An adaptive fMRI paradigm of direction-specific, time-critical grip-force transitions.

Rapid transitions between force states, including fast increases and rapid releases, are fundamental to voluntary movement and everyday object interaction. Converging evidence from movement disorders suggests that rapid force reduction can be disproportionately impaired relative to force production, motivating the hypothesis that these transition directions rely on partly distinct control mechanisms. Brain imaging studies suggest direction-sensitive neural contributions, but existing paradigms make it difficult to determine whether differences between force production and force reduction reflect transition direction itself or other task-related differences. Here, we present the YANK task, a new open-source grip-force paradigm that manipulates rapid force production and rapid force reduction within the same visuomotor task. As an initial clinical proof-of-concept, pilot data from a single participant with Parkinson's disease demonstrate within-participant, direction-specific modulation of yank. Trials designed to elicit positive yank produced higher peak scaled positive yank (p <.001), whereas trials designed to elicit negative yank produced more peak scaled negative yank (p <.001). The accompanying neuroimaging data demonstrate that the paradigm can be implemented during fMRI and provide qualitative within-subject proof-of-concept evidence of task-evoked BOLD responses in visuomotor and sensorimotor regions. Together, these findings position the YANK task as a novel, neuroimaging-compatible paradigm for investigating direction-specific rapid grip-force transitions.