Thalamo-hippocampal pathway regulates incidental memory capacity in mice

Area of Science:

• Neuroscience
• Cognitive Science
• Animal Behavior

Background:

• The dorsal hippocampus (dHP) is implicated in memory consolidation and handling high memory loads.
• Mechanisms underlying sex differences in incidental memory and hippocampal function remain unclear.

Purpose of the Study:

• To investigate sex-based differences in incidental memory capacity and the underlying neural mechanisms.
• To explore the role of the ventral midline thalamus (VMT) and its pathway to the dHP in memory consolidation.

Main Methods:

• Utilized a different object recognition task (DOT) with varying retention delays (1h, 24h) and memory loads (6 objects).
• Measured neural activation using c-Fos expression in male and female mice.
• Employed optogenetics and chemogenetics to manipulate the VMT-dHP pathway during memory consolidation.

Main Results:

• Female mice, despite similar short-term memory (STM) capacity, transferred fewer objects (4/6) to long-term memory (LTM) compared to males (6/6) after 24h.
• Male mice exhibited greater dHP activation, while females showed greater VMT activation.
• Inhibiting the VMT-dHP pathway improved LTM in females; activating VMT impaired LTM in males.

Conclusions:

• Sex differences exist in incidental memory consolidation, linked to distinct neural activation patterns in the VMT and dHP.
• The VMT exerts inhibitory control over the dHP, influencing LTM capacity.
• Modulating sub-cortical control over the hippocampus alters incidental memory performance.