Ten- to 12-Hz EEG Oscillation in the Rat Hippocampus and Rhinal Cortex That Is Modulated by Environmental Familiarity

Abstract

A characteristic feature of the electroencephalogram (EEG) of the hippocampus and rhinal (entorhinal and perirhinal) cortex of the freely moving rat is theta rhythm, a prominent oscillation of approximately 8 Hz. Here we demonstrate that a novel rhythm that occurs at the border between the theta and alpha range of frequencies (10-12 Hz) can also be recorded from these structures. This rhythm (referred to here as "flutter") appears to be of non-theta origin as it can occur simultaneously with theta and it does not display the phase inversion across the hippocampus that characterizes theta activity. Flutter is observed in locomoting rats that are foraging for food reward in a familiar environment. Flutter disappears when rats are placed into a novel (although visually identical) environment, even though their foraging behavior does not appear to be altered. It is, at the present time, unclear what function flutter subserves. The presence of flutter may relate to a particular motivational state of the animal or to a particular type of information processing.

Medial Temporal Theta/Alpha Power Enhancement Precedes Successful Memory Encoding: Evidence Based on Intracranial EEG

“…For instance, alpha power was found to be increased in "dorsal-stream" areas devoted to processing of spatial relations during working memory maintenance of a face identity but not during maintenance of a face direction, suggesting an active role of alpha in the inhibition of task-irrelevant areas (Jokisch and Jensen, 2007). Furthermore, a rhinal and hippocampal alpha rhythm (between 10 and 12 Hz) has been detected in rats, which was prominent in a familiar environment, but disappeared in a novel environment (Nerad and Bilkey, 2005). This result is consistent with the idea of an alpha-related inhibitory control of memory formation, because there is no need for fresh encoding of the familiar environment.…”

Effect of aging on treadmill exercise induced theta power in the rat

“…The alpha power, beta power, and theta power of the EEG are dominant during the waking state (Nerad and Bilkey 2005). The increase in brain activity indicated by the alpha and beta powers of the EEG may be associated with the vigilance, alertness, and attention (Makeig and Jung 1995).…”

“…For each 16-s time segment, we quantified the total power (TP, 0.5-32 Hz), delta power (0.5-4 Hz), theta power (6-10 Hz), alpha power (10-13 Hz), and beta power (13-32 Hz) of the EEG spectrogram (Nerad and Bilkey 2005) as well as the power of the EMG spectrogram. We also calculated the mean power frequency (MPF) of the EEG spectrogram, which covered all these components using the following equation (Kuo et al 2004a, b):…”

“…The theta power of the electroencephalogram (EEG) is usually far more prominent during active waking (Nerad and Bilkey 2005). Evidence from humans (Cummins and Finnigan 2007;Doppelmayr et al 2000;Klimesch 1999;Laukka et al 1995) and rats (Landfield et al 1972;Olvera-Cortes et al 2004;Orr et al 2001) has suggested that the theta power of the EEG represents some special cognitive functions and/or special learning-related functions.…”

“…In addition to theta power, there are other rhythmic components of the EEG such as alpha power, beta power, and delta power. Alpha power and beta power are also related to the waking state (Makeig and Jung 1995;Nerad and Bilkey 2005). Delta power, in contrast, is related to sleep and is usually used to indicate the depth of sleep (Yang et al 2003).…”