Transforming the thermal grill effect by crossing the finger
Previous research has linked the amount of pain to the specific location of the stimulation in external space. For example, crossing the arms reduces the intensity of pain when receiving painful stimuli on the hand.
The current study uses the thermal grill illusion (TGI, an alternating pattern of warm and cold stimuli, that causes a strange burning and painful sensation) and combined this with crossing the fingers to investigate whether nociceptive sensations depend on the somatotopic or spatiotopic thermal organisation.
Stimuli were applied on the index, middle and ring fingers of the hand in four different conditions (uncrossed or crossed fingers), with some fingers receiving neutral temperature stimulation and other warm stimulation. The combination of neutral and warm stimuli evokes the unpleasant and sometimes painful thermal grill effect. This was measured as an overestimation of the target temperature relative to baseline.
An overestimation in temperature was found when the target was on the middle finger (warm-cold-warm) but not on the index finger (cold-warm-warm). Crossing the fingers reduced the thermal grill effect when the middle finger was the target but increased when the index finger was the target. The authors speculate that changes in posture of affected and unaffected body regions could potentially influence chronic pain.
> From: Marotta et al., Curr Biol 25 (2015) 1-5. All rights reserved to Elsevier Ltd. Click here for the Pubmed summary.