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PubMed1987

Biochemical evidence for glutamate and/or aspartate as neurotransmitters in fibers from the visual cortex to the lateral posterior thalamic nucleus (pulvinar) in rats.

The effects of visual cortex ablation on several neurotransmitter parameters in the lateral thalamic nucleus (pulvinar) in rats have been investigated. We found a 57% decrease in high affinity uptake of D-[3H]aspartate in the pulvinar after ablation of the ipsilateral visual cortex. The KCl-evoked release of exogenous D-[3H]aspartate and endogenous glutamate were decreased by 33 and 37%, respectively. Moreover, the contents of endogenous glutamate and aspartate were decreased by 35%, each. The glutamate decarboxylase and choline acetyltransferase activities and the contents of other amino acids were not affected by the lesion. Our biochemical data indicate that glutamate and/or aspartate may be transmitters in the fibers from visual cortex to pulvinar in rats.

Animals↗
PubMed2000

The effects of binocular suture and dark rearing on the induction of c-fos protein in the rat visual cortex during and after the critical period.

It has been demonstrated in kittens that binocular lid suture has more deleterious and irreversible effects on plasticity of the developing visual system than rearing in complete darkness. The present study using immunocytochemistry focuses on the effects of the two types of visual deprivation on the inducibility of c-fos protein in visual cortical neurons of rats. Rats were subjected to binocular suture or dark rearing for 1 week during (postnatal days 14-21; P14-P21) and after (P50-P57) the critical period for activity-dependent modifiability of cortical ocular dominance. In rats of both age groups reared in the normal light-dark condition, only a small number of Fos-immunoreactive neurons was obtained in the visual cortex. By contrast, in dark-reared pups and adult rats, numerous c-fos neurons were detected in the layers II-IV and VI of the visual cortex following a brief light exposure (1 h). In rats of both ages subjected to binocular suture, Fos neurons were detected in the same layers as in the dark-reared rats, but significantly less in number. We speculate that the reduced plasticity of the visual cortex in the rats subjected to binocular suture may be due partly to the repressed AP-1 activity in visual cortical neurons. No significant difference was detected in c-fos expression in the visual cortex between visually manipulated pups and adult rats.

Aging↗
PubMed2005

Evaluation of extraocular electrodes for a retinal prosthesis using evoked potentials in cat visual cortex.

OBJECTIVE: To assess the efficacy of a device using extraocular electrodes as a retinal prosthesis by evaluating the responses evoked in the visual cortex to electrical stimulation. METHODS: In anaesthetised cats, a lateral orbital dissection and ipsilateral parietal craniotomy was performed. Two extraocular retinal prosthesis (ERP) disc electrodes were sutured to the sclera on the lateral and superior aspects of the globe. Retinal stimulation was performed with charge-balanced constant-current pulses. Potentials evoked in the visual cortex were measured with a ball electrode placed on the lateral gyrus after removal of the dura. RESULTS: Stable attachment of the ERP electrodes to the globe was achieved with scleral sutures. Visual cortex responses were recorded with the electrodes in bipolar and monopolar configurations. The evoked response consisted of an early component with a peak around 8 ms, and a late component with a peak after 50 ms. Thresholds for evoking a response occurred at current intensities as low as 500 microA. Through extrapolation from evoked response amplitude data, thresholds as low as 300 microA were calculated. Cathodal monopolar stimulation demonstrated lower thresholds than anodal stimulation for evoking cortical responses. CONCLUSIONS: The ERP electrodes can be easily attached to the globe and are effective in electrically stimulating the retina, evoking responses in the primary visual cortex. Threshold charge-density was within safe limits for neural stimulation.

Animals↗
PubMed2005

Rapid eye movement sleep deprivation in post-critical period, adolescent rats alters the balance between inhibitory and excitatory mechanisms in visual cortex.

Suppression of rapid eye movement sleep (REMS) in developing animals has both anatomical and physiological consequences. We have recently shown that initiating REMS deprivation (REMSD) prior to the end of the critical period in young rats delays termination of the critical period (CP) in visual cortex, and, consequently, the synaptic plasticity mechanisms that support a developmentally regulated form of long-term potentiation (LTP) are maintained in an immature state [J.P. Shaffery, C.M. Sinton, G. Bisset, H.P. Roffwarg, G.A. Marks, Rapid eye movement sleep deprivation modifies expression of long-term potentiation in visual cortex of immature rats, Neuroscience, 110 (2002) 431-443]. In CP animals, high-frequency, theta burst stimulation (TBS) directed at the white matter (WM) below visual cortex produces LTP in the post-synaptic cells in layer II/III (LTPWM-III). However, LTPWM-III can be induced in cortical tissue taken from REMS-deprived animals for up to a week beyond the usual end of the CP [J.P. Shaffery, C.M. Sinton, G. Bisset, H.P. Roffwarg, G.A. Marks, Rapid eye movement sleep deprivation modifies expression of long-term potentiation in visual cortex of immature rats, Neuroscience, 110 (2002) 431-443]. Further, in post-CP, adolescent animals (as late as postnatal day 60), REMSD appears to unmask synaptic plasticity mechanisms that allow for production of developmentally regulated LTPWM-III [J.P. Shaffery, J. Lopez, G. Bissette, H.P. Roffwarg, Rapid eye movement sleep deprivation revives a form of developmentally regulated synaptic plasticity in the visual cortex of post-critical period rats, Neurosci Lett., (2005), in press]. It has been proposed that REMSD's effects on production of LTPWM-III result from a reduction in efficiency of the inhibitory mechanisms thought to precipitate termination of the CP of brain development [J.P. Shaffery, J. Lopez, G. Bissette, H.P. Roffwarg, Rapid eye movement sleep deprivation revives a form of developmentally regulated synaptic plasticity in the visual cortex of post-critical period rats, Neurosci Lett., (2005), in press]. In this study we tested the hypothesis that low-frequency stimulation (LFS) of the fibers of the WM, which usually produces the related form of synaptic plasticity, long-term depression (LTD), will also reflect the reduction in inhibitory tone. We report here that LFS protocols, which in normally sleeping, adolescent rats usually produce either LTD or no change in response magnitude, in REMS-deprived, adolescent rats are more likely to produce LTP.

Age Factors↗
PubMed1977

Responses of single cells in cat visual cortex to prolonged stimulus movement: neural correlates of visual aftereffects.

1. The activity of single cortical cells in area 17 of anesthetized and unanesthetized cats was recorded in response to prolonged stimulation with moving stimuli. 2. Under the appropriate conditions, all cells observed showed a progressive response decrement during the stimulation period, regardless of cell classification, i.e., simple, complex, or hypercomplex. 3. The observed response decrement was shown to be largely cortical in origin and could be adequately described with an exponential function of the form R = Rf +(R1-Rf)e-t/T. Time constants derived from such calculations yielded values ranging from 1.92 to 12.45 s under conditions of optimal-stimulation. 4. Most cells showed poststimulation effects, usually a brief period of reduced responsiveness that recovered exponentially. Recovery was essentially complete in about 5-35 s. 5. The degree to which stimuli were effective at inducing response was shown to have significant effects on the magnitude of the response decrement. 6. Several cells showed neural patterns of response and recovery that suggested the operation of intracortical inhibitory mechanisms. 7. A simple two-process model that adequately describes the behavior of all the studied cells is presented. 8. Because the properties of the cells studied correlate well with human psychophysical measures of contour and movement adaptation and recovery, a causal relationship to similar neural mechanisms in humans is suggested.

Anesthesia, General↗
PubMed2003

[Changes in electrophysiological and morphological properties of neurons during the development of the visual cortex in the rat].

To investigate the intracellular mechanism of activity-dependent synapses formation and redistribution, we studied the electrophysiological and morphological characteristics of neurons of the developing visual cortex, and observed the level of synchronism of age and changes in the properties. Whole cell patch-clamp recordings and intracellular biocytin staining were used to record postsynaptic currents (PSCs) from neurons in the visual cortex of Sprague-Dawley rats (postnatal d 4-28). The histological processing was made. There were three types of PSCs in 156 cells: silent response, monosynaptic response and polysynaptic response, during the first developmental month. Before eyes opened the number of the neurons with the silent response (57.3%) was significantly higher than that after the eyes opened (11.9%) (P<0.001). However, the incidence of polysynaptic PSCs increased from 12.4% before eyes opened to 28.9% after eyes opened (P<0.01). During postnatal week 1, all cells were classified as immature. The immature cells had very high input resistances (R(N)>1.0 G Omega), low amplitude (-0.87 mA) and short decay time (-0.98 ms). During postnatal week 4, all cells were mature with lower input resistance (R(N)<310 M Omega), larger amplitude (-66 mA), and longer decay time (-225 ms). From postnatal weeks 1 to 3, the cells had electrophysiological properties that were intermediate between the immature and mature types of cells. With biocytin intracellular staining, five types of neurons were obtained: pyramidal cells, satellite cells, basket cells, neuroglial cells and immature cells. On the basis of their electrophysiological and morphological characteristics, pyramidal cells were classified into three categories: immature, intermediate, and mature cell types. During postnatal week 1, cells were immature with very high input resistance. Morphologically immature cells had short simple dendritic arborizations which incompletely penetrated the layer where the cell body lies. From postnatal weeks 2 to 4, the cells were mature with low input resistance. They were morphologically more complex with dendritic arborizations which completely penetrated the whole layers of the visual cortex. From postnatal weeks 1 to 2, a third, intermediate cell type had electrophysiological properties that were intermediate between the immature and mature cell types. Three distinctive types of pyramidal cells in visual cortex only co-exist during postnatal weeks 1 to 2. Data show that activity-dependent synapes are formed and integrated into local neuronal networks with visual stimulation. In the critical period of visual development, the level of synchronism of age and changes in electrophysiological and morphological properties in the visual cortex is higher than that in the subcortex.

Animals↗
PubMed1992

Proportion of glutamate- and aspartate-immunoreactive neurons in the efferent pathways of the rat visual cortex varies according to the target.

Immunohistochemistry, with antisera directed against glutamate (Glu) or aspartate (Asp), was combined with wheat germ agglutinin-horseradish peroxidase (WGA-HRP) histochemistry to examine the distribution, morphology, and proportions of Glu- and Asp-containing neurons that give rise to corticofugal and callosal projections of the rat visual cortex. WGA-HRP injections in the dorsal lateral geniculate nucleus resulted in retrograde labelling of small and medium-sized cells throughout layer VI of the visual cortex. Of these cells, 60% were also Glu-immunoreactive and 61% Asp-positive. WGA-HRP injections in the superior colliculus labelled large and medium-sized neurons in the upper portion of layer V of the visual cortex. Of these cells, 46% were also stained for Glu and 66% for Asp. Injections in the pontine nuclei resulted in retrograde labelling of cells in the deeper part of cortical layer V. Retrogradely labelled cells, which were also immunoreactive for Glu or Asp, were large pyramidal cells. Corticopontine neurons, which were also Glu-positive, accounted for 42% of the total number of WGA-HRP labelled cells, whilst for Asp-positive neurons this percentage was 51%. Finally, after injections in the visual cortex, retrogradely labelled small and medium-sized cells were found throughout layers II-VI in the contralateral visual cortex. Of these neurons, 38% were also labelled for Glu while 49% were also Asp-immunoreactive. The present results demonstrate that substantial proportions of projection neurons in the rat visual cortex are immunoreactive for Glu or Asp, suggesting that these excitatory amino acids are the major transmitters used by the cortical efferent systems examined. Furthermore, the proportions of these immunoreactive neurons in the efferent pathways vary according to the target.

Animals↗
PubMed1992

[Visual recognition processes in monkeys and their neuronal correlates in the visual cortex: the effect of an M-cholinoreceptor blocker].

Unit activity was studied in the visual cortex prior to and after amyzyl administration in monkeys trained for delayed visual differentiation of different colour stimuli. The data obtained suggests that the cholinergic mechanisms of the visual cortex are involved in the visual recognition and seem to play different functional roles at different stages of the behaviour.

Acoustic Stimulation↗
PubMed1986

Visual cortex controls retinal output in the rat.

The first objective of the present investigation was to shed more light on corticofugal influences on the retina by providing an analysis of the type and proportion of retinal ganglion cells that are affected by cooling the visual cortex in rats. The second question was to determine if the pretectum participates in functional cortico-retinal relationships. In urethane-anesthetized and paralyzed hooded rats, axonal activity of retinal ganglion cells was recorded with glass micropipettes at optic chiasm level. Units were classified as ON, OFF, suppressed-by-light and concentric. The visual cortex was inactivated by cooling its surface with a 4 mm2 steel probe using the Peltier effect. The pretectum was blocked with microinjections of 50 to 100 nanoliters of cobalt ions, lidocaine hydrochloride or KCl. The inactivations and recoveries at both sites were monitored by simultaneously recording evoked field potentials. Interrupting corticofugal impulses caused modifications of the evoked discharge pattern in all types of cells. The concentric type was the group least affected by cortical cooling. A common trend emerged suggesting that cooling of the visual cortex led to an enhancement of the initial evoked excitation. This was often followed by an enhanced post-excitatory inhibition. The Pearson coefficient allowed us to measure the degree of similarity between two histograms. When all data were pooled, a weak correlation between control and test histograms (r = 0.29, N = 56) was found, while the control and recovery patterns averaged a correlation of more than twice that size (r = 0.68). In a second series of experiments, the pretectum and visual cortex (VC) were simultaneously inactivated. It is shown that both sites summed their influence and acted synergistically upon the pattern of ganglion cell responses. The results strongly suggest that the visual cortex exerts a major control over the response pattern of thirty percent of retinal ganglion cells, and that the pretectum participates in the functional relationships between visual cortex and retina in rats.

Animals↗
PubMedDate not supplied

Adaptation to left-right reversed vision rapidly activates ipsilateral visual cortex in humans.

The brain mechanisms of adaptation to visual transposition are of increasing interest, not only for research on sensory-motor coordination, but also for neuropsychological rehabilitation. Sugita [Nature 380 (1996) 523] found that after adaptation to left-right reversed vision for one and a half months, monkey V1 neurons responded to stimuli presented not only in the contralateral visual field, but also in the ipsilateral visual field. To identify the underlying neuronal mechanisms of adaptation to visual transposition, we conducted fMRI and behavioral experiments for which four adult human subjects wore left-right reversing goggles for 35/39 days, and investigated: (1) whether ipsilateral V1 activation can be induced in human adult subjects; (2) if yes, when the ipsilateral activity starts, and what kind of behavioral/psychological changes occur accompanying the ipsilateral activity; (3) whether other visual cortices also show an ipsilateral activity change. The results of behavioral experiments showed that visuomotor coordinative function and internal representation of peripersonal space rapidly adapted to the left-right reversed vision within the first or second week. Accompanying these behavioral changes, we found that both primary (V1) and extrastriate (MT/MST) visual cortex in human adults responded to visual stimuli presented in the ipsilateral visual field. In addition, the ipsilateral activity started much sooner than the one and a half months, which had been expected from the monkey neurophysiological study. The results of the present study serve as physiological evidence of large-scale, cross-hemisphere, cerebral plasticity that exists even in adult human brain.

Adaptation, Physiological↗
PubMed1996

Nerve growth factor induced modification of presynaptic elements in adult visual cortex in vivo.

Nerve growth factor (NGF) has been shown to play important roles in neuronal survival, growth and differentiation. Recently, we have found that intracortical infusion of NGF into adult cat visual cortex can recreate ocular dominance plasticity, suggesting that NGF is also involved in activity-dependent modification of synaptic connectivity in the adult brain. To further explore the mechanisms of NGF-induced plasticity in adult visual cortex, we studied two presynaptic markers: GAP-43 and synaptophysin. Immunocytochemical staining showed that NGF-treatment of adult visual cortex selectively increased the level of the phosphorylated form of GAP-43, while the total level of GAP-43 was not changed. These results demonstrate that NGF-treatment stimulates phosphorylation processes of GAP-43 in vivo. In addition, NGF-treatment of adult visual cortex increased the level of synaptophysin immunoreactivity. Since the phosphorylated form of GAP-43 is known to be enriched in the membrane skeleton of growth cones and of developing synapses, and the phosphorylation of GAP-43 has been linked with events that underlie synaptic plasticity, and since synaptophysin is a major component of presynaptic vesicles, our results suggest that NGF-treatment of adult visual cortex modulates presynaptic terminals, possibly by inducing axonal sprouting and formation of new synapses, and that these changes may play a role in the NGF-induced functional plasticity.

Animals↗
PubMed1981

Receptive field properties of neurons in the visual cortex of the rat.

The receptive field properties of neurons were examined in the visual cortex, area 17, of Long--Evans pigmented rats. Visually responsive cells comprised 90% of cells recorded in area 17. Five percent of these cells responded only to stationary stimuli, while the remaining responded to both stationary and moving stimuli or only to movement. Cells of the latter category were classified as complex (44%), simple (27%), hypercomplex (13%) or non-oriented (16%). The results presented here show that, contrary to existing reports, neurons in the rat visual cortex have well-defined receptive field properties.

Animals↗
PubMed1994

Ocular dominance column development: strabismus changes the spacing of adjacent columns in cat visual cortex.

To investigate the role of visual experience for the gross layout of ocular dominance (OD) columns in the visual cortex, I compared the respective patterns in normally raised and strabismic cats. OD domains were visualized by (1) transneuronal labeling of the afferents from the left or right eye with intraocular 3H-proline injections or (2) 14C-2-deoxyglucose autoradiography after monocular visual stimulation in awake animals. To obtain the complete pattern of OD columns, flat-mount sections were prepared from the unfolded cortical hemispheres. Eliminating correlated activity between the two eyes by making the animals strabismic influenced the gross layout of the OD domains. In area 17, OD domains become more sharply delineated than in normal animals and spaced more widely. Spatial frequency analyses revealed a mean spacing of adjacent columns of 1100-1300 microns in strabismic and of 800-1000 microns in normal cats. In area 18, the spacing of the ocular dominance domains is larger than in area 17 for both normal and strabismic cats (1500-1650 microns), but little influenced by strabismus. These results indicate that in area 17 decreased correlation of activity between the eyes alters the periodicity of OD columns. In addition, these observations suggest that not only the segregation of afferents into distinct columns but also the final expression of the columnar grid is influenced by visual experience, and in particular by the temporal patterning of neural activity. This is further evidence for the hypothesis that the development of OD columns is governed by activity-dependent self-organizing principles.

Animals↗
PubMed1974

Cell structure and function in the visual cortex of the cat.

1. The organization of the visual cortex was studied with a technique that allows one to determine the physiology and morphology of individual cells. Micro-electrodes filled with the fluorescent dye Procion yellow were used to record intracellularly from cells in area 17 of the cat. The visual receptive field of each neurone was classified as simple, complex, or hypercomplex, and the cell was then stained by the iontophoretic injection of dye.2. Fifty neurones were successfully examined in this way, and their structural features were compared to the varieties of cell types seen in Golgi preparations of area 17. The majority of simple units were stellate cells, whereas the majority of complex and hypercomplex units were pyramidal cells. Several neurones belonged to less common morphological types, such as double bouquet cells. Simple cells were concentrated in layer IV, hypercomplex cells in layer II + III, and complex cells in layers II + III, V and VI.3. Electrically inexcitable cells that had high resting potentials but no impulse activity were stained and identified as glial cells. Glial cells responded to visual stimuli with slow graded depolarizations, and many of them showed a preference for a stimulus orientation similar to the optimal orientation for adjacent neurones.4. The results show that there is a clear, but not absolute correlation between the major structural and functional classes of cells in the visual cortex. This approach, linking the physiological properties of a single cell to a given morphological type, will help in furthering our understanding of the cerebral cortex.

Action Potentials↗
PubMed1991

Development of the laminar distribution of thalamocortical axons and corticothalamic cell bodies in the visual cortex of the wallaby.

The distribution of afferents from the dorsal lateral geniculate nucleus (LGNd) and the lateral posterior nucleus (LP) and of cell bodies projecting to these nuclei has been studied in the visual cortex of the wallaby (Macropus eugenii) throughout development to determine how the characteristic laminar distribution of afferents and efferents of the mature cortex is achieved. Young are born after 26-28 days of gestation and do not open their eyes until around 140 days after birth. Horseradish peroxidase conjugated to wheatgerm agglutinin was injected in the visual thalamus in adults and in pouch young aged from 22 days after birth, just after thalamic axons first reach the visual cortex, to 118 days, when cortical lamination resembles the adult. From 22 to 65 days, the developing visual cortex consists of a marginal zone (MZ), cortical plate (CP), and intermediate zone (IZ) including the superficial subplate (SP), subventricular zone, and ventricular zone. There is a thin compact cell zone (CCZ) at the top of the CP and below it a less densely packed region that increases in thickness with age. Retrogradely labelled cells in two bands were first seen at 40 days, one in the CCZ and the other at the base of the CP. Two bands of cells were seen at all subsequent times if the injection covered both LGNd and LP, and by 76 days, these cells were located within cytoarchitectonically recognizable layers V and VI. Anterograde label prior to 45 days was distributed densely and evenly throughout the IZ and the CP up to the CCZ. Label in MZ was first seen at 25 days and was substantial by 54 days. Anterograde label than became gradually reduced in the IZ, whereas in the CP it remained evenly and densely distributed until 82 days. At this age, coincident with the emergence of layer IV, label within the CP first showed variations in density and by 99 days was concentrated over layer IV and, to a lesser extent, over layer VI. By 118 days label resembled the adult after injections covering both LGNd and LP, with label concentrated in layer I, IV, and VI with a less dense projection to lower layer III and upper layer V. There is a relatively earlier initial ingrowth of axons into the visual cortex in the wallaby and throughout development thalamocortical axons appear to be more widely distributed in the depth of the visual cortex than has been demonstrated for placental mammals.(ABSTRACT TRUNCATED AT 400 WORDS)

Aging↗
PubMed1984

[Afferent connections of the visual cortex in the albino mouse].

The afferent connections of the visual cortex of the albino mouse have been studied with the aid of the enzyme Horseradish peroxidase (HRP). Ipsilateral HRP-positive cells have been found in areas 17, 18a, 18b and the temporal cortex; in the contralateral cortex, they were located in areas 17, 18a and in the temporal cortex, the greatest number of labeled cells being situated near the 17/18a border. Apart from the Nucleus dorsalis corporis geniculati, more thalamic nuclei project to the visual cortex; the Nucleus lateralis thalami, pars posterior contains regularly positive cells, whereas other nuclei (Nucleus lateralis thalami, Nucleus medialis thalami, pars lateralis, Nucleus ventralis thalami, pars lateralis and pars medialis) only in some cases show labeled cells. Sporadically, a few labeled cells were observed in the Nuclei medialis and lateralis tractus optici, Nucleus praetectalis thalami and the Nucleus centralis medialis. The afferent connections from the brain stem have not always been visualized. The most frequent afferent connections come from the Nucleus dorsalis tegmenti pontis, followed by the Nucleus reticularis tegmenti pontis and the Nucleus Locus coerulei. Occasionally, a few HRP-positive cells were found in the Nucleus ventralis tegmenti, Nucleus raphe dorsalis, Nucleus parabrachialis lateralis and in the Nucleus centralis superior. The morphology of the projecting neurons in different centres was studied and compared after HRP-filling and after Golgi-impregnation.

Animals↗
PubMed1996

Evidence for greater sight in blindsight following damage of primary visual cortex early in life.

This review compares the behavioral, physiological and anatomical repercussions of lesions of primary visual cortex incurred by developing and mature humans, monkey and cats. Comparison of the data on the repercussions following lesions incurred earlier or later in life suggests that earlier, but not later, damage unmasks a latent flexibility of the brain to compensate partially for functions normally attributed to the damaged cortex. The compensations are best documented in the cat and they can be linked to system-wide repercussions that include selected pathway expansions and neuron degenerations, and functional adjustments in neuronal activity. Even though evidence from humans and monkeys is extremely limited, it is argued on the basis of known repercussions and similarity of visual system organization and developmental sequence, that broadly equivalent repercussions most likely occur in humans and monkeys following early lesions of primary visual cortex. The extant data suggest potentially useful directions for future investigations on functional anatomical aspects of visual capacities spared in human patients and monkeys following early damage of primary visual cortex. Such research is likely to have a substantial impact on increasing our understanding of the repercussions that result from damage elsewhere in the developing cerebral cortex and it is likely to contribute to our understanding of the remarkable ability of the human brain to adapt to insults.

Adaptation, Physiological↗
PubMed1999

Functional magnetic resonance image-guided surgery of tumors in or near the primary visual cortex.

OBJECTIVE: To assess the accuracy of functional magnetic resonance imaging (fMRI) of the primary visual cortex in patients undergoing surgery for tumors in the occipital lobe. METHODS: Two patients with nondominant occipital lobe tumors were studied, one with a solitary lung metastasis and another with radiation necrosis after radiosurgery for a low-grade astrocytoma. At surgery, visual evoked potentials (VEPs) were stimulated using Light-emitting-diode goggles and recorded using cortical grids placed immediately after brain exposure. The location of the peak VEP was compared to that predicted by the registered functional scan. RESULTS: In each case, the epicenter of visual activation as represented on the registered fMRI corresponded to the site of peak VEP recording. Prediction error for the visual cortex, measured in patient 1, was 1.0 mm. Visual confirmation showed the registration in the second patient to be accurate as well. CONCLUSION: As previously demonstrated for sensorimotor fMRI, visual fMRI accurately predicts the location of the primary visual cortex. Additional confirmation is expected with more clinical experience.

Adult↗