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At least 145 records · Page 8Linked to original sources
PubMed1984

GABA-related phenomena, models of nervous system function, and seizures.

Models of nervous system function are presented that place particular emphasis on the roles in nervous system function of inhibitory neurons that liberate gamma-aminobutyric acid (GABA) as neurotransmitter. The nervous system is considered to be highly restrained, with inhibitory neurons acting like reins that serve to keep the neuronal "horses" from running away. In behavioral sequences, whether innate or learned, preprogrammed circuits are released to function at varying rates and in various combinations. This release is accomplished largely by the disinhibition of pacemaker neurons whose activities are under the control of tonically active inhibitory command neurons, many of which may use GABA as a transmitter. In addition to their restraining function, local circuit GABAergic neurons participate in feed-forward, feedback, surround, and presynaptic inhibition and in presynaptic facilitation. Information arriving from several sources is integrated in specialized analyzing regions, such as the cerebellar cortex, basal ganglia, and reticular nucleus of the thalamus. Monosynaptic inhibitory GABAergic outputs reflecting this analysis then play upon neural elements in the direct channels, making their activity optimally compatible temporally and spatially with that of neural elements elsewhere in the central nervous system. Seizures are prototypical of incoordination between inhibition and excitation. Major causes of seizures may be the loss of inhibitory GABAergic terminals at the site of focal cortical epilepsy or a disturbance in various aspects of GABAergic function.

Animals↗
PubMed2001

Fractal encoding in a chaotic neural network.

We analyze a model of a chaotic neural network consisting of three neurons, namely a chaotically forcing neuron and two neurons comprizing a stable response system with a contraction mapping property, for digital encoding with chaotic dynamics. We show that dynamics of the chaotically forcing neuron is embedded in the form of a code sequence on a fractal attractor of the two-neuron response system. We consider the relation between the state transition of the chaotically forcing neuron and the hierarchical fractal structure on the attractor in the state space of the contracting system. We also report hardware implementation of the presented model with an analog electronic circuit to investigate the fractal attractor of the chaotic neural network as a realistic system.

Journal Article↗
PubMedDate not supplied

[Neural bases of perception and recognition of faces].

OBJECTIVE: To analyze the neural bases of perception and the recognition of faces. First of all we consider the concept of functional hemisphere specialization; then we look at the results obtained with regard to the neuroanatomy of processing faces and finally refer to the disorders of recognition of faces in humans. For this we review the clinical evidence obtained from the neuropsychological studies of prosopagnostic patients and the data derived from psychophysiological experiments done using intracranial recordings of nonhuman primates. DEVELOPMENT: The agreement between the results analysed allows us conclude that in both cerebral hemispheres there are neural mechanisms specialized in the perception and recognition of faces, and in particular the ventral and posterior regions of the occipito-temporal cortex play a decisive part in these processes. Similarly experimental findings in nonhuman primates permits explanation of the neural nature of certain neuropsychological disorders seen in man, such as the case of the dissociation between disorders of the recognition of facial identity and disorders of recognition of emotional expression, and also dissociation between the difficulty in recognizing familiar faces and difficulty in recognizing non-familiar faces. CONCLUSION: The use of modern neuroimaging techniques and electrophysiological studies using evoked potentials are necessary for greater understanding of these and other disorders related to processing facial information.

Affect↗
PubMedDate not supplied

[Activity of 3-neuron cortical microsystems in the cat during conditioned reflex switchover].

Multiunit activity in two projection cortical areas (visual and motor) was studied in cats at conditioned switch-over of defensive and alimentary responses to electrostimulation of the visual pathways. Interneuronal relations of three-neuronal cortical microsystems (intra-analyzer connections) and relations between microsystems in the visual and motor cortical areas (inter-analyzers connections) were analysed by the method of crosscorrelation of action potential trains. Similar interneuronal relations were revealed in the motor microsystems and different relations were found in visual ones at elaboration of conditioned switch-over. This apparently indicates the leading role of the cortical projection of the signal stimulus in integration of adaptive behavioural act. On the other hand, the presence of common bonds for alimentary and defensive situations as well as of specific ones for each of them was shown in the distribution of interneuronal connections between the analyzers. The former apparently provide for the realization of the conditioned effector movement of the animal occurring in both situations with participation of the same effector organ (the tongue) The latter determine the character of the specific adaptive reaction.

Animals↗