Mild traumatic brain injury alters function in the dorsolateral prefrontal cortex: a TMS-EEG study

OBJECTIVE: The neurophysiological effects of mild traumatic brain injury (mTBI) in cognitive brain areas remains limited. We addressed this limitation by using electroencephalography to index responses to transcranial magnetic stimulation (TMS-EEG) over the dorsolateral prefrontal cortex (DLPFC). METHODS: TMS-EEG was used to index cortical inhibition (via paired-pulse TMS) and long-term depression (LTD)-like plasticity (via continuous theta burst stimulation [cTBS]) within DLPFC in 18 mTBI patients and 22 controls. Functional effects of injury were assessed via the N-back and Trail Making Test. Responses were quantified in both temporal (i.e., TMS-evoked potentials; TEPs) and spectral (i.e., TMS-related oscillations; TROs) domains. RESULTS: For TEPs, measures of inhibition and plasticity both tended to be reduced by mTBI. In contrast, TRO data suggested an increased response of patients to both paired-pulse stimulation and cTBS that was specific to high-frequency bands. In addition, while TMT performance was reduced in the mTBI group, this was unrelated to neurophysiological effects of injury. CONCLUSIONS: While DLPFC function is altered following mTBI, the nature of this effect depends on how the data is examined (considering evoked vs. induced activity). SIGNIFICANCE: These findings highlight novel effects of mTBI on DLPFC neurophysiology, possibly reflecting dysregulated cortical inhibitory function and neuroplasticity.