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PubMed1993

Development of orientation selectivity in ferret visual cortex and effects of deprivation.

The orientation selectivity of cells in ferret primary visual cortex was studied during normal development and in animals deprived of vision or of visual cortical activity. In normal animals from the age when visual responses were first recorded (postnatal day 23) through postnatal week 5, only about 25% of cells showed orientation-selective responses. By postnatal week 7, cortical responses had matured to an adult-like state, with approximately 75% of cells clearly selective for orientation. This development of orientation selectivity was not merely a reflection of the development of cortical cell responsiveness: at all ages studied, there was no correlation between responsiveness and selectivity. Infusion of TTX into visual cortex to silence neuronal activity completely blocked the maturation of orientation selectivity. Visual deprivation by bilateral lid suture impaired but did not completely block the normal development of orientation selectivity. We conclude that the maturation of orientation-selective responses in ferret primary visual cortex requires cortical neuronal activity, and that normal development requires visually driven activity.

Animals↗
PubMedDate not supplied

Basic information processing and higher cognition: does the mammalian cerebral cortex deal with them at different hierarchical levels?

1. The primary visual cortex has been generally considered as a feature processing area where the neurons code for basic stimulus attributes, such as orientation, colour and direction of movement. Higher cognitive functions, such as attention and memory, were believed to be mediated by extrastriate regions at higher levels in a hierarchy of visual areas. However, the experiments reported here suggest that the function of the primary visual cortex is more than basic information processing in at least two respects. 2. First, significant modulation of visual responses occur in the primary visual cortex (V1) of the monkey depending upon attentional factors. There appears to be a feedback to V1 from extrastriate regions that facilitates neuronal responses in areas of attention and suppresses responses in other regions of the visual field. 3. Second, one would expect a region that is concerned with coding basic stimulus features to be rather resistant to plastic changes, as cells need to be reliable feature detectors for meaningful behaviour by the organism. However, the experiments on anaesthetized cats reported here show that a subset of neurons in visual area 17 of the cat have a potential for synaptic plasticity. Their response properties can undergo long-term changes under certain circumstances. To induce these changes, specific visual stimuli were combined with iontophoretic administration of NMDA and the GABA antagonist, bicuculline, which are believed to provide the molecular milieu for long-term potential and long-term depression.

Animals↗
PubMed2005

Orientation-tuned FMRI adaptation in human visual cortex.

Adaptation is a general property of almost all neural systems and has been a longstanding tool of psychophysics because of its power to isolate and temporarily reduce the contribution of specific neural populations. Recently, adaptation designs have been extensively applied in functional MRI (fMRI) studies to infer neural selectivity in specific cortical areas. However, there has been considerable variability in the duration of adaptation used in these experiments. In particular, although long-term adaptation has been solidly established in psychophysical and neurophysiological studies, it has been incorporated into few fMRI studies. Furthermore, there has been little validation of fMRI adaptation using stimulus dimensions with well-known adaptive properties (e.g., orientation) and in better understood regions of cortex (e.g., primary visual cortex, V1). We used an event-related fMRI experiment to study long-term orientation adaptation in the human visual cortex. After long-term adaptation to an oriented pattern, the fMRI response in V1, V2, V3/VP, V3A, and V4 to a test stimulus was proportional to the angular difference between the adapting and test stimuli. However, only V3A and V4 showed this response pattern with short-term adaptation. In a separate experiment, we measured behavioral contrast detection thresholds after adaptation and found that the fMRI signal in V1 closely matched the psychophysically derived contrast detection thresholds. Similar to the fMRI results, adaptation induced threshold changes strongly depended on the duration of adaptation. In addition to supporting the existence of adaptable orientation-tuned neurons in human visual cortex, our results show the importance of considering timing parameters in fMRI adaptation experiments.

Adaptation, Physiological↗
PubMed1996

The calcarine sulcus as an estimate of the total volume of human striate cortex: a morphometric study of reliability and intersubject variability.

The human primary visual cortex consists of a region buried in the calcarine sulcus and a region outside this sulcus on the free surface of the occipital lobe. Since the depth of the calcarine sulcus can be easily estimated in magnetic resonance images of the living human brain, in vivo morphometry of the human primary visual cortex would be feasible for studying development, intersubject variability and interhemispheric asymmetry if the sulcal depth or a correlated measure such as the intracalcarine surface area would be a precise and reliable estimate of the total volume of the human primary visual cortex. The correlations between total volume of the striate cortex and its intra- and extra-calcarine surface areas were therefore tested in the present observations. The total volume of the striate cortex and the surface areas of its intra-and extracalcarine portions were measured in Nissl-stained serial sections through 20 adult human hemispheres. The intra- and extracalcarine portions of the striate area are not significantly correlated with each other, but correlated with the total volume of the striate cortex. The intracalcarine surface area or the depth of the calcarine sulcus are thus useful parameters for in vivo estimates of the total size of the striate cortex.

Adolescent↗
PubMed1988

The effects of ablation of visual cortex in neonatal rabbits on the organization of retinothalamic and retinopretectal projections.

Primary visual cortex was ablated unilaterally in neonatal rabbits. Following a survival of 2-4 months, retrograde degeneration of the dorsal lateral geniculate nucleus (LGd) was assessed, and reorganization of retinofugal pathways was studied using methods of anretrograde transport of [3H]proline or of horseradish peroxidase. A complete lesion of primary visual cortex resulted in complete retrograde degeneration of the LGd with no sparing of any class of neurons. The terminations of retinofugal axons in the pretectum and thalamus were compared with those observed in normal animals. No major reorganization of ipsilateral retinofugal projections was observed in either the thalamus and pretectum ipsilateral to the ablated cortex, or in the thalamus and pretectum contralateral to the ablated cortex. However, contralateral retinofugal projections to the thalamus and to the pretectum ipsilateral to the ablated cortex were significantly different from normal. In the thalamus, the projections to the lateral posterior nucleus were expanded in area and increased in density. In the pretectum, the projections to the rostral pretectal areas were greatly increased in area, especially in the region of the olivary pretectal nucleus and posterior pretectal nucleus. However, the density of these projections was not increased relative to normal. Consideration of these results in relation to other published data on the anatomical consequences of neonatal visual cortex lesions, both in mammals which show behavioral sparing following neonatal visual cortex lesions and in mammals which, like the rabbit, show no behavioral sparing, suggests that: (1) behavioral sparing may correlate with patterns of survival or death of neurons in the thalamus and retina; and (2) reorganization of retinofugal pathways is not necessarily associated with behavioral sparing.

Animals↗
PubMed1996

Age-related changes in oligodendrocytes in monkey cerebral cortex.

Compared with those in young monkeys (5-12 years of age), oligodendrocytes in area 46 of frontal cortex and primary visual cortex of monkeys over 25 years of age develop bulbous swellings along their processes. Such swellings are filled with characteristic inclusions that resemble age pigment, and other accumulations of these inclusions occur within the cell bodies of the oligodendrocytes in old monkeys. In addition, whereas the oligodendrocytes in young monkeys most commonly occur singly, in old monkeys it is common to find oligodendrocytes in groups or rows. These aggregates are often situated close to capillaries, and in some instances it is found that the cell bodies of the oligodendrocytes abut the basal lamina surrounding the capillary, so that the normally intervening astrocytic glial limiting membrane is absent. In these groups and rows, the perikarya of the oligodendrocytes are squashed close together, and it is common to find tight junctions formed between them. The cortices of the old monkeys also show extensive degeneration of myelin, and it is supposed that this is linked to the changes in the oligodendrocytes. It is hypothesized that the alterations in the oligodendrocyte-myelin system lead to changes in the rates of conduction along fibers whose myelin sheaths are affected, and this may be one of the causes of the behavioral changes associated with aging in primates.

Aging↗
PubMed2004

A [17F]-fluoromethane PET/TMS study of effective connectivity.

We used transcranial magnetic stimulation (TMS) in combination with positron emission tomography (PET) to investigate the effective connectivity of four cortical regions within the same study. By employing [17F]-[CH3F] ([17F]-fluoromethane) as a radiotracer of blood-flow, we were able to obtain increased sensitivity compared to [15O]-H2O for both cortical and subcortical structures. The brain areas investigated were left primary motor cortex, right primary visual cortex, and left and right prefrontal areas. We found that each site of stimulation yielded a different pattern of activation/deactivation consistent with its anatomical connectivity. Moreover, we found that TMS of prefrontal and motor cortical areas gave rise to trans-synaptic activation of subcortical circuits.

Adult↗
PubMed2005

Brain SPECT analysis by 3D-SSP and phenotype of Parkinson's disease.

OBJECTIVES: We hypothesize that the regional pattern of blood flow reduction in the brain is different between tremor-dominant Parkinson's disease (PD) and postural instability gait difficulty (PIGD)-dominant PD. We therefore investigated the association of phenotypes in untreated PD with brain perfusion on SPECT using three-dimensional stereotactic surface projection (3D-SSP) technique. PATIENTS AND METHODS: Thirty-three patients who had PD without dementia (12 men and 21 women with a mean age of 67.1+/-6.4 years) were included in this study. Their symptoms were rated using the Unified Parkinson's Disease Rating Scale (UPDRS). Patients were grouped in two phenotypes: tremor and PIGD-dominant groups based on UPDRS components. Around the same time, all patients were examined by N-isopropyl-p[123I] iodoamphetamine single photon emission computed tomography (123I-IMP SPECT), and obtained images were analyzed with 3D-SSP using an image-analysis software, NEUROSTAT. Data on brain surface perfusion extracted by 3D-SSP analysis were compared between the PD patients and the normal control group. The same comparisons were made for subgroups of PD patients. RESULTS: Cerebral perfusion was decreased at the anterior cingulate cortex and primary visual cortex of the PD patients, and especially by the pixel-by-pixel comparison, perfusion was significantly decreased at the right anterior cingulate cortex compared with the normal controls. In the PIGD-dominant group, more severe hypoperfusion was seen at the same regions. In the tremor-dominant group, significant hypoperfusion was not seen compared with the normal controls. CONCLUSIONS: The regional pattern of blood flow reduction in the brain was found to be different between tremor-dominant PD and PIGD-dominant PD. These regional differences were considered to suggest different and disease-specific combinations of underlying pathophysiological and neurochemical processes.

Aged↗
PubMed2002

Functional anatomy of top-down visuospatial processing in the human brain: evidence from rTMS.

The hypothesis was tested that visuospatial mental imagery relies on processing in the posterior parietal lobe. Using repetitive transcranial magnetic stimulation (rTMS) in a cross-over, sham-controlled design, we compared involvement of right posterior parietal cortex with primary visual cortex. Subjects received rTMS over the parietal and occipital cortices during 20 min, after which they performed a behaviorally controlled visuospatial mental imagery task. Performance deteriorated significantly after rTMS over the parietal, but not occipital, cortex. These data support a causal link between parietal activation and top-down spatial processing.

Adult↗
PubMed2006

Vernier acuity is normal in migraine, whereas global form and global motion perception are not.

PURPOSE: A recent study has demonstrated that some people with migraine display impairments of intermediate stages of motion and form processing. Deficits were identified by using tasks that required that local stimulus attributes be integrated into global percepts. Neurons capable of global processing of form and motion are known to be present in extrastriate cortical areas V4 and V5, respectively. It is not clear from the literature whether deficits of global processing in migraineurs are likely to arise from reduced input to extrastriate cortex from primary visual cortex (V1). The purpose of the study was to compare presumed measures of V1 performance (vernier acuity) to measures of global form and motion perception in migraineurs. METHODS: Thirty migraineurs (17 with aura, and 13 without) and 20 age-matched nonheadache control subjects participated. Intermediate level motion and form perceptions were measured using global dot motion stimuli and Glass patterns, respectively. Vernier stimuli were broad vertical bars composed of small dot elements. Both a static luminance stimulus and a motion defined form vernier stimulus were used. RESULTS: Mean migraine and control group performance were not significantly different for either vernier task (static: t(48)=0.39, P=0.70; motion: t(48)=0.29, P=0.77). Mean migraine group performance was significantly worse than in control subjects for both the global form (t(48)=2.06, P=0.04) and global motion (t(48)=2.87, P<0.01) tasks. CONCLUSIONS: On average, migraineurs demonstrate abnormalities of intermediate stages of both motion and form processing. These abnormalities do not appear to arise from dropout of performance at V1, as vernier acuity was normal in the same individuals.

Adolescent↗
PubMed1996

Fluoro-deoxyglucose positron emission tomography in diffuse Lewy body disease.

We report six demented individuals with pathologically verified diffuse Lewy body disease (DLBD) studied with fluoro-deoxyglucose positron emission tomography (FDG-PET). Three subjects had pure DLBD and three subjects had combined DLBD and Alzheimer's disease (DLBD-AD) pathology. FDG-PET revealed evidence of diffuse cerebral hypometabolism in both pure DLBD and DLBD-AD with marked declines in association cortices with relative sparing of subcortical structures and primary somatomotor cortex, a pattern reported previously in AD. Unlike AD, however, these subjects also had hypometabolism in the occipital association cortex and primary visual cortex. These findings indicate the presence of diffuse cortical abnormalities in DLBD and suggest that FDG-PET may be useful in discriminating DLBD from AD antemortem.

Aged↗
PubMedDate not supplied

[Vision in Alzheimer's disease].

Disturbances of visual function can be the first symptom of Alzheimer disease (AD). Several cases of pathologically proven AD associated with Balint's syndrome have been reported, and, in most of them, an unusual occipito-parietal predominance of neurofibrillary tangles (NFT) and neuritic plaques (NP) was found. Systematic assessment of visual functions in groups of patients presenting with dementia of Alzheimer type (DAT) have shown deficits in several tests, especially in stereo-acuity, in motion sensitivity, in contrast sensitivity for low spatial frequencies and in backward masking sensitivity. In electrophysiological studies, abnormalities of flash visual evoked potentials, contrasting with preservation of pattern visual evoked potentials, have been repeatedly reported. Moreover, decreased glucose metabolism in visual association cortex and in partietal cortex is frequent in DAT. Quantitative studies of regional distribution of NFT and NP in AD indicate constant involvement of associative visual cortex and preservation of primary visual cortex. All these findings, taken together, suggest that the occipito-parietal cortex which constitutes the dorsal visual system and subtends visuo-spatial functions, is selectively affected in AD.

Alzheimer Disease↗
PubMed2006

Prediction of the main cortical areas and connections involved in the tactile function of the visual cortex by network analysis.

We explored the cortical pathways from the primary somatosensory cortex to the primary visual cortex (V1) by analysing connectional data in the macaque monkey using graph-theoretical tools. Cluster analysis revealed the close relationship of the dorsal visual stream and the sensorimotor cortex. It was shown that prefrontal area 46 and parietal areas VIP and 7a occupy a central position between the different clusters in the visuo-tactile network. Among these structures all the shortest paths from primary somatosensory cortex (3a, 1 and 2) to V1 pass through VIP and then reach V1 via MT, V3 and PO. Comparison of the input and output fields suggested a larger specificity for the 3a/1-VIP-MT/V3-V1 pathways among the alternative routes. A reinforcement learning algorithm was used to evaluate the importance of the aforementioned pathways. The results suggest a higher role for V3 in relaying more direct sensorimotor information to V1. Analysing cliques, which identify areas with the strongest coupling in the network, supported the role of VIP, MT and V3 in visuo-tactile integration. These findings indicate that areas 3a, 1, VIP, MT and V3 play a major role in shaping the tactile information reaching V1 in both sighted and blind subjects. Our observations greatly support the findings of the experimental studies and provide a deeper insight into the network architecture underlying visuo-tactile integration in the primate cerebral cortex.

Algorithms↗
PubMed1999

Impairment of depth perception in multiple sclerosis is improved by treatment with AC pulsed electromagnetic fields.

Multiple sclerosis (MS) is associated with postural instability and an increased risk of falling which is facilitated by a variety of factors including diminished visual acuity, diplopia, ataxia, apraxia of gait, and peripheral neuropathy. Deficient binocular depth perception may also contribute to a higher incidence of postural instability and falling in these patients who, for example, find it an extremely difficult task to walk on uneven ground, over curbs, or up and down steps. I report a 51 year old woman with secondary progressive MS who experienced difficulties with binocular depth perception resulting in frequent falls and injuries. Deficient depth perception was demonstrated also on spontaneous drawing of a cube. Following a series of transcranial treatments with AC pulsed electromagnetic fields (EMFs) of 7,5 picotesla flux density, the patient experienced a major improvement in depth perception which was evident particularly on ascending and descending stairs. These clinical changes were associated with an improvement in spatial organization and depth perception on drawing a cube. These findings suggest that in MS impairment of depth perception, which is encoded in the primary visual cortex (area 17) and visual association cortex (areas 18 and 19), may be improved by administration of AC pulsed EMFs of picotesla flux density. The primary visual cortex is densely innervated by serotonergic neurons which modulate visual information processing. Cerebral serotonin concentrations are diminished in MS patients and at least some aspects of deficient depth perception in MS may be related to dysfunction of serotonergic transmission in the primary visual cortex. It is suggested that transcranial AC pulsed applications of EMFs improve depth perception partly by augmenting serotonergic transmission in the visual cortex.

Depth Perception↗
PubMed2006

Model-based analysis of excitatory lateral connections in the visual cortex.

Excitatory lateral connections within the primary visual cortex are thought to link neurons with similar receptive field properties. Here we studied whether this rule can predict the distribution of excitatory connections in relation to cortical location and orientation preference in the cat visual cortex. To this end, we obtained orientation maps of areas 17 or 18 using optical imaging and injected anatomical tracers into these regions. The distribution of labeled axonal boutons originating from large populations of excitatory neurons was then analyzed and compared with that of individual pyramidal or spiny stellate cells. We demonstrate that the connection patterns of populations of nearby neurons can be reasonably predicted by Gaussian and von Mises distributions as a function of cortical location and orientation, respectively. The connections were best described by superposition of two components: a spatially extended, orientation-specific and a local, orientation-invariant component. We then fitted the same model to the connections of single cells. The composite pattern of nine excitatory neurons (obtained from seven different animals) was consistent with the assumptions of the model. However, model fits to single cell axonal connections were often poorer and their estimated spatial and orientation tuning functions were highly variable. We conclude that the intrinsic excitatory network is biased to similar cortical locations and orientations but it is composed of neurons showing significant deviations from the population connectivity rule.

Animals↗
PubMed1989

Intraocular injections of tetrodotoxin reduce transiently expressed acetylcholinesterase activity in developing rat visual cortex.

Geniculo-recipient layers of primary visual cortex in the rat display a transient pattern of acetylcholinesterase (AChE) activity during the second postnatal week of life. Previous work has demonstrated that neonatal enucleations markedly reduce the transient AChE activity in visual cortex. The present studies were undertaken to determine the effects of reduced afferent neural activity on expression of the transient pattern of AChE activity. Rat pups received intraocular injections of tetrodotoxin (TTX) on postnatal days (PND) 3, 5, 7, 9 and 11 and were sacrificed on PND 12. Some animals were enucleated on PND 3. Brain sections were processed for AChE histochemistry and analyzed by optical densitometry. These experiments show that uniocular injections result in a markedly decreased level of AChE activity in layer IV of the medial part of cortical area 17 contralateral to the injected eye. The degree of reduction of AChE activity from repeated TTX injections was similar to the degree of reduction following enucleation on PND 3. Binocular injections of TTX result in a reduction of AChE activity in layer IV throughout cortical area 17, similar to the effects of binocular enucleation on PND 3. Experiments combining injection of horseradish peroxidase along with TTX on PND 11 demonstrate that retinal ganglion cells of TTX injected eyes are still capable of anterograde axonal transport. These data demonstrate that normal innervation and afferent activity are necessary for the transient expression of AChE activity by geniculocortical neurons.

Acetylcholinesterase↗
PubMedDate not supplied

Monocular enucleation prevents retinal ganglion-cell loss following neonatal visual cortex damage in cats.

Damage to primary visual cortex (VC) in young cats leads to severe retrograde degeneration of the dorsal lateral geniculate nucleus (dLGN) and selective transneuronal retrograde degeneration of a class of retinal ganglion cells (RGCs) that have a medium-size soma. Previous studies have shown that "programmed" RGC death associated with normal development in one eye can be attenuated by removal of the other eye, suggesting that binocular interactions can influence developmental RGC death. The present study investigated whether removal of one eye also attenuates the ganglion cell loss that accompanies an early VC lesion. Five one-week-old cats received a unilateral VC lesion (areas 17, 18, and 19), and three of these cats also underwent monocular enucleation at the same time. Two normal control animals also were examined. RGC measurements were made from flat-mounted retinae when the animals were 5 weeks old. Sampling was restricted to a retinal area corresponding to the retinotopic representation included in the VC lesion. Results indicate that there is a marked loss of medium-size RGCs in the hemiretinae projecting to the damaged hemisphere in cats that received a VC lesion alone. However, there is no such loss in VC-lesion animals that also have a monocular enucleation. These results indicate that the transneuronal RGC loss that occurs after an early visual cortex lesion can be influenced by binocular interactions.

Aging↗
PubMed1999

Spatiotemporal patterning of glutamate receptors in developing ferret striate cortex.

We have studied glutamate receptor levels during very early phases of cortical formation by using quantitative in vitro autoradiography to map the expression of NMDA, AMPA and kainate receptors in the developing primary visual cortex of the ferret. NMDA and non-NMDA receptors exhibit very different developmental profiles in primary visual cortex. NMDA receptor density is low at birth and increases throughout the first 2 postnatal months, rising between threefold (layers II/III) and ninefold (layer VI). In contrast, AMPA receptors are abundant at birth and their density remains constant for the first postnatal month, before rising by a maximum of 1.7-fold (layer I) at around the time of eye-opening (postnatal day 32). Kainate receptors are also present in high levels at birth and their expression levels rise in the early postnatal period by between 1. 5-fold (layer I) and threefold (layers V/VI) to a peak just after eye-opening. The proportion of the total ionotropic glutamate receptor binding contributed by NMDA receptors thus rises from 5% at birth to a maximum of 22% at 2 months of age, while the AMPA receptor contribution falls from 87% to 72% over the same period. Below cortex, all three glutamate receptor subtypes are expressed in the subplate region for the first 3 postnatal weeks. These developmental patterns, combined with the fact that AMPA receptors are densely expressed in the proliferative zones underlying presumptive area 17, indicate that non-NMDA receptor expression levels in primary visual cortex are mostly specified much earlier than those of NMDA receptors.

Animals↗