Assessing cortical network properties using TMS–EEG

TLDR

TMS–EEG has become feasible in the past decade thanks to hardware, amplifier, and processing advances that reduce artifacts, enabling direct assessment of cortical excitability and connectivity. This review examines online and offline artifact‑reduction methods and the physiological insights obtainable from TMS‑evoked cortical responses. TMS–EEG records cortical responses to directly measure excitability, connectivity, and oscillatory tuning, and is applied to study inhibition, plasticity, and network dynamics at rest and during tasks. © 2012 Wiley Periodicals, Inc.; Hum Brain Mapp 2013.

Abstract

Abstract The past decade has seen significant developments in the concurrent use of transcranial magnetic stimulation (TMS) and electroencephalography (EEG) to directly assess cortical network properties such as excitability and connectivity in humans. New hardware solutions, improved EEG amplifier technology, and advanced data processing techniques have allowed substantial reduction of the TMS‐induced artifact, which had previously rendered concurrent TMS–EEG impossible. Various physiological artifacts resulting from TMS have also been identified, and methods are being developed to either minimize or remove these sources of artifact. With these developments, TMS–EEG has unlocked regions of the cortex to researchers that were previously inaccessible to TMS. By recording the TMS‐evoked response directly from the cortex, TMS–EEG provides information on the excitability, effective connectivity, and oscillatory tuning of a given cortical area, removing the need to infer such measurements from indirect measures. In the following review, we investigate the different online and offline methods for reducing artifacts in TMS–EEG recordings and the physiological information contained within the TMS‐evoked cortical response. We then address the use of TMS–EEG to assess different cortical mechanisms such as cortical inhibition and neural plasticity, before briefly reviewing studies that have utilized TMS–EEG to explore cortical network properties at rest and during different functional brain states. Hum Brain Mapp, 2013. © 2012 Wiley Periodicals, Inc.