Is electrical coupling involved in the generation of posterior hypothalamic theta rhythm?

The Role of the Posterior Hypothalamus in the Modulation and Production of Rhythmic Theta Oscillations

Theta rhythm recorded as an extracellular synchronous field potential is generated in a number of brain sites including the hippocampus. The physiological occurrence of hippocampal theta rhythm is associated with the activation of a number of structures forming the ascending brainstem-hippocampal synchronizing pathway. Experimental evidence indicates that the supramammillary nucleus and posterior hypothalamic nuclei, considered as the posterior hypothalamic area, comprise a critical node of this ascending pathway. The posterior hypothalamic area plays an important role in movement control, place-learning, memory processing, emotion and arousal. In the light of multiplicity of functions of the posterior hypothalamic area and the influence of theta field oscillations on a number of neural processes, it is the authors' intent to summarize the data concerning the involvement of the supramammillary nucleus and posterior hypothalamic nuclei in the modulation of limbic theta rhythmicity as well as the ability of these brain structures to independently generate theta rhythmicity.

The role of the posterior hypothalamic area in the generation of theta rhythm

Theta rhythm is one of the best synchronized patterns of the oscillatory activity recorded in the mammalian brain. In humans, this rhythm is associated with REM sleep, spatial navigation, memory functions, analytical and language processes. On the other hand, it can be treated as a non-specific marker of such pathological states of the central nervous system as Alzheimer’s disease or epilepsy. The hippocampal formation is the key structure involved in the generation of this bioelectric phenomenon, both in humans and rodents (the most commonly studied laboratory animals). Theta rhythm appearance in the hippocampus is dependent on the interaction of multiple different structures of the nervous system. One of them is the posterior hypothalamic area (PHa), which constitutes a crucial part of the neuronal system modulating the ability of the hippocampal formation to generate theta rhythm. Although the research results encompassed in this paper emphasize the essential role of the PHa as a modulator of the hippocampal theta rhythm, it was the authors’ intent to indicate that this area is also capable of generating local rhythmical theta oscillations, independently of the influence of other brain structures.