Perfusion MRI Indexes Variability in the Functional Brain Effects of Theta-Burst Transcranial Magnetic Stimulation

Transcranial Magnetic Stimulation (TMS) is an important tool for testing causal relationships in cognitive neuroscience research. However, the efficacy of TMS can be variable across individuals and difficult to measure. This variability is especially a challenge when TMS is applied to regions without well-characterized behavioral effects, such as in studies using TMS on multi-modal areas in intrinsic networks. Here, we examined whether perfusion fMRI recordings of Cerebral Blood Flow (CBF), a quantitative measure sensitive to slow functional changes, reliably index variability in the effects of stimulation. Twenty-seven participants each completed four combined TMS-fMRI sessions during which both resting state Blood Oxygen Level Dependent (BOLD) and perfusion Arterial Spin Labeling (ASL) scans were recorded. In each session after the first baseline day, continuous theta-burst TMS (TBS) was applied to one of three locations: left dorsolateral prefrontal cortex (L dlPFC), left anterior insula/frontal operculum (L aI/fO), or left primary somatosensory cortex (L S1). The two frontal targets are components of intrinsic networks and L S1 was used as an experimental control. CBF changes were measured both before and after TMS on each day from a series of interleaved resting state and perfusion scans. Although TBS led to weak selective increases under the coil in CBF measurements across the group, individual subjects showed wide variability in their responses. TBS-induced changes in rCBF were related to TBS-induced changes in functional connectivity of the relevant intrinsic networks measured during separate resting-state BOLD scans. This relationship was selective: CBF and functional connectivity of these networks were not related before TBS or after TBS to the experimental control region (S1). Furthermore, subject groups with different directions of CBF change after TBS showed distinct modulations in the functional interactions of targeted networks. These results suggest that CBF is a marker of individual differences in the effects of TBS

Non-invasive brain stimulation in human stroke survivors

The use of electromagnetic currents toward understanding and curing human disease has long been of interest. In the 1980s, a dramatic increase in our understanding of brain function, along with parallel improvements in non-invasive brain stimulation (NIBS) technologies, subsequently caused rapid expansion of the field. Intraoperative monitoring techniques that incorporated single pulse stimulation were developed concurrently for the purpose of measuring corticospinal integrity (Merton & Morton, 1980a, 1980b); however, with the introduction of transcranial magnetic stimulation (TMS), the use of NIBS decisively exploded, opening a new window into the exploration and modulation of the brain (Barker and Jalinous, Lancet, 1(8437):1106–1107, 1985). Single pulse TMS, used initially to study inter-cortical physiology of the intact corticospinal tract, was thereafter investigated toward the rehabilitation of neurological and psychiatric conditions