Poster F102, Tuesday, March 28, 8:00 – 10:00 am, Pacific Concourse
Identification of frontal-striatal circuits with simultaneous TMS-fMRI
Christopher Muse-Fisher1, Justin Riddle1, Jason Scimeca1, Mark D'Esposito1; 1UC Berkeley
Transcranial Magnetic Stimulation (TMS) allows for direct stimulation of the human neocortex and has proven to be fundamental for causally testing hypotheses in cognitive neuroscience. It has yet to be shown that spreading activation from TMS is confined to anatomically specific circuits and whether cortical TMS can reliably activate connected subcortical structures. By administering TMS simultaneously with functional Magnetic Resonance Imaging (fMRI), the effect of cortical TMS on activity in subcortical structures can be quantified by varying the levels of TMS intensity. The basal ganglia are an ideal target because of their distinct anatomically defined circuits with neocortex, or “loops”. For sensorimotor processing, primary motor cortex (M1) forms a loop with the putamen, while dorsolateral prefrontal cortex (DLPFC) forms a loop with the caudate (Alexander et al. 1986). Strafella et al. (2001, 2003) demonstrated that following TMS to M1 or DLPFC, there is increased dopamine release in posterior putamen or dorsal caudate respectively, as measured by positron emission tomography. In our experiment, two separate groups of healthy human subjects participated in concurrent TMS and resting state fMRI while receiving TMS to either DLPFC or M1. We found that increasing TMS intensity to the DLPFC caused increasing BOLD signal in the dorsal caudate with no change in the posterior putamen. In contrast, TMS to M1 increased BOLD signal in the posterior putamen with no change in the dorsal caudate. These results demonstrate the use of simultaneous TMS-fMRI to target deep brain structures with known anatomical connectivity with cortical regions.
Topic Area: METHODS: Neuroimaging