[Structure and correlation of "fast" and "slow" background impulse activity of visual cortex neurons]

Background and optically modified impulse activity of neurons in visual cortex of unanaesthetized rabbits was analyzed. By means of joint interval histograms it was shown that neurons can be distinguished by the ratio of burts (intervals to 15-40 ms) and extraburst activity and by the shape of transition from one from of activity to another. The extraburst activity comprises 63% of impulses and its ratio to bursts of 2 or 3 and more impulses was 27:3:1. Burts impulse distribution showed a relative stability of timing pattern within bursts and small number of burst impulses (2.4 on the average). Bursts of 3 and more impulses (3.6 on the average) are not rhythmical and 79% of them contained long intervals (18.6 +/- 2.4 ms) before the shortest one (7.9 +/- 0.9 ms). Optical stimulation resulted in bursts containing core impulses, shorter intervals and beginning with the shortest interval in most neurons. This may testify to the increase of the EPSP steepness and amplitude. 20% of cortical neurons showed background bursts containing more impulses and shorter intervals in comparison with evoked bursts.