Transcortical descending pathways through granular insular cortex conveying orofacial proprioception

Area of Science:

• Neuroscience
• Motor Control
• Somatosensation

Background:

• Motor behavior relies on proprioceptive feedback.
• The neural circuits for jaw proprioception are not fully understood.
• Previous work identified a pathway from jaw-closing muscle spindles (JCMSs) to the insular cortex via the trigeminal mesencephalic nucleus (Me5) and ventral posteromedial thalamus (VPMcvm).

Purpose of the Study:

• To investigate the brain areas receiving input from the dorsal granular insular cortex (dGIrvs2) related to jaw movements.
• To elucidate the downstream targets of dGIrvs2 in the context of jaw proprioception.

Main Methods:

• Injection of an anterograde tracer (biotinylated dextranamine) into the dGIrvs2.
• Analysis of labeled axon terminal distribution to identify projection targets.
• Examination of connections to pontomedullary areas and the VPMcvm.

Main Results:

• Anterogradely labeled axons from dGIrvs2 were found in pontomedullary areas, including the supratrigeminal nucleus (Su5), and in and around the VPMcvm.
• These targets are known to receive jaw proprioceptive inputs and contain premotoneurons for jaw-closing motoneurons.
• No labeled terminals were observed on Me5 neurons or jaw-closing motoneurons in the trigeminal motor nucleus (Mo5).

Conclusions:

• Jaw movements, initiated by the reflex arc from peripheral JCMS proprioception, may be modulated by transcortical feedback.
• The dGIrvs2 projects back to the VPMcvm and Su5, suggesting a role in regulating jaw motor control.
• This highlights a potential cortical feedback loop influencing jaw proprioception and motor output.