Ventral hippocampal shock encoding modulates the expression of trace cued fear

Area of Science:

• Neuroscience
• Behavioral Neuroscience

Background:

• The hippocampus is vital for associative fear learning, especially trace and contextual conditioning.
• The ventral hippocampus's role in fear learning is less understood than the dorsal hippocampus, despite its connections to emotional networks.
• It's unclear if the ventral hippocampus's fear learning function stems from affective processing, associative encoding, or both.

Purpose of the Study:

• To investigate the ventral hippocampus's contribution to associative fear memory acquisition.
• To determine if shock encoding in the ventral hippocampus is necessary for learning fear memories.
• To assess the impact of ventral hippocampal activity during shock on fear memory expression.

Main Methods:

• Used trace fear conditioning in mixed-sex cohorts.
• Recorded neuronal activity in the ventral hippocampus during conditioning.
• Optogenetically silenced ventral hippocampus during the unconditioned stimulus (UCS) to test necessity of shock encoding.

Main Results:

• Ventral CA1 neurons primarily encoded the shock unconditioned stimulus (UCS), not the trace interval.
• Silencing ventral hippocampus during the UCS did not impair fear acquisition but prolonged conditioned stimulus (CS) freezing in males.
• Contextual fear learning remained largely intact, with some sex-specific variations.

Conclusions:

• Shock encoding in the ventral hippocampus modulates, rather than dictates, fear memory expression.
• This modulation appears to be sex-specific, with males showing prolonged fear responses.
• The ventral hippocampus's role in fear learning may be more complex than simple associative encoding.