SEARCH · PubMed Health

Results for “cortex”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

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

At least 1,027 records · Page 57Linked to original sources

PubMed2006

Why does brain damage impair memory? A connectionist model of object recognition memory in perirhinal cortex.

Object recognition is the canonical test of declarative memory, the type of memory putatively impaired after damage to the temporal lobes. Studies of object recognition memory have helped elucidate the anatomical structures involved in declarative memory, indicating a critical role for perirhinal cortex. We offer a mechanistic account of the effects of perirhinal cortex damage on object recognition memory, based on the assumption that perirhinal cortex stores representations of the conjunctions of visual features possessed by complex objects. Such representations are proposed to play an important role in memory when it is difficult to solve a task using representations of only individual visual features of stimuli, thought to be stored in regions of the ventral visual stream caudal to perirhinal cortex. The account is instantiated in a connectionist model, in which development of object representations with visual experience provides a mechanism for judgment of previous occurrence. We present simulations addressing the following empirical findings: (1) that impairments after damage to perirhinal cortex (modeled by removing the "perirhinal cortex" layer of the network) are exacerbated by lengthening the delay between presentation of to-be-remembered items and test, (2) that such impairments are also exacerbated by lengthening the list of to-be-remembered items, and (3) that impairments are revealed only when stimuli are trial unique rather than repeatedly presented. This study shows that it may be possible to account for object recognition impairments after damage to perirhinal cortex within a hierarchical, representational framework, in which complex conjunctive representations in perirhinal cortex play a critical role.

Brain Injuries↗

PubMed2004

Interaction between perirhinal and medial prefrontal cortex is required for temporal order but not recognition memory for objects in rats.

The present study investigated the roles of the perirhinal cortex, medial prefrontal cortex, and intrahemispheric interactions between them in recognition and temporal order memory for objects. Experiment 1 assessed the effects of bilateral microinfusions of the sodium channel blocker lidocaine into either the anterior perirhinal or medial prefrontal cortex immediately before memory testing in a familiarity discrimination task and a recency discrimination task, both of which involved spontaneous exploration of objects. Inactivation of the perirhinal cortex disrupted performance in both tasks, whereas inactivation of the medial prefrontal cortex disrupted performance in the recency, but not the familiarity, discrimination task. In a second experiment, the importance of intrahemispheric interactions between these structures in temporal order memory were assessed by comparing the effects of unilateral inactivation of either structure alone with those of crossed unilateral inactivation of both structures on the recency discrimination task. Crossed unilateral inactivation of both structures produced a significant impairment, whereas inactivation of either structure alone produced little or no impairment. Collectively, these findings suggest that the perirhinal cortex, but not the medial prefrontal cortex, contributes to retrieval of information necessary for long-term object recognition, whereas both structures, via intrahemispheric interactions between them, contribute to retrieval of information necessary for long-term object temporal order memory. These data are consistent with models in which attributed information is stored in posterior cortical sites and supports lower-order mnemonic functions (e.g., recognition memory) but can also be retrieved and further processed via interactions with the prefrontal cortex to support higher-order mnemonic functions (e.g., temporal order memory).

Animals↗

PubMed2006

Transient suppression of ipsilateral primary somatosensory cortex during tactile finger stimulation.

The whole human primary somatosensory (SI) cortex is activated by contralateral tactile stimuli, whereas its subarea 2 displays neuronal responses also to ipsilateral stimuli. Here we report on a transient deactivation of area 3b of the ipsilateral SI during long-lasting tactile stimulation. We collected functional magnetic resonance imaging data with a 3 T scanner from 10 healthy adult subjects while tactile pulses were delivered at 1, 4, or 10 Hz in 25 s blocks to three right-hand fingers. In the contralateral SI cortex, activation [positive blood oxygenation level-dependent (BOLD) response] outlasted the stimulus blocks by 20 s, with an average duration of 45 s. In contrast, a transient deactivation (negative BOLD response) occurred in the ipsilateral rolandic cortex with an average duration of 18 s. Additional recordings on 10 subjects confirmed that the deactivation was not limited to the right SI but occurred in the SI cortex ipsilateral to the stimulated hand. Moreover, the primary motor cortex (MI) contained voxels that were phasically deactivated in response to both ipsilateral and contralateral touch. These data indicate that unilateral touch of fingers is associated, in addition to the well known activation of the contralateral SI cortex, with deactivation of the ipsilateral SI cortex and of the MI cortex of both hemispheres. The ipsilateral SI deactivation could result from transcallosal inhibition, whereas intracortical SI-MI connections could be responsible for the MI deactivation. The shorter time course of deactivation than activation would agree with stronger decay of inhibitory than EPSP at the applied stimulus repetition rates.

Adult↗

PubMed1995

Functional magnetic resonance imaging of the human motor cortex.

Functional magnetic resonance (MR) imaging of the brain was performed during motor task activation in five normal subjects and a patient with meningioma using conventional fast low-angle shot sequences and a 2.0 T system. A high intensity area in the motor cortex was observed in all normal subjects. Single-slice studies showed the right-sided finger task produced an increase of 1.9-23.5% (6.67 +/- 4.36%) in the signal intensity of the left motor cortex, while the left-sided finger task increased the signal by 1.5-18.2% (6.09 +/- 3.34%) in the right motor cortex. There was no significant difference between the sides. Multiple-slice studies also showed the activated motor cortex as a high intensity area. The maximum signal intensity increase in the activated motor area was 11.0% for the left motor cortex and 8.8% for the right motor cortex. There was no significant difference between the sides. Preoperative mapping of the patient with meningioma showed that the motor cortex was displaced posteriorly by the tumor. Functional MR imaging is possible with a standard MR imaging system and conventional gradient echo sequences. Useful clinical information can be obtained by preoperative mapping of the motor cortex.

Afferent Pathways↗

PubMed1997

Processing of complex sounds in the auditory cortex of cat, monkey, and man.

One of the fundamental features in the organization of sensory cortices which has emerged from 30 years of research in the visual system is the existence of multiple representation of the sensory world in the cerebral cortex. Compared with the visual system much less information exists about the functional specialization of multiple maps in the central auditory system. This is surprising, since an understanding of central auditory representations seems necessary for an understanding of higher auditory processing, including the perception of speech and the perception of auditory space. We have recorded single neuron activity in higher areas of auditory cortex of cats and rhesus monkeys. In cats, activity was recorded in the caudal part of the anterior ectosylvian (AE) cortex (areas AEA and AAF). More than half of the neurons were clearly tuned to the location of a sound source in azimuth and elevation. Frequency-modulated (FM) sounds elicited best responses at fast rates of modulation. By contrast, neurons in the posterior ectosylvian (PE) areas (PAF, VPAF) responded better to slow FM rates. This suggests a possible specialization for the processing of spatial attributes in the AE cortex, and a possible preference for auditory "patterns" in PE. In macaque monkeys, we explored the question of parallel processing in the higher auditory pathways by combining lesion and anatomical tracer techniques with single unit recording. Inactivation of primary auditory cortex (AI) abolished pure-tone responses in the caudomedial area (CM), but not in the rostral area (R). Injections of retrograde fluorescent tracers into R showed strong labeling of the main, ventral nucleus of the medial geniculate (MGv). Both findings suggest the existence of parallel pathways in the auditory cortex, originating at more peripheral sites and possibly specialized for the processing of auditory space vs. auditory patterns. The auditory pattern pathway in Macaque auditory cortex was further explored by using complex stimuli including Macaque-specific communication sounds. Neurons in the lateral belt areas (AL, ML, and CL) respond very selectively to bandpassed noise stimuli, to FM sounds of a certain rate and direction, as well as to certain classes of monkey calls. We are now in the process of exploring higher areas of human auditory cortex by measuring cortical activation with noninvasive functional magnetic resonance imaging (fMRI) while stimulating with complex auditory sounds.

Animals↗

PubMed1986

[Visual information processing from the retina to the prefrontal cortex].

Studies on the neural bases of visual information processing were reviewed by tracing connections from the retina to the prefrontal cortex in the monkey; i.e., retina--lateral geniculate body (LGB)--striate cortex--prestriate cortex--inferotemporal (IT) cortex or posterior parietal (PP) cortex--prefrontal cortex. The retinotopy exists up to the level of prestriate cortex, but it is lost in the IT or PP cortex. A general tendency is observed that the later is the stage of information processing, the longer is the latency of cell activity changes, the larger is the size of receptive field, and more complex become trigger features. Small spot stimuli activate retinal ganglion cells or LGB cells while bars or edges with proper orientation are trigger stimuli for striate and some prestriate cells. In restricted prestriate areas, cells which are selective to color or movement are observed. IT cells are activated by complex pattern stimuli, while PP cells are selective to spatial aspects of the stimulus. Some prefrontal cells encode the meaning of the stimulus independent of its physical properties.

Animals↗

PubMed1999

Barrels and septa: separate circuits in rat barrels field cortex.

The neural circuitry within sensory cortex determines its functional properties, and different solutions have evolved for integrating the activity that arises from an array of sensory inputs to cortex. In rodent, circumscribed receptors, such as whiskers, are represented in somatic sensory (S-I) cortex in islands of cells in layer IV called "barrels" surrounded by narrow channels that separate barrels called "septa." These two cortical domains were previously shown to receive sensory inputs through parallel subcortical pathways. Here, by using small biocytin injections, we demonstrate that distinct intrinsic and corticocortical circuitries arise from barrel and septal columns. The intracortical S-I projections originating from barrel columns are rather short-ranged, terminating for the most part within the far boundaries of the most immediate neighboring barrel columns, whereas corticocortical projections reach the second somatosensory (S-II) cortex. In contrast, the intrinsic projections arising from septal columns extend two to three barrels' distance along the row of whisker representation, producing terminals preferentially in other septal columns. Septal corticocortical projections terminate in the dysgranular cortex anterior to E-row barrels and in the posteromedial parietal cortex in addition to S-II. Whereas layer IV barrels are largely isolated from lateral connections, septa are the main conduits of intracortical projections arising from neighboring barrel and septal columns. These results indicate that the two subcortical pathways from whiskers to cortex continue as two distinct partially segregated pathways in cortex.

Animals↗

PubMed2000

Patterns of corticocortical, corticotectal, and commissural connections in the opossum visual cortex.

Patterns of connections of the visual cortex of the South American opossum, Didelphis aurita, were revealed by using neuronal tracers to identify and characterize visual specializations of the peristriate cortex (PS). The visuotopy of corticotectal connections of the anterolateral portion of PS (PSal) is symmetrical to that of the striate cortex (ST or primary visual area [V1]). Three consecutive bands of commissural connections coincide, respectively, with the ST-PS border, the limit between the caudal and rostral PSal halves (PSc and PSr), and the border of PS with the parietal and temporal cortices. PSc and PSr contain regular commissural rings similar to those present in the peristriate cortex of eutherian mammals. ST projections define in PSc two strings of periodical foci consecutively concentric to V1 and a single focus in PSr. Although they were organized topographically, ascending, descending, and commissural connections between ST and PSal showed a high degree of convergence and divergence. These results conform to the model of a single area homologous to the second visual area (V2) bordering V1. Moreover, they suggest the possibility that PSal includes either one or two additional belt-like areas successively anterior to V2. Along with the finding of alternating bands of high and low cytochrome oxidase activity in PSal, the data further suggest that this region contains modular specializations similar to those of the peristriate cortex of primates and other eutherian mammals. The posterolateral peristriate cortex (PSpl) constitutes another visual area, since it consists of a distinct focus of reciprocal corticocortical and interhemispheric connections and a separate source of corticotectal projections. Finally, a visuomotor function for the orbital cortex is proposed based on its direct projections to optical tectal layers. The close cladistic relationship of opossums to mammalian ancestral forms suggests that the PSal parcelation into belt-like areas that contain modules reflects the primitive organization of the visual cortex. Moreover, a highly diffuse pattern of corticocortical connections may represent a requirement for a brain with few visual areas to perform global processing.

Animals↗

PubMed2000

Medial frontal cortex mediates perceptual attentional set shifting in the rat.

If rodents do not display the behavioral complexity that is subserved in primates by prefrontal cortex, then evolution of prefrontal cortex in the rat should be doubted. Primate prefrontal cortex has been shown to mediate shifts in attention between perceptual dimensions of complex stimuli. This study examined the possibility that medial frontal cortex of the rat is involved in the shifting of perceptual attentional set. We trained rats to perform an attentional set-shifting task that is formally the same as a task used in monkeys and humans. Rats were trained to dig in bowls for a food reward. The bowls were presented in pairs, only one of which was baited. The rat had to select the bowl in which to dig by its odor, the medium that filled the bowl, or the texture that covered its surface. In a single session, rats performed a series of discriminations, including reversals, an intradimensional shift, and an extradimensional shift. Bilateral lesions by injection of ibotenic acid in medial frontal cortex resulted in impairment in neither initial acquisition nor reversal learning. We report here the same selective impairment in shifting of attentional set in the rat as seen in primates with lesions of prefrontal cortex. We conclude that medial frontal cortex of the rat has functional similarity to primate lateral prefrontal cortex.

Animals↗

PubMed2001

Effects of chronic ethanol intake and its withdrawal on the expression and phosphorylation of the creb gene transcription factor in rat cortex.

This investigation examined the effects of chronic ethanol treatment (15 days) and its withdrawal (24 h) on the expression and phosphorylation of cyclic AMP-response element-binding (CREB) protein in the rat cortex. The effects of chronic ethanol treatment and withdrawal on protein kinase A (PKA) activity and on the expression of the regulatory RII-beta- and the alpha-subtype catalytic subunits of PKA, and on the protein expression of Ca(2+)/calmodulin-dependent protein kinase IV (CaM kinase IV) and calcineurin in the rat cortex were also investigated. It was found that ethanol withdrawal but not ethanol treatment produced a significant decrease in the phosphorylated CREB (p-CREB) and CaM kinase IV protein levels in the frontal, parietal, and piriform cortex. Ethanol treatment and its withdrawal had no effect on the protein levels of total CREB in the frontal, parietal, and piriform cortex. On the other hand, ethanol treatment produced a significant reduction in the protein levels of CREB, p-CREB, and CaM kinase IV in the cingulate gyrus, and these changes reverted to normal levels during ethanol withdrawal. Total CREB protein levels were significantly higher in the cingulate gyrus during ethanol withdrawal. It was also observed that mRNA levels of CREB were significantly higher in the rat cortex during ethanol withdrawal but not during ethanol treatment. The protein levels of RII-beta- and alpha-subtype catalytic subunits of PKA and PKA activity were not modified in the rat cortex by chronic ethanol treatment and its withdrawal. Furthermore, the expression of calcineurin in the rat cortex was not altered during ethanol treatment and withdrawal. Taken together, these results suggest the possibility that decreased CREB-dependent events in the neurocircuitry of the frontal, parietal, and piriform cortex may play an important role in the phenomenon of alcohol dependence and also that decreased CREB-dependent events in the neurocircuitry of the cingulate gyrus may play a role in alcohol tolerance.

Animals↗

PubMed2001

[Auditory perception and language: functional imaging of speech sensitive auditory cortex].

Since the description of cortical deafness, it has been known that the superior temporal cortex is bilaterally involved in the initial stages of language auditory perception but the precise anatomical limits and the function of this area remain debated. Here we reviewed more than 40 recent papers of positron emission tomography and functional magnetic resonance imaging related to language auditory perception, and we performed a meta-analysis of the localization of the peaks of activation in the Talairach's space. We found 8 studies reporting word versus non-word listening contrasts with 54 activation peaks in the temporal lobes. These peaks clustered in a bilateral and well-limited area of the temporal superior cortex, which is here operationally defined as the speech sensitive auditory cortex. This area is more than 4cm long, located in the superior temporal gyrus and the superior temporal sulcus, both anterior and posterior to Heschl's gyrus. It do not include the primary auditory cortex nor the ascending part of the planum temporale. The speech sensitive auditory cortex is not activated by pure tones, environmental sounds, or attention directed toward elementary components of a sound such as intensity, pitch, or duration, and thus has some specificity for speech signals. The specificity is not perfect, since we found a number of non-speech auditory stimuli activating the speech sensitive auditory cortex. Yet the latter studies always involve auditory perception mechanisms which are also relevant to speech perception either at the level of primitive auditory scene analysis processes, or at the level of specific schema-based recognition processes. The dorsal part of the speech sensitive auditory cortex may be involved in primitive scene analysis processes, whereas distributed activation of this area may contribute to the emergence of a broad class of "voice" schemas and of more specific "speech schemas/phonetic modules" related to different languages. In addition, this area is activated by language-related lip movement, suggesting that a multimodal integration of the auditory and the visual information relevant in speech perception occurs at this level. Finally, there is a task-related top-down modulation of the pattern of activation of the speech sensitive auditory cortex which may reflect the fact that the different parts of this structure are connected to different down-stream cortical regions involved in the neural processing of different types of tasks.

Auditory Cortex↗

PubMed1992

Neuronal mechanisms of interaction of Deiters nucleus with the cerebral cortex.

The effects of stimulation of the vestibular nerve and five different cerebral cortex areas on the neuronal activity of the lateral vestibular nucleus of Deiters were studied. Stimulation of the cerebral cortex is shown to lead to antidromic and synaptic activation of Deiters neurons. The synaptic potentials of Deiters neurons evoked from the cerebral cortex were of mono- and polysynaptic origin. In particular, stimulation of the cerebral cortex evoked in Deiters neurons mono- and polysynaptic excitatory postsynaptic potentials. Collaterals of vestibulospinal neurons reaching different cortex fields as well as convergence of influences from these cortex fields on Deiters neurons were revealed. Inhibitory effects of the cerebral cortex on Deiters neurons were of polysynaptic origin and occurred rarely. The topical correlation between Deiters nucleus and different areas of the cerebral cortex was found. The peculiarities and functional significance of the effects obtained are discussed.

Action Potentials↗

PubMed1991

Characterization and distribution of [125I]epidepride binding to dopamine D2 receptors in basal ganglia and cortex of human brain.

The distribution and pharmacology of the binding of [125I]epidepride, a substituted benzamide with high affinity and selectivity for dopamine (DA) D2 receptors in rat brain (Neve et al., J. Pharmacol. Exp. Ther. 252: 1108-1116, 1990), is described in human brain. Saturation analysis of the binding of [125I]epidepride to membranes derived from striatum and regions of cortex demonstrated similar Kd values (34 and 28-33 pM, respectively) but differing maximum density of binding site values (152 and 3-8 fmol/mg of protein, respectively). The pharmacological profile of binding in cortex was also similar to striatum (epidepride greater than spiperone greater than butaclamol = flupenthixol greater than clozapine) except that an additional low-affinity site, blocked by the alpha-2 adrenergic antagonist idazoxan, was present in cortex. Quantification by autoradiography also demonstrated the greatest binding in the basal ganglia, with the striatum exhibiting greater binding than the pallidal complex or midbrain regions. For the pallidum, binding in the external segment was higher than the internal segment. Within the midbrain the binding of [125I]epidepride correlated well with the known distribution of DA-containing cell bodies, with the substantia nigra (pars compacta and pars lateralis) and ventral tegmental area (A10) higher than area A8 and central gray. Binding in frontal and parietal cortex was highest in the internal layers (layers V and VI). Temporal cortex showed a 2-fold higher density of binding than other cortical regions and a trilaminar pattern; binding was greater in the external (layers I and II) and internal layers than in the middle layers (III and IV). This pattern changed in the parahippocampal complex. Within the lateral occipitotemporal cortex, binding was densest in layers I to III and very low in layers IV to VI, but binding was almost nonexistent in the adjacent entorhinal cortex. Within the hippocampal complex, binding was evident in the subiculum, CA3 and dentate gyrus and almost nonexistent in the presubiculum or other fields of the hippocampus. This pattern of binding in the parahippocampal gyrus is unique to human brain and represents sites of action for DA in limbic cortex.

Adult↗

PubMed1990

The organization and connections of somatosensory cortex in marmosets.

Microelectrode mapping methods were used to define and describe 3 representations of the body surface in somatosensory cortex of marmosets: S-I proper or area 3b of anterior parietal cortex, S-II, and the parietal ventral area (PV) of the upper bank of the lateral sulcus. In the same animals, injections of anatomical tracers were placed into electrophysiologically determined sites in area 3b or S-II. Mapping results and patterns of connections were later related to architectonic fields that were delimited in sections cut parallel to the surface of manually flattened cortex and stained for myelin. There were several major results. (1) Recordings from area 3b revealed a characteristic somatotopic organization of foot to face in a mediolateral sequence as previously reported in other members of the marmoset family (Carlson et al., 1986). (2) Multiple injections of WGA-HRP in area 3b demonstrated dense, patchy interconnections with ipsilateral S-II, PV, area 3a, and area 1, less dense interconnections with primary motor cortex (M-I), the supplementary motor area (SMA), limbic cortex of the medial wall (L), and rostrolateral parietal cortex of the lateral sulcus (PR), and callosal connections with areas 3b, S-II, and PV. Injections of 3 different tracers into the representation of 3 body regions in area 3b indicated that the connections with areas 3a, 3b, 1, S-II, and PV are topographically organized. (3) Recordings from cortex on the upper bank of the lateral sulcus demonstrated a somatotopic representation of the body surface that matches that of S-II of other mammals. S-II immediately adjoined areas 3b along the dorsal lip of the lateral sulcus. The face representation in S-II was adjacent to the face representation in 3b while the trunk, hindlimb, and forelimb were represented in a caudorostral sequence deeper in the sulcus. (4) Injections in S-II revealed ipsilateral connections with areas 3a, 3b, 1, a presumptive area 2, PV, PR, M-I, SMA, limbic cortex, the frontal eye fields, and the frontal ventral visual area. Dense callosal connections were with S-II and PV. (5) The recordings also revealed a systematic representation just rostral to S-II that has not been previously described in primates.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1987

[Recent contributions concerning the development and distribution of dopaminergic innervation in the cerebral cortex of the rat].

Tyrosine hydroxylase was used as an immunocytochemical marker of dopaminergic axons in the cerebral cortex either in fetuses or in postnatal life after lesion of the noradrenergic input. The lesion was controlled by the absence of dopamine-beta-hydroxylase immunoreactivity. Fluorescence histochemistry also allowed the specific visualization of the dopaminergic system following uptake of exogenous amines in tissue sections in presence of selective high affinity transport inhibitors. Two main dopaminergic (DA) subpopulations reach the medial cortex of the rat: 1) a deep one, first detected in the anterior frontal cortex on day 16 of embryonic life, was well developed at birth and extended caudally in layer V and/or layer VI toward the splenium of corpus callosum; 2) a superficial one was detected in layer I of the anterior cingulate cortex (area 24) on postnatal day 3 to 5 and invaded layer III from day 6 to 14. The adult distribution pattern and striking varicose aspect were not reached until day 21 to 30. In addition to these medial fields, a dopaminergic innervation of low density was detected laterally along a dorsal sagittal strip which encompassed several distinct cytoarchitectonic areas in the sensorimotor and visual cortex (medial and lateral agranular field, area 18b) as well as in discrete zones of the retrosplenial granular 29c, b, and agranular 29d areas. Several characteristics of this newly observed DA input were similar to that of the superficial field described in the anterior cingulate cortex; these similarities suggested that the subpopulation of DA neurons which provides projections to the anterior cingulate cortex could also contribute to the motor and visual cortex and thus play a role in sensorimotor integration. A DA terminal field was also demonstrated in the temporal part (ventral and caudal) of the hippocampal formation, the subiculum especially the prosubiculum and the adjacent CA1 hippocampal field being the main targets. This DA terminal field in the hippocampal formation matches with the area which projects toward the accumbens nucleus. Thus, the hippocampo-striatal projections which represent a link of functional importance between the limbic and central motor systems, could be modulated by the dopaminergic meso-cortico-limbic pathway. The predictive values of these data in the ascent of the phylogenetic scale are further considered.

Animals↗

PubMed1985

Glutamic acid decarboxylase in the striate cortex of normal and monocularly deprived kittens.

Degeneration of the thalamic fibers in the visual cortex of turtles leads to an increase in the numerical density of cortical synapses with flattened vesicles and symmetrical membrane differentiations (Smith, L. M., and F. F. Ebner (1980) Soc. Neurosci. Abstr. 6: 328). This change correlates with an increase in the cortical activity of glutamic acid decarboxylase (GAD), the synthetic enzyme for gamma-aminobutyric acid (GABA). These data are consistent with the hypothesis that removal of thalamic input activity is the stimulus for cortical GABAergic neurons to form new synapses. Pharmacological evidence suggests that even simple environmental deprivation may induce a similar increase in the numerical density of GABAergic synapses in kitten striate cortex (Duffy, F. H., S. R., Snodgrass, J. L. Burchfiel, and J. L. Conway (1976) Nature 260: 256-257). We have examined this possibility in monocularly deprived kittens using methods to localize and measure GAD. GAD in kitten striate cortex was localized using immunocytochemistry. GAD-positive cells were found in all layers and were uniformly distributed in layers II to VI. Immunoreactivity associated with axon terminals (puncta), in contrast, was laminated with a distinct band in layer IV. Monocular deprivation (MD), by either unilateral enucleation or lid closure, had no detectable effect on the distribution of GAD in striate cortex. The band of layer IV puncta remained uniform even under conditions that produced alterations in layer IV cytochrome oxidase activity. We measured GAD activity in homogenates of striate cortex to address the possibility that MD causes an absolute change in the density of GABAergic synapses. Again, however, GAD activity in the binocular and monocular segments of striate cortex was found to be unaffected by early enucleation. These data suggest two conclusions: first, that the numerical density of GABAergic synapses in visual cortex is not regulated directly by thalamic activity, and second, that changes in GABAergic synapse density do not account for the ocular dominance shift observed in kitten striate cortex after MD.

Animals↗

PubMed1987

Importance of the visual and vestibular cortex for self-motion perception in man (circularvection).

Circularvection (CV), the optokinetically induced perception of self-motion, is based neurophysiologically upon visual-vestibular convergence. It is yet not known which visual pathways--subcortical accessory optic tract and/or cortical striate projection--convey optokinetic information to the central vestibular system in order to make possible the convergence that has been found: the vestibular nuclei, the thalamus and the vestibular cortex. The functional significance of the visual cortex was demonstrated in 12 patients with homonymous hemianopia who neither perceived CV nor exhibited a postural destabilization when exposed to optokinetic pattern motion (yaw or roll) restricted to the scotoma. The functional significance of the vestibular cortex as well as ipsilateral visual-vestibular interaction was demonstrated in 4 (out of 20) patients with tumour lesions involving the vestibular cortex areas. They either failed to perceive CV or showed a significant increase of CV-latencies when monocular optokinetic stimulation was restricted to the ipsilateral visual cortex. Arguments for and against the following hypothesis are discussed: circularvection is induced by visual motion stimulation of the primary visual cortex which then activates vestibular nuclei neurons by descending pathways and which also informs the vestibular cortex that self-motion with a perceptual direction is involved. Determination of the velocity of CV is mediated by direct visual-vestibular cortex interaction, which most probably is also involved in the perceptual interpretation of motion perception: Self-motion versus object-motion.

Adult↗

PubMedDate not supplied

[Effect of morphine on the change in the nociceptive and non-nociceptive evoked potentials in the orbitofrontal and secondary somatosensory areas of the cerebral cortex in different functional states].

The effect of morphine on alterations in nociceptive and non-nociceptive evoked potentials (EP) elicited in the second somatosensory (S2) and orbito-frontal cortex of the brain was studied in acute experiments on cats. Administration of morphine in a dose of 5 mg/kg to the above-mentioned structures caused an increase in the amplitude of EP to non-nociceptive stimulation and a decrease of EP to nociceptive stimulation. Under alternate functional inactivation of the orbito-frontal cortex and S2 a unidirectional effect of the projection cortex on the associative orbito-frontal cortex was observed, manifested by a decrease of EP in the orbito-frontal cortex. Administration of morphine with the S2 cooled led to further decrease of EP followed by their restoration in the orbito-frontal cortex, in response to both nociceptive and non-nociceptive stimulation. Meanwhile administration of morphine, with the orbito-frontal cortex cooled, elicited the response in the S2 analogous to that observed after administration of morphine with intact orbito-frontal cortex: a decrease of EP to nociceptive stimulation and an increase of EP to non-nociceptive stimulation. It is suggested that the S2 plays an important role in control of nociceptive and non-nociceptive input to the CNS.

Animals↗