Project Summary/Abstract
Transcranial direct current stimulation (tDCS) is a non-invasive neuromodulation technique that shows promise
as a therapeutic aid in treating neurological disorders, such as stroke and disorders of consciousness.
However, significant debate exists as to its efficacy and mechanisms of action. To make progress, it is first
necessary to determine where the currents flow in the brain and what the acute effects of these currents are
on neural activity. Traditional, targeted current flow is performed by placing a large electrode directly on top of
a targeted cortical region. More recently, tDCS electrode placement for targeted current flow has been assisted
by sophisticated computer simulations. However, these computer simulations suffer from significant
inaccuracies due to substantial differences across patients with highly varying lesioned brain anatomies.
Empirically mapping where electric current flows in the brain is vital to verifying that tDCS is targeting brain
region(s) of interest. Equally important is to verify that the targeted brain region, or networks related to it, have
indeed altered their functional output in any measurable way. Yet, there are no neuroimaging techniques
available that can measure neural effects during stimulation without generating artefactual signals. We propose
to develop concurrent magnetic resonance imaging (MRI)/tDCS acquisition and processing techniques to fill
this methodological gap. We will use 3D multi-gradient-recalled echo MRI to measure magnetic fields produced
by tDCS and from them calculate the electric current flow. We will validate the measures with analytic
predictions for phantoms and computational simulations for in vivo human recordings. Further, to accurately
compare brain function during tDCS, we propose a concurrent tDCS/functional MRI acquisition and signal
processing method that can measure blood-oxygen level dependent (BOLD) responses without stimulation
artefacts. We will validate the approach on phantom models and in humans during rest and task performance.
The goal of this validation work is to establish a functional MRI technique that can be trusted to measure the
acute effects of tDCS. We anticipate that the results of the proposed experimental plan will provide invaluable
tools towards a better understanding of the mechanisms of action of tDCS and in the future enable
individualized targeted treatment. We will make these customized MRI acquisition protocols and analysis tools
publicly available with a web-based platform for support among users.
