A dorsal subiculum-medial mammillary body pathway for spatial memory

Area of Science:

• Neuroscience
• Cognitive Neuroscience
• Systems Neuroscience

Background:

• The extended hippocampal system is vital for spatial memory.
• The precise role of the dorsal subiculum (dSub) to medial mammillary body (MM) projection remains unclear.

Purpose of the Study:

• To investigate the function of the dSub-MM projection in spatial memory.
• To map the projection targets of dSub neurons projecting to the MM.

Main Methods:

• Utilized c-fos mapping, fiber photometry, and optogenetics.
• Employed behavioral paradigms for spatial memory assessment.
• Mapped single neuron projectome using fluorescence micro-optical sectioning tomography (fMOST).

Main Results:

• The dSub-MM monosynaptic connection is essential for spatial memory retrieval.
• This pathway's activity is sensitive to bidirectional perturbations.
• Individual dSub neurons project to bilateral MM and collateralize to retrosplenial cortex (RSP) and entorhinal cortex (ENT).

Conclusions:

• The dSub-MM circuit plays a key role in spatial memory retrieval.
• Identified novel projection neuron subtypes and organizational principles in the MM afferent circuitry.
• Elucidated the circuit mechanisms underlying the dSub-MM contribution to spatial memory.