Twist and turn into chronic disorders of consciousness: potential role of the auditory stapedial reflex

Background: Patients suffering from chronic disorders of consciousness (DOC), including minimally conscious state (MCS) and unresponsive wakefulness syndrome (UWS), typically show an awareness impairment paralleled by a significant reflex hyper-excitability, which depend on the cortical deafferentation following brain-damage-induced thalamocortical system deterioration. Nonetheless, recent studies have shown a residual preservation of cortico-subcortical pathways that may sustain residual fragments of awareness in some DOC patients. Objective: The aim of our study was to assess whether the cortical modulation of auditory stapedial reflex (ASR) could be a marker of a higher degree of brain network connectivity, which is a fundamental prerequisite for awareness generation and maintenance. Methods: We applied a repetitive transcranial magnetic stimulation (rTMS) protocol over the primary auditory area and measured the neuromodulation effects on ASR threshold (ASRt) in a DOC sample and a healthy control group (HC). Results: We observed an ASRt reduction in all the HC and MCS individuals, in parallel to a better sound-induced motor responsiveness in MCS sample, while all the UWS patients, but two, did not show any significant ASRt modulation. Conclusion: We hypothesize that our conditioning protocol may have entrained and potentiated some spared cortico-subcortical networks that sustained the clinical and electrophysiological amelioration we found. Our data electrophysiologically demonstrate for the first time that primary the auditory area can influence ASR elicitation, and such finding may support the DOC differential diagnosis