Cortical Integration in Humans: An Intracranial Investigation of Neural Synchrony

University Of California, San Diego, La Jolla CA

Investigators

Abstract

PROJECT SUMMARY / ABSTRACT It is unknown how the 16 billion neurons in the human cortex coordinate to integrate diverse streams of information into coherent perception, cognition, and action. Understanding the mechanisms of cortical integration is crucial for unraveling how the brain orchestrates thought and behavior—a problem that is at the heart of all neurosciences. However, the mechanisms of cortical integration remain unclear for two primary reasons (1) recording devices typically used in humans, such as EEG and fMRI, are limited in spatial and temporal resolution, which constrains our ability to measure neural activity; and (2) although much research has focused on the localization of specific cognitive functions to different cortical areas, less attention has been paid to understanding how functional activity in those areas is integrated. This proposal aims to leverage rare intracranial recordings in humans during cognitive tasks to investigate the neural mechanisms underlying cortical integration across multiple domains. These invasive recordings of local field potentials (LFP) and single units offer unparalleled spatial and temporal resolution. Recent work in human intracranial electrophysiology has identified cortical ripples as a promising indicator of cortical integration. These brief, high-frequency oscillations co-occur and synchronize across distant regions of the cortex during cognitive tasks. Specifically, synchronized ripples form a highly interconnected frontoparietal network prior to correct semantic judgments. Furthermore, coordination of single-neuron firing in different cortical locations is enhanced when both locations are rippling. Together, these results suggest that ripples are a strong candidate for involvement in cortical integration. This study will expand upon these observations by investigating ripple co-occurrence in new contexts to better understand their function in the brain. To date, ripple synchrony has only been rigorously studied in semantic judgment tasks to visual words. This work aims to explore whether ripple synchronization extends to other sensory modalities (auditory words) and cognitive domains (facial processing). Ripple-modulation of single units has only been studied during spontaneous behavior at short-range. This study will expand upon those results to determine whether ripple- modulation of units extends to other tasks and longer ranges. Finally, ripple networks during tasks have only been studied in the left hemisphere. This study will investigate if ripple synchronization occurs in and between both hemispheres. This study will use a combination of archival, open source, and novel data with a variety of recording types to accomplish these goals. The results of this project will provide critical insights into the function, distribution, and dynamics of the brain and will shed light on the mechanisms of cortical integration in humans.