Decoding Graded Grip‐Force Intensity From fMRI Data Reveals a Transformation From Abstract to Effector‐ and Movement‐Specific Codes Prior to Execution

ABSTRACT

Motor planning entails a progressive transformation of neural representations ‐ from abstract motor goals, which represent intended action‐outcomes independent of any particular effector (i.e., the body part executing the action), to effector‐specific movement plans. Functional MRI (fMRI) studies have shown that parametric variations in parietal activity patterns reflect the encoding of intended force‐intensities in effector‐specific regions, even before detailed movement parameters are specified. However, how these intended force‐intensities are initially represented in an abstract, effector‐independent format and subsequently transformed into effector‐ and movement‐specific plans remains unclear. To address this, human‐participants performed a delayed grip‐force task during fMRI. They first prepared two of four possible force‐intensities, then received a cue indicating which hand should apply which force, and finally executed both grips simultaneously. Using time‐resolved support vector regression (SVR) combined with a searchlight approach, we identified brain‐regions that parametrically code grip‐force intensities across two 6‐s delay periods. During the first delay, above‐chance decoding was observed in a medial section of the posterior parietal cortex spanning the precuneus and superior parietal lobule (PCu/SPL), whereas during the second delay it emerged in effector‐specific regions, including the contralateral intraparietal sulcus (pIPS/aIPS), primary somatosensory cortex (S1), dorsal premotor cortex (PMd), and supplementary motor area (SMA). Cross‐decoding confirmed effector‐independent coding in the PCu/SPL, while cross‐temporal generalization revealed stable representations in the contralateral IPS and PMd from the second delay through execution. Together, these findings indicate a progressive transformation from abstract representations of intended force‐intensity in the PCu/SPL to effector‐ and movement‐specific plans in the IPS and PMd.