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59:(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. The predominant frequency of LIA is slower than that of theta waves. LIA is often accompanied by
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It has been suggested that the theta state is inactive during the presence of LIA and think that theta ordinarily provides an inhibitory process which locks most of the pyramidal cells so that only a few can fire at any time. When LIA is present large numbers of pyramidal cells are activated. There
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Theta rhythm with its low frequency of around 6–7 Hz in a steady oscillation has been observed in rats that are motionless but alert. This extends to that sleeping cycle characterised by rapid eye movement (REM). When eating, grooming, drowsy, or sleeping in
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are quite small and diffuse and from the deeper smaller hippocampus they are much more difficult to register. This has meant the study of hippocampal activity has been largely restricted to that of the rat and less often the mouse.
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The theta state is thought to be involved in the process of learning, and retrieval, and LIA is thought to be involved in the consolidation of older memories. However the mechanism of these two field oscillations remains unknown.
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is always a delay of a few seconds between the onset of behaviour related to LIA, such as resting and the subsequent sharp wave and ripples, suggesting the release from active inhibition.
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of a higher frequency than that of theta. LIA accompanies the small irregular activity state to which the term LIA has been used to describe overall (termed by
Vanderwolf, 1969).
39:. The theta state is characterised by a steady slow oscillation of around 6–7 Hz. LIA has a predominantly lower oscillation frequency but contains some sharp spikes, called
247:"Chaotic dynamics as a possible mechanism of rapid change of hippocampal local field activity between theta rhythm and large irregular activity"
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of the hippocampus is activated it tends to oscillate at theta frequencies. It has also been noted that a fair proportion of hippocampal
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Buzsáki, G (29 November 1986). "Hippocampal sharp waves: their origin and significance".
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Tokuda, Keita; Katori, Yuichi; Aihara, Kazuyuki (16 July 2012).
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Jarosiewicz, B; McNaughton, BL; Skaggs, WE (15 February 2002).
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EEG signals picked up in the human (or any large mammalian)
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35:. The other field state is that of the
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