Transcranial Magnetic Stimulation (TMS)
We use perturbations of brain function, via focal transcranial magnetic stimulation (TMS), to support causal inference about the roles of particular brain regions. We probe the necessity of targeted brain regions to performance, assessing the functional role of activations we measure with fMRI.
TMS delivers brief pulses on the scalp--via quickly changing magnetic gradients--which can temporarily perturb the electrical activity in the stimulated region (and in connected regions). TMS can be delivered in a range of frequencies, intensities, and temporal patterns, which can produce distinct impacts on the stimulated region of cortex. TMS can consequently have disruptive or facilitative impacts on behavior, depending on the stimulation parameters (as well as on characteristics of the individual, the context, and the stimulated region).
“Offline” TMS can be delivered before or after participants perform one of our cognitive tasks. This form of repetitive TMS is designed to perturb neural activity for a period of time that outlasts the duration of the stimulation itself (i.e., up to ~an hour). For instance, participants may perform a task after the stimulation has ceased, but during a period when it should continue to affect neural activity (as well as cognitive processes that depend on that activity).
We also use "online" TMS--which is delivered while participants perform a cognitive task--for temporally precise assessments of the targeted region’s contributions to particular cognitive processes. This sort of TMS can be delivered in single pulses, or in brief trains of rhythmic pulses at frequencies that may underlie oscillatory neural processes for distinct cognitive functions.
We use stereotactic neuronavigation to position the TMS coil over our anatomical or functional target of interest, and we use EMG to calibrate TMS intensity based on each participant’s sensitivity.