Hypothalamic Supramammillary Control of Cognition and Motivation

Abstract

The supramammillary nucleus (SuM) is a small region in the ventromedial posterior hypothalamus. The SuM has been relatively understudied with much of the prior focus being on its connection with septo-hippocampal circuitry. Thus, most studies conducted until the 21st century examined its role in hippocampal processes, such as theta rhythm and learning/memory. In recent years, the SuM has been "rediscovered" as a crucial hub for several behavioral and cognitive processes, including reward-seeking, exploration, and social memory. Additionally, it has been shown to play significant roles in hippocampal plasticity and adult neurogenesis. This review highlights findings from recent studies using cutting-edge systems neuroscience tools that have shed light on these fascinating roles for the SuM.

Figure 1.

A survey of SuM connectivity and functions in cognition. Schematics represent a flat map adopted and modified from Swanson (2004). Left, A highly simplified summary of several SuM pathways related to cognitive processes that are highlighted in this review. Arrows are color-coded to match text in the key in the bottom portion of the schematic. Right, Efferent (yellow), afferent (blue), and reciprocal (green) projections of the SuM are indicated. The medial/lateral subdivisions of the SuM are ignored. For a visual overview of SuM medial/lateral connectivity and cytoarchitecture, see Pan and McNaughton, 2004 (their Fig. 3). ATN, Anterior nuclei, dorsal thalamus; BST, bed nucleus of stria terminalis; CA2, cornu ammonis 2 of the hippocampus; CG, cingulate cortex; CL, centrolateral thalamic nucleus; CM, central medial thalamic nucleus; CN, cerebellar nuclei; DB, diagonal band of Broca; dHIP, dorsal hippocampus; DG, dentate gyrus; DP, dorsal peduncular cortex; DR, dorsal raphe nucleus; ENT, entorhinal area; IL, infralimbic cortex; IP, interpeduncular nucleus; LC, locus coeruleus; LDTg, laterodorsal tegmental nucleus; LHb, lateral habenular nucleus; LS, lateral septal area; MM, medial mammillary nucleus; mMD, medial mediodorsal thalamic nucleus; MPO, medial preoptic area; MR, median raphe nucleus; MS, medial septal area; mVP, medial ventral pallidum; NTS, nucleus of the solitary tract; PAG, periaqueductal gray; PB, parabrachial nucleus; PH, posterior hypothalamic nucleus; PL, prelimbic cortex; PT, paratenial thalamic nucleus; PV, paraventricular thalamic nucleus; pVTA, posterior VTA; RE, reuniens thalamic nucleus; RMTg, rostromedial tegmental nucleus; SUB, subiculum; SuM, supramammillary nucleus; vStr, ventral striatum. Right, Modified from Ikemoto (2010, their Fig. 8).