Disruption of theta-timescale spiking impairs learning but spares hippocampal replay

Disrupting theta-timescale spiking in rats during locomotion impairs learning in a spatial alternation task while preserving hippocampal replay during immobility.

• Why it matters: Theta-associated temporal structure during movement is linked to spatial coding, but its specific role in learning versus replay has been unclear.
• What they did: Rats received closed-loop, theta phase-specific optogenetic activation of septal parvalbumin-expressing GABAergic neurons to reduce theta power shortly after stimulation onset, disrupting theta sequences while preserving individual place codes.
• The result: Theta disruption during locomotion produced pronounced deficits in the cognitively challenging alternation component despite targeting only ~66% of trials, without changing replay rate, length, or content during immobility.

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