Reaching to a location in space is supported by a cortical network that operates in a variety of reference frames. Computational models and recent fMRI evidence suggest that this diversity originates from neuronal populations dynamically shifting between reference frames as a function of task demands and sensory modality. In this human fMRI study, we extend this framework to non-manipulative grasping movements, an action that depends on multiple properties of a target, not only its spatial location. By presenting targets visually or somaesthetically, and by manipulating gaze direction, we investigate how information about a target is encoded in gaze- and body-centered reference frames in dorsomedial and dorsolateral grasping-related circuits. Data were analyzed using a novel multivariate approach that combines classification and cross-classification measures to explicitly aggregate evidence in favor of and against the presence of gaze- and body-centered reference frames. We used this approach to determine whether reference frames are differentially recruited depending on the availability of sensory information, and where in the cortical networks there is common coding across modalities. Only in the left anterior intraparietal sulcus (aIPS), coding of the grasping target was modality-dependent: predominantly gaze-centered for visual targets, body-centered for somaesthetic targets. Left superior parieto-occipital cortex consistently coded targets for grasping in a gaze-centered reference frame. Left anterior precuneus and premotor areas operated in a modality-independent body-centered frame. These findings reveal how dorsolateral grasping area aIPS could play a role in the transition between modality-independent gaze-centered spatial maps and body-centered motor areas.
Significance Statement: Computational models of sensorimotor control suggest that neuronal populations dynamically shift between reference frames dependent on task demands and sensory modality. This fMRI study distinguished the reference frames used to plan a reach-to-grasp visual or somaesthetic targets. Using a novel analysis approach, combining multivariate classification and cross-classification evidence, we distinguished between gaze- and body-centered frames in dorsomedial and dorsolateral grasp circuits. While most parietal regions in these circuits employ modality-independent gaze-centered coordinates and premotor regions employ modality-independent body-centered coordinates, the anterior intraparietal area (aIPS) switches its reference frame dynamically, depending on the sensory modality of the grasp target. We conclude that aIPS operates as an important hub in the transition between modality-independent gaze-centered spatial maps and body-centered grasp areas.