Retrospective Evaluation of Autonomic Activity Through Electrodermal Activity Measurement During Rehabilitation

Severe acquired brain injury (sABI) is a clinical condition characterised by brain damage severe enough to result in coma, with a worst Glasgow Coma Scale (GCS) score of ≤ 8 during the acute phase and a duration of more than 24 hours. Acute brain injury may be traumatic, vascular, anoxic, metabolic, infectious, or tumour-related in origin and may result in complex neurological and multisystem sequelae. During the post-acute and rehabilitation phases, many patients present with altered levels of consciousness, reduced responsiveness to stimuli, cognitive and motor deficits, and often dysregulation of the autonomic nervous system (ANS). The ANS plays an essential role in modulating arousal, adapting to environmental stimuli, and responding to stress, all of which are crucial to recovery and participation in rehabilitation interventions.

Several lines of evidence indicate that autonomic dysfunction is common after severe brain injury. In patients with traumatic brain injury (TBI), for example, reduced electrodermal reactivity has been observed, together with less differentiated physiological responses to emotional or cognitive stimuli. Likewise, in patients with severe disorders of consciousness (DoC), sympathovagal regulation is frequently impaired, with alterations in both baseline tone and responses to environmental changes. In this context, electrodermal activity (EDA) measurement is a promising tool for noninvasive, real-time assessment of autonomic nervous system activity. In the present study, the EmbracePlus EDA device (Empatica Inc., Cambridge, MA, USA), a wrist-worn device, was used in routine clinical practice. EDA directly reflects the activity of eccrine sweat glands, which are innervated by sympathetic cholinergic fibers, and is considered a sensitive indicator of physiological arousal, emotional processing, and cognitive load. Continuous recording of changes in skin conductance during clinical activities provides an opportunity to monitor autonomic responses even in patients whose behavioural manifestations are limited or absent. Recent studies have begun to explore the use of EDA in sABI populations. For example, exposure to an immersive virtual reality environment has been shown to produce a significant increase in sympathetic activity in patients with DoC, suggesting that the response to rehabilitation treatment may be associated with ANS responses. Other studies have investigated the relationship between EDA and dysautonomic phenomena such as paroxysmal sympathetic hyperactivity (PSH), showing that sudden changes in skin conductance may be associated with acute autonomic episodes in patients with severe TBI.

Despite growing interest in the use of EDA in neurology, the literature remains extremely limited regarding its use during conventional rehabilitation sessions. Most existing studies focus on controlled experimental protocols (e.g., visual, emotional, auditory, or virtual reality stimuli), whereas evidence is lacking on how the autonomic nervous system responds to different rehabilitation interventions during the rehabilitation pathway-whether motor, sensory, or cognitive-in patients with sABI. Given that rehabilitation success also depends on the patient's ability to maintain an adequate level of arousal and respond to therapeutic stimuli, objective assessment of autonomic activation could make an important contribution to the personalisation of interventions.

A retrospective observational study based on EDA data collected during clinical practice represents a unique opportunity to provide information in this field. Analysis of electrodermal signals associated with different types of rehabilitation treatment may help to describe patterns of autonomic activation during different phases of the sessions, understand the relationship between physiological arousal and level of responsiveness, and provide an objective basis for modulating the intensity, duration, and modality of rehabilitation interventions to optimise patient engagement and response.

In light of these considerations, there is a clear need to improve understanding of ANS dynamics during post-acute rehabilitation in patients with severe acquired brain injury. The use of EDA as a physiological monitoring tool remains poorly explored in this setting, and a retrospective analysis of available data may represent an important first step toward the systematic integration of objective measures of autonomic arousal into routine rehabilitation practice.