iTBS/fMRI Study of Apex Control

The Comprehensive Control Task (CCT) was designed to examine hierarchical control in a single, well-controlled factorial task. On each trial, participants view a letter surrounded by a colored shape at a particular screen location. Color cues the relevant feature, letter or location, for a block of trials. The first trial of a block requires a decision of whether the stimulus is the first position of a circular sequence (sequence start). Subsequent trials require a decision of whether the viewed stimulus follows the previous stimulus in a circular sequence (sequence 1-back). The letter sequence (T-A-B-L-E-T) and spatial sequence (Top-Bottom Right-Left-Right-Bottom Left-Top) are difficulty-matched.

Shape cues the task to perform. Squares indicate the standard baseline task, and each block begins and ends with baseline trials. Different shapes indicate sub-tasks. In Switching blocks, shape-switches (e.g. from square to circle or circle to square) cue the sequence start task. Shape-repeats cue the sequence 1-back task. In Planning blocks, triangle shapes indicate that the stimulus can be ignored (automatic "no" response). All the while, the last square-shaped stimulus must be retained as a reference for the next square-shaped stimulus. Finally, in Dual blocks, diamond shapes indicate switching (sequence start) and also planning. The reversion back to square shapes requires sequence matching to the distal, previous square.

The design is factorial with stimulus-domain x contextual control x temporal control orthogonally manipulated. Full details of the CCT have been previously described in published work.

The focus in this study will be comparison of MFG-TMS, IPL-TMS, and S1-TMS in an interleaved fMRI-TMS-fMRI design. The logic is to test the apical status of the MFG/IPL through the extent to which TMS impacts other PFC/PPC areas and behavior.

Each experiment will begin with 1 session of the CCT with fMRI to localize TMS targets. Each participant will then perform 3 counter-balanced sessions wherein a different site will be targeted by TMS followed immediately by fMRI on the CCT.