Intracranial EEG reveals working memory-related dynamics and connectivity in human white matter.

White matter dysfunction is increasingly implicated in working memory impairment across neurological and psychiatric disorders, yet the electrophysiological basis of white matter involvement in working memory remains poorly understood. Although recent functional MRI studies suggest that white matter tracts exhibit task-related BOLD modulation, these methods cannot resolve the fast, frequency-specific electrophysiological interactions associated with working memory. Here, we recorded intracranial stereotactic EEG (sEEG) from 20 patients with drug-resistant epilepsy performing an N-back working memory task to characterize neural activity and connectivity within human white matter. Working memory load evoked robust, tract- and frequency-specific modulations of local field potentials: gamma and high-gamma power increased in the frontal blade tract but decreased in the splenium of the corpus callosum/superior parietal blade tract, whereas the temporal blade exhibited enhanced theta power with relatively stable high-frequency responses. Although within-frequency functional connectivity among white matter regions remained highly stable across task conditions, cross-frequency connectivity, particularly theta-high-gamma coupling, was selectively enhanced with increasing working memory load. These findings provide intracranial electrophysiological evidence that human white matter exhibits load-dependent, tract-specific, and frequency-resolved functional dynamics during working memory.