Opossum somatic sensory cortex: a microelectrode mapping study

Area of Science:

• Neuroscience
• Comparative Anatomy
• Sensory Systems

Background:

• The organization of the somatic sensory cortex provides insights into sensory processing.
• Previous studies by Lende (1963) established a foundational understanding of opossum somatic sensory cortex organization.

Purpose of the Study:

• To detail the organization of the Virginia opossum's somatic sensory cortex.
• To investigate the representation of facial vibrissae, rhinarium, and postcranial structures.
• To compare opossum cortical organization with that of placental mammals.

Main Methods:

• Microelectrode penetrations (0.25-0.5 mm apart) were used to map cortical activity.
• Delicate mechanical stimulation of body surfaces, including facial vibrissae, was employed.
• Neuronal responses were recorded and analyzed for receptive field properties and directional specificity.

Main Results:

• A detailed double representation of mystacial vibrissae and rhinarium was identified, forming mirror images.
• Approximately 40% of vibrissa units exhibited directional specificity, with medial units showing greater specificity.
• Extensive and precise representation of the contralateral forelimb was observed, contrasting with minimal hindlimb and tail representation.
• A small region of bilateral representation, potentially homologous to SmII, was confirmed.

Conclusions:

• The study confirms and refines the general organization of the opossum somatic sensory cortex.
• Specific areas (contralateral postcranial, medial rhinarium/vibrissa) are homologous to SmI in placental mammals.
• Lateral vibrissa and rhinarium areas represent unique specializations within the opossum's somatic sensory cortex, distinct from placental mammals.