Tickle Stimulation in Disorders of Consciousness (DoC)

During the experimental session, patients will undergo the CRS-R and the Nociception Coma Scale-Revised (NCS-R) to ensure that any responses to tickling are not influenced by pain sensations. Subsequently, fNIRS detection optodes will be placed using a non-invasive frontal headband. A 10-minute resting-state recording will be performed. Next, patients will be subjected to tickling: they will be tickled bilaterally in the three most ticklish areas identified in a pilot study with healthy subjects-namely, the soles of the feet, the armpits, and the ribs-plus a control area, the forehead. The stimulation will be manual and will be performed by rubbing the targeted body part while opening and closing fingers in pairs in an arched motion. Additionally, patients will also receive a neutral stimulation (in the same body areas), which consists of simply touching the area without inducing tickling. The order of stimulations will follow a randomized list. Each stimulation will last for 5 seconds, followed by 5 seconds of rest, repeated twice. In total, patients will be stimulated for 10 seconds plus 5 seconds of rest (15 seconds in total) for each body area. There will be a 1-minute pause between each area. Afterward, an additional 10 minute resting-state fNIRS recording will be conducted. During the experimental session, patients will be filmed so that the videos can be analyzed by two different experimenters, who will assess differences between stimulations based on facial expressions, verbalizations/vocalizations, body movements, and changes in emotional state (e.g., crying, smiling, grimacing). At the end of the protocol, the fNIRS optodes will be removed. In total, the experiment will last approximately one hour and fifteen minutes: 30 minutes for CRS-R/NCS-R and 45 minutes for the tickling protocol and fNIRS recording.