Psychophysiology

Processing of sensory stimuli is controlled by the top-down influences that shape oscillations in the synchrony form revealed in the EEG. However, little is known about the nature of these influences. The present study investigated the contribution of "evoked oscillations" in the perception of auditory stimuli during passive and active attention from the position of pacemaker hypothesis on the origin of gamma rhythm. To analyze the problem, the author suggests a special method based on the narrow frequency filtering event-related potentials, localization of dipole sources of gamma oscillations over the structural MRI slices. Computation of equivalent dipoles for the discrete frequencies demonstrates interaction between prefrontal and auditory cortex during active attention to auditory stimuli. The obtained results are compatible with the pacemaker hypothesis.

Intracellular research of land snail Helix lucorum L. eye demonstrates two types of visual cells responding to flashes of white light by slow sustained depolarization (D-type) and by slow sustained hyperpolarization (H-type), respectively. Peaks of spectral sensitivity of both cell types at 465-500 nm coincide with peak of spectral sensitivity of photopigment "rhodopsin". The two-channel vector model of achromatic vision of snail is proposed. According to the model, responses of D- and H-cells constitute two-dimensional 'excitation vector' of constant length, the direction of which is the code of light intensity. The two-dimensional vector model of light encoding in snails' eye is analogous with achromatic vision models of achromatic vision in vertebrates based on psychophysical and neurophysiological data in fish, rabbit, monkey and human. So, intracellular data in snail taken together with data on vertebrate animals testify in favor of the hypothesis that 2-dimensioanl module of "bright" and "dark" cells is the universal opponent mechanism of "vector encoding" of light intensity in neuronal nets for vision.