Proprioceptive pathways to posterior parietal areas MIP and LIPv from the dorsal column nuclei and the postcentral...

The posterior parietal cortex (PPC) serves as an interface between sensory and motor cortices by integrating multisensory signals with motor-related information. Sensorimotor transformation of somatosensory signals is crucial for the generation and updating of body representations and movement plans. Using retrograde transneuronal transfer of rabies virus in combination with a conventional tracer, we identified direct and polysynaptic somatosensory pathways to two posterior parietal areas, the ventral lateral intraparietal area (LIPv) and the rostral part of the medial intraparietal area (MIP) in macaque monkeys. In addition to direct projections from somatosensory areas 2v and 3a, respectively, we found that LIPv and MIP receive disynaptic inputs from the dorsal column nuclei as directly as these somatosensory areas, via a parallel channel. LIPv is the target of minor neck muscle-related projections from the cuneate (Cu) and the external cuneate nuclei (ECu), and direct projections from area 2v, that likely carry kinesthetic/vestibular/optokinetic-related signals. In contrast, MIP receives major arm and shoulder proprioceptive inputs disynaptically from the rostral Cu and ECu, and trisynaptically (via area 3a) from caudal portions of these nuclei. These findings have important implications for the understanding of the influence of proprioceptive information on movement control operations of the PPC and the formation of body representations. They also contribute to explain the specific deficits of proprioceptive guidance of movement associated to optic ataxia.