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.