Hypnotizability-related cerebral oxygenation during actual and imagined movements

Hypnotizability is an individual trait measured by standard scales and associated with several physiological differences including the neural functional equivalence of actual and imagined action. EEG studies also revealed different information processing in these conditions in participants with high (highs) and low (lows) hypnotizability scores, in that it is scarcely localized in highs and specifically network-related in lows. The study aimed to confirm the EEG findings using near-infrared spectroscopy (NIRS), which measures the intensity of synaptic activity based on the levels of oxygenated [OHb] and deoxygenated [HHb] hemoglobin. NIRS was applied to 10 highs and 9 lows, classified according to the Stanford Hypnotic Susceptibility Scale:A during actual (M) and imagined (MI) sequential movements of the left arm and hand. The ability to be deeply absorbed in tasks and sensory imagination through the visual and kinesthetic modalities was preliminarily assessed by the Tellegen Absorption Scale (TAS) and the Betts questionnaire, respectively. The results showed task-related [OHb] increases in prefrontal areas only in the lows group, whereas the premotor area exhibited greater [OHb] during tasks in both groups. Hypnotizability-related differences were not observed in sensorimotor areas. TAS and Betts scores sustained some of the observed changes. Correlational analysis between the areas [OHb] showed that hypnotizability plays a greater role in motor imagery than in actual movement. In conclusion, NIRS findings support the earlier EEG findings regarding the different information processing of highs and lows by showing lower brain synaptic activity in highs than in lows during actual and imagined movement.