conversion disorder", the idea being that emotional problems are "converted" into physical ailments).
Consider hand paralysis, which some patients complain of in the absence of any neurological injury or disease. In a new study led by Martin Pyka at the University of Marburg, hand paralysis was induced in 19 healthy participants through hypnosis, thus providing a model of what may be going on in conversion hand paralysis. The hypnotised participants had their brains scanned while they rested calmly, and these results were then compared against a second scanning session in which the participants were not hypnotised.
The main result is that hypnosis-induced hand paralysis was associated not with brain areas involved with inhibiting movement (e.g. the supplementary motor area, located towards the front of the brain), but with increased coupling between regions associated with representation of the self (especially the precuneus, located in the parietal lobe, and the posterior cingulate cortex), and with regions that represent and monitor one's own movements (the dorsolateral prefrontal cortex). This suggests it's not so much that the participants' hand control was suppressed, but that they no longer believed they had the power to move their hands. This fits the findings from an earlier brain imaging study of a woman with conversion paralysis, which found changes in brain areas associated with self-monitoring and auto-biographical memory, but not areas associated with motor inhibition.
"We believe that the suggestions given during induction of hypnosis, which started with metaphors such as 'the left hand feels weak, heavy, adynamic,' 'any energy leaves the hand,' and continued with direct instructions like 'the left hand is paralysed, you cannot move the hand anymore,' induced an altered self-perception of the participants and their motor abilities," the researchers said. They acknowledged that a weakness of their study was that they'd deliberately recruited highly suggestible participants: "Thus, it is unclear whether the reported functional coupling can only be attributed to the neurofunctional impact of hypnosis or also to the selection of the subjects," they said.
As an aside, Jean-Martin Charcot, the "Napoleon of neurology", considered hyponosis-proneness to be a hallmark of patients with hysteria - a now defunct catch-all diagnosis, which included patients with conversion disorder. At the end of the 19th century at the Salpêtrière Hospital in Paris, Charcot often hypnotised his hysterical patients during his series of hugely popular public demonstrations of the condition. Hypnosis also became a common means of treatment for hysteria (although Charcot himself was not an advocate), whereby the entranced patient revealed, often via new emerging "personalities", the past traumas and fixed ideas at the root of their physical ailments. Hypnosis as a treatment fell out of favour with Freud's rise to prominence: he believed it was possible to get to the root of a patient's subconscious problems by talking to them directly, without the need for hypnosis.
Pyka, M., Burgmer, M., Lenzen, T., Pioch, R., Dannlowski, U., Pfleiderer, B., Ewert, A., Heuft, G., Arolt, V., and Konrad, C. (2011). Brain correlates of hypnotic paralysis—a resting-state fMRI study. NeuroImage, 56 (4), 2173-2182 DOI: 10.1016/j.neuroimage.2011.03.078
This post was written by Christian Jarrett for the BPS Research Digest.