The somatosensory homunculus, like the motor homunculus opposite it, expanded representations of the face and hand because those body parts have higher peripheral receptor densities and project to larger cortical territories. Patients who learn Braille show measurable expansion of the cortical representation of the reading fingertip on functional imaging, demonstrating that the somatotopic map remains plastic into adulthood.

Beyond S1 itself, the postcentral gyrus connects forward to M1 (closed-loop for sensory feedback during movement), backward to the supramarginal gyrus and posterior parietal cortex (for higher-order somatosensory integration and tactile object recognition), and across the corpus callosum to homologous right-hemisphere cortex.

Cortical sensory loss differs from peripheral sensory loss in that the primary sensory modalities (light touch, pinprick) are often only mildly reduced, while higher-order discriminative functions (stereognosis, graphaesthesia, two-point discrimination) are markedly impaired. This pattern reflects the cortex’s primary role in integrating and discriminating sensory information rather than detecting its mere presence.