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G F Poggio

Publications and source records attributed to G F Poggio.

18 recordsLinked to original sources
PubMed2002

Neural substrates of memory, affective functions, and conscious experience.

This review presents an account of the areas and circuits of the brain that are thought to be involved in such cognitive functions as memory, affect and consciousness. Considerable progress has been made in the past two decades in the identification of the cerebral areas and in our understanding of the brain mechanisms involved in these functions, thanks in large parts to a number of imaging observations (PET and fMRI), together with many clinical neurological and experimental studies. Thus, there is now convincing evidence that these high level functions are represented in a complex organization of interconnected cortical and subcortical areas that operate as spatially distributed systems, specialized for the different cognitive activities. Despite the progress that has been made, it is still not known how genetic and environmental factors interact during early development and throughout life to create the necessary conditions out of which these cognitive capacities emerge, nor is it evident to what extent they are shaped by adaptive changes in synaptic organization and other forms of neuronal plasticity.

Brain Mapping↗
PubMed1991

Adaptation of the Reitboeck method of multiple microelectrode recording to the neocortex of the waking monkey.

We adapted to the neocortex of waking monkeys a method for multiple microelectrode recording devised by Reitboeck. A sliding platform allows micropositioning of 7 electrodes independently, in 2 microns steps. Microelectrodes are quartz glass filaments (80 microns o.d.) with central metal cores (30 microns) of tungsten-platinum alloy. Filaments are drawn in a high temperature chamber, and ground to the desired form and tip size. The microdrive is held over the region to be explored, and the microelectrodes passed through 300 microns o.d. guide tubes fixed in implant thimbles of chosen size an and x - y arrangement of tubes, sealed by an O-ring into a small craniotomy opening. A microprocessor controlled recording system provides gain, noise and wave-shape filtering, impedance testing, and differential amplitude discrimination for each channel. Electrode movement is obtained via the microprocessor which displays and updates on the console terminal the electrode depth, impedance, and the channel assignment of each electrode. A second microprocessor based system is used to collect, buffer, and encode in real time all event data, which are transferred whenever convenient to a minicomputer that controls the experiment. Exploratory recordings were made in the posterior parietal, somatic sensory, and motor cortical areas. The system has now been used successfully in a number of investigations.

Action Potentials↗
PubMed1990

Influences of uniform and textured backgrounds on the impulse activity of neurons in area V1 of the alert macaque.

The influences of the visual background on the spontaneous and evoked activity of neurons in the striate cortex (V1) of the awake and behaving macaque were investigated using uniform (dark and bright) and textured (dynamic random-dot) large fields (10 degrees) centered on the receptive field of the cell under study. Rhesus monkeys were trained to fixate a small target while visual patterns were presented on monitor displays and the impulse activity of single cortical neurons recorded extracellularly with metal microelectrodes. The discharge rates of the ongoing, spontaneous activity of the vast majority of V1 neurons, as well as their responses to optimally adjusted bar stimuli, were not significantly influenced by the luminance of a uniform background. On the other hand, the activity of more than 50% of V1 neurons was clearly affected by a textured background. Comparison of the effects of a uniformly dark background and a background of dynamic random dots showed that the neuron's spontaneous discharge rate was typically higher in the presence of the textured background, while the evoked response was often reduced in amplitude or even suppressed. The opposite effects were observed in only a few neurons. These findings indicate that neurons in area V1 are highly sensitive to a textured background of dynamic random dots which exert on them an activating effect, chiefly by stimulation of the neuron's receptive field, with consequent increase in the ongoing discharge and a reduction of the dynamic range of impulse activity, leading to a reduction in the amplitude of the response evoked by a contrast stimulus.

Action Potentials↗
PubMed1990

Dynamic stabilization of receptive fields of cortical neurons (VI) during fixation of gaze in the macaque.

The positions of receptive field borders of striate cortical neurons were measured repeatedly in awake monkeys during attentive fixation of a small target. The border position, as marked by the onset of evoked activity in response to a moving stimulus, did not show the variability expected from previous measures of eye position variability during fixation. Measured variability was smaller than expected. Trial-by-trial comparisons suggest that receptive field borders are not shifted by the small eye movements occurring during attentive fixation. It is our hypothesis that attentive fixation engages a mechanism that gates incoming information to achieve a stabilization of the receptive field relative to the external world. Such a dynamic positional compensation may underlie preliminary evidence showing that the response of stereo-sensitive neurons in striate cortex is consistent with stimulus disparity measures and, within limits, does not reflect the retinal disparities produced by the changes in binocular alignment during fixation.

Animals↗
PubMed1988

Stereoscopic mechanisms in monkey visual cortex: binocular correlation and disparity selectivity.

The neural signals in visual cortex associated with positional disparity and contrast texture correlation of binocular images are the subject of this study. We have analyzed the effects of stereoscopically presented luminous bars and of dynamic random-dot patterns on the activity of single neurons in cortical visual areas V1, V2, and V3-V3A of the alert, visually trained rhesus macaque. The interpretation of the results and considerations of possible neural mechanisms led us to recognize 2 functional sets of stereoscopic neurons. (1) A set of neurons, tuned excitatory (T0) or tuned inhibitory (TI), which respond sharply to images of zero or near-zero disparity. Objects at or about the horopter drive the T0 neurons and suppress the TI, while objects nearer and farther have the opposite effects on each type, inhibition of the T0 and excitation of the TI. The activity of these neurons may provide, in a reciprocal way, the definition of the plane of fixation, and the basic reference for binocular single vision and depth discrimination. (2) A second set of neurons includes tuned excitatory at larger crossed or uncrossed disparities (TN/TF) and neurons with reciprocal excitatory and inhibitory disparity sensitivity with cross-over at the horopter (NE/FA). Binocularly uncorrelated image contrast drives these neurons to a maintained level of activity, which shifts, in response to correlated images, toward facilitation or suppression as a function of positional disparity. These neurons may operate in the neural processing leading to stereopsis, both coarse and fine, and also provide signals for the system controlling binocular vergence. These results indicate that cortical visual neurons are binocularly linked to respond to the relative position and contrast of the images over their receptive fields, and also that both these aspects of binocular stimulation may be utilized by the brain as a source of stereoscopic information.

Animals↗
PubMed1985

Responses of neurons in visual cortex (V1 and V2) of the alert macaque to dynamic random-dot stereograms.

A substantial proportion of both simple and complex neurons in the cortex subserving central vision are differentially sensitive to binocular disparity of isolated line patterns (local stereopsis), a sensitivity based on a positional disparity between the neuron's receptive fields in the two eyes. In addition, a subset of cortical neurons, nearly all complex neurons, responds to dynamic random-dot stereograms containing no depth cues other than disparity. These neurons are capable of signaling the correct binocular matches among a multitude of false matches in the stereograms (global stereopsis). The discovery of cyclopean neurons in striate cortex, at early stages of the processing neural network for stereoscopic vision provides a new insight of the basic neural mechanisms underlying binocular depth perception.

Animals↗
PubMed1984

Binocular fixation in the rhesus monkey: spatial and temporal characteristics.

The horizontal and vertical components of the positions of both eyes of rhesus monkeys were measured during periods of binocularly stable eye positions (eye pauses) while the animals fixated a small target. Differences between monocular and binocular viewing, as well as effects of target size and background illumination, were assessed and found to be comparable to similar measures for humans. The scatter of eye position for either eye during binocular viewing had a standard deviation of 6-8 min arc in the horizontal and 7-13 min arc in the vertical meridia. Measurements of vergence and vertical misalignment, taken from binocular positional disparity, showed that for nearly 60% of eye pause time the eyes were misaligned on the fixation target by more than 7 min arc along both horizontal and vertical axes. In addition, the line of gaze during the trial was found to follow certain idiosyncratic tendencies for each monkey, although the positional variability remained relatively constant throughout the fixation trial. These observations suggest that during binocular fusion and stereopsis a mechanism exists that dynamically compensates for the relatively large shifts in retinal image position during fixation.

Animals↗
PubMed1981

Mechanisms of static and dynamic stereopsis in foveal cortex of the rhesus monkey.

1. The sensation of stereoscopic depth rests on the central neural processing of signals evoked by the two retinal images of a single object in space. It was our purpose in this study to investigate in the behaving monkey the binocular cortical mechanisms that might underlie the ability to recognize the relative position and motion of objects in three-dimensional space.2. The large majority of neurones studied in A17 (n = 245), and all neurones studied in A18 (n = 21), were functionally connected to both eyes, and a substantial proportion (75%) of these neurones were sensitive to positional binocular disparity. On the basis of their depth sensitivity profile, four types of stereoscopic neurones were recognized, each type characteristically sensitive to visual contours appearing in depth farther than, at, or nearer than the point of binocular fixation.3. Tuned excitatory and tuned inhibitory neurones display binocular facilitation and binocular suppression respectively, to stimuli over a narrow range of small disparities, including zero disparity, with more or less pronounced reciprocal responses to stimuli with larger disparities. These neurones, the tuned excitatory in particular, may be considered to be the substrate for central fusion of slightly disparate retinal images, and to provide the basis for the neural mechanisms leading to three-dimensional perception of objects with high stereoacuity (fine stereopsis).4. Two other sets of reciprocally organized neurones, near and far neurones, respond differentially to wider ranges of crossed and uncrossed disparities. The near neurones are activated by stimuli in front of and inhibited by stimuli behind fixation. The far neurones have the reciprocal depth sensitivity. These neural elements may be regarded as active in the processing of binocular information leading to qualitative depth estimates in the presence of double vision (coarse stereopsis).5. Binocular response selectivity for the direction of object motion-in-depth depends chiefly upon monocular sensitivity to the direction of retinal image motion, a property we observed in about one half of the foveal neurones. Cortical neurones with the same directional sensitivity for monocular stimuli in both eyes display coarse binocular selectivity for the trajectory of object motion but provide unambiguous signals for the direction of motion, towards the right or towards the left within the depth domain of the neurone. A small group of neurones (3%) displays opposite and opponent directional sensitivity for stimuli in the two eyes. Their binocular response, therefore, is best when the two retinal images move in opposite directions at the same time, a condition that obtains with motion directly towards or away from the animal with little or no lateral movement. These directionally dual-opponent cells usually have coarse or no selectivity for position-in-depth.6. The results of this study indicate that basic mechanisms for the stereoscopic analysis of the position (static) and motion (dynamic) of objects in space relative to one another are present at early stages of binocular interaction in the visual cortex of primates, and that they are in effective action during normal binocular vision.

Animals↗
PubMed1979

Depth sensitivity of binocular cortical neurons of behaving monkeys.

Activity of neurons if foveal striate and prestriate cortex of trained rhesus monkeys was recorded with metal microelectrodes. While animals fixated a small spot at a given fixation distance (38 or 57 cm), bright or dark bars moving across a frontoparallel plane were presented at different depths in a range of +/- 10 cm about the fixation distance. Almost all cells showed binocular interaction. Neurons with balanced ocularity (approximately equal monocular responses) usually facilitated each other and were tuned to depth around the plane of fixation often with inhibitory flanks nearer and further. Neurons with unbalanced ocularity either inhibited each other or had asymmetric depth sensitivity profiles, i.e. activation by stimuli in front and suppression by stimuli behind the fixation plane (near cells) or vice versa (far cells). Thus striate and prestriate cortex of the monkey contains four subsets of binocular cells which may contribute to depth perception.

Animals↗
PubMed1975

Spatial and chromatic properties of neurons subserving foveal and parafoveal vision in rhesus monkey.

The response properties of neurons in the region of striate cortex subserving central retina (0 degrees-2 degrees) and in a region of representation of parafoveal retina (4 degrees-7 degrees) were studied in unanesthetized paralyzed macaque monkeys. Neurons sensitive to the orientation of the stimulus in the visual field (simple, complex, and hypercomplex), and neurons lacking orientation selectivity (concentric, and a new class termed uniform) were found. In foveal cortex non-oriented cells were more numerous, and orientation sensitive cells had less strict spatial stimulus requirements than in parafoveal cortex. Most neurons received a monocular input, either exclusively or very predominantly. Three types of neurons were recognized on the basis of their responses to chromatic stimuli. (1) Luminosity neurons (about half the population) gave the same qualitative response to all effective wayelengths and had a spectral sensitivity similar to that of the macaque, determined behaviorally. Cells with all spatial types of receptive fields, except simple, occurred in this group. (2) Spectrally-treated neurons also responded in the same manner to different wavelengths, but over a narrower range than luminosity neurons, and their maximal sensitivity was shifted toward one or the other end of the visible spectrum. All tuned neurons had uniform or complex receptive field. (3) Spectrally-opponent neurons were either excited or inhibited by long wavelengths and responded in the opposite manner to short wavelengths. For cells with uniform or complex receptive fields the two opponent systems were coextensive. Simple or concentric neurons often had dual-opponent organization. The distribution of functional types among different cortical layers was similar in parafoveal and foveal cortex. The functional attributes of ocular dominance and orientation sensitivity were found to be statistically independent dimensions of cortical organization. On the other hand, the correlation between spatial and chromatic properties did not vary between different cytoarchitectonic layers, a finding suggesting that these neuronal properties depend on conjoined projectional and intracortical connecting mechanisms.

Animals↗