| This dissertation investigates the mechanisms of information transfer between brain areas. Oscillations in the brain are likely key players in information processing. Therefore, prospective directions of research on information processing include investigation of interactions between oscillations and neuronal activity in the same and different structures and the relationship between behavior/experience and oscillations. In this thesis, I explore the implications of oscillations in two information processing functions: memory consolidation and development of sensory-motor representation. My thesis includes the following three studies.; The first study (Sirota et al., 2003) examines the relationship between the network activities of the hippocampus and the neocortex during slow wave sleep. Here we demonstrate that their interaction spans both slow and fast time scales. Neuronal bursts in deep cortical layers, associated with sleep spindles and delta waves(slow rhythm), bias the timing of hippocampal discharges related to fast (ripple) oscillations. We hypothesize that oscillations-mediated temporal links coordinate specific information transfer between neocortical and hippocampal cell assemblies.; The second study (Isomura et al, under review) investigates the effect of the neocortical slow oscillation on the hippocampal networks. This study uses simultaneous extracellular and intracellular recordings. We find that neocortical, entorhinal and subicular cortical neurons alternate in unison between UP and DOWN states, with a corresponding bimodal distribution of their membrane potentials. In contrast, hippocampal granule cells and CA3 and CA1 pyramidal cells show unimodal distribution. The power of gamma oscillations and rate of neuronal discharges in the dentate gyrus vary in parallel with neocortical activity. However, in CA1-3 networks, self-organized gamma and tipple oscillations can emerge even in the absence of neocortical-dentate activity. Thus, distinct networks in the neo/paleocortex and the hippocampus can function either cooperatively or independently.; The last study (Khazipov et al., 2004) describes the endogenous neocortical network patterns of activity in the developing somatosensory cortex. Furthermore, it establishes their direct relationship to the sensory-motor system of the rat. We report that in the intact somatosensory cortex of the newborn rat in vivo, spatially-confined spindle-bursts represent the first and only organized network pattern. The localized spindles are selectively triggered in a somatotopic manner by spontaneous muscle twitches, motor patterns analogous to human fetal movements. We suggest that the interaction between movement-triggered sensory feedback signals and self-organized spindle-oscillations shapes the formation of cortical connections required for sensonmotor coordination. |
