Role of the prefrontal--thalamic axis in classical conditioning

Area of Science:

• Neuroscience
• Behavioral Neuroscience
• Cardiovascular Physiology

Background:

• Classical conditioning involves learning associations between stimuli, often resulting in physiological responses.
• Visceral changes, such as heart rate deceleration (bradycardia), are key indicators of learned responses.
• The prelimbic cortex (PFCag) is a brain region implicated in various cognitive and emotional processes.

Purpose of the Study:

• To investigate the role of the prelimbic cortex (PFCag) in the acquisition of conditioned bradycardia.
• To determine the specific subregions within the PFCag critical for learned cardiac inhibition.
• To examine the neural mechanisms underlying conditioned bradycardia in relation to PFCag activity.

Main Methods:

• Lesion studies targeting different subregions of the PFCag (PFCm, lag).
• Neuroanatomical tract-tracing to identify projections from the PFCag to medullary nuclei.
• Electrophysiological recordings (MUA, single unit) in the PFCag during classical conditioning.
• Electrical stimulation of the PFCm to assess its role in parasympathetic activity.

Main Results:

• Damage to the PFCm significantly attenuated or abolished learned bradycardia.
• The PFCm projects to medullary nuclei (NTS, DVM, nucleus ambiguous) involved in visceral control.
• PFCm neuronal activity (MUA) increased in response to the conditioned stimulus (CS) and correlated with bradycardia.
• Lesions of the lag region had minimal impact on conditioned bradycardia.

Conclusions:

• The prelimbic cortex, particularly the medial part (PFCm), plays a primary and necessary role in establishing conditioned bradycardia.
• Learned bradycardia involves inhibitory visceral changes mediated by PFCm projections to the brainstem.
• PFCm neuronal activity during conditioning reflects associative learning and contributes to the expression of conditioned bradycardia.