Tactile Stimulation in Disorders of Consciousness (DoC)

Overview

The aim of this project is to evaluate the behavioural and neurophysiological responses to pleasant touch in patients with disorders of consciousness (DoC) and to determine whether these responses are related to the level of consciousness. Specifically, the study aims to: 1. explore the relationship between pleasant tactile stimulation and behavioural and neurophysiological responses in patients with DoC; 2. determine whether behavioural responses to pleasant touch stimulation correlate with the level of consciousness; 3. assess whether behavioural responses vary depending on the valence of the stimulus (pleasant, neutral, or unpleasant); 4. examine neurophysiological responses to tactile stimulation using functional near-infrared spectroscopy (fNIRS), and evaluate whether brain activation patterns are associated with behavioural responses; 5. improve diagnostic accuracy in patients with DoC by exploring the value of somatosensory responses in distinguishing unresponsive wakefulness syndrome (UWS) from minimally conscious state (MCS) or conscious patients; 6. explore the potential usefulness of implementing this type of stimulation within rehabilitation programs to support better recovery of consciousness.

Patients will be enrolled at the participating centers and included in the study only after at least two evaluations using the Coma Recovery Scale-Revised (CRS-R), in order to ensure a stable diagnosis of the level of consciousness. At the beginning of the protocol, non-invasive fNIRS optodes will be placed on the patient's forehead using a frontal headband, and 15 minutes of resting-state brain activity will be recorded. The Simplified Evaluation of CONsciousness Disorders (SECONDs) will then be administered to assess the patient's level of consciousness, followed by the tactile stimulation protocol. The tactile stimulation protocol involves 8 areas of the body (anterior and posterior forearm, palm and back of the hand, on both right and left sides) and 6 stimuli grouped into three categories: pleasant objects (makeup brush, plush fabric), neutral objects (sponge, rubber fabric), and unpleasant objects (dishnet, hairbrush). Each stimulus is mounted on a 10 cm wooden stick attached to a cork base. Each stimulation lasts 15 seconds and is manually administered using light circular movements over an area of approximately 5 cm² at a speed of 5 cm/s, following a randomized sequence. A 10-second rest period will be provided between stimulations. Patients will receive three distinct blocks of stimulation: unpleasant stimuli (first block), pleasant stimuli (second block), and neutral stimuli (third block), with the block order randomized across participants. After each block, the SECONDs will be re-administered to detect any changes in the level of consciousness. An additional 15-minute resting-state fNIRS recording will follow the stimulation phase. All sessions will be video-recorded to allow two independent experimenters to evaluate behavioural responses (e.g., facial expressions, vocalizations, body movements, and emotional reactions such as crying, smiling, or grimacing) and compare the effects of different stimulations. At the end of the session, fNIRS optodes will be removed. The entire experimental procedure will last approximately 90 minutes.