Understanding the role of the primary somatosensory cortex: Opportunities for rehabilitation

Abstract

Emerging evidence indicates impairments in somatosensory function may be a major contributor to motor dysfunction associated with neurologic injury or disorders. However, the neuroanatomical substrates underlying the connection between aberrant sensory input and ineffective motor output are still under investigation. The primary somatosensory cortex (S1) plays a critical role in processing afferent somatosensory input and contributes to the integration of sensory and motor signals necessary for skilled movement. Neuroimaging and neurostimulation approaches provide unique opportunities to non-invasively study S1 structure and function including connectivity with other cortical regions. These research techniques have begun to illuminate casual contributions of abnormal S1 activity and connectivity to motor dysfunction and poorer recovery of motor function in neurologic patient populations. This review synthesizes recent evidence illustrating the role of S1 in motor control, motor learning and functional recovery with an emphasis on how information from these investigations may be exploited to inform stroke rehabilitation to reduce motor dysfunction and improve therapeutic outcomes.

Keywords: Motor control; Motor learning; Neuroimaging; Noninvasive brain stimulation; Primary somatosensory cortex; Rehabilitation; Stroke.

Fig. 1

Theoretical model of information exchange between primary somatosensory (S1) and motor (M1) regions. According to the "optimal control" theory (a) S1 modulates M1 activity. According to the "active inference" theory (b), M1 modulates S1 activity. In addition, S1 exchanges and integrates information to and from other primary sensory areas, such as visual (V1) and auditory (A1).

Fig. 2

Projections between primary somatosensory (S1), motor (M1), and association cortices. Sensory information is projected directly from S1 to M1 and somatosensory association cortices (BA 5; blue arrows). Secondary projections occur from BA 5 to additional somatosensory cortices (BA 7) and premotor and supplementary motor cortices (BA 6; red arrows). Inset (dashed green box): cross-section of the cortex including M1, S1, and somatosensory association cortices. Cytoarchitecture of the subgroups of S1 (BA 3a, 3b, 1, and 2) is shown. Adapted from (Kandel et al., 2000; Saper et al., 2000). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)