Experiential modification of the trigeminal reflex blink circuit

Area of Science:

• Neuroscience
• Neurophysiology

Background:

• The trigeminal nerve plays a crucial role in facial sensation and reflexes, including the blink reflex.
• Understanding the plasticity of the trigeminal reflex blink circuit is essential for deciphering normal function and pathological conditions.

Purpose of the Study:

• To characterize the organization and plasticity of the trigeminal reflex blink circuit in alert rats.
• To investigate if the blink circuit follows rules similar to synaptic plasticity, such as spike-timing-dependent plasticity.

Main Methods:

• Blink-evoking supraorbital (SO) and infraorbital (IO) nerve stimuli were applied to alert rats.
• Interactions between SO and IO stimulation were analyzed, including simultaneous, asynchronous, and synchronous pairings with varying intervals.
• The effects of these pairings on blink responses and input strength to the blink circuit were quantified.

Main Results:

• Stimulation of one trigeminal nerve branch modulated subsequent blinks evoked by the other, showing both inhibition and facilitation.
• The degree of facilitation depended on the relative strengths of the IO and SO stimuli.
• Pairing patterns mimicking synaptic plasticity rules were observed, where input timing relative to circuit activity determined input strengthening or weakening.

Conclusions:

• The trigeminal reflex blink circuit demonstrates input-output plasticity analogous to synaptic plasticity.
• Blink-evoking stimuli act as "presynaptic inputs" and blink circuit activity as "postsynaptic spikes."
• These plasticity mechanisms may contribute to maladaptive reorganization of trigeminal inputs in neurological disorders like hemifacial spasm.