Conditioning-specific reflex modification of rabbit (Oryctolagus cuniculus) heart rate

Area of Science:

• Neuroscience
• Behavioral Psychology
• Physiology

Background:

• Conditioning-specific reflex modification (CRM) is a phenomenon observed in rabbit nictitating membrane responses (NMR).
• Previous research has established CRM in NMR but its occurrence in other physiological systems remains unclear.
• Understanding CRM's generalizability is crucial for comprehending associative learning mechanisms.

Purpose of the Study:

• To investigate whether conditioning-specific reflex modification (CRM) occurs in rabbit heart rate (HR) responses.
• To determine if HR CRM can be induced following classical conditioning of heart rate.
• To explore the physiological underpinnings of HR CRM.

Main Methods:

• Rabbits underwent classical conditioning procedures pairing a tone (conditioned stimulus) with electrodermal stimulation (unconditioned stimulus).
• Heart rate (HR) and electrocardiograms (ECG) were monitored throughout the conditioning and testing phases.
• The unconditioned stimulus (US) was presented alone after conditioning to assess for CRM in HR.

Main Results:

• Conditioning-specific reflex modification (CRM) of rabbit heart rate (HR) was observed.
• A US that initially elicited HR acceleration was found to elicit HR deceleration after conditioning.
• Increased PQ intervals, indicative of parasympathetic function, correlated with both HR conditioning and CRM.

Conclusions:

• Conditioning-specific reflex modification (CRM) is not limited to the nictitating membrane response system and can occur in rabbit heart rate.
• Conditioned heart rate deceleration can generalize from the conditioned stimulus to the unconditioned stimulus.
• The findings suggest a role for parasympathetic nervous system activity in mediating HR CRM.