A Synthetic View of Local and Extrahypothalamic Neural Circuits

Abstract

If intrahypothalamic organization is compared to the distribution of external afferents to the MBH, another aspect of hypothalamic organization becomes apparent: the morphological possibility of a hierarchic-sequential processing of information. This is shown in Fig. 31. The three elements of the above module (NVM, NA, ME) are indicated on three successive levels. Depending on the amount of input and direction of connections each information channel is indicated by arrows. The scheme, of course, simplifies the situation if it is assumed that this module is a general one. (It seems likely that various craniocaudal modules possess different afferentations.) The NVM appears to process the entering information first; this nucleus has the richest external afferentation. Usually the same structures send fibers to both the NVM and NA, but the former receives many more. As there is only a minimal interconnection between the NA portions, afferents from the NVM affect a relatively narrow part of the NA. Thus, the information remains “segmental” and is relayed accordingly to the ME, where neural input is translated to chemical signals. The importance of the monoaminergic afferents is that they can modulate hypothalamic activity at all levels of this postulated construction.