Decoding Effector-Specific Parametric Grip-Force Anticipation From fMRI-Data

Abstract

Planning motor-actions involves the neuronal representation of key parameters such as force and timing prior to execution. Functional magnetic resonance imaging (fMRI) studies have shown that activity in premotor and parietal areas covaries with these parameters during motor-preparation. While previous research has demonstrated that parametric codes reflect graded grip-force intensities before and after their transformation into motor-codes, it remains unclear whether these representations are encoded in effector-specific brain-regions. To address this, we conducted an fMRI-study using a delayed grip-force task in which participants prepared one of four force-intensities with either their right or left cued-hand, with the hand to-be-used being switched in 50% of the trials midway through the delay. Using time-resolved multivoxel pattern analysis (MVPA) with a searchlight approach, we identified brain-regions encoding anticipated grip-force intensities of the cued-hand across the two 6-s delay-periods. In addition, cross-decoding analyses tested whether force-intensities were represented in an effector-specific or effector-independent format. We found above-chance decoding in two lateralized networks: the contralateral intraparietal sulcus (r−/l-IPS), as well as the lateral occipitotemporal cortex (r−/l-LOTC) during the first, and the contralateral primary motor cortices (r−/l-M1) during the second delay. These results indicate effector-specific coding of anticipated grip-force intensities, which is revealed by systematic lateralization of decoding-accuracy depending on the hand to-be-used. Cross-decoding corroborated effector-specific representation in these regions. Together, our results show that contralateral IPS and LOTCs encode effector-specific parametric information prior to M1s, likely reflecting a transformation process in which the intended grip-force intensity is selected, maintained, and then converted into detailed movement-plans.