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R Desimone

Publications and source records attributed to R Desimone.

At least 19 recordsLinked to original sources
PubMed1995

Responses of cells in monkey visual cortex during perceptual filling-in of an artificial scotoma.

When we view a scene through one eye, we typically do not see the scotomas created by the optic disc and the blood vessels overlying the retinal surface. Similarly, when a texture field containing a hole is steadily viewed in peripheral vision (artificial scotoma), the hole appears to fill in with the surrounding texture in a matter of seconds, demonstrating that the visual system fills in information across regions where no information is available. Here we show that, in monkeys viewing a similar texture field with a hole, the responses of extrastriate visual neurons with receptive fields covering the hole increase gradually to a level comparable to that elicited by the same texture without a hole. The time course of these dynamic changes in activity parallels the time course of perceived filling-in of the hole by human observers, suggesting that this process mediates perceptual filling-in.

Animals↗
PubMed1995

Responses of cells in the tail of the caudate nucleus during visual discrimination learning.

1. The tail of the caudate nucleus and adjacent ventral putamen (ventrocaudal neostriatum) are major projection sites of the extrastriate visual cortex. Visual information is then relayed, directly or indirectly, to a variety of structures with motor functions. To test for a role of the ventrocaudal neostriatum in stimulus-response association learning, or habit formation, neuronal responses were recorded while monkeys performed a visual discrimination task. Additional data were collected from cells in cortical area TF, which serve as a comparison and control for the caudate data. 2. Two monkeys were trained to perform an asymmetrically reinforced go-no go visual discrimination. The stimuli were complex colored patterns, randomly assigned to be either positive or negative. The monkey was rewarded with juice for releasing a bar when a positive stimulus was presented, whereas a negative stimulus signaled that no reward was available and that the monkey should withhold its response. Neuronal responses were recorded both while the monkey performed the task with previously learned stimuli and while it learned the task with new stimuli. In some cases, responses were recorded during reversal learning. 3. There was no evidence that cells in the ventrocaudal neostriatum were influenced by the reward contingencies of the task. Cells did not fire preferentially to the onset of either positive or negative stimuli; neither did cells fire in response to the reward itself or in association with the motor response of the monkey. Only visual responses were apparent. 4. The visual properties of cells in these structures resembled those of cells in some of the cortical areas projecting to them. Most cells responded selectively to different visual stimuli. The degree of stimulus selectivity was assessed with discriminant analysis and was found to be quantitatively similar to that of inferior temporal cells tested with similar stimuli. Likewise, like inferior temporal cells, many cells in the ventrocaudal neostriatum had large, bilateral receptive fields. Some cells had "doughnut"-shaped receptive fields, with stronger responses in the periphery of both visual fields than at the fovea, similar to the fields of some cells in the superior temporal polysensory area. Although the absence of task-specific responses argues that ventrocaudal neostriatal cells are not themselves the mediators of visual learning in the task employed, their cortical-like visual properties suggest that they might relay visual information important for visuomotor plasticity in other structures. (ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1993

The modular organization of projections from areas V1 and V2 to areas V4 and TEO in macaques.

In addition to the major anatomical pathways from V1 into the temporal lobe, there are other smaller, "bypass" routes that are poorly understood. To investigate the direct projection from V1 to V4 (bypassing V2) and from V2 to TEO (bypassing V4), we injected the foveal and parafoveal representations of V4 and TEO with different retrograde tracers in five hemispheres of four macaques and analyzed the distributions of labeled neurons in V1 and V2 using flattened preparations of the cortex. In V1, labeled neurons were seen after injections in V4 but not TEO. The V4-projecting neurons were located in the foveal representation of V1, in both cytochrome oxidase (CO)-rich blobs and CO-poor interblob regions. In V2, TEO-projecting neurons were intermingled with V4-projecting neurons, although the former were far sparser than the latter. Across the cases, 6-19% of the TEO-projecting neurons were double labeled, that is, also projected to area V4. Both V4- and TEO-projecting neurons formed bands that ran orthogonal to the V1/V2 border, and both were located in CO-rich thin stripes and CO-poor interstripe regions. In some cases, a continuous band of V4-projecting neurons was also found along the V1/V2 border in the foveal representation of V2. The results indicate that the pathways from V1 to V4 and from V2 to TEO involve anatomical subcompartments thought to be concerned with both color and form. These "bypass" routes may allow coarse information about color and form to arrive rapidly in the temporal lobe. The bypass route from V2 to TEO might explain the partial sparing of color and form vision that is seen after lesions of V4. By analogy, given the bypass route from the foveal representation of V1 to V4, lesions of V2 affecting the foveal visual field would also be insufficient to block color and form vision.

Amidines↗
PubMed1992

Predicting responses of nonlinear neurons in monkey striate cortex to complex patterns.

The overwhelming majority of neurons in primate visual cortex are nonlinear. For those cells, the techniques of linear system analysis, used with some success to model retinal ganglion cells and striate simple cells, are of limited applicability. As a start toward understanding the properties of nonlinear visual neurons, we have recorded responses of striate complex cells to hundreds of images, including both simple stimuli (bars and sinusoids) as well as complex stimuli (random textures and 3-D shaded surfaces). The latter set tended to give the strongest response. We created a neural network model for each neuron using an iterative optimization algorithm. The recorded responses to some stimulus patterns (the training set) were used to create the model, while responses to other patterns were reserved for testing the networks. The networks predicted recorded responses to training set patterns with a median correlation of 0.95. They were able to predict responses to test stimuli not in the training set with a correlation of 0.78 overall, and a correlation of 0.65 for complex stimuli considered alone. Thus, they were able to capture much of the input/output transfer function of the neurons, even for complex patterns. Examining connection strengths within each network, different parts of the network appeared to handle information at different spatial scales. To gain further insights, the network models were inverted to construct "optimal" stimuli for each cell, and their receptive fields were mapped with high-resolution spots. The receptive field properties of complex cells could not be reduced to any simpler mathematical formulation than the network models themselves.

Animals↗
PubMed1991

A neural mechanism for working and recognition memory in inferior temporal cortex.

Inferior temporal (IT) cortex is critical for visual memory, but it is not known how IT neurons retain memories while new information is streaming into the visual system. Single neurons were therefore recorded from IT cortex of two rhesus monkeys performing tasks that required them to hold items in memory while concurrently viewing other items. The neuronal response to an incoming visual stimulus was attenuated if it matched a stimulus actively held in working memory, even when several other stimuli intervened. The neuronal response to novel stimuli declined as the stimuli became familiar to the animal. IT neurons appear to function as adaptive mnemonic "filters" that preferentially pass information about new, unexpected, or not recently seen stimuli.

Analysis of Variance↗
PubMed1991

Visual topography of area TEO in the macaque.

Previous studies have mapped the visuotopic organization of visual areas from V1 through V4 in the occipital cortex and of area TE in the temporal cortex, but the cortex in between, at the occipito-temporal junction, has remained relatively unexplored. To determine the visuotopic organization of this region, receptive fields were mapped at 1,200 visually responsive sites on 370 penetrations in the ventral occipital and temporal cortex of five macaques. We identified a new visual area, roughly corresponding to cytoarchitectonic area TEO, located between the ventral portion of V4 and area TE. Receptive fields in TEO are intermediate in size between those in V4 and TE and have a coarse visuotopic organization. Collectively, receptive fields in TEO appear to cover nearly the entire contralateral visual field. The foveal and parafoveal representation of TEO is located laterally on the convexity of the inferior temporal gyrus, and the peripheral field is represented medially on the ventral surface of the hemisphere, within and medial to the occipitotemporal sulcus. Beyond the medial border of TEO, within cyteoarchitectonic area TF, is another visually responsive region, which we have termed VTF; this region may also have some crude visual topography. Bands of constant eccentricity in TEO appear to be continuous with those in V2, V3v, and V4. The upper field representation in TEO is located adjacent to that in ventral V4, with a representation of the horizontal meridian forming the boundary between the two areas. The lower field representation in TEO is located just anterior to the upper field but is smaller. In contrast to the orderly representation of eccentricity in TEO, we found little consistent representation of polar angle, other than the separation of upper and lower fields. The results of injecting anatomical tracers in two animals suggest that TEO is an important link in the pathway that relays visual information from V1 to the inferior temporal cortex. TEO is thus likely to play an important role in pattern perception.

Animals↗
PubMed1991

Performance of dynamic cardiomyoplasty related to the functional state of the heart.

Cardiomyoplasty (CMP) was performed with the left Latissimus dorsi in five beagles (group 1) with intact hearts and seven foxhounds (group 2) in whom the left ventricle was enlarged by 31 +/- 11.9% of cross-sectional area. Ventricular function curves were constructed at filling pressures ranging from 15-40 mmHg (group 2). Myocardial contraction patterns were investigated by epicardial 2-D echocardiography. Skeletal muscle contraction caused a significant increase in aortic pressure, dP/dt, stroke volume, work and performance in all animals. Function curves were shifted upward in a parallel manner. Echocardiography showed an increase of the LV cross-sectional delta area of 14.8% +/- 5.8% (group 1) and of 39.5% +/- 15.1%, and approximation of the edges of the wall defects (group 2). In conclusion, dynamic CMP as applied in this acute model, increased the performance of normal canine hearts and hence, a model of cardiac failure may not be a prerequisite for the investigation of certain technical aspects of CMP. In the failing heart, a parallel upward shift of myocardial function curves suggested increased performance of the heart/skeletal muscle complex over a wide range of filling pressures. However, the descending limb of the function curve with increasing filling pressures was observed despite skeletal muscle contraction. Hence, similar to other assist systems, the residual function of the heart may be of considerable importance in the overall performance of dynamic CMP.

Acute Disease↗
PubMed1991

Organization of visual inputs to the inferior temporal and posterior parietal cortex in macaques.

It has been proposed that visual information in the extrastriate cortex is conveyed along 2 major processing pathways, a "dorsal" pathway directed to the posterior parietal cortex, underlying spatial vision, and a "ventral" pathway directed to the inferior temporal cortex, underlying object vision. To determine the relative distributions of cells projecting to the 2 pathways, we injected the posterior parietal and inferior temporal cortex with different fluorescent tracers in 5 rhesus monkeys. The parietal injections included the ventral intraparietal (VIP) and lateral intraparietal (LIP) areas, and the temporal injections included the lateral portions of cytoarchitectonic areas TE and TEO. There was a remarkable segregation of cells projecting to the 2 systems. Inputs to the parietal cortex tended to arise either from areas that have been implicated in spatial or motion analysis or from peripheral field representations in the prestriate cortex. By contrast, inputs to the temporal cortex tended to arise from areas that have been implicated in form and color analysis or from central field representations. Cells projecting to the parietal cortex were found in visual area 2 (V2), but only in the far peripheral representations of both the upper and lower visual field. Likewise, labeled cells found in visual areas 3 (V3) and 4 (V4) were densest in their peripheral representations. Heavy accumulations of labeled cells were found in the dorsal parieto-occipital cortex, including the parieto-occipital (PO) area, part A of V3 (V3A), and the dorsal prelunate area (DP). In the superior temporal sulcus, cells were found within several motion-sensitive areas, including the middle temporal area (MT), the medial superior temporal area (MST), the fundus of the superior temporal area (FST), and the superior temporal polysensory area (STP), as well as within anterior portions of the sulcus whose organization is as yet poorly defined. Cells projecting to areas TE and TEO in the temporal cortex were located within cytoarchitectonic area TG at the temporal pole and cytoarchitectonic areas TF and TH on the parahippocampal gyrus, as well as in noninjected portions of area TE buried within the superior temporal sulcus. In the prestriate cortex, labeled cells were found in V2, V3, and V4, but, in contrast to the loci labeled after parietal injections, those labeled after temporal injections were concentrated in the foveal or central field representations. Although few double-labeled cells were seen, 2 regions containing intermingled parietal- and temporal-projection cells were area V4 and the cortex at the bottom of the anterior superior temporal sulcus.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1990

Organization of visual cortical inputs to the striatum and subsequent outputs to the pallido-nigral complex in the monkey.

To determine the organization of visual inputs and outputs of the striatum, we placed multiple retrograde and anterograde tracers into physiologically identified portions of the striatum known to receive inputs from visual cortex in seven macaques. The injection sites included the tail and genu of the caudate nucleus (14 cases), the head of the caudate (1 case), and the ventral putamen (3 cases). Retrogradely labeled cells were located predominantly in layer 5 of the ipsilateral cortex but were also found in layers 3 and 6. After caudate injections, labeled cells were found both in large, nearly continuous regions of cortex topographically related to the site of the injection, and in several smaller cortical regions that were discontinuous and common to many or all of the injection sites. The continuously labeled regions included nearly all known visual cortical areas, except for the striate cortex. After injections in the rostral tail, the continuously labeled region included the rostral portion of Bonin and Bailey's (Urbana: University of Illinois Press. '47) area TE and adjacent portions of TF, TH, TG, and, occasionally, area 35 (Brodmann, Leipzig: J.A. Barth. '09). After injections into the posterior tail and ventral genu, the labeled region shifted posteriorly in TE and TF, and into TEO and the ventral parts of prestriate areas V4, V3, and (sparsely) V2. As the injection site was advanced into the dorsal genu, the labeled region shifted dorsally toward the parietal lobe, including prestriate areas MT and PO, parietal area PG (Brodmann's area 7), the ventral and lateral intraparietal sulcal areas (VIP and LIP, respectively), and area PE and adjacent area LC (Brodmann's areas 5 and 23, respectively). The discontinuous areas labeled by many different injections included the principal sulcus/frontal eye field region, the anterior cingulate cortex, and the superior temporal polysensory area. Thus, whereas temporal, occipital, and parietal visual cortical areas project into the caudate largely according to proximity, certain multimodal cortical areas seem to have a much wider projection. To determine whether visual cortical areas have additional projections to the caudate beyond the territory of our retrograde injection sites in the tail and genu. 3H-labeled amino acids were injected into areas TE, V4, and MT in three additional monkeys. The topographic location of label in the tail and genu of the caudate in these cases was consistent with the results from injections of retrograde tracers into the caudate.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMed1990

Pathways for motion analysis: cortical connections of the medial superior temporal and fundus of the superior temporal visual areas in the macaque.

To identify the cortical connections of the medial superior temporal (MST) and fundus of the superior temporal (FST) visual areas in the extrastriate cortex of the macaque, we injected multiple tracers, both anterograde and retrograde, in each of seven macaques under physiological control. We found that, in addition to connections with each other, both MST and FST have widespread connections with visual and polysensory areas in posterior prestriate, parietal, temporal, and frontal cortex. In prestriate cortex, both areas have connections with area V3A. MST alone has connections with the far peripheral field representations of V1 and V2, the parieto-occipital (PO) visual area, and the dorsal prelunate area (DP), whereas FST alone has connections with area V4 and the dorsal portion of area V3. Within the caudal superior temporal sulcus, both areas have extensive connections with the middle temporal area (MT), MST alone has connections with area PP, and FST alone has connections with area V4t. In the rostral superior temporal sulcus, both areas have extensive connections with the superior temporal polysensory area (STP) in the upper bank of the sulcus and with area IPa in the sulcal floor. FST also has connections with the cortex in the lower bank of the sulcus, involving area TEa. In the parietal cortex, both the central field representation of MST and FST have connections with the ventral intraparietal (VIP) and lateral intraparietal (LIP) areas, whereas MST alone has connections with the inferior parietal gyrus. In the temporal cortex, the central field representation of MST as well as FST has connections with visual area TEO and cytoarchitectonic area TF. In the frontal cortex, both MST and FST have connections with the frontal eye field. On the basis of the laminar pattern of anterograde and retrograde label, it was possible to classify connections as forward, backward, or intermediate and thereby place visual areas into a cortical hierarchy. In general, MST and FST receive forward inputs from prestriate visual areas, have intermediate connections with parietal areas, and project forward to the frontal eye field and areas in the rostral superior temporal sulcus. Because of the strong inputs to MST and FST from area MT, an area known to play a role in the analysis of visual motion, and because MST and FST themselves have high proportions of directionally selective cells, they appear to be important stations in a cortical motion processing system.

Animals↗
PubMed1990

Spectral properties of V4 neurons in the macaque.

Spectral properties of 129 cells in the V4 area of 5 macaque monkeys were studied quantitatively with narrow-band and broad-band colored lights. The large majority of cells exhibited some degree of wavelength sensitivity within their receptive fields. The half-bandwidth of the primary peak in the spectral-response curve was less than 50 nm for 72% of the cells; the mean half-bandwidth of these cells, 27 nm, is similar to that found for color-opponent ganglion cells and cells in the parvocellular dorsal lateral geniculate nucleus (dLGN). Contrast-response functions indicated that the narrow spectral tuning of these cells derived from cone opponent interactions. From comparison of receptive-field sizes, we suggest that a typical V4 neuron sums inputs that ultimately derive from several thousand ganglion or parvocellular dLGN cells. In spite of their wavelength sensitivity, most V4 cells had properties that would not fit some simple criteria for classification as "color selective." First, few cells showed overt signs of color opponency, namely, on-inhibition or off-excitation to spectrally opponent wavelengths. Second, about 30% of the cells in V4 had spectral-response curves with 2 peaks. (The wavelength distribution of these second peaks was almost identical to that of primary peaks, and combinations of peak wavelengths were fairly random.) Third, most cells responded to white light; overall, the response to white light was about 60% of that to the best narrow-band or broad-band colored light. Similarly, most V4 cells gave at least a small response to all or nearly all of the different broad-band colored lights we presented. Therefore, a given V4 cell is very likely to respond to most of the colored or white surfaces in natural scenes. These combinations of response properties probably explain the widely divergent percentages of "color" cells reported in previous studies of V4. The most unusual spectral property we found in V4 was a large, spectrally sensitive surround outside the "classical receptive field" of most cells. Although stimulation of the surround by itself did not cause any response, surround stimulation could completely suppress the response to even the optimally colored stimulus in the receptive field. In general, the optimal wavelengths for receptive-field excitation and surround suppression were the same or nearly so. Thus, "color contrast" may be computed in V4. In some cases, contrasting wavelengths in the surround caused moderate enhancement of response to a receptive-field stimulus.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1988

Behavioral neurophysiology: insights into seeing and grasping.

One marvels at a batter's ability to hit a baseball traveling at 150 kilometers per hour or a monkey's skill in snatching a flying insect. Indeed, the ability of many animals to reach out, grasp, and manipulate objects is a feat of biological engineering unmatched by even state-of-the-art robots. But how are the objects of our attention chosen and how are the eyes and hands directed to it? Recent progress in behavioral neurophysiology has clarified some of the brain mechanisms at work.

Animals↗
PubMed1988

Increased attention enhances both behavioral and neuronal performance.

Single cells were recorded from cortical area V4 of two rhesus monkeys (Macaca mulatta) trained on a visual discrimination task with two levels of difficulty. Behavioral evidence indicated that the monkeys' discriminative abilities improved when the task was made more difficult. Correspondingly, neuronal responses to stimuli became larger and more selective in the difficult task. A control experiment demonstrated that changes in general arousal could not account for the effects of task difficulty on neuronal responses. It is concluded that increasing the amount of attention directed toward a stimulus can enhance the responsiveness and selectivity of the neurons that process it.

Animals↗
PubMed1987

Local precision of visuotopic organization in the middle temporal area (MT) of the macaque.

The representation of the visual field in the middle temporal area (MT) was examined by recording from single neurons in anesthetized, immobilized macaques. Measurements of receptive field size, variability of receptive field position (scatter) and magnification factor were obtained within the representation of the central 25 degree. Over at least short distances (less than 3 mm), the visual field representation in MT is surprisingly orderly. Receptive field size increases as a linear function of eccentricity and is about ten times larger than in V1 at all eccentricities. Scatter in receptive field position at any point in the visual field representation is equal to about one-third of the receptive field size at that location, the same relationship that has been found in V1. Magnification factor in MT is only about one-fifth that reported in V1 within the central 5 degree but appears to decline somewhat less steeply than in V1 with increasing eccentricity. Because the smaller magnification factor in MT relative to V1 is complemented by larger receptive field size and scatter, the point-image size (the diameter of the region of cortex activated by a single point in the visual field) is roughly comparable in the two areas. On the basis of these results, as well as on our previous finding that 180 degrees of axis of stimulus motion in MT are represented in about the same amount of tissue as 180 degrees of stimulus orientation in V1, we suggest that a stimulus at one point in the visual field activates at least as many functional "modules" in MT as in V1.

Animals↗