Biomedical subjects

R Gattass

Publications and source records attributed to R Gattass.

At least 19 recordsLinked to original sources

PubMed2005

Changes of ongoing activity in Cebus monkey perirhinal cortex correlate with behavioral performance.

A Cebus apella monkey weighing 4 kg was trained in a saccadic eye movement task and while the animal performed the task we recorded the extracellular activity of perirhinal cortical neurons. Although the task was very simple and maintained at a constant level of difficulty, we observed considerable changes in the performance of the monkey within each experimental session. The behavioral states responsible for such variation may be related to arousal, motivation or attention of the animal while engaged in the task. In approximately 20% (16/82) of the units recorded, long-term direct or inverse correlations could be demonstrated between the monkey's behavioral state and the cells' ongoing activity (independent of the visual stimulation or of the specific behavior along a trial). The perirhinal cortex and other medial temporal structures have long been associated with normal memory function. The data presented here were interpreted in terms of recent reports focusing on the subcortical afferents to temporal lobe structures and their possible role in controlling arousal, motivation, or attention.

Animals↗

PubMed2004

Effects of inactivation of the lateral pulvinar on response properties of second visual area cells in Cebus monkeys.

1. In the present study, we investigated the influence of the pulvinar nucleus upon response properties of single cells in the second visual area (V2) of Cebus monkeys. The method used consisted of the inactivation of a portion of the lateral pulvinar by GABA injections while studying the response properties of cells in V2 at the same visuotopic location as that of the inactivation. 2. After GABA injection in the pulvinar, most cells in V2 (67%) showed changes in spontaneous and/or stimulus-driven activities. Contrary to the effect found with inactivation of the striate cortex, which promotes a reduction in the response of V2 neurons, we found that the main effect of pulvinar inactivation was an increment in stimulus-driven responses of V2 cells (39% of units studied). A reduction of responses was observed in 27% of units. 3. A change in orientation and/or direction selectivity was found in 91% of cells after inactivation of the pulvinar. Most commonly, the orientation selectivity of a neuron was decreased during pulvinar inactivation. 4. The inactivation results indicate that the pulvinar projections have a modulatory effect on the activity of V2 cells.

Animals↗

PubMed2003

Contributions of stimulus valence and arousal to visual activation during emotional perception.

Neuroimaging experiments have revealed that the visual cortex is involved in the processing of affective stimuli: seeing emotional pictures leads to greater activation than seeing neutral ones. It is unclear, however, whether such differential activation is due to stimulus valence or whether the results are confounded by arousal level. In order to investigate the contributions of valence and arousal to visual activation, we created a new category of "interesting" stimuli designed to have high arousal, but neutral valence, and employed standard neutral, unpleasant, and pleasant picture categories. Arousal ratings for pleasant and neutral pictures were equivalent, as were valence ratings for interesting and neutral pictures. Differential activation for conditions matched for arousal (pleasant vs neutral) as well as matched for valence (interesting vs neutral) indicated that both stimulus valence and arousal contributed to visual activation.

Adult↗

PubMed2001

Distribution of calbindin, parvalbumin and calretinin in the lateral geniculate nucleus and superior colliculus in Cebus apella monkeys.

We studied the distribution of the calcium-binding proteins calbindin, parvalbumin and calretinin, in the superior colliculus and in the lateral geniculate nucleus of Cebus apella, a diurnal New World monkey. In the superior colliculus, these calcium-binding proteins show different distribution patterns throughout the layers. After reaction for calretinin one observes a heavy staining of the neuropil with few labeled cells in superficial layers, a greater number of large and medium-sized cells in the stratum griseum intermediale, and small neurons in deep layers. The reaction for calbindin revealed a strong staining of neuropil with a large number of small and well stained cells, mainly in the upper half of the stratum griseum superficiale. Intermediate layers were more weakly stained and depicted few neurons. There were few immunopositive cells and little neuropil staining in deep layers. The reaction for parvalbumin showed small and medium-sized neurons in the superficial layers, a predominance of large stellate cells in the stratum griseum intermediale, and medium-sized cells in the deep layers. In the lateral geniculate nucleus of Cebus, parvalbumin is found in the cells of both the P and M pathways, whereas calbindin is mainly found in the interlaminar and S layers, which are part of the third visual pathway. Calretinin was only found in cells located in layer S. This pattern is similar to that observed in Macaca, showing that these calcium-binding proteins reveal different components of the parallel visual pathways both in New and Old World monkeys.

Animals↗

PubMed2001

The brain decade in debate: VI. Sensory and motor maps: dynamics and plasticity.

This article is an edited transcription of a virtual symposium promoted by the Brazilian Society of Neuroscience and Behavior (SBNeC). Although the dynamics of sensory and motor representations have been one of the most studied features of the central nervous system, the actual mechanisms of brain plasticity that underlie the dynamic nature of sensory and motor maps are not entirely unraveled. Our discussion began with the notion that the processing of sensory information depends on many different cortical areas. Some of them are arranged topographically and others have non-topographic (analytical) properties. Besides a sensory component, every cortical area has an efferent output that can be mapped and can influence motor behavior. Although new behaviors might be related to modifications of the sensory or motor representations in a given cortical area, they can also be the result of the acquired ability to make new associations between specific sensory cues and certain movements, a type of learning known as conditioning motor learning. Many types of learning are directly related to the emotional or cognitive context in which a new behavior is acquired. This has been demonstrated by paradigms in which the receptive field properties of cortical neurons are modified when an animal is engaged in a given discrimination task or when a triggering feature is paired with an aversive stimulus. The role of the cholinergic input from the nucleus basalis to the neocortex was also highlighted as one important component of the circuits responsible for the context-dependent changes that can be induced in cortical maps.

Animals↗

PubMed2000

Visual cortical projections and chemoarchitecture of macaque monkey pulvinar.

We investigated the patterns of projections from the pulvinar to visual areas V1, V2, V4, and MT, and their relationships to pulvinar subdivisions based on patterns of calbindin (CB) immunostaining and estimates of visual field maps (P(1), P(2) and P(3)). Multiple retrograde tracers were placed into V1, V2, V4, and/or MT in 11 adult macaque monkeys. The inferior pulvinar (PI) was subdivided into medial (PI(M)), posterior (PI(P)), central medial (PI(CM)), and central lateral (PI(CL)) regions, confirming earlier CB studies. The P(1) map includes PI(CL) and the ventromedial portion of the lateral pulvinar (PL), P(2) is found in ventrolateral PL, and P(3) includes PI(P), PI(M), and PI(CM). Projections to areas V1 and V2 were found to be overlapping in P(1) and P(2), but those from P(2) to V2 were denser than those to V1. V2 also received light projections from PI(CM) and, less reliably, from PI(M). Neurons projecting to V4 and MT were more abundant than those projecting to V1 and V2. Those projecting to V4 were observed in P(1), densely in P(2), and also in PI(CM) and PI(P) of P(3). Those projecting to MT were found in P(1)- P(3), with the heaviest projection from P(3). Projections from P(3) to MT and V4 were mainly interdigitated, with the densest to MT arising from PI(M) and the densest to V4 arising from PI(P) and PI(CM). Because the calbindin-rich and -poor regions of P(3) corresponded to differential patterns of cortical connectivity, the results suggest that CB may further delineate functional subdivisions in the pulvinar.

Animals↗

PubMed2000

"Third tier" ventral extrastriate cortex in the New World monkey, Cebus apella.

The ventral extrastriate cortex adjacent to the second visual area was studied in the New World monkey Cebus apella, using anaesthetised preparations. The visuotopic organisation and myeloarchitecture of this region demonstrate the existence of a distinct strip of cortex, 3-4 mm wide, with an ordered representation of the contralateral upper visual quadrant, up to 60 degrees eccentricity. This upper-quadrant representation is probably homologous to the ventral subdivision of the third visual complex (V3v) of Old World monkeys, also known as the ventral posterior area. The representation of the horizontal meridian in V3v forms its posterior and medial border with V2, while the upper vertical meridian is represented anterior and laterally, forming a congruent border with the fourth visual area (V4). Central visual fields are represented in posterior and lateral portions of V3v, in the inferior occipital sulcus, while the periphery of the visual field is represented anteriorly, on the tentorial surface. Cortex anterior to V3v, at the ventral occipitotemporal transition, had neurones that had poor visual responses. No representation of the lower quadrant was found adjacent to V3v in ventral cortex. However, we observed cells with perifoveal receptive fields centred in the lower quadrant immediately dorsal to V3v, around the junction of the inferior occipital and lunate sulci. These observations argue against the idea that V3v is an area restricted to the ventral cortex in New World monkeys and support the conclusions of previous anatomical studies in Cebus that showed a continuity of myeloarchitecture and connectional patterns between ventral and lateral extrastriate cortices. Together, these data suggest that V3v may be part of a larger area that extends into dorsolateral extrastriate cortex, overlapping to some extent with the caudal subdivision of the dorsolateral area described in other New World monkeys.

Animals↗

PubMed1999

Filling-in in topographically organized distributed networks.

We propose a framework for understanding visual perception based on a topographically organized, functionally distributed network. In this proposal the extraction of shape boundaries starts at retinal ganglion cells with concentric receptive fields. This information, relayed through the lateral geniculate nucleus, creates a neural representation of negative and positive boundaries in a set of topographically connected and organized visual areas. After boundary extraction, several processes involving contrast, brightness, texture and motion extraction take place in subsequent visual areas in different cortical modules. Following these steps of processing, filling-in processes at different levels, within each area, and in separate channels, propagate locally to transform boundary representations onto surfaces representations. These partial representations of the image propagate back and forth in the network, yielding a neural representation of the original image. We propose that completion takes places in a wide cortical circuit that heavily relies on V1, where long-range information helps determine contour responses at specific topographically organized locations. Neural representations of illusory contours would emerge in circuits involving primarily area V2. The neural representation of filling-in of a peripheral stimulus in a dynamic surround (such as in texture filling-in) would depend on circuits involving primarily cells in areas V2 and V3, and would include competitive mechanisms required for figure to ground segregation. Finally, we suggest that multiple representations of the stimulus engage competitive mechanisms that select the "most likely hypothesis". Such choice behavior would rely on winner-take-all mechanisms capable of constructing a single neural representation of perceived objects.

Form Perception↗

PubMed1998

Area V4 in Cebus monkey: extent and visuotopic organization.

We used electrophysiological mapping and myeloarchitectural criteria in order to define the location, extent and visual topography of the fourth visual area (V4) in anesthetized and paralyzed Cebus monkey. Based on these criteria, the borders of V4 with surrounding areas were defined both on the dorsal and ventral cortical surfaces. In addition, to better visualize the visuotopic organization and to evaluate its regularity, we constructed bidimensional maps and projected the recording sites onto them. Area V4 has an almost complete representation of the binocular visual field with the lower visual field represented dorsally (V4d) and the upper field ventrally (V4v). We found this representation to be more extensive than those previously described. The representation of the central portion of the visual field is largely expanded in comparison with that of the periphery. This emphasis in central vision could be related with the involvement of V4 in the ventral stream of visual information processing. Receptive field size increases with increasing eccentricity, while cortical magnification factor decreases. The cortical magnification factor measured along isopolar lines is, on average, 1.5-2.0 times greater than that measured along the isoeccentric lines, suggesting the existence of a small anisotropy in central and peripheral V4.

Animals↗

PubMed1997

Tangential distribution of cytochrome oxidase-rich blobs in the primary visual cortex of macaque monkeys.

We studied the tangential distribution of cytochrome c oxidase (CytOx)-rich blobs in four striate cortices of three normal monkeys (Macaca mulatta). The spatial density and cross-sectional area of blobs were analyzed in CytOx-reacted tangential sections of flat-mounted preparations of the striate cortex (V1). Well-delimited CytOx-rich blobs were found in the middle portion of cortical layer III of the V1. Throughout the binocular field representation, the spatial density of blobs was nearly constant with a mean value of four to five blobs per mm2. In the monocular portions of V1, however, blob spatial density diminished. In all cases, the mean cross-sectional area of blobs was constant in the V1. The small variation of CytOx blob topography with visual field eccentricity contrasts with the variation described in previously published material.

Animals↗

PubMed1997

GABAergic retinocollicular projection in the New World monkey Cebus apella.

GABA immunoreactivity was examined in the retina of the New World monkey Cebus apella. Labeled cell bodies were identified as horizontal, bipolar, interplexiform, amacrine and a population of putative ganglion cells. To determine whether ganglion cells were immunoreactive to GABA, double-labeling experiments were performed using Fast Blue as retrograde neuronal tracer injected into the superior colliculus. Retinas containing FB-labeled ganglion cells were subsequently incubated with antiserum against GABA. Although retinocollicular ganglion cells were found in three different layers (ganglion cell layer, inner nuclear layer and inner plexiform layer), our experiments revealed GABA-positive ganglion cells only in the outer half of the ganglion cell layer.

Amidines↗

PubMed1997

Cortical projections of area V2 in the macaque.

To determine the locus, extent and topograhic organization of cortical projections of area V2, we injected tritiated amino acids under electrophysiological control into 15 V2 sites in 14 macaques. The injection sites included the foveal representation and representations ranging from central to far peripheral eccentricities in both the upper and lower visual fields. The results indicated that all V2 sites project topographically back to V1 and forward to V3, V4 and MT. There is also a topographically organized projection from V2 to V4t, but this projection is limited to the lower visual field representation. V2 thus appears to project to virtually all the visual cortex within the occipital lobe. In addition to these projections to occipital visual areas, V2 sites representing eccentricities of approximately 30 degrees and greater project to three visual areas in parietal cortex-the medial superior temporal (MST), parieto-occipital (PO) and ventral intraparietal (VIP) areas. This peripheral field representation of V2 also projects to area VTF, a visual area located in area TF on the posterior parahippocampal gyrus. Projections from the peripheral field representation of V2 of parietal areas could provide a direct route for rapid activation of circuits serving spatial vision and spatial attention.

Amino Acids↗

PubMed1996

Neurofilament protein is differentially distributed in subpopulations of corticocortical projection neurons in the macaque monkey visual pathways.

Previous studies of the primate cerebral cortex have shown that neurofilament protein is present in pyramidal neuron subpopulations displaying specific regional and laminar distribution patterns. In order to characterize further the neurochemical phenotype of the neurons furnishing feedforward and feedback pathways in the visual cortex of the macaque monkey, we performed an analysis of the distribution of neurofilament protein in corticocortical projection neurons in areas V1, V2, V3, V3A, V4, and MT. Injections of the retrogradely transported dyes Fast Blue and Diamidino Yellow were placed within areas V4 and MT, or in areas V1 and V2, in 14 adult rhesus monkeys, and the brains of these animals were processed for immunohistochemistry with an antibody to nonphosphorylated epitopes of the medium and heavy molecular weight subunits of the neurofilament protein. Overall, there was a higher proportion of neurons projecting from areas V1, V2, V3, and V3A to area MT that were neurofilament protein-immunoreactive (57-100%), than to area V4 (25-36%). In contrast, feedback projections from areas MT, V4, and V3 exhibited a more consistent proportion of neurofilament protein-containing neurons (70-80%), regardless of their target areas (V1 or V2). In addition, the vast majority of feedback neurons projecting to areas V1 and V2 were located in layers V and VI in areas V4 and MT, while they were observed in both supragranular and infragranular layers in area V3. The laminar distribution of feedforward projecting neurons was heterogeneous. In area V1, Meynert and layer IVB cells were found to project to area MT, while neurons projecting to area V4 were particularly dense in layer III within the foveal representation. In area V2, almost all neurons projecting to areas MT or V4 were located in layer III, whereas they were found in both layers II-III and V-VI in areas V3 and V3A. These results suggest that neurofilament protein identifies particular subpopulations of corticocortically projecting neurons with distinct regional and laminar distribution in the monkey visual system. It is possible that the preferential distribution of neurofilament protein within feedforward connections to area MT and all feedback projections is related to other distinctive properties of these corticocortical projection neurons.

Animals↗

PubMed1996

Responses of cells in the superior colliculus during performance of a spatial attention task in the macaque.

Previous studies have reported that superficial layer cells in the superior colliculus (SC) give an enhanced response to a stimulus when it is the target for an eye movement. However, in a peripheral detection paradigm, no such enhancement was found when a stimulus was attended, in the absence of an eye movement. Inasmuch as behavioral studies have found attention deficits in the absence of eye movements following SC lesions or deactivation, we investigated this issue in a paradigm that is very sensitive to effects of attention. In a matching-to-sample paradigm, a sample stimulus was presented at one location followed by a brief test stimulus at that (relevant) location and a distracter at another (irrelevant) location. While maintaining fixation, the monkey indicated whether the sample and the test stimulus matched, ignoring the distracter. The relevant and irrelevant locations were switched from trial to trial. SC cells in the superficial layers tended to give enhanced responses when the attended test stimulus was inside the receptive field compared to when the (physically identical) distracter was inside the field. We found that responses to attended targets in the receptive field were larger than to physically identical, but ignored, distracter stimuli. These effects were found only in an "automatic" attentional cueing paradigm, in which a peripheral stimulus explicitly cued the animal as to the relevant location in the receptive field. No attentional effects were found in a "central" or "cognitive" cueing paradigm, in which the monkey had to learn the relevant location in a given block of trials. The larger responses to attended targets in the automatic cueing paradigm appeared to be due to a sustained elevation of cells' baseline activity when attention was directed to the receptive field, as well as a transient enhancement of the target response. Thus, responses of SC cells appear to be modulated by directed attention, even in absence of eye movements, probably reflecting the properties of cortical cells projecting to the SC.

Animals↗

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↗

PubMed1994

Identification and visuotopic organization of areas PO and POd in Cebus monkey.

Two visual areas of the anterior bank of the parietooccipital sulcus, areas PO and POd, were identified and their visual field representations were studied in six anesthetized and paralyzed Cebus monkeys. The definition of these areas was based on electrophysiological mapping and myeloarchitecture. PO is located in the ventral aspect of the anterior bank of the parietooccipital sulcus and ventral precuneate gyrus. It borders area V2 posteriorly and ventrally in the depth of the parietooccipital sulcus, area V3d laterally, and another undescribed visual area medially. POd was located dorsal to area PO and ventral to architectonic area PE. The representations of the visual field in areas PO and POd are complex. In each hemisphere, these areas have a virtually complete representation of the contralateral visual hemifield. Different from the previously described visual areas, in PO and POd there is a precise organization of isopolar lines and a complex organization of the isoeccentric ones. In PO, as well as in POd, the representation of the horizontal meridian runs dorsoventrally along the parietooccipital sulcus. The upper visual quadrant is represented medially and the lower visual quadrant laterally. A large and complex representation of the periphery, from 20 degrees to 60 degrees eccentricity is present at the lateral and medial portions of these areas. By contrast, the representation of the central 20 degrees is very small in both PO and POd. The central visual field is represented ventrally in PO and dorsally in area POd. Area POd shows a more stratified myeloarchitectonic pattern than PO and both areas can be distinguished from other surrounding areas by their heavier myelinated pattern.

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

Dynamic surrounds of receptive fields in primate striate cortex: a physiological basis for perceptual completion?

Visual receptive fields (RFs) were mapped inside and outside the cortical representation of the optic disk in the striate cortex (area V1) of anesthetized and paralyzed Cebus monkeys. Unexpectedly, most cells were found to be binocularly driven, and the RFs mapped with contralateral-eye stimulation progressed in a topographically appropriate fashion as the optic disk sector was crossed. Activation of these neurons by the contralateral eye was shown to depend on stimulation of the parts of the retina around the optic disk. Outside the optic disk representation, a similar effect was demonstrated by obstructing the "classical" RF with masks 5-10 times larger in size. In all cases, visual stimuli presented around the mask could be used to accurately interpolate the position of the hidden RF. These properties reflect, at a cellular level, the process of "filling in" that allows for completion of the visual image across natural and artificially induced scotomas.

Animals↗