What distinguishes primary (S1) from secondary somatosensory cortex function in tactile processing?

• A. S1 encodes texture and shape; S2 encodes basic tactile features.
• B. S1 encodes basic tactile features; S2 and higher areas integrate texture, shape, and learned representations.
• C. S1, S2, and higher areas all perform the same functions.
• D. S2 is primarily involved in proprioception.

Answer: (B)

In tactile processing, the primary somatosensory cortex handles the basic attributes of touch, such as where on the body the stimulus is, and the basic quality and intensity of that stimulus. S1 provides a precise, topographic map of the body surface and encodes simple features like modality, location, and strength of the touch signals as they first arrive from the thalamus.

As information moves to the secondary somatosensory cortex and higher areas, processing becomes more integrated and abstract. S2 and beyond combine inputs across fingers and sensory modalities to extract more complex properties like texture and shape and to form learned representations of objects we’ve touched. This is what enables recognition by touch and more sophisticated perceptual judgments.

So the statement that S1 encodes basic tactile features while S2 and higher areas integrate texture, shape, and learned representations best captures how these regions specialize along the processing hierarchy. The idea that S1 handles texture and shape or that all levels do the same thing doesn’t fit the distinct roles these areas have, and S2 isn’t primarily about proprioception.