Sensory Information Organization:

• Discriminative touch, proprioception, pain, and thermal sensations are segregated within the somatosensory cortex.

• Modality-specific information is kept separate up to the cortex to maintain fidelity in stimulus representation.

Processing Up to the Cortex:

• Up to the cerebral cortex, little mixing of information from different receptor types occurs.

• Different adaptive properties are maintained in pathways, ensuring specific relay of information.

• Within the cortex, modality-specific information converges, and neuron response properties become more complex.

Receptive Fields:

• Subcortical somatosensory neurons respond to modality-specific stimuli in specific body or face regions.

• Receptive fields are anatomically defined areas of sense organs, conveying information about stimulus location and modality.

• Receptive fields vary in size, being smallest for finger pads, lips, and tongue, and largest for shoulders, back, and legs.

Spatial Information Mapping:

• Somatosensory cortex neurons have a somatotopic map representing the spatial layout of the body and face.

• Neuron location within sensory pathways correlates with their receptive field.

• Adjoining body areas are represented in adjoining cortical areas.

Cortical Regions:

1. Primary Somatosensory Cortex (SI):

• Located in the postcentral gyrus and posterior paracentral lobule.

• Exclusive response to somatosensory stimuli.

• Lesions result in severe somatosensory deficits, including impairments in touch and proprioception.

• Integrates information for shape, texture, size, weight, and movement perception.

2. Secondary Cortical Receiving Area (SII):

• Located in the pars opercularis of the parietal lobe.

• Sends information to SI, association cortex, motor cortex, and insula.

• Influences tactile learning and memory, contributes to object recognition by size and texture.

3. Association Cortical Area:

• Located in the superior parietal lobes (os posterior parietal cortex).

• Receives input from SI, SII, and visual system.

• Critical for higher-order processing and recognition of objects based on context.

• Lesions may result in neglect, where the patient ignores stimuli contralateral to the stimulus.

4. Cortical Areas for Pain Sensation:

• Pain information processed in multiple pathways involving various thalamic nuclei and cortical areas.

• Besides the somatosensory cortex, pain stimuli activate the rostral cingulate gyrus and insula.

• Lesions in the primary somatosensory cortex affect pain sensation quality and localization.