Reorganization of retinotopic cortical maps in adult mammals after lesions of the retina

The organization of the visual cortex has been considered to be highly stable in adult mammals. However, 5 degrees to 10 degrees lesions of the retina in the contralateral eye markedly altered the systematic representations of the retina in primary and secondary visual cortex when matched inputs from the ipsilateral eye were also removed. Cortical neurons that normally have receptive fields in the lesioned region of the retina acquired new receptive fields in portions of the retina surrounding the lesions. The capacity for such changes may be important for normal adjustments of sensory systems to environmental contingencies and for recoveries from brain damage.     

Visual experience modifies distribution of horizontally and vertically oriented receptive fields in cats

Cats were raised from birth with one eye viewing horizontal lines and one eye viewing vertical lines. Elongated receptive fields of cells in the visual cortex were horizontally or vertically oriented-no oblique fields were found. Units with horizontal fields were activated only by the eye exposed to horizontal lines; units with vertical fields only by the eye exposed to vertical lines.     

Visual receptive fields of neurons in inferotemporal cortex of the monkey

Neurons in inferotemporal cortex (area TE) of the monkey had visual receptive fields which were very large (greater than 10 by 10 degrees) and almost always included the fovea. Some extended well into both halves of the visual field, while others were confined to the ipsilateral or contralateral side. These neurons were differentially sensitive to several of the following dimensions of the stimulus: size and shape, color, orientation, and direction of movement.     

Experimentally induced visual projections into auditory thalamus and cortex

Retinal cells have been induced to project into the medial geniculate nucleus, the principal auditory thalamic nucleus, in newborn ferrets by reduction of targets of retinal axons in one hemisphere and creation of alternative terminal space for these fibers in the auditory thalamus. Many cells in the medial geniculate nucleus are then visually driven, have large receptive fields, and receive input from retinal ganglion cells with small somata and slow conduction velocities. Visual cells with long conduction latencies and large contralateral receptive fields can also be recorded in primary auditory cortex. Some visual cells in auditory cortex are direction selective or have oriented receptive fields that resemble those of complex cells in primary visual cortex. Thus, functional visual projections can be routed into nonvisual structures in higher mammals, suggesting that the modality of a sensory thalamic nucleus or cortical area may be specified by its inputs during development.     

Interhemispheric transfer of plasticity in the cerebral cortex

Each half of the body surface is represented topographically in the contralateral cerebral hemisphere. Physiological data are presented showing that homotopic regions of primary somatosensory cortex are linked such that plasticity induced in one hemisphere, in the form of receptive field expansion brought about by a small peripheral denervation, is immediately mirrored in the other hemisphere. Neurons which display the plasticity show no responsiveness to stimulation of the ipsilateral body surface. This suggests that the pathways and mechanisms mediating this transfer are specific to the role of maintaining balance, or integration, between corresponding cortical fields.     

Neural basis of orientation perception in primate vision

Orientational differences in human visual acuity can be related parametrically to the distribution of optimal orientations for the receptive fields of neurons in the striate cortex of the rhesus monkey. Both behavioral measures of acuity and the distribution of receptive fields exhibit maximums for stimuli horizontal or vertical relative to the retina; the effect diminishes with distance from the fovea. The anisotropy in the neuronal population and in visual acuity appear to be determined by postnatal visual experience.     

Encoding of spatial location by posterior parietal neurons

The cortex of the inferior parietal lobule in primates is important for spatial perception and spatially oriented behavior. Recordings of single neurons in this area in behaving monkeys showed that the visual sensitivity of the retinotopic receptive fields changes systematically with the angle of gaze. The activity of many of the neurons can be largely described by the product of a gain factor that is a function of the eye position and the response profile of the visual receptive field. This operation produces an eye position-dependent tuning for locations in head-centered coordinate space.     

Visual receptive fields sensitive to absolute and relative motion during tracking

Some neurons in the visual cortex of awake monkeys visually tracking a moving target showed receptive fields that were excited only by stimulus motion relative to a background, while other neurons responded to any kind of stimulus motion. This result was found with two methods, one in which tracking eye movements were identical in both relative-motion and absolute-motion conditions, and another in which stimulus motions on the retina were identical in both conditions. This response pattern can differentiate translation of the retinal image during eye movement from motion of objects in the world.     

Visual patterned reflex present during hypothalamically elicited attack

A cat from which attack is elicited by electrical stimulation of the hypothalamus lunges more frequently toward a mouse presented to the eye contralateral to the stimulated site than it does to a mouse presented to the ipsilateral eye. This differential effect does not appear to be attributable to a temporary or permanent defect in the ipsilateral eye.     

Dynamics of depolarization and hyperpolarization in the frontal cortex and saccade goal

The frontal eye field and neighboring area 8Ar of the primate cortex are involved in programming and execution of saccades. Electrical microstimulation in these regions elicits short-latency contralateral saccades. To determine how spatiotemporal dynamics of microstimulation-evoked activity are converted into saccade plans, we used a combination of real-time optical imaging and microstimulation in behaving monkeys. Short stimulation trains evoked a rapid and widespread wave of depolarization followed by unexpected large and prolonged hyperpolarization. During this hyperpolarization saccades are almost exclusively ipsilateral, suggesting an important role for hyperpolarization in determining saccade goal.     

Visual fields of cats with cortical and tectal lesions

When cats were tested for visual field perimetry, the field of vision for each eye separately was from 45 degrees contralateral to 90 degrees ipsilateral. After either bilateral occipitotemporal lesions (with a split of the tectal commissure) or bilateral area 17, 18, and 19 lesions, the cats could see with each eye only from the midline to 90 degrees ipsilateral. A cat that became nearly totally blind as a result of bilateral occipitotemporal decortication had a subsequent tectal split which enabled it to see with each eye from the midline to 90 degrees ipsilateral.     

Ocular dominance column development: analysis and simulation

The visual cortex of many adult mammals has patches of cells that receive inputs driven by the right eye alternating with patches that receive inputs driven by the left eye. These ocular dominance patches (or "columns") form during early life as a consequence of competition between the activity patterns of the two eyes. A mathematical model of several biological mechanisms that can account for this development is presented. Analysis of this model reveals the conditions under which ocular dominance segregation will occur and determines the resulting patch width. Simulations of the model also exhibit other phenomena associated with early visual development, such as topographic refinement of cortical receptive fields, the confinement of input cell connections to patches, monocular deprivation plasticity including a critical period, and the effect of artificially induced strabismus. The model can be used to predict the results of proposed experiments and to discriminate among various mechanisms of plasticity.     

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.     

Somatosensory system: organizational hierarchy from single units in monkey area 5

The receptive fields of single cells in area 5 of monkey parietal cortex were studied by extracellular recording. Cells were driven primarily by gentle manipulation of multiple joints residing on one or more limbs. Both excitatory and inhibitory convergence were demonstrated. It is postulated that the multijoint receptive fields of area 5 are the result of convergence from single-joint cells of the primary receiving area. An analogy is drawn between the modification of information in the visual and somatosensory systems.     

Cat's ability to discriminate oblique rectangles

Cats were trained to discriminate either between a horizontal and vertical rectangle or between two oblique rectangles, one at 45 degrees , the other at 135 degrees to horizontal. All animals were first trained with both shapes (one in each orientation) presented together, and then retrained with only one shape shown at a time. Throughout the experiment the animals being trained with oblique rectangles performed as well as those being trained with horizontal and vertical rectangles. This finding is in marked contrast with results obtained from other species. The results suggest that the ability of a species to discriminate between rectangles in different orientations may depend upon the relative numbers of cells in the visual system having receptive fields in each orientation.     

Sparse coding and decorrelation in primary visual cortex during natural vision

Theoretical studies suggest that primary visual cortex (area V1) uses a sparse code to efficiently represent natural scenes. This issue was investigated by recording from V1 neurons in awake behaving macaques during both free viewing of natural scenes and conditions simulating natural vision. Stimulation of the nonclassical receptive field increases the selectivity and sparseness of individual V1 neurons, increases the sparseness of the population response distribution, and strongly decorrelates the responses of neuron pairs. These effects are due to both excitatory and suppressive modulation of the classical receptive field by the nonclassical receptive field and do not depend critically on the spatiotemporal structure of the stimuli. During natural vision, the classical and nonclassical receptive fields function together to form a sparse representation of the visual world. This sparse code may be computationally efficient for both early vision and higher visual processing.     

Interocular transfer of orientational effects

Prolonged exposure of one eye to a diagonal line grating produces masking or decreased sensitivity for similar test gratings presented to the contralateral eye. These aftereffects are orientationally selective and suggest that narrow orientationally tuned channels found by electrophysiological methods in the visual cortex of the cat and the monkey may have neural correlates in the human brain.     

Superior colliculus cell responses related to eye movements in awake monkeys

Single cell responses were recorded from the superior colliculus of awake monkeys trained to move their eyes. A class of cells that discharged before eye movements was found in the intermediate and deep layers of the colliculus. The response of the cells was most vigorous before saccadic eye movements within a particular range of directions. These cells had no visual receptive fields, and visually guided eye movements were not necessary for their discharge, since they responded in total darkness before spontaneous eye movements and vestibular nystagmus.     

Ventral posterior thalamic neurons differentially responsive to noxious stimulation of the awake monkey

Of 76 cutaneously activated neurons recorded from the ventral posterior thalamus of awake, behaving monkeys, nine were weakly excited by innocuous skin stimulation and responded maximally only when noxious mechanical cutaneous stimuli were delivered within small, contralateral receptive fields. These results show that neurons capable of encoding the spatial and temporal features of noxious stimuli are located in the ventral posterior thalamus of the awake primate.     

Temporal specificity in the cortical plasticity of visual space representation

The circuitry and function of mammalian visual cortex are shaped by patterns of visual stimuli, a plasticity likely mediated by synaptic modifications. In the adult cat, asynchronous visual stimuli in two adjacent retinal regions controlled the relative spike timing of two groups of cortical neurons with high precision. This asynchronous pairing induced rapid modifications of intracortical connections and shifts in receptive fields. These changes depended on the temporal order and interval between visual stimuli in a manner consistent with spike timing-dependent synaptic plasticity. Parallel to the cortical modifications found in the cat, such asynchronous visual stimuli also induced shifts in human spatial perception.