From focal stroke to cortical islands: the impact of lesions on brain complexity and consciousness

The functional consequences of brain injury are known to depend on neuronal alterations extending beyond the area of structural damage. Although a lateralized EEG slowing over the injured hemisphere was known since the early days of clinical neurophysiology, its electrophysiological mechanisms were not systematically investigated. These EEG events reflect brief interruptions of neuronal firing (OFF-periods) that can occur locally and have prominent consequences on network and behavioral functions. Previous works, probing cortical circuits with transcranial magnetic stimulation coupled with EEG (TMS/EEG) proved as an effective way to reveal the tendency of cortical circuits to transiently plunge into silent OFF-periods. Here, using this approach, we show that the intact cortex surrounding focal brain injuries engages locally in pathological sleep-like dynamics. Specifically, we employed TMS/EEG in a cohort of ten conscious awake patients with chronic focal injuries of various etiologies. The data set consists of preprocessed TMS/EEG stimulus-responses (hundreds of trials per stimulus) and allows to perform complementary analysis with respect to the Perturbational Complexity Index used in this study.