields and included, collectively, most of MT. Projections from MT to the superior colliculus are topographically organized and in register with projections from striate cortex to the colliculus. Unlike projections from striate cortex, those from MT are not limited to the upper layer of the stratum griseum superficiale but rather extend ventrally from the upper through the lower layer of the stratum griseum superficiale and even include the stratum opticum. Projections from MT to the pulvinar are organized into three separate fields. One field (P1) is located primarily in the inferior pulvinar but extends into a portion of the adjacent lateral pulvinar. The second field (P2) partially surrounds the first and is located entirely in the lateral pulvinar. The third and heaviest projection field (P3) is located posteromedially in the inferior pulvinar but also includes small portions of the lateral and medial pulvinar that lie dorsal to the brachium of the superior colliculus. While projections from MT to P1 and P2 are topographically organized, there appears to be a convergence of MT inputs to P3. Projections from MT to the reticular nucleus of the thalamus are located in the ventral portion of the nucleus, approximately at the level of the caudal pulvinar. There was some evidence that MT sites representing central vision project more caudally than do those representing peripheral vision. Projections from MT to the caudate, putamen, and claustrum are localized to small, limited zones in each structure. Those to the caudate terminate within the most caudal portion of the body and the tail. Similarly, projections to the putamen are always to its most caudal portion, where the structure appears as nuclear islands. Projections to the claustrum are located ventrally, approximately at the level of the anterior part of the dorsal lateral geniculate nucleus. Projections from MT to the pons terminate rostrally in the dorsolateral nucleus, the lateral nucleus, and the dorsolateral portion of the peduncular nucleus.(ABSTRACT TRUNCATED AT 400 WORDS)

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PubMed1984

Columnar organization of directionally selective cells in visual area MT of the macaque.

We recorded from single neurons in visual area MT of the macaque in order to examine the spatial distribution of its directionally selective cells. The animals were paralyzed and anesthetized with nitrous oxide. All MT neurons (n = 614) responded better to moving stimuli than to stationary stimuli. For 55% of the neurons, responses to moving stimuli were independent of stimulus color, shape, length, or orientation. For the remaining cells, stimulus length affected the response magnitude and tuning bandwidth but not the preferred direction. MT neurons were divided into four categories on the basis of their sensitivity to moving stimuli: 60% responded exclusively to one direction of motion, 24% responded best to one direction with a weaker response in the opposite direction, 8% responded equally well to two opposite directions of motion, and 8% responded equally well to all directions of motion. The direction preferences of successively sampled cells on a penetration either changed by small increments or occasionally by approximately 180 degrees. Thus, there is a systematic representation of direction of motion. The representation of axis of motion, i.e., the orientation of the path along which a stimulus moves, is more continuous than the representation of direction of motion. There was a systematic relationship between penetration angle and rate of change of preferred axis of motion, indicating that cells with a similar axis of motion preference are arranged in vertical columns. Furthermore, axis of motion columns appear to exist in the form of continuous slabs in area MT. The size of these slabs is such that 180 degrees of axis of motion are represented in 400-500 micron of cortex. There was also a systematic relationship between penetration angle and frequency of 180 degrees reversals, indicating that cells with a similar direction of motion preference are also organized in vertical columns and cells with opposite direction preferences are located in adjacent columns within a single axis of motion column. Just as in macaque striate cortex where approximately 500 micron of cortex contain the mechanism for the local analysis of stimulus orientation, so in MT approximately 500 micron of cortex contain the mechanism for the local analysis of stimulus motion.

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PubMed1984

Stimulus-selective properties of inferior temporal neurons in the macaque.

Previous studies have reported that some neurons in the inferior temporal (IT) cortex respond selectively to highly specific complex objects. In the present study, we conducted the first systematic survey of the responses of IT neurons to both simple stimuli, such as edges and bars, and highly complex stimuli, such as models of flowers, snakes, hands, and faces. If a neuron responded to any of these stimuli, we attempted to isolate the critical stimulus features underlying the response. We found that many of the responsive neurons responded well to virtually every stimulus tested. The remaining, stimulus-selective cells were often selective along the dimensions of shape, color, or texture of a stimulus, and this selectivity was maintained throughout a large receptive field. Although most IT neurons do not appear to be "detectors" for complex objects, we did find a separate population of cells that responded selectively to faces. The responses of these cells were dependent on the configuration of specific face features, and their selectivity was maintained over changes in stimulus size and position. A particularly high incidence of such cells was found deep in the superior temporal sulcus. These results indicate that there may be specialized mechanisms for the analysis of faces in IT cortex.

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PubMed1983

Shape recognition and inferior temporal neurons.

Inferior temporal cortex plays an important role in shape recognition. To study the shape selectivity of single inferior temporal neurons, we recorded their responses to a set of shapes systematically varying in boundary curvature. Many inferior temporal neurons were selective for stimuli of specific boundary curvature and maintained this selectivity over changes in stimulus size or position. The method of describing boundary curvature was that of Fourier descriptors.

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PubMed1980

Prestriate afferents to inferior temporal cortex: an HRP study.

The inferior temporal (IT) cortex of 6 macaques was injected with horseradish peroxidase. HRP-labeled cells were found throughout IT cortex itself (outside the injection area) but were not found in the polysensory areas that surround IT dorsally, anteriorly and ventrally. Posterior to IT, labeled cells were found in the anterior parts of prestriate cortex. In one animal, the anterior prestriate region was injected with HRP. Labeled cells were then found in the regions of posterior prestriate cortex that receive direct projections from striate cortex. These results suggest that IT cortex receives information from striate cortex after at least two stages of processing in prestriate cortex.

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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.

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PubMedDate not supplied

Comparison of subcortical connections of inferior temporal and posterior parietal cortex in monkeys.

To investigate the subcortical connections of the object vision and spatial vision cortical processing pathways, we injected the inferior temporal and posterior parietal cortex of six Rhesus monkeys with retrograde or anterograde tracers. The temporal injections included area TE on the lateral surface of the hemisphere and adjacent portions of area TEO. The parietal injections covered the posterior bank of the intraparietal sulcus, including areas VIP and LIP. Our results indicate that several structures project to both the temporal and parietal cortex, including the medial and lateral pulvinar, claustrum, and nucleus basalis. However, the cells in both the pulvinar and claustrum that project to the two systems are mainly located in different parts of those structures, as are the terminals which arise from the temporal and parietal cortex. Likewise, the projections from the temporal and parietal cortex to the caudate nucleus and putamen are largely segregated. Finally, we found projections to the pons and superior colliculus from parietal but not temporal cortex, whereas we found the lateral basal and medial basal nuclei of the amygdala to be reciprocally connected with temporal but not parietal cortex. Thus, the results show that, like the cortical connections of the two visual processing systems, the subcortical connections are remarkably segregated.

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PubMedDate not supplied

A role for the corpus callosum in visual area V4 of the macaque.

The classically defined receptive fields of V4 cells are confined almost entirely to the contralateral visual field. However, these receptive fields are often surrounded by large, silent suppressive regions, and stimulating the surrounds can cause a complete suppression of response to a simultaneously presented stimulus within the receptive field. We investigated whether the suppressive surrounds might extend across the midline into the ipsilateral visual field and, if so, whether the surrounds were dependent on the corpus callosum, which has a widespread distribution in V4. We found that the surrounds of more than half of the cells tested in the central visual field representation of V4 crossed into the ipsilateral visual field, with some extending up to at least 16 deg from the vertical meridian. Much of this suppression from the ipsilateral field was mediated by the corpus callosum, as section of the callosum dramatically reduced both the strength and extent of the surrounds. There remained, however, some residual suppression that was not further reduced by addition of an anterior commissure lesion. Because the residual ipsilateral suppression was similar in magnitude and extent to that found following section of the optic tract contralateral to the V4 recording, we concluded that it was retinal in origin. Using the same techniques employed in V4, we also mapped the ipsilateral extent of surrounds in the foveal representation of V1 in an intact monkey. Results were very similar to those in V4 following commissural or contralateral tract sections. The findings suggest that V4 is a central site for long-range interactions both within and across the two visual hemifields. Taken with previous work, the results are consistent with the notion that the large suppressive surrounds of V4 neurons contribute to the neural mechanisms of color constancy and figure-ground separation.

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PubMedDate not supplied

Cue-dependent deficits in grating orientation discrimination after V4 lesions in macaques.

To examine the role of visual area V4 in pattern vision, we tested two monkeys with lesions of V4 on tasks that required them to discriminate the orientation of contours defined by several different cues. The cues used to separate the contours from their background included luminance, color, motion, and texture, as well as phase-shifted abutting gratings that created an "illusory" contour. The monkeys were trained to maintain fixation on a fixation target while discriminating extrafoveal stimuli, which were located in either a normal control quadrant of the visual field or in a quadrant affected by a lesion of area V4 in one hemisphere. Comparing performance in the two quadrants, we found significant deficits for contours defined by texture and for the illusory contour, but smaller or no deficits for motion-, color-, and luminance-defined contours. The data suggest a specific role of V4 in the perception of illusory contours and contours defined by texture.

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PubMedDate not supplied

Subcortical connections of visual areas MST and FST in macaques.

To examine the subcortical connections of the medial superior temporal and fundus of the superior temporal visual areas (MST and FST, respectively), we injected anterograde and retrograde tracers into 16 physiologically identified sites within the two areas in seven macaque monkeys. The subcortical connections of MST and FST were found to be very similar. Both areas were found to be reciprocally connected with the pulvinar, mainly with its medial subdivision, and with the claustrum. Nonreciprocal projections from both MST and FST were consistently found in the striatum (caudate and putamen), reticular nucleus of the thalamus, and the pontine nuclei. The labeled terminals in the pons were in the dorsolateral, lateral, dorsal, and peduncular nuclei. Additional nonreciprocal projections were found in one MST and one FST case to the nucleus of the optic tract, and, in one FST case, to the lateral terminal nucleus. Finally, three cases showed a nonreciprocal projection to FST from the basal forebrain. The subcortical structures containing label following MST and FST injections were largely the same as those labeled after injections of the middle temporal visual area (MT), but the label within each structure after MST and FST injections was more widespread than that from MT, overlapping the distribution of label that has been reported after injections of parietal visual areas. This finding is consistent with the known contributions of MST and FST to the functions of parietal cortex, such as eye-movement control.

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PubMedDate not supplied

Inferior temporal mechanisms for invariant object recognition.

The specific size and retinal location of an object are readily perceived, yet recognition of an object's identity is hardly affected by transformations of its size or location. To explore how such stimulus transformations are treated by known mechanisms for visual short-term memory in inferior temporal (IT) cortex, IT cells were recorded in monkeys performing a delayed matching-to-sample task. The stimuli were pictures of complex objects, and the monkeys ignored differences in size and retinal location when matching the test items to the sample held in memory. The sensory information communicated by cells was assessed in their responses to the sample stimuli, and mnemonic information was assessed in their responses to the test stimuli. In the sensory domain, the ordering of relative stimulus preferences for nearly all cells was invariant over changes in size or location; however, some cells nonetheless preferred stimuli of a given size or location. In the mnemonic domain, the responses of many cells were modulated according to whether the test stimulus matched the sample held in memory, and these memory effects were invariant over the relative sizes and locations of the stimuli. Thus, IT neuronal populations may mediate not only the recognition and memory of object identity, which are invariant over size and location, but also the perception of the transformations themselves.

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