In order to reexamine the cortical distribution of the callosal connection, as well as its topographical relation to the binocular area in the rabbit , the distribution of cortical responses evoked by electrical stimulation of the optic nerve and by direct cortical stimulation of the opposite visual area were studied in thirty immobilized animals.
1. The early response to ipsilateral optic nerve stimulation was similar in latency and waveform to that of the contralateral stimulation, and the area giving this response was determined as the binocular area. The binocular area which was a band of 6-7mm wide extended from the anteromedial to the posterolateral portion across the .
2. Besides the early response, the binocular area showed the later response to ipsilateral optic nerve stimulation. The later response was found to be mediated via the corpus callosum, because it was abolished by cooling the opposited . The interval between the beginning of the early and late responses was comparable with the latency of the transcallosal response elicited by direct cortical stimulation. The transcallosal response was also abolished permanently by cutting the posterior half of the corpus callosum. The area of transcallosal response and the area effective in eliciting this response were found to be in good agreement with each other and with the binocular area.
3. The callosal connection between the two binocular areas was not necessarily homotopic. For diffusely distributed points of stimulation in the binocular area of one cortex the points showing the maximal callosal responses in the other cortex were arranged in a narrow band in the middle of the binocular area. This band, about 1mm wide and running obliquely about 45 degrees to the midline, seemed to correspond to the projection line of the vertical meridian (decussation line) determined by Thompson et al.
These results suggest that the whole binocular area of both hemispheres in the rabbit are interconnected via the corpus callosum, and that the callosal fibers from the binocular area of one cortex terminate most densely in the middle of the opposite binocular area.

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Interaction between responses elicited in the somatosensory cerebral cortex, following single shock stimulation of the visual cerebral area and the superficial radial nerve or the contralateral somatosensory area, was studied in cats anesthetized with chloralose and immobilized with Faxedil. The range of latencies of discharges for the initial spikes from stimulation of the primary varied from 8 to 30msec in the somatosensory cortex. Spike discharges, recorded from a single cortical neuron, were reciprocally interacted by a conditioning-testing procedure and were blocked by a preceding response in some neurons; in other neurons, temporal summation was shown.The depressive effect following the first stimulus was found often to last more than 100 msec. Blocking of spike discharges following stimulation of the was produced by the hyperpolarized afterpotential in the response elicited from stimulation of the sensory nerve. These results suggest that associative volleys from another cortical area modify activity of the somatosensory cortical neuron as depression or temporal summation.

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In this article, we discuss the mathematical analysis of neuronal firing in the brain based on the formulation by Sompolinsky (Sompolinsky, Proc. Natl. Acad. Sci., 1990). We first establish a Fokker-Planck equation corresponding to the original stochastic differential equation-based model, then discuss its well-posedness and global-in-time solvability. The asymptotic stability of the incoherence and some properties from the dynamical system aspect are also discussed.

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Color percept is a subjective experience and, in general, it is impossible for other people to tell someone's color percept. The present study demonstrated that the simple image-classification analysis of brain activity obtained by a functional magnetic resonance imaging (fMRI) technique enables to tell which of four colors the subject is looking at. Our results also imply that color information is coded by the responses of hue-selective neurons in human brain, not by the combinations of red-green and blue-yellow hue components.

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The retrosplenial cortex is located at a critical juncture between the and hippocampal formation. Herein we show how signals traveling from the behave in local circuits of the retrosplenial cortex, using optical recording methods and application of caffeine to rat brain slices. Electrical signals evoked in the primary penetrated into the deep layer of the retrosplenial granular a cortex (RSGa), and propagated further toward postsubiculum and upper layer. Non-NMDA receptor-dependent initial traveling signal from the triggered NMDA receptor-dependent neural oscillation in the RSGa. Oscillatory signals originated from the local area in the deep layer of the RSGa, and the signal spread back and forth toward the and postsubiculum, in addition to spreading toward the upper layer. From the perspective of the RSGa, extrinsic signal inputs from the switched on neural oscillators in the RSGa that deliver NMDA receptor-dependent intrinsic signal outputs. Opening and strengthening of non-NMDA receptor-dependent input pathways from the required NMDA receptor-dependent oscillatory neural activities. These input and output relationships indicate that the retrosplenial cortex may represent an important relay station between the and hippocampal formation. [J Physiol Sci. 2006;56 Suppl:S165]

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In a previous study we investigated the effects of callosal transected lesions made 10 weeks earlier (the 10-week-old callosal transected lesions), either at 3 weeks of age or at 13 weeks of age, upon the acquisition of a black-white (BW) discrimination in rats either with one eye removed at birth (OEB) or at 13 weeks of age (OET) following lesions of the contralateral (CT) to the remaining eye. The CT lesions were performed right before the training of BW discrimination. We found that the 10-week-old callosal transected lesions facilitated the acquisition in OEBs when the callosal lesions were given at 3 weeks of age, and to a lesser extent at 13 weeks of age. We also found that the same type of callosal transected lesions did not do so in OETs, regardless of the age when the callosal lesions were made.
Since the CT lesions inevitably result in damage of the callosal neurons, and lead to de-generation of the callosal afferents in the ipsilateral (IP) , the present study was undertaken to investigate if the CT lesions made 10 weeks earlier (the 10-week-old CT lesions), made either at 3 weeks of age or 13 weeks of age, would affect the acquisition of BW discrimination in OEBs and OETs, like the 10-week-old callosal transected lesions employed in the previous study mentioned above.
We found that in both OEBs and OETs the overall pattern of the facilitation effects of the 10-week-old CT lesions on the acquisition of BW discrimination is, in general, the same as that observed in the 10-week-old callosal transected lesions, but the facilitative effect of the 10-week-old CT lesions is more prevailing and pronounced. The findings are discussed in relation to the possible involvement of neurotrophic factors, released when the CT lesions were made, in synaptic reorganization, and also in relation to the possibility of the increased use of the uncrossed visual pathways.

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Unitary discharges were extracellularly recorded from cortical cells in the rabbit's visual area. Most of the cortical units were responsive to large-field illumination which was turned on and off at about 0.8/sec. Response characteristics of cortical cells were largely similar to those of retinal ganglion cells. One hundred and twenty-nine units which were analyzed successfully were categorized into four classes according to the features of their receptive fields: simple, asymmetric, complex and compound. Especially, compound receptive fields were so named on the basis of the finding that the whole receptive field consisted of three separable complex fields.
A columnar arrangement of cortical neurons was suggested on the basis of the fact that the localization of the receptive fields of units involved in a particular column was almost identical in the visual field. No other common properties to specialize the column was detected. Most of the receptive fields of units which were localized in the visual streak were oval in shape with their long axis horizontal as described in retinal ganglion cells. It is likely that in the rabbit's no more elaborate analysis is made on in-coming visual information, but rather some integrative action is carried out for further processing.

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Electrical activities of the cerebral cortex, spontaneous and evoked, were studied in free behaving cats after both eyes were enucleated. The observa-tions were continued mostly for one month after eye enucleation.
1) The evoked potentials were recorded from the visual and sensorimotor cortices (VC and SMC) before and after eye enucleation, keeping the stimulus parameters unchanged. The postsynaptic component (C₄) of the VC evoked potential to stimulation of the lateral geniculate body or the optic radiation was potentiated after eye emucleation and this potentiation was maintained over 30 post-operative days with a gradual subsidence. The presynaptic component (C₁) was also enhanced after eye enucleation, but this facilitation was far smaller than that of C₄ component and was kept at the same level for a long period of post-enucleation.
2) The strength of potentiation of the VC evoked potential was different depending upon the vigilance level of experimental animals; the strongest potentiation was seen during light sleep and the weakest one during arousal.
3) The post-excitatory recovery process of the deafferented VC was more or less delayed as compared with that of the intact VC.
4) The visual deafferentation did not induce any marked change in the SMC evoked potential.
5) During arousal 10-16c/s waves appeared as a dominant component of the EEG of the deafferented VC and during deep sleep bursts of 14-20c/s spindle-like waves were seen with seemingly normal phasic waves (cortical deep sleep waves). A decrease in the wave components faster than 30 c/s was evident during arousal and deep sleep. In the sensorimotor cortical EEG those fast wave components were increased.

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Spectral response behavior of single units was investigated in the of the unanesthetized macaque monkeys with test stimuli of 0.5° in visual angle.
1. Cortical and optic radiation units were distinguished by the configuration of spikes and spontaneous discharge rate.
2. “On” units responding to a narrow-band of the spectrum were designated as “chromatic” or C type units. Their response maxima were found in three selected regions of the spectrum, orange-red (600-640 mμ), green (520-540 mμ) and blue (460 mμ) respectively. Most units showed one or two submaxima besides the dominant peak in their spectral response curves.
3. Some units responded to a certain limited region of the spectrum with “on” or “off”, but to another with “off” or “on”, thus changing discharge type depending on the wavelengths. These units were designated as “opponent” or O type units.
4. Some units responded to the whole parts of the spectrum, but showed no clear-cut response maxima anywhere in the visible parts of the spectrum.
5. Some “on-off” units and pure “off” units showed two response maxima towards both ends of the spectrum.
6. Two kinds of units, A and B, relating to rod receptors were distinguished. The common feature of these units was that the sensitivity maximum was found at about 500 mμ The unit A had a large receptive field and gave “on-off” discharges. Its photosensitivity is low compared with that of B. The unit B was always linked with photopic units and worked in a range of low intensities in which the linked photopic unit was almost inactive. Its receptive field was very small as compared with that of A.

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We used magnetoencephalography (MEG) to investigate the timing and location of cortical activity related to perceived brightness. Participants passively observed 1 of 5 disks of different luminance (1, 3.2, 10, 32, and 100 cd/m²) during MEG recording, and rated the perceived brightness of the disk before and after the MEG recording. The perceived brightness showed an almost perfect log-linear dependence on luminance intensity. The MEG results showed that the stimulus presentation evoked neuromagnetic responses in the occipital region approximately 150 ms after stimulus onset. The average magnitude of the response was positively correlated with the subjective ratings of perceived brightness as well as the log-scaled stimulus luminance. These findings suggest that the neuromagnetic responses in the occipital cortex reflect subjective brightness perception and that the completes the brightness assignment as early as 150 ms after stimulus onset. The possible clinical application of these results is discussed.

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We report that the mRNAs of two serotonin receptor subtypes, 5-HT1B and 5HT2A, are specifically expressed in the primary (V1) of macaque monkeys and that the strength of expression is controlled in an activity-dependent manner. To elucidate functional roles of these receptors in vivo, we performed electrophysiological recordings of visual responses from 101 V1 neurons with microiontophoretic administration of specific drugs for each receptor subtypes in anesthetized and paralyzed monkeys. The effects of activating these receptors seemed to be bidirectional depending on the activity levels of each neuron. The effect of agonist for 5-HT1B receptor, CP93129, was more facilitatory when the firing rate was high, but the effect was more suppressive when the firing rate was low. The effect of DOI, agonist for 5-HT2A receptor, was opposite in direction. That is, the effect of DOI was more suppressive when the firing rate was high, but more faciliatatory when the firing rate was low. Highly restricted expressions of these receptors and their neural-activity-dependent actions in V1 suggest that 5-HT1B and 5-HT2A receptors complementarily control the gain of input-output relation of V1 with an activity-dependent manner, which could modulate further processing in the cortical network. [J Physiol Sci. 2007;57 Suppl:S100]

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Our ability to recognize surface qualities and infer the materials that make up objects allows us to interact appropriately with the objects. Little is known, however, about the mechanisms of material representation in the brain. In this study, we investigated how information about various materials is processed in the brain using a combination of multivoxel pattern analysis of functional magnetic resonance imaging data and perceptual and image-based physical measures of material properties. We found that information about materials is transformed from image-based representations in early visual areas into perceptual category representations along the ventral pathway.

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The postnatal development of the corticotectal projection was investigated by injecting the axon tracer DiI into the of mouse pups. It was found that DiI-labeled axons arrive at the ipsilateral superior colliculus and enter the optic nerve layer of this structure on postnatal days 3 and 4 (P3-P4). These corticotectal axons extend into the caudal end of the superior colliculus on P4 and give off small collateral branches that ascend vertically to the superficial gray layer. During the first two postnatal weeks, the collateral branches do not form a demarcated terminal zone, but rather diffusely spread within the superficial gray layer of the superior colliculus. These collateral branches continue to dichotomize and form a bright terminal zone within the superficial gray layer on P11. The terminal zone decreases in size during the second and third postnatal weeks, and appears to be of the same size when compared with the adult counterpart by P19. The terminal zone of the corticotectal axons from the is established by P19. In parallel with the maturation of the terminal zone of the corticotectal projection, the distal segment of the corticotectal axons is lost during the second postnatal week. We conclude that the growing tips of the corticotectal axons do not strictly project to their future terminal zone within the superior colliculus, and 'misdirected' axons are eliminated during the early postnatal period.

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We studied the postnatal development of the corticopontine tract in mice by the injection of the axon tracer DiI into the . In the postnatal day (P) 0.5 mouse, labeled pyramidal tract fibers pass through the internal capsule and cerebral peduncle, grow over the basilar pontine gray, and enter into the medullary pyramid (in this study, P0 refers to the first 24 hours after birth). Small collateral branches arise from these pyramidal tract fibers on P0.5-1.0, and elongate quickly into the basilar pontine gray around P2-4. These collateral branches give off many secondary branches on P4 and form the bright terminal zone in the rostral portion of the lateral basilar pontine gray on P9. In the P16 mouse, this terminal zone is more restricted, suggesting, on the basis of the anterograde DiI labeling technique, that the visual corticopontine projection matures by P16. DiI-labeled pyramidal tract fibers distal to the branching point of the pontine collaterals are found during the postnatal two weeks, but disappear by the later stages. We conclude that the visual corticopontine tract develops as collateral branches of the transient pyramidal tract fibers arising from the of the mouse, as just described in the rat (O'Leary and Terashima, Neuron 1: 901-910,1988).

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There is a shift in ocular dominance of cells recorded in the which occurs after closure of one eye during a critical period lasting from eye opening to puberty. Three criteria distin-guish factors that are crucially related to ocular dominance plasticity: 1) the factor should be more concentrated or active at the peak of the critical period; 2) dark rearing, which makes the cortex less plastic early in the critical period and more plastic late in the critical period, should have a similar effect on the factor, and 3) antagonists or inhibitors of the factor should block ocular dominance plasticity. The second criterion can be used to distinguish activity-related factors that may simply increase or de-crease with development from factors that are more specifically related to plasticity. Two factors cur-rently fulfill these criteria, namely N-methyl-D-asparate (NMDA) receptors and protein kinase A (PKA). PKA and NMDA receptors are linked through calcium, since calcium influx through the NMDA receptor increases the production of cyclic AMP by calcium-sensitive adenylate cyclase, which in turn activates PKA. PKA is specifically involved, since protein kinase G and protein kinase C antagonists do not inhibit ocular dominance plasticity. However, NMDA agonists and PKA activators by themselves are not known to bring back plasticity. Thus there may be two or more pathways for ocular dominance plasticity acting in parallel with each other: for example, metabotropic glutamate receptors may act in parallel with NMDA receptors to change calcium levels within the cell.

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We can summarize the transformation of color signals in the early stages as follows. First, color is represented by the relative activities of three types of cone photoreceptors. Secondly, linear combination of cone signals occurs in regular manners and color is represented by two axes, namely L–M and S axes (two-axes representation). Finally, signals tuned to various directions in the chromaticity diagram starts to be formed in V1 resulting in hue selective neurons as well as neurons selective for saturation. We can call this third stage as having “multi-axes representation of color”. Color representation based on hue and saturation seems a principle way ubiquitous across different areas in the cortical visual areas.

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The purpose of the present study was to investigate the organization of choline acetyltransferase (ChAT)-immunoreactive (IR) fibers in the

of the microbat, using standard immunocytochemistry and confocal microscopy. ChAT-IR fibers were distributed throughout all layers of the , with the highest density in layer III and the lowest density in layer I. However, no ChAT-IR cells were found in the microbat . ChAT-IR fibers were classified into two types: small and large varicose fibers. Previously identified sources of cholinergic fibers in the mammalian , the nucleus of the diagonal band, the substantia innominata, and the nucleus basalis magnocellularis, all contained strongly labeled ChAT-IR cells in the microbat. The average diameter of ChAT-IR cells in the nucleus of the diagonal band, the substantia innominata, and the nucleus basalis magnocellularis was 16.12 μm, 13.37 μm, and 13.90 μm, respectively. Our double-labeling study with ChAT and gamma-aminobutyric acid (GABA), and triple labeling with ChAT, GABA, and post synaptic density 95 (PSD-95), suggest that some ChAT-IR fibers make contact with GABAergic cells in the microbat . Our results should provide a better understanding of the nocturnal bat visual system.

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Coding of color in the retina and lateral geniculate nucleus is dominated by cone opponency, and selectivities cluster around the corresponding color space axes. In the

, a more distributed representation for color stimuli is found. Comparison of this population code for color with the coding of other visual features such as orientation indicates similar coding mechanisms for both features. Further similarities can be observed with respect to contextual interactions. The visual context affects processing and perception of both color and orientation, and results of psychophysical measurements indicate that the properties of these interactions in both domains are similar. These findings suggest that the makes use of the same neural mechanisms for the processing of color as for other visual features.

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