New Hippocampal and Medial Frontal Cortex Circuits
Paola Alemán-Andrade, Menno P. Witter, Ken-Ichiro Tsutsui, and Shinya Ohara
(see article e0217252025)
Memory and emotion regulation rely on projections from the ventral hippocampus to the medial frontal cortex (MFC). In this issue, Alemán-Andrade and colleagues unveiled previously unknown circuits between these brain regions in mice. Through the use of anterograde transsynaptic tracing and ex vivo electrophysiology, they found a pathway between the dorsal-caudal hippocampus to distinct subregions of the ventral MFC. This pathway essentially works to strongly inhibit the ventral MFC through parvalbumin- and somatostatin-expressing interneurons. The authors also found, via retrograde transsynaptic tracing in rats, that ventral MFC subregions project back to the ventral hippocampus. Though the behavioral relevance of these circuits remains unexplored, these findings point to a new link between cognition (regulated by dorsal caudal hippocampus) and emotion regulation (supported by ventral MFC and ventral hippocampus). Furthermore, according to the authors, this study may inform future work looking at the strength of these circuits in neurological disease states.
Shown is expression and colocalization of GFP (green), parvalbumin (red), and somatostatin (violet). This immunohistological strategy helped map innervations onto both parvalbumin and somatostatin interneurons in the mouse MFC. See Alemán-Andrade et al. for more information.
Distinct Neural Processes for Discriminating between Scenes
Marie-Lucie Read, Carl Hodgetts, Andrew D. Lawrence, C. John Evans, Krish D. Singh et al.
(see article e1700242025)
Research suggests that the hippocampal posteromedial system supports the ability to perceive, recall, and imagine complex visual scenes. However, more work is needed to understand the functional and structural properties of this system, especially during perceptual experiences that do not involve memory. Read et al. used a combined electrophysiological and microstructural imaging approach to explore the hippocampal posteromedial system in 40 people. They discovered that accurately discriminating between scenes presented from different viewpoints was associated with theta power modulation of the hippocampus and, independently, with fiber restriction of the fornix. Thus, complex visual scene perception may involve multiple processing streams embedded within the medial temporal lobe.
Footnotes
This Week in The Journal was written by Paige McKeon
