Primary Somatosensory Cortex

Anatomy

• Postcentral gyrus and the posterior paracentral lobule; BA 3a, 3b, 1 and 2.
• Somatotopic organization (sensory homunculus): hand, lips and tongue have large representations.
• Receives input from the thalamic VPL (trunk and limbs) and VPM (face) nuclei. S2 lies in the parietal operculum.
• Blood supply: MCA (lateral), ACA (medial — leg).

Functions

• Touch, pressure, vibration; localization of pain and temperature.
• Proprioception: joint and muscle position (BA 3a).
• Discrimination of texture and shape: stereognosis, two-point discrimination, graphesthesia (BA 1, 2).
• Fine-tuning movement with sensory feedback; contribution to the body schema.

Connections and chemistry

• Thalamus VPL/VPM (dorsal column–medial lemniscus and spinothalamic pathways)
• Primary motor cortex
• Posterior parietal cortex
• Insula (S2 and interoception)

Development

Developmental course through childhood and adolescence.

• Touch is among the earliest sensory systems to develop prenatally.
• Somatosensory maps are shaped by experience; early tactile experience matters.
• Affective touch in infancy (C-tactile fibers, with the insula) is linked to attachment and emotion regulation.

Clinical

• ASD: sensory over- or under-responsivity (a DSM-5 criterion), tactile defensiveness.
• ADHD and sensory modulation difficulties.
• Tourette syndrome: S1/S2 and insula involvement in sensory phenomena and premonitory urges.
• Differences in pain processing in self-harm.

Treatment

This region from the perspective of medication, psychotherapy and neuromodulation. Letter badges are evidence levels.

• Sensory integration therapies: the American Academy of Pediatrics (2012) advises against using “sensory processing disorder” as a separate diagnosis and recommends assessing for underlying ASD, ADHD, motor or anxiety disorders. Evidence for these therapies is limited and inconsistent; if used, functional goals should be set and progress measured. B
• Sensory over-responsivity in ASD: environmental adaptations (noise-cancelling headphones, predictable routines) and graded exposure; CBT if anxiety co-occurs. C
• Differences in pain threshold in self-harm are a marker, not a treatment target; dialectical behavior therapy (DBT) reduced suicide attempts and self-harm more than supportive therapy in 173 adolescents at high suicide risk (McCauley et al., 2018); the first well-established treatment in this area. A

Assessment

Neuropsychological tasks and measures that probe this region's function.

• Two-point discrimination, stereognosis, graphesthesia
• Position and vibration sense examination
• Sensory Profile (Dunn) — sensory processing patterns

Lesions and damage

Clinical findings expected with damage or dysfunction.

• Contralateral sensory loss, astereognosis, loss of graphesthesia.
• Sensory ataxia from impaired proprioception; focal sensory seizures.

In the model

How this structure is defined in the 3D model, and the data source.

Postcentral gyrus (CerebrA); in the paracentral lobule, HCP-MMP1.0 areas 3a, 3b, 1, 2 and 5m, 5L, 5mv.

References

Full citations for the card; links go to the paper (DOI) or a PubMed search.

1. American Academy of Pediatrics. Sensory integration therapies for children with developmental and behavioral disorders. Pediatrics 2012;129(6):1186–1189. Search PubMed
2. McCauley E et al. Efficacy of dialectical behavior therapy for adolescents at high risk for suicide: a randomized clinical trial. JAMA Psychiatry 2018;75(8):777–785. Search PubMed