Representation pattern in the second somatic sensory area of the monkey cerebral cortex

Area of Science:

• Neuroscience
• Somatosensory system research
• Primate brain anatomy

Background:

• The functional organization of the second somatic sensory area (SII) remains incompletely understood.
• Investigating the body representation within SII is crucial for understanding somatosensory processing.

Purpose of the Study:

• To map the body representation in the macaque SII by tracing projections from the first somatic sensory area (SI).
• To elucidate the connection patterns and columnar organization between SI and SII.

Main Methods:

• Anatomical tracing techniques were used to study projections from SI to SII in macaques.
• Cytoarchitecture and thalamic connections identified SII.
• Anterograde and retrograde tracers combined to map cortico-cortical connections.

Main Results:

• SII receives projections exclusively from SI within the lateral sulcus.
• Distinct body part representations (face, digits, arm, trunk, hindlimb) were identified within SII.
• Projections from SI to SII form vertically oriented columnar arrays.
• Reciprocal connections between SI and SII show precise columnar alignment.
• SII neurons projecting back to SI are located in supragranular layers and layer VI.

Conclusions:

• SII contains a detailed somatotopic map with distinct representations for different body parts.
• The columnar organization suggests a highly structured processing of somatosensory information between SI and SII.
• Reciprocal connections highlight the integrated nature of sensory processing within the somatosensory cortex.