A newly identified nociresponsive region in the transitional zone (TZ) in rat sensorimotor cortex

Area of Science:

• Neuroscience
• Somatosensory research
• Pain perception

Background:

• The primary somatosensory cortex (S1) has distinct regions for different sensory inputs.
• Two nociceptive regions exist in primate S1: area 1 for sharp pain (Aδ fibers) and area 3a for burning pain (C fibers).

Purpose of the Study:

• To investigate if the rat transitional zone (TZ) between S1 and M1 is the functional equivalent of the primate area 3a's nociceptive region.
• To characterize the response properties of TZ neurons to noxious stimuli.

Main Methods:

• Extracellular recordings of TZ neuron activity in anesthetized rats.
• Application of noxious heat stimuli (48-51°C water bath) to the paw.
• Selective inactivation of TZ using topical lidocaine.

Main Results:

• TZ neurons showed minimal response to non-noxious stimuli but significant response to noxious heat in a slow temporal summation pattern.
• This response pattern mirrors that of nociresponsive neurons in primate area 3a.
• TZ inactivation suppressed or delayed the nociceptive withdrawal reflex.

Conclusions:

• The rat TZ is a functional homolog of the primate area 3a's nociceptive region.
• This region may play a role in the autonomic aspects of nociception.