Abstract
Severe brain injury is a common cause of coma. In some cases, despite vigilance improvement, disorders of consciousness (DoC) persist. Several states of impaired consciousness have been defined, according to whether the patient exhibits only reflexive behaviors as in the vegetative state/unresponsive wakefulness syndrome (VS/UWS) or purposeful behaviors distinct from reflexes as in the minimally conscious state (MCS). Recently, this clinical distinction has been enriched by electrophysiological and neuroimaging data resulting from a better understanding of the physiopathology of DoC. However, therapeutic options, especially pharmacological ones, remain very limited. In this context, electroceuticals, a new category of therapeutic agents which act by targeting the neural circuits with electromagnetic stimulations, started to develop in the field of DoC. We performed a systematic review of the studies evaluating therapeutics relying on the direct or indirect electro-magnetic stimulation of the brain in DoC patients. Current evidence seems to support the efficacy of deep brain stimulation (DBS) and non-invasive brain stimulation (NIBS) on consciousness in some of these patients. However, while the latter is non-invasive and well tolerated, the former is associated with potential major side effects. We propose that all chronic DoC patients should be given the possibility to benefit from NIBS, and that transcranial direct current stimulation (tDCS) should be preferred over repetitive transcranial magnetic stimulation (rTMS), based on the literature and its simple use. Surgical techniques less invasive than DBS, such as vagus nerve stimulation (VNS) might represent a good compromise between efficacy and invasiveness but still need to be further investigated.
Highlights
Loss of consciousness and arousal are frequent after severe brain injuries
The same authors showed that transcranial direct current stimulation (tDCS) stimulation led to an increased fronto-parietal coherence in the theta band (Bai et al, 2016). These results suggest that tDCS is able to modify the functional connectivity of consciousness-related networks as can be seen in healthy volunteers (Kunze et al, 2016) and could restore partially preserved long-range connectivity inside cortico-thalamic networks, explaining the better response rate observed in minimally conscious state (MCS) patients
Current evidence tends to support the efficacy of deep brain stimulation (DBS) and non-invasive brain stimulation (NIBS) on consciousness in disorders of consciousness (DoC) patients (Thibaut and Schiff, 2018)
Summary
Loss of consciousness and arousal are frequent after severe brain injuries. Usually, patients recover from this transient state of coma to a normal state of consciousness even though they can suffer from various cognitive deficits. Targets and Parameters of Stimulation Multiple targets have been tested including the reticular formation (McLardy et al, 1968; Tsubokawa et al, 1990; Yamamoto et al, 2010), the central nucleus of the thalamus (McLardy et al, 1968; Tsubokawa et al, 1990; Cohadon and Richer, 1993; Schiff et al, 2007; Yamamoto et al, 2010; Wojtecki et al, 2014; Adams et al, 2016; Chudy et al, 2018), the anterior intralaminar nuclei and paralaminar areas (Magrassi et al, 2016). The impact of the parameters of stimulation on the clinical response remains unclear (Kundu et al, 2018)
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