Memory, Attention, and Default Mode Processes in Human Posteromedial Cortex

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DESCRIPTION (provided by applicant): Human mind is hallmarked by a continuous interplay between processing information from the physical environment and processing spontaneously generated information from long-term memory in the form of current concerns, future plans, wishes and recollections. This proposal aims to explore how this interplay is made possible by specific brain structures. For this purpose, we propose to study the function of the human posteromedial cortex (PMC) and determine its interaction with lateral parietal cortex (LPC) and medial temporal lobe (MTL) structures known to subserve attention and memory. The PMC is an important part of the brain structures that demonstrate reduced activity during the performance of externally directed attention tasks, while demonstrating higher activity during resting states when subjects are not engaged in any external interactions and when their minds wander. To date, the neurophysiological correlates of PMC function in the human brain, including its anatomical and temporal specificity, remain unexplored. We will address this gap of knowledge by directly monitoring and reversibly altering the activity of the PMC during cognitive tasks of attention and memory in conscious human subjects who are implanted with intracranial electrodes, as part of routine presurgical epilepsy evaluation. The proposed work will be the first to combine direct electrocorticography (ECoG) and electrical brain stimulation (EBS) in the human PMC. The neurophysiological activity of each PMC subregion will be directly recorded with high temporal resolution and individual subject anatomical precision, and will be altered to test the effect of 'transient lesions' in each subregion of the PMC during attention and memory conditions. Our overarching framework is that two PMC subregions, namely the posterior cingulated cortex (PCC) and the retrosplenial cortex (RSC), have non-overlapping roles and selective interactions with the networks of attention and memory, respectively. The resulting progress promises to shed light on the deficits associated with PMC dysfunction, in patients with attention deficit disorders, autism, epilepsy, and dementia.