Oscillatory Heritage of the Grastyán School

György Buzsáki
2006 Hungarian Studies  
Two major structural designs characterize the cerebral cortex: the scalable, modular neocortex and the single-module hippocampus. Functions attributed to the hippocampal formation have varied over the past several decades and include episodic memory in human lesion studies, spatial mapping in single unit recordings and voluntary exploration of the environment in field recording studies in animals. I suggest that the common thread across these parallel developments is that each captures the
more » ... h captures the essence of episodic coding: items are organized in spatio-temporal context. I suggest that theta oscillations, studied extensively in the Grastyán school in Pécs, is the key temporal metric. Ordered sequences of items are encoded by the strict temporal relations of hippocampal cell assemblies nesting within cycles of theta oscillation. Such a temporal compression mechanism brings neuronal assemblies together in the time window of synaptic plasticity and allows the linking of first order (neighbor) and higher order relations. Seven to nine interleaving assemblies, representing overlapping past, present and future items, can be combined into an episode in a single theta cycle. During recall, the entire hippocampal connection matrix can be searched in the time period of the theta cycle (120 -140 msec). I suggest that the hippocampus is an efficient search engine for the reconstruction of complex episodes from fragmentary information. What Makes Us Individuals? When it comes to the complex organization of the brain, we tend to think of the large cerebral cortex. Its structure and the functions its anatomical organization supports are tuned mainly to detect orderly, species-and individual-invariant relationships in our environment. The perceptions of natural scenes, speech and music, body image as well as our occasional illusions can be attributed largely to the unique organization of the isocortex. Brains with these features only would be useful as long as they are embedded in an unchanging environment. However, we Hungarian Studies 20/1 (2006) 0236-6568/2003/S20.00
doi:10.1556/hstud.20.2006.1.11 fatcat:f6ut23xhxvb5vk5yq4yboka56m