Perirhinal cortex contributes to accuracy in recognition memory and perceptual discriminations

Area of Science:

• Neuroscience
• Cognitive Psychology
• Neuroimaging

Background:

• The medial temporal lobe (MTL) is traditionally associated with long-term declarative memory.
• Emerging evidence suggests the perirhinal cortex (PRc) within the MTL may also contribute to perceptual tasks, especially those involving stimuli with significant visual overlap.
• Previous human studies on this topic yielded inconclusive results due to large and variable lesions in patient cohorts.

Purpose of the Study:

• To investigate the role of the perirhinal cortex (PRc) in perceptual discriminations using functional magnetic resonance imaging (fMRI) in healthy individuals.
• To compare PRc involvement in a perceptual oddball task with its known role in recognition memory, while controlling for behavioral performance levels.
• To determine if PRc activation is performance-related and if declarative memory demands influence its engagement in perceptual tasks.

Main Methods:

• Functional magnetic resonance imaging (fMRI) was employed in healthy participants.
• A perceptual oddball task using morphed faces (high visual feature overlap) was designed.
• A recognition memory task involving forced-choice identification of previously studied faces was also conducted.
• Behavioral performance levels were matched across tasks to allow for direct comparison of brain activity.

Main Results:

• Comparable activation was observed in the right perirhinal cortex (PRc) for both the perceptual oddball task and the recognition memory task when behavioral performance was matched.
• Activity in the right PRc demonstrated a performance-related modulation, differentiating between accurate and inaccurate trials in both tasks.
• Introducing declarative memory demands into a matched perceptual task did not necessarily increase PRc involvement.

Conclusions:

• Performance-related engagement of the perirhinal cortex (PRc) is not solely dependent on declarative memory demands.
• The findings suggest that the distinction between declarative memory and perception at the level of MTL functioning is less clear-cut than previously assumed.
• The perirhinal cortex (PRc) plays a role in perceptual processing, particularly when dealing with complex visual stimuli, in addition to its established role in memory.