Primary manipulation knowledge of objects is associated with the functional coupling of pMTG and aIPS

Correctly using hand-held tools and manipulable objects typically relies not only on sensory and motor-related processes, but also centrally on conceptual knowledge about how objects are typically used (e.g. grasping the handle of a kitchen knife rather than the blade avoids injury). A wealth of fMRI connectivity-related evidence demonstrates that contributions from both ventral and dorsal stream areas are important for accurate tool knowledge and use. Here, we investigate the combined role of ventral and dorsal stream areas in representing "primary" manipulation knowledge - that is, knowledge that is hypothesized to be of central importance for day-to-day object use. We operationalize primary manipulation knowledge by extracting the first dimension from a multi-dimensional scaling solution over a behavioral judgement task where subjects arranged a set of 80 manipulable objects based on their overall manipulation similarity. We then relate this dimension to representational and time-course correlations between ventral and dorsal stream areas. Our results show that functional coupling between posterior middle temporal gyrus (pMTG) and anterior intraparietal sulcus (aIPS) is uniquely related to primary manipulation knowledge about objects, and that this effect is more pronounced for objects that require precision grasping. We reason this is due to precision-grasp objects requiring more ventral/temporal information relating to object shape, material and function to allow correct finger placement and controlled manipulation. These results demonstrate the importance of functional coupling across these ventral and dorsal stream areas in service of manipulation knowledge and accurate grasp-related behavior.