The Cholinergic Basal Forebrain Links Auditory Stimuli with Delayed Reinforcement to Support Learning

Area of Science:

• Neuroscience
• Learning and Memory
• Auditory Processing

Background:

• Auditory cortex (ACx) plasticity supports fear learning when conditioned stimuli (CSs) overlap with unconditioned stimuli (USs).
• Acetylcholine release from the basal forebrain is crucial for this temporal overlap and ACx reorganization.

Purpose of the Study:

• To investigate if fear learning and ACx plasticity occur with delayed US presentation.
• To elucidate the mechanisms in the basal forebrain that support learning with extended CS-US intervals.

Main Methods:

• Auditory fear conditioning with a 5-second CS-US gap.
• Optogenetic identification and manipulation of basal forebrain neurons.
• In vivo calcium imaging of basal forebrain cholinergic neuron activity.

Main Results:

• Robust fear learning and acetylcholine-dependent ACx plasticity were observed despite the 5-second CS-US delay.
• Basal forebrain neurons encoding the US rapidly increased responses to the CS and coupled functionally with ACx.
• Sustained, sound-evoked activity in basal forebrain cholinergic neurons filled the temporal gap preceding the US.

Conclusions:

• The basal forebrain exhibits plasticity that bridges significant temporal gaps between sensory cues and reinforcement.
• This plasticity in the basal forebrain is critical for forming associations with delayed rewards.
• Findings reveal a novel mechanism for learning associations across extended time intervals.