Involvement of the Postrhinal and Perirhinal Cortices in Microscale and Macroscale Visuospatial Information Encoding

Area of Science:

• Neuroscience
• Cognitive Neuroscience
• Memory Research

Background:

• The postrhinal cortex (POR) integrates spatial information, while the perirhinal cortex (PRC) encodes objects for spatial learning.
• Both POR and PRC project to the hippocampus, crucial for associative memory formation.
• Hippocampal encoding of item-place memories involves immediate early genes (IEGs), with distinct patterns for macroscale versus microscale learning.

Purpose of the Study:

• To investigate the extent to which the PRC and POR support hippocampal processing of different item-place representations.
• To examine the differential effects of macroscale and microscale item-place learning on IEG expression in the PRC and POR.

Main Methods:

• Utilized fluorescence in situ hybridization (FISH) to measure the nuclear expression of the IEG, Arc.
• Compared Arc mRNA levels following macroscale (overt, landmark) and microscale (subtle, discrete) item-place learning tasks.

Main Results:

• Macroscale item-place learning significantly increased Arc mRNA in the caudal PRC (area 35) and caudal POR.
• Microscale item-place learning did not induce significant changes in Arc mRNA in these regions.
• Specific subregions of the PRC (area 36) and POR showed no response to either learning type.

Conclusions:

• Macroscale items, likely possessing a strong identity component, are processed by specific compartments within the PRC and POR.
• Small, microscale items are not encoded by the POR or PRC, suggesting item dimensions influence the involvement of these structures.
• These findings highlight a dimensional role for the PRC and POR in item processing within spatial memory.