Abstract
Manipulation of an object requires us to transport our hand towards the object (reach) and close our digits around that object (grasp). In current models, reach-related information is propagated in the dorso-medial stream from posterior parietal area V6A to medial intraparietal area, dorsal premotor cortex, and primary motor cortex. Grasp-related information is processed in the dorso-ventral stream from the anterior intraparietal area to ventral premotor cortex and the hand area of primary motor cortex. However, recent studies have cast doubt on the validity of this separation in separate processing streams. We investigated in 10 male rhesus macaques the whole-brain functional connectivity of these areas using resting state fMRI at 7-T. Although we found a clear separation between dorso-medial and dorso-ventral network connectivity in support of the two-stream hypothesis, we also found evidence of shared connectivity between these networks. The dorso-ventral network was distinctly correlated with high-order somatosensory areas and feeding related areas, whereas the dorso-medial network with visual areas and trunk/hindlimb motor areas. Shared connectivity was found in the superior frontal and precentral gyrus, central sulcus, intraparietal sulcus, precuneus, and insular cortex. These results suggest that while sensorimotor processing streams are functionally separated, they can access information through shared areas.
Highlights
Manipulation of an object requires us to transport our hand towards the object and close our digits around that object
The dorso-medial pathway extends from the primary visual cortex over V6A, to the medial intraparietal area (MIP) and to the dorsal premotor cortex, while the dorso-ventral pathway goes over the anterior intraparietal area (AIP) towards the ventral premotor cortex[4] and the primary motor cortex (M1), which is well supported by tracer studies[5,6,7,8,9,10,11,12,13,14]
Damage to MIP and V6A, which are often summarized as the parietal reach region P RR19, leads to a condition known as optic ataxia that comprises reach deficits as well as minor grasp impairments that are likely a consequence of the patient’s reach uncertainty[20]
Summary
Manipulation of an object requires us to transport our hand towards the object (reach) and close our digits around that object (grasp). Grasp-related information is processed in the dorsoventral stream from the anterior intraparietal area to ventral premotor cortex and the hand area of primary motor cortex. Shared connectivity was found in the superior frontal and precentral gyrus, central sulcus, intraparietal sulcus, precuneus, and insular cortex These results suggest that while sensorimotor processing streams are functionally separated, they can access information through shared areas. We analyzed rs-fMRI data in a population of 10 lightly anesthetized macaque monkeys with seeds placed in six cortical areas in the dorso-medial and the dorso-ventral stream We show that both processing streams form clearly separated functional networks, there are specific areas to which both networks are connected, suggesting a possible communication link between the dorso-medial and dorso-ventral network
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