Delineating the Neural Circuitry Underlying Crossmodal Object Recognition in Rats
Previous research has indicated that the perirhinal cortex (PRh) and posterior parietal cortex (PPC) functionally interact to mediate crossmodal object representations in rats; however, it remains to be seen whether other cortical regions contribute to this cognitive function. The prefrontal cortex (PFC) has been widely implicated in crossmodal tasks and might underlie either a unified multimodal or amodal representation or comparison mechanism that allows for integration of object information across sensory modalities. The hippocampus (HPC) is also a strong candidate, with extensive polymodal inputs, and has been implicated in some aspects of object recognition. A series of lesion based experiments assessed the roles of HPC, PFC and PFC sub regions [medial prefrontal (mPFC) and orbitofrontal cortex (OFC)], revealing functional dissociations between these brain regions using two versions of crossmodal object recognition: 1. spontaneous crossmodal matching (CMM), which requires rats to compare between a stored tactile object representation and visually-presented objects to discriminate the novel and familiar stimuli; and 2. crossmodal object association (CMA), in which simultaneous pre-exposure to the tactile and visual elements of an object enhances CMM performance across long retention delays. Notably, while inclusive PFC lesions impaired both CMM and CMA tasks, selective OFC lesions disrupted only CMM, whereas selective mPFC damage did not impair performance on either task. Furthermore, there was no impact of HPC lesions on either CMM or CMA tasks. Thus, the PFC and the OFC play a selective role in crossmodal object recognition but the exact contributions and interactions of the regions will require further research to elucidate.