Perirhinal cortex removal dissociates two memory systems in matching-to-sample performance in rhesus monkeys

Area of Science:

• Neuroscience
• Cognitive Psychology
• Animal Behavior

Background:

• Traditional cognitive tests struggle to isolate individual memory processes when multiple systems contribute to performance.
• Habits and one-trial memory are distinct memory systems often assessed using separate tasks.
• Understanding the neural basis of these memory systems requires methods that can quantify their independent contributions.

Purpose of the Study:

• To adapt and apply the process dissociation procedure (PDP) in monkeys to measure the contributions of habit and one-trial memory.
• To investigate the role of the perirhinal cortex in these distinct memory processes.
• To establish a method for comparing memory neurobiology across species.

Main Methods:

• Utilized a visual matching-to-sample task adapted for PDP in monkeys.
• Manipulated image frequencies across days to establish habit formation.
• Quantified habit contributions based on choices favoring high-frequency images.
• Quantified one-trial memory based on choices favoring the sample image.
• Assessed the impact of perirhinal cortex removal on these memory components.

Main Results:

• The adapted PDP successfully measured contributions of habit and one-trial memory in monkeys.
• Perirhinal cortex removal significantly reduced the contribution of one-trial memory to performance.
• Habit formation and the ability to discriminate images remained intact after perirhinal cortex removal.

Conclusions:

• PDP provides a quantitative method to dissociate memory processes in nonhuman animals.
• The perirhinal cortex is crucial for one-trial memory but not for habit formation or basic image discrimination.
• This approach facilitates comparative studies of memory neurobiology across species.