The Role of Oscillatory Processes in Encoding Information by the Hippocampal System

Neural coding means the representation of external stimuli and/or behavioral processes in the electrical activity of nerve cells. In recent years, many facts have been revealed that indicate the need to generate oscillations for such a representation in a normal brain. The hippocampus and its directly related structures (dentate gyrus, subiculum, and entorhinal cortex) generate many types of field rhythmic activity, the main of which are theta (~4-12 Hz), beta (~15-30 Hz), gamma (~25-100 Hz), and ripple oscillations (~120-500 Hz). With the participation of oscillatory activity generated in these frequency bands, both spatial and non-spatial information (temporal, auditory, olfactory, tactile, gustatory, etc.) is represented in the brain. It has been found that oscillations underlie many critical brain functions such as learning and memorization. However, a fundamental question remains to be fully resolved: what specific role do different types of oscillations generated in the hippocampal system play in cognitive functions (in particular, in encoding information), and what are the mechanisms of their participation in these functions? This paper is devoted to a review of the literature data on the role of oscillatory processes in encoding signals entering the brain both from the external environment and from the body itself. The issues of the participation of oscillations in the memorization and reproduction of stored information are also discussed. The main focus is on examining oscillatory activity directly in the hippocampus; the material obtained from the study of structures belonging to the hippocampal system and some neocortical regions are also evaluated.