Oscillatory Activity and Cross-Frequency Interactions in the Hippocampus and Connected Brain Structures during Sensory Information Processing

It has been suggested that oscillations, or rhythms, are required for the execution of many cognitive functions, as they support rapid and flexible interactions between neurons in different brain structures [Livanov, 1977; Fries, 2005; Womelsdorf et al., 2007]. Until recently, little attention was focused on the question of how different types of oscillations are synchronized during the processing of information arriving in the brain. We report here an analysis of the extent and correlations of rhythmic activity in the θ, α, and γ ranges in animals in two behavioral states: during calm consciousness and during the perception of sensory signals. Local field potentials (LFP) were recorded in eight brain structures (cortical and subcortical). Many areas showed increases in oscillatory activity in different frequency bands on delivery of sensory stimuli. The main result of this study was a sharp increase in the cross-frequency interactions of all rhythms in both cortical and subcortical structures during sensory information processing. We suggest that the increase in interfrequency interactions between different rhythms in different parts of the brain is required for detailed assessment of environmental signals and their registration in the memory system.