The Septum as a Pacemaker for the Hippocampal Theta Rhythm
Before one can deal with the rhythmic interplay between hippocampus and iso-cortex, many questions need to be resolved about the physical mechanism of the theta rhythm. In the next two chapters the focus is on the mechanisms controlling the initiation and frequency of the theta rhythm. Chapter 5 concentrates on the theta rhythm per se, while Chapter 6 considers evidence that there is more than one variety of theta rhythm and control mechanism. Here, the following questions are addressed: What brain mechanisms initiate theta activity? What mechanism sets the frequency of the theta rhythm? It appears that the septal region is involved in both these processes; but is the septum sufficient to initiate rhythmic activity in the hippocampus, or does the hippocampus contribute any rhythmic capacity of its own to the theta rhythm? How does the septum control initiation and frequency of theta activity? Is it here that the frequency is set, or in some of its afferent signals arriving from the brainstem and elsewhere? In any case, how does the rest of the brain control the production and frequency of the theta rhythm?
KeywordsNicotine Atropine Carbachol Physostigmine Arecoline
Unable to display preview. Download preview PDF.