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

It has been suggested that synchronization of action potentials encodes div erse features of a single image. However, properties of the synchronization , which occurs on a time scale of approximate to 1-5 ms, are still poorly u nderstood. 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 a nd single-cell recordings in area 17. Initially, a patch of sine-wave drift ing 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 st imuli were two sine-wave patches placed above and below the central compoun d receptive field. Only the contrast of contextual targets changed. Results show that the larger the differential contrast the higher the synchronizat ion. The second contextual stimulus was a lateral shift of a sinewave patch . Data show that the wider the distance between the central and peripheral patches the better the synchronization. Furthermore, results suggest that t he synchrony pattern computed by cross correlating multiunit recordings fro m two sites differs when the cross correlation is carried out between indiv idual units belonging to each multiunit recording. Together with our previo us results it appears that synchronization is stimulus dependent and its st rength increases with larger disparities included in the whole stimulating image.