Page "Hippocampus" Paragraph 39

Because of its densely packed neural layers, the hippocampus generates some of the largest EEG signals of any brain structure.

In some situations the EEG is dominated by regular waves at 3 – 10 Hz, often continuing for many seconds.

These reflect subthreshold membrane potentials and strongly modulate the spiking of hippocampal neurons and synchronise across the hippocampus in a travelling wave pattern.

This EEG pattern is known as a theta rhythm.

Theta rhythmicity is very obvious in rabbits and rodents, and also clearly present in cats and dogs.

Whether theta can be seen in primates is a vexing question.

In rats ( the animals that have been the most extensively studied ), theta is seen mainly in two conditions: first, when an animal is walking or in some other way actively interacting with its surroundings ; second, during REM sleep.