PubMed HealthSearch

PubMed · 9116691

A computer model of the visual cortex.

Abstract

A three-layered simulation of the visual cortex was constructed, receiving inputs from 252 retinal photoreceptors. Lateral geniculate body was taken as a simple relay station. In the cortical module afferent neurons with circular receptive fields, orientation selective simple cells, tuned complex cells, excentricity neurons and different kinds of inhibitory neurons were included. The model reproduces neuronal and network responses recorded in experiments and some sensory illusions, of which one is here demonstrated.

Explore related subjects

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

O Fehér, T Virág. 1996. A computer model of the visual cortex.. https://pubmed.ncbi.nlm.nih.gov/9116691/

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related citations

Calretinin in pretecto- and olivocerebellar projections in the chick: immunohistochemical and experimental study.

Calretinin (CaR) is a calcium-binding protein that is distributed extensively in the central nervous system. It is localized in the cell bodies and neurites of specific neuronal populations and serves, therefore, as a reliable anatomical marker. Some components of the pretectocerebellar projection, which connects specific pretectal nuclei to caudal cerebellar folia, are concerned with the cerebellar control of visual reflexes. We investigated the distribution of pretectocerebellar-projecting neurons in relation to cells that show CaR immunoreactivity. Cells that project to the cerebellar cortex in the diencephalic primary visual nuclei and in other grisea, like the nucleus spiriformis medialis and the nucleus dorsofrontalis, colocalized with those that appeared to be immunolabeled intensely with anti-CaR antiserum. To explore the hypothesis of a common developmental origin of these pretectal cerebellopetal neurons, we also investigated the development of CaR-immunopositive cells in the chick pretectum and the arrival of their fibers in the cerebellum, from 10 days of incubation (stage 36) to posthatching stages. Finally, we analyzed the source of CaR+ climbing fibers and found a subpopulation of CaR+ cells in the inferior olivary nucleus. On the whole, these results suggest that there is a common developmental origin of pretectal cerebellopetal neurons, some of which share the property of CaR expression. The functional significance of this correlation needs to be investigated.

Afferent Pathways

Developmental changes in human cerebellum: expression of intracellular calcium receptors, calcium-binding proteins, and phosphorylated and nonphosphorylated neurofilament protein.

Few recent data are available on the development of the precise projection maps of the cerebellar cortex in humans. To address this topic, we studied temporal and spatial distribution of several antigens involved in calcium (Ca)-dependent processes: the intracellular Ca receptors, inositol 1,4,5-trisphosphate receptor type 1 (IP3R1) and ryanodine receptor (RyR); the Ca-binding proteins, calbindin D-28k (CB), parvalbumin (PV), and synaptophysin; and phosphorylated (SMI 31) and nonphosphorylated (SMI 32) forms of neurofilament protein. All antigens were studied in the human cerebellum during intrauterine development. The results of this study show that immunocytochemical markers appeared in the following sequence: CB and both forms ofneurofilament protein were observed at 4-5 gestational weeks (g.w.), PV appeared in the external granular layer and in a few Purkinje cells at 11 g.w., a diffuse immunostaining for IP3R1 and synaptophysin were observed at 13 g.w., whereas RyR was observed at 17-18 g.w. From 24 g.w. on, Purkinje cells expressed all four examined markers of intracellular Ca signaling as well as two forms of neurofilament protein. At the same time, compartmentation of the Purkinje cell layer was detected with three intracellular Ca-signaling molecules (IP3R1, CB, and PV) and with SMI 32. These results indicate that the developmentally regulated expression of antigens studied here may play a role in establishing a highly regular organization of terminal fields in the human cerebellar cortex. Moreover, the initial expression of these antigens is correlated temporally with other developmental processes in the cerebellum, such as cellular maturation, revealed by the immunoreaction to cytoskeletal protein, and synaptogenesis, revealed by immunoreaction to synaptophysin.

Afferent Pathways

Central projection of proprioceptive information from the wrist joint via a forearm 'muscle' nerve in the cat.

1. Peripheral nerves arising in joint capsules are known to contain a 'contaminating' contribution from muscle afferent fibres. In the present report we provide the first electrophysiological evidence that some joint afferent fibres may take an 'ectopic' path to the central nervous system via a nearby muscle nerve. 2. Experiments were conducted in anaesthetized cats in which a distal extension of the indicis proprius nerve was observed to project beyond its own muscle to the dorsal surface of the wrist joint capsule which is also supplied by the 'classic' wrist joint nerve, a branch of the dorsal interosseous nerve. Both the proximal and distal segments of the indicis proprius nerve were exposed for recording, by means of silver hook electrodes, while each segment remained in continuity. 3. Individual wrist joint afferent fibres with receptive fields on the dorsal surface of the joint capsule could be identified electrophysiologically within the distal segment of the indicis proprius nerve. In each of these cases the same fibre could also be identified at the proximal recording site. The identity of each of these simultaneously recorded units was established (1) by the short fixed interval between their times of spike occurrence, (2) from the exact correspondence of the capsular receptive field for the simultaneously recorded spikes, and (3) by the unfailing correlation in the presence, or absence, of the distally and proximally recorded spikes in association with either manual or controlled stimulation of the wrist joint capsule. Most joint afferent fibres identified with this projection path were in the group II range of conduction velocities and had conventional properties but group III fibres also appeared to be represented. 4. The present demonstration that some joint afferent fibres may be located within 'muscle' nerves emphasizes the importance of activating deep inputs, of joint or muscle origin, by adequate stimulation of the peripheral receptors in order to examine selectively the central actions of either source of input. Electrical stimulation of the peripheral nerves may lead to interpretative ambiguities.

Afferent Pathways