Lateralization of the effects of the benzodiazepine drug oxazepam on medial olivocochlear system activity in humans

Benzodiazepines (Bzd) are known to interact with GABAergic inhibitory neurotransmission. Previous research on their effect on human auditory efferent pathways – through evoked otoacoustic emissions suppression by contralateral acoustic stimulation (CAS) – indicated a decrease in medial olivocochlear (MOC) efferent system inhibitory activity, after oral intake of oxazepam – representative of the Bzd drug class. To date, this pharmacological effect was only assessed in the right ear. Since a leftward asymmetry of Bzd receptors localization in human auditory cortex has been described recently, we explored in this study the hypothesis of an asymmetrical action of Bzd on MOC efferent functioning. The results revealed a significant difference of Bzd effect probing the right ear versus the left ear, with CAS-induced suppression being less effective in the right than left ear after oxazepam intake. This finding raises the question of possible neurochemical left–right asymmetry in the descending auditory pathways. The potential localization of this asymmetry is discussed.