Cellular mechanisms of hippocampal gamma frequency oscillations

Gamma oscillations are known as cognitive rhythms due to their occurrence during the cognitive functions such as working memory, episodic memory, memory encoding and retrieval, sensory binding and attention. Gamma oscillations can be easily transferred into epileptic activity. Altered gamma rhythms are seen during the brain disorders such as schizophrenia, dementia and autism. Hence, studying the mechanisms of gamma rhythms is of great importance. Recent discoveries revealed new details of gamma oscillations. The classical view about the parvalbumin containing perisomatic basket cells that drives the gamma oscillation is valid for CA3 region of hippocampus but it may not be so for CA1 region. However, medial ganglionic eminence (MGE) derived axo-axonic cells action potential discharge follows the gamma rhythm in CA1 together with caudal ganglionic eminence (CGE) derived trilaminar and back-projecting interneurons. Oriense-Lacunosum-Moleculare (OLM) cells appear to have dual origine and can be modulated by gamma frequency. Using the modern technologies and relying on the current knowledge and new insights about neuronal elements in gamma frequency oscillation will help the scientists to study the mechanisms of cognitive rhythms in more details.