Discrete parieto-frontal functional connectivity related to grasping.

The human inferior parietal lobule (IPL) is known to have neuronal connections with the frontal lobe, and these connections have been shown to be associated with sensorimotor integration to perform various types of movement such as grasping. The function of these anatomical connections has not been fully investigated. We studied the judgment of graspability of objects in an event-related functional MRI study in healthy subjects, and found activation in two different regions within IPL: one in the left dorsal IPL extending to the intraparietal sulcus and the other in the left ventral IPL. The former region was activated only in the judgment of graspable objects, whereas the latter was activated in the judgment of both graspable and nongraspable objects although the activation was greater for the graspable objects. Psychophysiological interaction analysis showed that these regions had similar but discrete functional connectivity to the lateral and medial frontal cortices. In relation to this particular task, the left dorsal IPL had functional connectivity to the left ventral premotor cortex, supplementary motor area (SMA) and right cerebellar cortex, whereas the left ventral IPL had functional connectivity to the left dorsolateral prefrontal cortex and pre-SMA. These findings suggest that the connection from the left dorsal IPL is associated specifically with automatic flow of information about grasping behavior. By contrast, the connection from the left ventral IPL might be related to motor imagination or enhanced external attention to the presented stimuli.