Mapping subcortical connectivity related to cortical gamma and theta oscillations

An open problem in signal processing and bioimaging involves the development of techniques to localize the circuits that subserve neural oscillations in the living human brain. This is an important challenge for basic and translational neuroscience since frequency-specific rhythms are hypothesized to code for sensorimotor and cognitive processes and aberrations in these rhythms develop as early markers of pathology in disorders such as epilepsy and Parkinson´s disease. Methods to reconstruct the subcortical white matter networks related to different frequency bands have been limited by the dual challenges of recording electrical activity directly from human cortex with high spatial resolution and the inability, until a decade ago, to map white matter connectivity in vivo. In the present study, a multi-modal fusion of electrocorticography (ECoG) and diffusion tensor imaging (DTI) tractography data collected from 9 neurosurgical patients performing a working memory task known to elicit robust distributed cortical gamma and theta oscillations is presented. A similarity analysis of connectivity underlying 629 intracranial electrodes revealed distinct patterns of white matter terminating near cortex that exhibited gamma, theta, and conjoint gamma and theta oscillatory power. Future applications of this method for parcellating neural circuitry in normal and pathological states are discussed.