Hippocampal and lateral entorhinal cortex physiological activity during trace conditioning under urethane anesthesia

Area of Science:

• Neuroscience
• Learning and Memory
• Anesthesia Research

Background:

• Delay conditioning acquisition can occur in unconscious states like anesthesia.
• The extent and type of conditioning possible in nonawake states remain unclear.
• Trace conditioning, with its time-discontinuous stimuli, is suitable for studying anesthesia-induced learning.

Purpose of the Study:

• To investigate if rats exhibit physiological responses during trace conditioning under anesthesia.
• To explore the brain activity in the hippocampus (HPC) and lateral entorhinal cortex (LEC) during this paradigm.
• To establish a novel preparation for studying memory acquisition of time-discontinuous events in nonawake brains.

Main Methods:

• Recorded HPC and LEC activity, electromyogram, and electrocardiogram in urethane-anesthetized rats.
• Utilized a trace conditioning protocol with two distinct auditory stimuli (CS- and CS+), where CS+ was paired with a footshock after a trace interval.
• Analyzed trial-average data for heart rate changes and high-frequency band power/coherence in HPC and LEC.

Main Results:

• Significant heart rate increases were observed during CS presentation and the trace period for both CS- and CS+ stimuli.
• Heart rate activity showed similar slopes but different intercepts for CS+ versus CS-.
• Increased power and coherence in HPC and LEC high-frequency bands (>100 Hz) occurred during CS presentation and trace, irrespective of stimulus type or brain state.

Conclusions:

• Rats demonstrate physiological responses consistent with trace conditioning acquisition under urethane anesthesia.
• This study provides the first evidence of trace conditioning under anesthesia, highlighting learning in nonawake states.
• The developed preparation offers a new avenue for investigating the neural mechanisms underlying the binding of time-discontinuous events in the nonawake brain.