Biomedical subjects

F Bretzner

Publications and source records attributed to F Bretzner.

4 recordsLinked to original sources

PubMed2004

Effects of excitation and inactivation in area 17 on paired cells in area 18.

This investigation examines how neighboring neurons of area 18 react when area 17 inputs are excited or depressed. In anesthetized cats, area 18 responses to a sine-wave grating in the receptive field were analyzed, while a second grating was positioned in its periphery and responses were recorded in area 17. This latter site was also inactivated with GABA. A waveform template process sorted out at least two individual, neighboring cells with similar orientation preferences in area 18. These cells frequently displayed opposite reactions to stimulation and inactivation in area 17. Experiments suggest that nearby neurons belonging to the same functional domain in the visual cortex may simultaneously carry disparate information.

Action Potentials↗

PubMed2001

Comparative computations of spike synchronization in visual cortex of cats.

In recent years it has been proposed that synchronous activity between neurons is a putative mechanism to bind together various trigger features of an image. Thus the measure of synchronization becomes an important issue since it may be an electrophysiological sign of visual perception. This paper describes and compares six techniques of computing synchronization strength, that is, the central peak of a cross-correlogram. Data were obtained in anesthetized cats prepared for electrophysiological recordings in a conventional fashion. Results indicate that: (1) eye fits are misleading. Visual inspection of cross-correlograms, may be interesting if one needs to estimate approximately synchronization strength and the presence of oscillations in the cross-correlograms, however it may be misleading if one wants to compare different cross-correlograms; (2) regression analysis to compare one method against the others yields a relatively poor correlation suggesting that methods are not directly comparable; (3) the sensitivity of each computational method is unequal. The results may indicate that some functional connections are either under- or over-evaluated depending upon the strategy employed to measure synchronization.

Animals↗

PubMed2001

Modulation of the synchronization between cells in visual cortex by contextual targets.

It has been suggested that synchronization of action potentials encodes diverse features of a single image. However, properties of the synchronization, which occurs on a time scale of approximately 1-5 ms, are still poorly understood. We have tested the modulation of synchronization by manipulating the contextual targets introduced in the surround of the receptive field. Experiments were carried out on anaesthetized cats prepared for multiunit and single-cell recordings in area 17. Initially, a patch of sine-wave drifting grating was positioned over the overlapping receptive fields of several neurons. If this coherent motion produced a significant synchronization in cross-correlograms, contextual targets were added. The first contextual stimuli were two sine-wave patches placed above and below the central compound receptive field. Only the contrast of contextual targets changed. Results show that the larger the differential contrast the higher the synchronization. The second contextual stimulus was a lateral shift of a sine-wave patch. Data show that the wider the distance between the central and peripheral patches the better the synchronization. Furthermore, results suggest that the synchrony pattern computed by cross correlating multiunit recordings from two sites differs when the cross correlation is carried out between individual units belonging to each multiunit recording. Together with our previous results it appears that synchronization is stimulus dependent and its strength increases with larger disparities included in the whole stimulating image.

Action Potentials↗

PubMed2000

Stimuli outside the classical receptive field modulate the synchronization of action potentials between cells in visual cortex of cats.

It is proposed that various attributes of an image are bound neuronally when responsive units fire in synchrony. Our investigations describe the influences of the contextual stimuli upon the occurrence of synchronization, in anaesthetized cats. Once a significant synchronization was recorded in the cross-correlogram (XCRG) between evoked action potentials of two groups of neurons in response to a drifting sine-wave grating, additional gratings were positioned outside the compound receptive field. The synchronization strength was then measured in relation to the difference between the orientations of the central and peripheral gratings. In the majority of cases results indicate that the synchronization is facilitated with larger orientation disparities. Thus, our data support the notion that contrasting features of images facilitate synchrony of activity between neurons.

Action Potentials↗