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In rats, theta wave rhythmicity is easily observed in the hippocampus, but can also be detected in numerous other cortical and subcortical brain structures. Hippocampal theta waves, with a frequency range of 6–10 Hz, appear when a rat is engaged in active motor behavior such as walking or exploratory sniffing, and also during REM sleep. [3]
It has been proposed that the trisynaptic circuit is responsible for the generation of hippocampal theta waves. These waves are responsible for the synchronization of different brain regions, especially the limbic system. [9] In rats, theta waves range between 3–8 Hz and their amplitudes range from 50 to 100 μV.
The theta wave is one of the largest signals seen on EEG, and is known as the hippocampal theta rhythm. [108] In some situations the EEG is dominated by regular waves at 3 to 10 Hz, often continuing for many seconds.
In the CA1 region of the hippocampus, where the place cells are located, these firing patterns give rise to theta waves. [7] Theta oscillations have classically been described in rats, but evidence is emerging that they also occur in humans. [8] In 1993, O'Keefe and Recce discovered a relationship between the theta wave and the firing patterns ...
When eating, grooming, drowsy, or sleeping in slow-wave sleep (SWS), there has been observed in hippocampal EEG, the non-rhythmic pattern of large irregular activity,(LIA). LIA has the predominant pattern of large amplitude slow waves that contain some fluctuations of sharp spikes (sharp waves) of 50–100 ms duration.
Ripples are only present when theta waves are relatively absent during sharp waves, whereas fast gamma waves occur during theta waves and sharp waves. [11] The magnitude and frequency of both ripples and fast gamma patterns are dependent on the magnitude of hippocampal sharp waves.
A major projection from the medial septal nucleus terminates in the hippocampal formation. [1] It plays a role in the generation of theta waves in the hippocampus. [2] Specifically, the GABAergic cells of the medial septum that act as theta pacemakers target dentate gyrus, CA3, and CA1 interneurons.
Buzsáki's primary interests is "neural syntax", i.e., how segmentation of neural information is organized by the numerous brain rhythms to support cognitive functions.He identified the cellular-synaptic basis of hippocampal theta, gamma oscillations and sharp waves with associated fast oscillations, their relationship to each other and to behavior and sleep.