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PubMed1984

Distribution of alpha 2-adrenergic receptors in the human brainstem: an autoradiographic study using [3H]p-aminoclonidine.

The distribution of alpha 2-adrenergic receptors in the human brainstem and some forebrain areas was examined by means of an in vitro autoradiographic technique using [3H]p-aminoclonidine as a ligand. High densities of alpha 2-adrenergic receptors were observed in the dorsal motor nucleus of the Xth nerve, the nucleus of the solitary tract, the locus coeruleus and the substantia grisea centralis. Other brainstem areas presenting significant densities of alpha 2-adrenergic receptors were the substantia gelantinosa of the Vth nerve, the nucleus cuneiformis, the superficial gray layer of the superior colliculus, the cortical mantle of the inferior colliculus and the inferior olivary nuclei. Of the forebrain areas studied, the highest density was seen in the primary visual cortex. The distribution observed presents some significant differences with that previously described for the rat. The localization of alpha 2-adrenergic receptors in the human brain correlates well with the distribution of noradrenergic neurons in the human brainstem and suggests sites of action of alpha 2-adrenergic drugs in the human brain.

Adrenergic alpha-Agonists↗
PubMed1991

[2- 14C]deoxyglucose uptake in rat visual system during flashing-diffuse and flashing-pattern stimulation over a 6 log range of luminance.

The 2-deoxyglucose autoradiographic technique was used to assess the metabolic activity of cortical area 17, the dorsal and ventral lateral geniculate nuclei, the lateral posterior nucleus, and the superior colliculus, during 5-Hz flashing-pattern (montage of black and white square-wave gratings) and flashing-diffuse (eye covered with white mask) stimulation at three intensities over a 6 log range. In area 17 flashing-pattern was found to be equally effective at elevating uptake of the functional label over the photopic-scotopic range of luminance levels tested, whereas flashing-diffuse was ineffective. In subcortical nuclei, however, flashing-diffuse was no less effective than flashing-pattern and uptake of the label correlated positively with intensity level. The results suggest that the subcortical components of the visual system do play an important role in the processing of intensity information and that primary visual cortex does not.

Animals↗
PubMed1989

The development of long-term potentiation in hippocampus and neocortex.

The development of long-term potentiation (LTP), an enduring alteration in synaptic efficacy following afferent activation, was examined in CA1 hippocampus and primary visual cortex of rat. Both regions show little LTP prior to postnatal day 5, demonstrate a maximal potentiated response around postnatal day 15, and a subsequent decline to adult levels. These results are discussed with respect to the underlying mechanism of action and behavioral significance of these critical-period phenomena.

Aging↗
PubMed1984

The effects of large orientation and spatial frequency differences on spatial discriminations.

We have examined two questions: (1) can the finest orientation discrimination be achieved only between stimuli with similar spatial frequency content? and likewise, (2) can the lowest spatial frequency discrimination thresholds be achieved only with parallel gratings? In 2 AFC tests we found that neither type of discrimination was affected by stimulus differences along the other dimension. However, some small decreases in method of adjustment matching accuracy were associated with large differences along the secondary dimensions. Considering the neurophysiological implications, these data suggest that fine orientation and spatial frequency discrimination can occur even though separate populations of neurones in the primary visual cortex may be activated by the two stimuli to be discriminated.

Discrimination, Psychological↗
PubMed1986

Optic flow.

This paper offers a quick review of the subject of "optic flow" in its conceptual and computational aspects. The theory is evaluated in terms of possible applications in the neurophysiology and experimental psychology of spatial sensorymotor behaviour and perception. The problem of which kind of detector is suited to extract various aspects of optic flow is given special attention. It is shown that the possibilities are actually much more various than is reflected in the current (even the frankly speculative) literature. It is argued that a system that is sensitive to the relative time changes of the orientation differences of image details is especially suited for an analysis of the optic flow with regard to the information concerning the three dimensional shape of objects such as is contained in the flow. Thus the orientation sensitive elements that are known to be abundantly present in the primary visual cortex of many vertebrates are hereby implicated as a quite likely substrate for the extraction of the solid shape of environmental objects. In our opinion this possibility should be investigated with the same ardour as the usual interpretation, which holds this system responsible for the initial extraction of the contours of flat (i.e. defined in the image) shapes. A new, partial solution to the "structure from motion problem" is offered, that not only covers the usual case of shape extraction in the presence of rigid motions of the object, but also the much wider class of (non-rigid) bending deformations (such as occur in the non-rigid deformations of inextensible shells). These solutions violate all conditions required by the well known "structure from motion theorem": the solutions are possible for point configurations in which no fourtuple of points moves as a rigid structure and for input data from merely two views. A numerical example illustrates how this algorithm can be used to predict side views of an object from very limited input data.

Form Perception↗
PubMed1987

Principal components analysis for source localization of VEPs in man.

This study defines and compares the topologies of the visual evoked potentials to various stimuli such as pattern onset/offset, pattern reversal, pattern motion and high frequency luminance flicker. The responses recorded from 24 occipital derivations were examined using a three sphere conductance model to represent the head, with the assumption that activity from an underlying cortical source is equivalent to a single dipole. Principal components analysis was used to find the dimensionality of the data space. From this analysis could be concluded that all stimuli evoked responses in the primary visual cortex. Only pattern onset, and to a lesser degree pattern offset and pattern reversal, yielded activity in higher visual areas. In particular it has been shown that the CI, CII interval of the pattern onset response has its origins in two different cortical regions. A fast positive (CI)-negative (part of the CII) component arises from area 18 (or 19), a slower negative (initial part of CII) component comes from area 17.

Evoked Potentials, Visual↗
PubMed1992

Analysis of striate activity underlying the pattern onset EP of children.

The checkerboard onset Evoked Potential (EP) does not obtain its adult form before puberty. To determine the site of origin of these processes we studied the origin of the checkerboard onset EP in a group of 10 children between the ages of 6 and 16 years. Since the development of the waveform of the pattern onset EP varies with check size we also studied the dependence of these EPs on check size. The child checkerboard onset EPs described in this paper are dominated by a single source. Following an equivalent dipole source localization approach, the position, orientation and variation in strength of the equivalent dipole is estimated. The position and orientation of this dipole indicates an origin in the primary visual cortex (area 17). The variation in strength of the dipole changes from a single positive deflection, specific for children of 8 years and younger, into a negative-positive complex for the children studied between the age of 9 and 16 years. These changes in waveform must be due to changes in the activity pattern of the striate cortex.

Adolescent↗
PubMed1995

Migraine phosphenes and the retino-cortical magnification factor.

Quantitative observations on the shape and position of migraine phosphenes within the visual field were obtained by controlled "perimetric" drawings of the phosphenes performed every 1-2 min during the aura state. The visual field eccentricity of the "fortification" or zig-zag patterns scintillating at about 10 Hz was plotted as a function of observation time. It is well described by an exponential function of time. This exponential function is the product of a first-order linear differential equation determined by the distribution of the retino-cortical magnification factor across the visual field and a constant diffusion speed of the cortical pathophysiological process leading to the migraine phosphene patterns. The observed "particle" size of the phosphene pattern and the width of the scotoma trailing the scintillating phosphenes could also be easily predicted from these assumptions. A model in which the main components are an increase in extracellular potassium concentration, a decrease in extracellular calcium concentration and the constant speed diffusion of the ions along the extracellular space of the stripe of Gennari within the primary visual cortex explains the observations.

Calcium↗
PubMed1994

Spatial summation among coextensive and parallel line segments across wide separations (50 degrees): egocentric localization and the great circle model.

The elevation at which an observer sets a target to appear at eye level (VPEL) is systematically related to the angle of pitch of the visual field and is only a little less for a visual field consisting of a single line in darkness than for a complexly structured field [Matin and Li (1994a) Vision Research, 34, 311-330]. Three experiments are described which measure the quantitative characteristics of spatial summation among individual pitched-from-vertical line segments that control the visual influence on VPEL. As the length of a one-line stimulus increased from 0 degrees to 64 degrees the slope of the VPEL-vs-pitch function (S) increased from 0 to +0.56 along a negatively accelerated exponential with a 15.1 degree space constant. The combined influence on S of two simultaneously-presented, parallel, pitched-from-vertical lines, horizontally separated by 50 degrees, is slightly greater than the combined influence of two coextensive line segments with the same total length. S saturates at a locus that lies beyond any separate neural locus for the processing of the individual line. The results are effectively treated by the Great Circle Model (GCM) which converts stimulus "nonlocality" to neural "locality" by mapping the intersections of the images of parallel line sets in a spherical approximation of the eye on to a set of neural nodes. A neurophysiological realization of GCM is compatible with mediation by the long horizontal connections afferent to layer 6 of primary visual cortex (V1). The combination of visual influences with extraretinal information is compatible with the characteristics of posterior parietal cortex downstream from V1. The increase in the effectiveness of a line with increase in length is in accord with a more general division between the utilization of long lines for egocentric orientation and short lines for figural processes; end-inhibition from elongated layer 6 cells (which process long lines) onto layer 4 cells (which process short lines) in V1 may provide a means for separating the two streams of information.

Darkness↗
PubMed1995

The nature of the inputs to cortical motion detectors.

Recently, Jagadeesh, Wheat and Ferster [(1993) Science, 262, 1901-1904] presented intracellular recordings from direction-selective simple cells in primary visual cortex and provided an analysis to support the idea that synaptic summation in simple cells is linear. New analysis presented in this study reveals that: (1) the number of subunits contributing to the analyzed simple cell inputs is two; (2) the subunits are nonlinear in the time domain; (3) each subunit linearly integrates the luminance across the receptive field being, thus, linear to local contrast; (4) the waveforms of the subunit signals are linearly modulated by local contrast at the subunit loci unless the contrast changes its sign; (5) the synaptic summation in the simple cell is linear; (6) nonlinearity of even harmonics has sufficient information for retrieving of relative spatial phase of the subunits and reconstruction of the exact temporal profiles of the subunit signals.

Animals↗
PubMed1996

Neural encoding of binocular disparity: energy models, position shifts and phase shifts.

Neurophysiological data support two models for the disparity selectivity of binocular simple and complex cells in primary visual cortex. These involve binocular combinations of monocular receptive fields that are shifted in retinal position (the position-shift model) or in phase (the phase-shift model) between the two eyes. This article presents a formal description and analysis of a binocular energy model with these forms of disparity selectivity. We propose how one might measure the relative contributions of phase and position shifts in simple and complex cells. The analysis also reveals ambiguities in disparity encoding that are inherent in these model neurons, suggesting a need for a second stage of processing. We propose that linear pooling of the binocular responses across orientations and scales (spatial frequency) is capable of producing an unambiguous representation of disparity.

Depth Perception↗
PubMed1996

Learning pop-out detection: specificities to stimulus characteristics.

Training induces dramatic improvement in the performance of pop-out detection. In this study, we examined the specificities of this improvement to stimulus characteristics. We found that learning is specific within basic visual dimensions: orientation, size and position. Accordingly, following training with one set of orientations, rotating target and distractors by 30 deg or more substantially hampers performance. Furthermore, rotation of either target or distractors alone greatly increases threshold. Learning is not transferred to reduced-size stimuli. Position specificity near fixation may be finer than 0.7 deg. On the other hand, learning transfers to the untrained eye, to expanded images, to mirror image transformations and to homologous positions across the midline (near fixation). Thus, learning must occur at a processing level which is early enough to maintain fine separability along basic stimulus dimensions, yet sufficiently high to manifest the described generalizations. We suggest that the site of early perceptual learning is one of the cortical areas which receive input from primary visual cortex, V1, and where top-down attentional control is present.

Adolescent↗
PubMed1978

Differential effects of convulsants on visually evoked responses in the albino rat.

Visually evoked responses (VERs) were recorded from primary visual cortex in unanesthetized albino rats during pharmacological modulation by one of the following convulsant agents: Physostigmine, picrotoxin, strychnine and Metrazol. The data were analyzed in terms of effects on VER components. The rat VER consists of six distinct waves constituted by three positive peaks (P1--P3) and three negative peaks (N1--N3). Results indicate a differential convulsant action on VER components. The administration of picrotoxin, resulted in a suppression of the peak amplitude of P1--N1 and delayed peak latencies of all components. Strychnine reliably shortened P1, N1 and P2 peak latencies, significantly increased N3 peak latency and only suppressed P3--N3 amplitude. Physostigmine essentially suppressed all component amplitudes but only increased peak latencies for P2 and P3 components. Metrazol, in general, was found to be relatively ineffective in the alteration of any VER component in a systematic manner. The data are discussed in terms of differential modes of convulsant action on the visual system. The results are likewise discussed with respect to their implications for convulsant modulation of photically evoked after-discharges.

Animals↗
PubMed1981

Anterograde tracing of horseradish peroxidase (HRP) with the electron microscope using the tetramethylbenzidine reaction.

A technique is described for anterograde horseradish peroxidase (HRP) tracing with the electron microscope using tetramethylbenzidine (TMB) histochemistry. Following HRP injection into the primary visual cortex or one eye of rabbits the superior colliculus was studied with the light and electron microscope in adjacent sections. In target preparations from the colliculus examined with the electron microscope labelled axons and axon terminals were found. The TMB reaction product was identified as crystal like electron-dense structures. In control sections from the opposite colliculus the neuropil was free from label.

Afferent Pathways↗
PubMed1995

Theory meets experiment: correlated neural activity helps determine ocular dominance column periodicity.

The development of ocular dominance columns in primary visual cortex has attracted much interest from both experimentalists and theoreticians. One key parameter of these columns is their periodicity - it is thus important to understand how this is determined. Novel experimental work demonstrates that the periodicity is influenced by the temporal patterning of afferent activity, as predicted by recent theoretical work.

Animals↗
PubMed1995

Receptive-field dynamics in the central visual pathways.

Neurons in the central visual pathways process visual images within a localized region of space, and a restricted epoch of time. Although the receptive field (RF) of a visually responsive neuron is inherently a spatiotemporal entity, most studies have focused exclusively on spatial aspects of RF structure. Recently, however, the application of sophisticated RF-mapping techniques has enabled neurophysiologists to characterize RFs in the joint domain of space and time. Studies that use these techniques have revealed that neurons in the geniculostriate pathway exhibit striking RF dynamics. For a majority of cells, the spatial structure of the RF changes as a function of time; thus, these RFs can be characterized adequately only in the space-time domain. In this review, the spatiotemporal RF structure of neurons in the lateral geniculate nucleus and primary visual cortex is discussed.

Animals↗
PubMed1981

New methods for analysis of vision in the gerbil.

The visual behavior of gerbils has been studied by adapting natural behaviors such as food pursuit, aperture detection, barrier negotiation and ladder climbing. Methods are described for measuring detection and discrimination thresholds using visual orienting tasks. Furthermore, studies of size-distance constancy, anticipation of a moving target's trajectory, and optimal planning of barrier detours show the usefulness of film records for quantitative analysis of complex perceptual abilities. Finally, preliminary studies of gerbils following ablation of primary visual cortex indicate that some visuomotor abilities are cortically dependent.

Animals↗
PubMed1983

Effects of unilateral and bilateral lesions of the lateral suprasylvian area on learning and interhemispheric transfer of pattern discrimination in the cat.

The aim of the present experiment was to evaluate the hypothesis that the lateral suprasylvian area is involved in the interhemispheric transfer of visual information. This area was surgically removed in 10 cats which had previously undergone a midsagittal transection of their optic chiasmas. The animals then learned a pattern discrimination using either one or the other hemisphere and were tested for transfer using the other, untrained hemisphere. The lateral suprasylvian area in the intact hemisphere was next ablated in 6 of these cats. Each hemisphere was trained on a new pattern discrimination and tested for transfer using the other. The results obtained with the unilaterally lesioned animals indicated that: (a) learning with the lesioned hemisphere was as rapid as with the intact hemisphere; and (b) that transfer in either direction was normal although slightly retarded, but not significantly so, when the information proceeded from the intact to the lesioned hemisphere. Learning with either hemisphere of the bilaterally lesioned animals also appeared to be normal. Learning with the hemisphere which was lesioned second and transferring to the one which was ablated first was within normal range whereas transfer was generally not as immediate when the procedure was reversed. As a whole, the results, when coupled with those of others, would tend to indicate that the lateral suprasylvian area is involved in interhemispheric transfer but shares this function with other callosally connected areas of the primary visual cortex.

Animals↗