Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Primary Visual Cortex”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 937 records · Page 52Linked to original sources
PubMed1993

Organization of long-range inhibitory connections with rat visual cortex.

We have studied the laminar organization of local long-range inhibitory connections within rat primary visual cortex (area 17) by combining retrograde tracing of nerve cell bodies with glutamic acid decarboxylase immunocytochemistry. While most inhibitory connections are confined to within 0.4 mm of the injection site, a subset of neurons at the layer 5/6 border provide long-range (> 1 mm) inhibitory connections within area 17. However, other cell layers that contain similar local long-range horizontal connections, that is, lower layer 2/3, upper layer 5, and lower layer 6 (Burkhalter and Charles, 1990), show a much more restricted distribution of inhibitory connections. This suggests that cells at the layer 5/6 border play a role in the direct inhibition of neurons at a distant point of the topographic map. Similar double labeling studies reveal long-range inhibitory connections between visual areas. Following injections of fluorescent tracers into area 17, in horizontal sections inhibitory connections can be identified that are up to 8 mm long, linking the extrastriate subdivisions 18a and 18b with striate cortex. Conversely, injections of fluorescent tracers into the cytoarchitectonic subdivision 18a reveal local long-range inhibitory connections within 18a, long-range inhibitory connections between 18a and the cytoarchitectonic subdivision 18b, and inhibitory forward connections from area 17 to 18a. These results suggest that the communication between different cortical areas can be influenced by direct inhibitory connections.

Animals↗
PubMed2006

Tuning to natural stimulus dynamics in primary auditory cortex.

The amplitude and pitch fluctuations of natural soundscapes often exhibit "1/f spectra", which means that large, abrupt changes in pitch or loudness occur proportionally less frequently in nature than gentle, gradual fluctuations. Furthermore, human listeners reportedly prefer 1/f distributed random melodies to melodies with faster (1/f0) or slower (1/f2) dynamics. One might therefore suspect that neurons in the central auditory system may be tuned to 1/f dynamics, particularly given that recent reports provide evidence for tuning to 1/f dynamics in primary visual cortex. To test whether neurons in primary auditory cortex (A1) are tuned to 1/f dynamics, we recorded responses to random tone complexes in which the fundamental frequency and the envelope were determined by statistically independent "1/f(gamma) random walks," with gamma set to values between 0.5 and 4. Many A1 neurons showed clear evidence of tuning and responded with higher firing rates to stimuli with gamma between 1 and 1.5. Response patterns elicited by 1/f(gamma) stimuli were more reproducible for values of gamma close to 1. These findings indicate that auditory cortex is indeed tuned to the 1/f dynamics commonly found in the statistical distributions of natural soundscapes.

Acoustic Stimulation↗
PubMed1986

A quantitative study of neuronal and glial numerical density in the visual cortex of the bottlenose dolphin: evidence for a specialized subarea and changes with age.

Neuronal and glial numerical densities were measured in the lateral gyrus of the cerebral hemisphere of dolphins (Tursiops truncatus) from the neonatal period to adulthood. The cortex studied is the area known to be visually excitable in evoked potential studies. Two distinct parts of the adult lateral gyrus are identifiable, one relatively anterior, in which neuronal density is 23,000/mm3, the other more posterior, with almost double this density. In a neonate, the neuronal density in the anterior lateral gyrus was found to be more than double that of the adult. No samples from the immature posterior area were available. Glial density varies much less than neuronal density, both with age and between areas. Soon after birth the glia/neuron ratio is 1.6 in anterior lateral gyrus, rising to around 3 in the adult anterior lateral area, and rather less in the posterior region, where neuronal density is high. We speculate that the existence of a high numerical density of neurons in the posterior part of the dolphin visual cortex could perhaps indicate a specialized area corresponding to the primate primary visual cortex, also known to have high neuronal density.

Age Factors↗
PubMed1991

Distribution of acetylcholinesterase and zinc in the visual cortex of the mouse.

The distributions of acetylcholinesterase (AChE) and zinc-containing boutons and their cells of origin in the visual cortex of the house mouse (Mus musculus domesticus) are described. The primary visual area is defined by both acetylcholinesterase and zinc staining. The AChE staining pattern is dark in upper layer I and layers IV and VI. It is light in layers II/III and V. The lack of a densely stained layer IV in the secondary visual cortices defines the borders between primary and secondary areas. Large, multipolar AChE-positive neurons are located throughout the cortical layers, but preferentially in layer VI. Dense zinc-positive neuropil in the primary visual cortex is apparent in layer Ib, upper layer II/III, and layers V and VI. Neurons that give rise to zinc-containing boutons are situated in layers II/III and VI. The medial and lateral borders can be distinguished by a bold contrast of staining in lower layer II/III; the secondary areas have more zinc-positive neurons, and the neuropil stains darker. A surprising observation of this study is the disparity between the mouse and rat visual cortex of the AChE staining pattern. Layer V is very light in the mouse, whereas a dark stain has been described in layer V of the rat. Layer VI stains heavily in the mouse while less AChE activity has been observed in layer VI of the rat.

Acetylcholinesterase↗
PubMed1998

The cell cycle gene SKP1 is regulated by light in postnatal rat brain.

During the early postnatal phase of high neuronal plasticity, an altered visual input leads to great modifications of visual cortex organization [Y. Frégnac, M. Imbert, Development of neuronal selectivity in primary visual cortex of cat, Physiol. Rev., 64 (1984) 375-434; D.H. Hubel, T.N. Wiesel, S. LeVay, Plasticity of ocular dominance columns in monkey striate cortex, Philos. Trans. R. Soc. London, Ser. B, 278 (1977) 377-409.]. We used refined differential screening of an organized cDNA library to identify the genes that may participate in this plasticity. We isolated a candidate plasticity gene encoding for a 163 aa protein that is closely related to the human and yeast Skp1p, a key factor in cell cycle progression [C. Baï, K. Hofman, L. Ma, M. Goebl, J.W. Harper, S.J. Elledge, SKP1 connects cell cycle regulators to the ubiquitin proteolysis machinery through a novel motif, the F-box, Cell, 86 (1996) 263-274; C. Connelly, P. Hieter, Budding yeast SKP1 encodes an evolutionary conserved kinetochore protein required for cell cycle progression, Cell, 86 (1996) 275-285; H. Zhang, R. Kobayashi, K. Galaktionov, D. Beach, p19Skp1 and p45Skp2 are essential elements of the cyclin A-CDK2 S phase kinase, Cell, 82 (1995) 915-925.]. Northern blot analysis showed that the expression of SKP1 (Skp1p gene) dramatically decreased after 2 h of light stimulation in the visual cortex of young dark-reared rats. This down regulation lasted at least 72 h. It was specific for the critical period as we did not observe any significant regulation of SKP1 mRNA by light in adult dark-reared rat brain. The down regulation was observed in the superior colliculus but also in the frontal cortex and in the hippocampus. The fact that this down regulation was not restricted to the visual system, suggested that it could be produced by dark rearing-induced hormonal changes. The significance of SKP1 expression in the brain and its regulation are discussed.

Animals↗
PubMed1987

Regional distribution of cholecystokinin receptors in primate cerebral cortex determined by in vitro receptor autoradiography.

Cholecystokinin (CCK) is a putative peptide neurotransmitter present in high concentration in the cerebral cortex. By using techniques of in vitro receptor autoradiography, CCK binding sites in primate cortex were labeled with 125I-Bolton-Hunter-labeled CCK-33 (the 33-amino-acid C-terminal peptide) and 3H-CCK-8 (the C-terminal octapeptide). Biochemical studies performed on homogenized and slide-mounted tissue sections showed that the two ligands labeled a high-affinity, apparently single, saturable site. Autoradiography revealed that binding sites labeled by both ligands were anatomically indistinguishable and were distributed in two basic patterns. A faint and diffuse label characterized portions of medial prefrontal cortex, premotor and motor cortices, the superior parietal lobule, and the temporal pole. In other cortical areas the pattern of binding was layer-specific; i.e., binding sites were concentrated within particular cortical layers and were superimposed upon the background of diffuse label. Layer-specific label was found in the prefrontal cortex, anterior and posterior cingulate gyrus, somatosensory cortex, inferior parietal lobule, retrosplenial cortex, insula, temporal lobe cortices, and in the primary visual and adjacent visual association cortices. The areal and laminar localization of layer-specific CCK binding sites consistently coincided with the cortical projections of thalamic nuclei. In prefrontal cortex, CCK binding sites were present in layers III and IV, precisely paralleling the terminal fields of thalamocortical projections from the mediodorsal and medial pulvinar nucleus of the thalamus. In somatosensory cortex, the pattern of CCK binding in layer IV coincided with thalamic inputs arising from the ventrobasal complex, while in the posterior cingulate gyrus, insular cortex, and retrosplenial cortex, layer IV and lower III binding mirrored the laminar distribution of cortical afferents of the medial pulvinar. CCK binding in layers IVa, IVc alpha, IVc beta, and VI of primary visual cortex corresponded to the terminal field disposition of lateral geniculate neurons, whereas in adjacent visual association cortex, binding in layers III, IV, and VI faithfully followed the cortical distribution of projections from the inferior and lateral divisions of the pulvinar nucleus of the thalamus. We interpret the diffusely labeled binding sites in primate cortex as being associated with the intrinsic system of CCK-containing interneurons that are distributed throughout all layers and areas of the cortex. The stratified binding sites, however, appear to be associated with specific extrinsic peptidergic projections.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1998

Horizontal or vertical optokinetic stimulation activates visual motion-sensitive, ocular motor and vestibular cortex areas with right hemispheric dominance. An fMRI study.

The differential effects of optokinetic stimulation with and without fixation suppression were analysed in an fMRI study in 10 right-handed healthy subjects. Horizontal and vertical small-field optokinetic stimulation activated the same multiple visual, ocular motor and vestibular cortical and subcortical areas in both hemispheres. The extent of activation in each hemisphere was independent of the stimulus direction. All activated areas representing cortical (occipitotemporal cortex, posterior parietal cortex, precentral and posterior median frontal gyrus, prefrontal cortex, medial part of the superior frontal gyrus) and subcortical (caudate nucleus, putamen, globus pallidus and paramedian thalamus) ocular motor structures were activated during optokinetic stimulation as well as during fixation suppression of optokinetic nystagmus. However, the activation was significantly stronger with optokinetc nystagmus compared with fixation suppression. The only relatively increased activity during fixation suppression was seen in the medial part of the superior frontal gyrus (supplementary eye field) and the anterior cingulate gyrus. The anterior insula and the posterior insula (human homologue of the parieto-insular vestibular cortex) were activated during optokinetic nystagmus but not during fixation suppression. A significant right hemispheric predominance (regardless of stimulus direction) was found under both conditions in the visual motion-sensitive and ocular motor areas of the cortex, except the supplementary eye field and anterior cingulate gyrus. This was most prominent in the occipitotemporal cortex, but did not occur in the primary visual cortex and in subcortical ocular motor structures (putamen, globus pallidus and caudate nucleus). Thus, cortical and subcortical activation patterns did not differ for horizontal and vertical optokinetic stimulation, and there was distinct right-hemisphere dominance for visual motion-sensitive and cortical ocular motor areas and the thalamus. Fixation suppression of optokinetic nystagmus yielded four different results: (i) increased activation in the supplementary eye field and anterior cingulate gyrus; (ii) unchanged activation in the visual cortex; (iii) decreased activation in most of the ocular motor areas; and (iv) suppressed activation in the anterior and posterior insula and the thalamus. Activation of the parieto-insular vestibular cortex may be related to ocular motor function rather than self-motion perception.

Adult↗
PubMed2000

Cortical activity related to cue-invariant shape perception in humans.

We used magnetoencephalography to search spatio-temporally for cortical activity related to the perception of shape defined by various visual cues in humans. The visual stimuli were three kinds of two-dimensional figures: two had fixed shapes (Diamond and Cross), the other did not (Noise). These figures were defined by three visual cues: difference of flicker, texture or luminance between the foreground and the background in the random dot pattern. Using this stimulus, we recorded the magnetic responses from the temporo-occipital regions of nine healthy subjects. Additionally, we measured the reaction time for the subjects to detect the figure by button-pressing. A magnetic component was identified in the responses. The properties of the first magnetic component differed for stimulus condition. The peak latency of the first magnetic component was different for the cues (270 ms for flicker, 360 ms for texture and 250 ms for luminance), but not for the figures. In contrast, the peak amplitude of the first magnetic component was different for the figures (96-144 fT for Diamond or Cross and 52-80 fT for Noise), but not for the cues. The signal source of the first magnetic component was estimated to lie on the ventral side of the extrastriate cortex: In the posterior part of the inferior temporal cortex, probably in the fusiform gyrus in four subjects, and in the lateral part of the occipital cortex which was outside of the primary visual cortex (visual area 1) in one subject. The signal source location was different inter-individually, but almost the same within each subject. Reaction time was 471 ms for flicker, 569 ms for texture and 426 ms for luminance, but the interval between the reaction time and the peak latency was constant (about 200 ms) for each cue. The first magnetic component was more clearly recorded from the right hemisphere than from the left.We found that the shape defined by the different visual cues activates the same localized site in the lateral extrastriate cortex. This spatial convergence suggests that there is a restricted locus that processes the visual shape regardless of the difference of the visual cue. The correspondence between the peak latency and the reaction time suggests that the activity of the area is responsible for the perception of visual shape. The inter-hemispheric difference suggests a dominance of the right hemisphere in visual shape processing.

Adult↗
PubMed2003

Bilateral impact of unilateral visual cortex lesions on the superior colliculus.

We examined the functional impact of a long-standing, unilateral primary visual cortex lesion on the superior colliculus (SC) using radiolabeled 2-deoxyglucose (2DG) as a marker of neural activity. In accord with known corticotectal connectivity and functional influence, 2DG uptake in the superficial layers of the ipsilesional SC was decreased. We also found a decrease in the superficial layers of the contralesional SC. These data suggest that modifications in activity in one SC can have a substantial influence on activity in its contralateral partner, and that processing in one visual hemifield does not occur independently of processing of signals in the opposite hemifield. The effects are not mediated by the contralateral hemisphere but are probably mediated by intercollicular circuitry.

Animals↗
PubMed2001

AMPA GluR2 subunit is differentially distributed on GABAergic neurons and pyramidal cells in the macaque monkey visual cortex.

The cellular and synaptic distribution of the AMPA receptor subunit GluR2 was analyzed in the monkey primary visual cortex (area V1), by immunocytochemistry and postembedding immunogold methods. GluR2 immunoreactivity was widely distributed in all of the layers of area V1. A quantitative double labeling analysis in layers II and III revealed that the vast majority of GABAergic interneurons in this area also contained GluR2. Postembedding immunogold analysis revealed that GluR2 immunoreactivity was present at asymmetric synapses on both GABAergic interneurons and pyramidal cells. A quantitative study indicated that the number of GluR2 immunogold particles at asymmetric synapses on pyramidal cells was significantly higher than that on GABAergic interneurons. These results from the primate neocortex are in agreement with and extend our previous studies on the rat hippocampus and amygdala. In view of the dominant role of the GluR2 subunit in regulating calcium flux through AMPA receptors, the differential synaptic distribution of GluR2 on different neuronal types might provide a mechanism for cell-specific response properties to glutamate as well as clues to selective neuronal vulnerability and cell death mediated by calcium-dependent excitotoxic mechanisms.

Animals↗
PubMed2000

The serotonin 5-HT2 receptor-phospholipase C system inhibits the induction of long-term potentiation in the rat visual cortex.

The effect of serotonin 5-HT2 receptor stimulation on long-term potentiation (LTP) in the primary visual cortex was investigated by using rat brain slices in vitro. Field potentials evoked by stimulation of layer IV were recorded in layer II/III. The 5-HT2 receptor agonist 1-(2,5-dimethyl-4-iodophenyl)-2-aminopropane (DOI) did not affect baseline synaptic potentials evoked by single-pulse test stimulation, but significantly inhibited the induction of LTP in a concentration-dependent manner (0.1-10 microM). The LTP-inhibiting effect of DOI (10 microM) was blocked by the 5-HT2,7 receptor antagonist ritanserin (10 microM), but not by the 5-HT1A receptor antagonist NAN-190 (10 microM) nor by the 5-HT3,4 receptor antagonist MDL72222 (10 microM). The inhibitory effect of DOI was also blocked by the phospholipase C inhibitor U73122, but not by its inactive analogue U73343. These results suggest that visual cortex LTP is inhibited by activation of the 5-HT2 receptor-phospholipase C system. In addition, the LTP-inhibiting effect of DOI was abolished by the presence of the GABAA receptor antagonist bicuculline (10 microM), suggesting that 5-HT2 receptor-mediated inhibition of visual cortex LTP is dependent on GABAergic inhibition.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed2003

Different inhibitory synaptic input patterns in excitatory and inhibitory layer 4 neurons of ferret visual cortex.

The synaptic mechanisms underlying the generation of orientation and direction selectivity in layer 4 of the primary visual cortex are still largely unclear. Previous in vivo work has shown that intra-cortical inhibition plays a major role in generating the properties of orientation and direction selectivity. Excitatory and inhibitory cortical neurons differ in their receptive field properties: excitatory neurons tend to be orientation- and direction-selective, inhibitory neurons tend to be orientation-, but not direction-selective. Here we have compared the relationship between direction preference maps recorded in vivo and synaptic input maps recorded in vitro from excitatory and inhibitory stellate cells in layer 4 of ferret visual cortex. Our goal was to test whether the differences in direction tuning between these cell populations might result from different inhibitory connectivity patterns. We found that excitatory neurons, which are direction tuned in vivo, receive approximately 50% of their inhibitory inputs from cortical regions of opposite direction preference whereas inhibitory cells, which are not or poorly direction tuned, receive only very few inputs from regions of opposite direction preference. This confirms that inhibitory connections arising in cortical regions of opposite direction preference may be required to create or strengthen direction tuning in their target neurons. Thus, differences in intracortical inhibitory circuit patterns may underlie the differences in receptive field properties observed between excitatory and inhibitory neurons in vivo.

Animals↗
PubMed1996

Functional neuroanatomy of visual object naming: a PET study.

BACKGROUND: The ability to name objects depends partly on visual perception. We used positron emission tomography (PET) to measure activity-related changes in regional cerebral blood flow (r-CBF) in order to identify regions of the brain activated during visual object naming. METHODS: Four right-handed volunteers were recruited. Following an intravenous injection of 15O-labeled water, r-CBF was measured during visual object naming, counting numbers, and resting. PET and MRI images were coregistered, the size of the brain was proportionally adjusted in each axis to Talairach's and Tournoux's atlas, and the comparison of stimulated versus resting blood flow images revealed activated brain regions. RESULTS: In the subtraction of resting from naming, activation was observed in the bilateral primary visual cortex, bilateral fusiform gyrus, left lingual gyrus, bilateral inferotemporal cortex, bilateral inferior frontal gyrus, bilateral precentral gyrus, anterior cingulate gyrus, left parietal operculum, and left putamen. In the subtraction of counting from naming, most of the those areas were activated, but no significant activity was observed in the left lingual gyrus, left parietal operculum, or bilateral precentral gyrus (motor cortex). The areas activated with the paradigm included those dedicated to visual perception (primary and associate visual cortex), visual recognition (inferior temporal cortex), and phonological output (Broca's area). CONCLUSION: Our results indicated that the major neural network from occipital lobe to frontal cortex, which is mainly involved in the ventral visual pathway, demonstrated activation in these tasks. Result of this study will serve as base line data for analyzing the findings in patients with impaired visual perception.

Adult↗
PubMedDate not supplied

Visual saliency and spike timing in the ventral visual pathway.

Visual saliency is a fundamental yet hard to define property of objects or locations in the visual world. In a context where objects and their representations compete to dominate our perception, saliency can be thought of as the "juice" that makes objects win the race. It is often assumed that saliency is extracted and represented in an explicit saliency map, which serves to determine the location of spatial attention at any given time. It is then by drawing attention to a salient object that it can be recognized or categorized. I argue against this classical view that visual "bottom-up" saliency automatically recruits the attentional system prior to object recognition. A number of visual processing tasks are clearly performed too fast for such a costly strategy to be employed. Rather, visual attention could simply act by biasing a saliency-based object recognition system. Under natural conditions of stimulation, saliency can be represented implicitly throughout the ventral visual pathway, independent of any explicit saliency map. At any given level, the most activated cells of the neural population simply represent the most salient locations. The notion of saliency itself grows increasingly complex throughout the system, mostly based on luminance contrast until information reaches visual cortex, gradually incorporating information about features such as orientation or color in primary visual cortex and early extrastriate areas, and finally the identity and behavioral relevance of objects in temporal cortex and beyond. Under these conditions the object that dominates perception, i.e. the object yielding the strongest (or the first) selective neural response, is by definition the one whose features are most "salient"--without the need for any external saliency map. In addition, I suggest that such an implicit representation of saliency can be best encoded in the relative times of the first spikes fired in a given neuronal population. In accordance with our subjective experience that saliency and attention do not modify the appearance of objects, the feed-forward propagation of this first spike wave could serve to trigger saliency-based object recognition outside the realm of awareness, while conscious perceptions could be mediated by the remaining discharges of longer neuronal spike trains.

Action Potentials↗
PubMed1995

Regional alterations in M1 muscarinic receptor-G protein coupling in Alzheimer's disease.

Previous studies examining the functional status of cortical muscarinic cholinergic M1 receptors have demonstrated an impairment in receptor-G protein coupling in Alzheimer's disease (AD) as measured by the inability of the receptor to form a high affinity agonist binding site. In order to investigate whether this alteration was a global phenomenon or a regional specific defect in signal transduction, we examined agonist binding at M1 receptors in three brain areas (superior frontal cortex, Brodmann areas 8 and 9; primary visual cortex, Brodmann area 17; and the dorsal striatum) within the same brain in controls and moderate to severe AD cases. Competition binding studies using the M1 antagonist 3H-pirenzepine (4 nM) in the presence of varying concentrations of the cholinergic agonist carbachol (50 nM to 1 mM) were performed in the presence and absence of GppNHp (100 microM), a non-hydrolyzable analog of GTP. In control membrane preparations, computer-assisted analysis of antagonist-agonist competition curves revealed that M1 receptor agonist binding fit a two site model with high and low affinity states in all three brain areas in the absence of GppNHp but only a single site in the presence of GppNHp. This is consistent with the ternary complex model of G protein-linked receptors. In contrast, curves obtained from both cortical regions from AD brains fit a single site model with low affinity in the presence or absence of GppNHp. On the other hand, agonist binding data obtained from the dorsal striatum of AD cases exhibited a two site fit, similar to that seen in controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1998

Major glutamatergic projection from subplate into visual cortex during development.

Subplate neurons, the first neurons of the cerebral cortex to differentiate and mature, are thought to be essential for the formation of connections between thalamus and cortex, such as the system of ocular dominance columns within layer 4 of visual cortex. To learn more about the requirement for subplate neurons in the formation of thalamocortical connections, we have sought to identify the neurotransmitters and peptides expressed by the specific class of subplate neurons that sends axonal projections into the overlying visual cortex. To label retrogradely subplate neurons, fluorescent latex microspheres were injected into primary visual cortex of postnatal day 28 ferrets, just prior to the onset of ocular dominance column formation. Subsequently, neurons were immunostained with antibodies against glutamate, glutamic acid decarboxylase (GAD-67), parvalbumin, neuropeptide Y (NPY), somatostatin (SRIF), or nitric oxide synthase (NOS). Retrograde labeling results indicate that the majority of subplate neurons projecting into the cortical plate reside in the upper half of the subplate. Combined immunostaining and microsphere labeling reveal that about half of cortically projecting subplate neurons are glutamatergic; most microsphere-labeled subplate neurons do not stain for GAD-67, parvalbumin, NPY, SRIF, or NOS. These observations suggest that subplate neurons can provide a significant glutamatergic synaptic input to the cortical plate, including the neurons of layer 4. If so, excitation from the axons of subplate neurons may be required in addition to that from lateral geniculate nucleus neurons for the activity-dependent synaptic interactions that lead to the formation of ocular dominance columns during development.

Animals↗
PubMed1999

Topographic organization of human visual areas in the absence of input from primary cortex.

Recently, there has been evidence for considerable plasticity in primary sensory areas of adult cortex. In this study, we asked to what extent topographical maps in human extrastriate areas reorganize after damage to a portion of primary visual (striate) cortex, V1. Functional magnetic resonance imaging signals were measured in a subject (G.Y.) with a large calcarine lesion that includes most of primary visual cortex but spares the foveal representation. When foveal stimulation was present, intact cortex in the lesioned occipital lobe exhibited conventional retinotopic organization. Several visual areas could be identified (V1, V2, V3, V3 accessory, and V4 ventral). However, when stimuli were restricted to the blind portion of the visual field, responses were found primarily in dorsal extrastriate areas. Furthermore, cortex that had formerly shown normal topography now represented only the visual field around the lower vertical meridian. Several possible sources for this reorganized activity are considered, including transcallosal connections, direct subcortical projections to extrastriate cortex, and residual inputs from V1 near the margin of the lesion. A scheme is described to explain how the reorganized signals could occur based on changes in the local neural connections.

Adult↗
PubMed1977

Effects of LSD on the response of single units in cat visual cortex.

The effects of intravenous doses (200 mug) of LSD on the activity of single neurones in the primary visual cortex have been studied in cats anaesthetized with urethane. Cells were stimulated with a bright bar of light moved over the receptive field, and orientation tuning was assessed quantitatively before and after administration of the drug. Changes in neuronal activity were compared with those observed in a control sample of cells recorded when the cats were given no drug. LSD increased the responsiveness of some cells to visual stimuli and decreased that of others, but some cells were not affected. The changes in responsiveness were dose dependent; the larger doses of the drug (expressed in mug/kg body weight) tended to depress the responses and the smaller doses to enhance them. The effects appeared earlier in complex cells than in simple cells. Changes in spontaneous activity, direction selectivity and orientational properties were found in some cells.

Animals↗