The Theta Rhythm of the Hippocampus: From Neuronal and Circuit Mechanisms to Behavior

Angel Nuñez,Washington Buño

doi:10.3389/fncel.2021.649262

Abstract

This review focuses on the neuronal and circuit mechanisms involved in the generation of the theta (θ) rhythm and of its participation in behavior. Data have accumulated indicating that θ arises from interactions between medial septum-diagonal band of Broca (MS-DbB) and intra-hippocampal circuits. The intrinsic properties of MS-DbB and hippocampal neurons have also been shown to play a key role in θ generation. A growing number of studies suggest that θ may represent a timing mechanism to temporally organize movement sequences, memory encoding, or planned trajectories for spatial navigation. To accomplish those functions, θ and gamma (γ) oscillations interact during the awake state and REM sleep, which are considered to be critical for learning and memory processes. Further, we discuss that the loss of this interaction is at the base of various neurophatological conditions.

Highlights

The hippocampus is the main structure involved in the generation of the 4- to 12-Hz theta (θ) rhythm, which is one of the most regular EEG oscillation that can be recorded from the mammalian brain
The above findings suggest that NMDA- and Ca2+-mediated spikes provide an important depolarizing drive, that boosts the otherwise small depolarization supplied by excitatory postsynaptic potentials (EPSPs), to generate the high-frequency rhythmic bursts of fast Na+-mediated action potentials that typifies pyramidal neuron activity during field θ
The results suggest that NMDA-induced oscillations relied on the negative slope conductance of the NMDA channel caused by the voltage-dependent Mg2+ block that underlies NMDA spikes (Schiller and Schiller, 2001; Antic et al, 2010) and on high-threshold Ca2+ spikes mediated by activation of L-type voltage-dependent Ca2+ channels (VDCC; Bonansco and Buño, 2003)

Summary

Introduction

The hippocampus is the main structure involved in the generation of the 4- to 12-Hz theta (θ) rhythm, which is one of the most regular EEG oscillation that can be recorded from the mammalian brain. The above results suggest that hippocampal θ oscillations critically depend on the rhythmic neuronal activity of the MS-DbB.

Results

Conclusion