Lingual Mechanoreceptive Information I

An Evoked-Potential Study of the Central Projections of Hypoglossal Nerve Afferent Information

Afferents present in the distal hypoglossal nerve of the rhesus monkey include fibers derived from lingual muscle spindles. Using the evoked-potential technique in rhesus monkeys, the objective of this study was to determine whether the medial lemniscus (ML) represents the rostral projection path for hypoglossal afferent information. Responses evoked by low-intensity stimulation of the XIIth nerve were recorded with bipolar macroelectrodes at medullary, pontine, and midbrain levels in pentobarbital or urethane anesthestized animals. Results indicate that fibers related to XIIth nerve afferents ascend in association with the contralateral ML. This projection mediates the contralateral thalamic and cerebrocortical potentials shown in previous studies to be evoked bv XIIth nerve stimuli. The role this projection may play in tongue sensorimotor function is discussed. Results also demonstrate the presence of contralateral responses in the medial portion of the pontine reticulotegmental nucleus. These medially located potentials were isolated from responses evoked from the ML bv intervening unresponsive electrode tracks suggesting that a component of the lemniscal projection may terminate in the "face zone" of this precerebellar relay nucleus.