Abstract
The mammillary body (MB) has been thought to implement mnemonic functions. Although recent animal studies have revealed dissociable roles of the lateral and medial parts of the MB, the dissociable roles of the lateral/medial MB in the human brain is still unclear. Functional connectivity using resting-state functional magnetic resonance imaging (fMRI) provides a unique opportunity to noninvasively inspect the intricate functional organization of the human MB with a high degree of spatial resolution. The present study divided the human MB into lateral and medial parts and examined their functional connectivity with the hippocampal formation, tegmental nuclei, and anterior thalamus. The subiculum of the hippocampal formation was more strongly connected with the medial part than with the lateral part of the MB, whereas the pre/parasubiculum was more strongly connected with the lateral part than with the medial part of the MB. The dorsal tegmental nucleus was connected more strongly with the lateral part of the MB, whereas the ventral tegmental nucleus showed an opposite pattern. The anterior thalamus was connected more strongly with the medial part of the MB. These results confirm the extant animal literature on the lateral/medial MB and provide evidence on the parallel but dissociable systems involving the MB that ascribe mnemonic and spatial-navigation functions to the medial and lateral MBs, respectively.
Highlights
The mammillary body (MB) receives inputs from the hippocampal formation and tegmental nuclei and sends outputs to the tegmental nuclei (Vann, 2010)
Recent animal research has revealed that, while the lateral and medial MBs are connected to the same overall structures, they are connected to different subregions of these structures, forming two parallel but dissociable pathways (Vann and Aggleton, 2004): the medial MB receives inputs from the subiculum and ventral tegmental nucleus and projects to the ventral tegmental nucleus, while the Networks of Human Mammillary Body lateral MB receives inputs from the pre/parasubiculum and dorsal tegmental nucleus and sends outputs to the dorsal tegmental nucleus (Vann, 2010; Dillingham et al, 2015)
Functional dissociation between the lateral and medial MBs has been demonstrated: behavioral studies of selective disconnections of the medial MB using discrete lesions of the mammillothalamic tract revealed that the medial MB is related to spatial memory (Vann and Aggleton, 2004), and electrophysiological studies reported that the lateral MB contains head-direction cells, indicating that the lateral MB contributes to spatial navigation (Blair et al, 1998; Stackman and Taube, 1998; Taube, 2007)
Summary
The mammillary body (MB) receives inputs from the hippocampal formation and tegmental nuclei and sends outputs to the tegmental nuclei (Vann, 2010). Recent animal research has revealed that, while the lateral and medial MBs are connected to the same overall structures, they are connected to different subregions of these structures, forming two parallel but dissociable pathways (Vann and Aggleton, 2004): the medial MB receives inputs from the subiculum and ventral tegmental nucleus and projects to the ventral tegmental nucleus, while the. Networks of Human Mammillary Body lateral MB receives inputs from the pre/parasubiculum and dorsal tegmental nucleus and sends outputs to the dorsal tegmental nucleus (Vann, 2010; Dillingham et al, 2015). Functional connectivity analyses of restingstate data obtained with functional magnetic resonance imaging (fMRI) (Fox and Raichle, 2007; Honey et al, 2009; Biswal et al, 2010; Yeo et al, 2011; Margulies et al, 2016; Miyashita, 2016) may identify the lateral-medial dissociation in the human MB. To attain a sufficient signal-to-noise ratio in functional images with a higher spatial resolution (1.25 × 1.25 × 1.25 mm3), each subject was highly sampled: 1,000 volumes in each of the 10 daily sessions
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