Intrafascicular multi-unit recordings from the human infra-orbital nerve

Area of Science:

• Neuroscience
• Human Physiology
• Sensory Systems

Background:

• The infra-orbital nerve (ION) transmits sensory information from the face.
• Understanding its fascicular organization and afferent activity is crucial for facial sensation and motor control.

Purpose of the Study:

• To investigate the fascicular organization of the human ION.
• To characterize the activity of low-threshold mechanoreceptive afferents and explore C-fibre activity.
• To map innervation zones and analyze sensorimotor interactions in the facial region.

Main Methods:

• Intrafascicular micro-electrode recordings from the human ION near the infra-orbital foramen.
• Tactile stimuli, vibration, and facial movements were used to evoke responses.
• Innervation zones were mapped on facial skin and the lip.
• Electromyography (EMG) was used to correlate afferent activity with motor responses.

Main Results:

• Mapped 66 fascicles, predominantly on the upper lip, indicating high innervation density with overlapping fields (median size 3.8 cm2).
• Skin indentation evoked dynamic on/off responses; static discharge was less pronounced.
• Facial muscle contractions and skin stretching elicited dynamic responses, crucial for sensorimotor integration during movements like speech.

Conclusions:

• The ION exhibits a complex fascicular organization supporting dense mechanoreceptor innervation of the upper lip.
• Dynamic mechanoreceptor responses are vital for sensorimotor control during facial movements.
• Sympathetic C-fibre activity was notably absent in ION recordings, unlike in the supra-orbital nerve.