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The mechanisms 

of hypnotic antalgia

M

odern imaging techniques such as 

functional magnetic resonance imag-

ing (fMRI) and positron emission tom-

ography (PET) have made it possible to objectify 

the effects observed in patients operated under 

hypno-anaesthesia. 

When the body receives a painful stimulus, 

brain activity differs significantly depending on 

whether one is under hypnosis or in a normal 

waking state. The anterior cingulate cortex (ACC), 

which is credited, among other things, with 

cognitive functions such as reward anticipation, 

decision-making, empathy and emotion, seems 

to play a leading role during hypnosis. During it 

we observe an activation of the middle part of 

the ACC and changes in connectivity between it 

and the cortical and subcortical regions. 

This particular brain activity would appear to 

permit a better encoding of nociceptive (= pain-

related) information, and ultimately to respond 

more appropriately to it. According to some 

researchers, hypnosis prevents information 

from reaching the higher cortical regions which 

are responsible for the perception of pain. Oth-

ers argue that it permits a better response, by 

more effectively activating the downward pain-

inhibiting paths. Which neurotransmitters are 

involved in these activities remains, however, 

unknown.

nearly 200 thyroidectomy and 21 cervical explo-

rations for hyperparathyroidism performed 

under hypno-sedation in Liège between 1994 

and 1997. All patients reported a ‘pleasant 

experience’. Compared to a similar population 

operated under a general anaesthetic, post-

operative pain was less, the use of analgesics 

reduced, patients’ recovery was significantly 

better, and their return to social and profes-

sional life was faster (

2

). Another study con-

ducted in Boston and published in The Lancet 

in April 2000 (

3

) also showed the cost, fre-

quency of complications and duration of sur-

gical interventions to be lower with hypnosis 

patients.