DOES HIPPOCAMPAL THETA EXIST IN THE HUMAN BRAIN?

Sunao Uchida, Masaki Nishida, Nobuhide Hirai, Fumikazu Miwakeichi

Department of Sleep Disorders Research, Tokyo Institute of Psychiatry, Tokyo 156-8585

Accepted in revised form 12 October 2001; recieved 28 August 2001

Summary

In several species of animal, a regular rhythm known as the hippocampal theta oscillation has been described. However, in humans, the presence of a comparable oscillation has not been established. In animal studies, the phase of theta activity has been related to important roles in the induction of LTP/LTD at the cellular level. The occurrence of theta has also been suggested to reflect the gating of memory related information processing. Thus, the presence or absence of theta oscillation in the human hippocampus has become an essential question. However, past studies have reported contradictory results. Recent results from our laboratory suggest the presence of beta-1 frequency oscillation, rather than theta is present in the human medial temporal lobe. A separate observation indicates that theta oscillation can be observed in the human anterior cingulate cortex. Implications of these findings for conceptualizing human memory functions, and their physiological significance are discussed.

Key Words: Human hippocampus, Electrocorticogram, Beta-1 oscillation, Theta oscillation, Rhythmic slow activity


Correspondence: Uchida Sunao, MD., PhD.,
Department of Sleep Disorders Research,
Tokio Institute of Psychiatri,
2-1-8 Kamikitazawa, Setagaya-ku, Tokio, 156-8585, Japan.
E-mail: sunao@uchidae.com