A German study demonstrates, with instrumental tests, that through hypnosis it is possible to question the so-called tactile discrimination
If done scientifically, hypnosis can really change the way our brain works. We are not talking about the shows heralded by the well-known phrase my eyes, but a form of learning and clinical conditioning linked to the interpersonal relationship with the doctor which goes beyond the transference defined in the 19th century by the Scottish surgeon James Braid for the treatment of pain and framed as a science in the 1900s by the American psychiatrist Milton Erickson, father of modern hypnotherapy. Now research published in the Scientific Reports journal, conducted by a diverse team of doctors, hypnological psychologists and philosophers headed by Hubert Dinse of the Neurological Clinic of the Ruhr University in Bochum, with varying degrees of hypnotic techniques has succeeded in changing the tactile perception of 24 subjects, having confirmation by means of electroencephalogram (EEG) and somato-sensory evoked potentials (SSPE), two instrumental methods of neurological evaluation which attested the variations of the cerebral electrical activity beyond the subjective affirmations provided by the participants. The results obtained shake the concept of stability of the organization of our tactile sense which lasted from the early 1900s when the German neurologist Korbinian Brodman identified in the so-called cerebral area 4 a nervous avatar called homunculus which holds the precise representation of our body. Each part of this homunculus, corresponding to the relative real body region, has a representation always directly proportional to the richness of the peripheral innervation and has given rise to the well-known caricature of the gnome-shaped homunculus with huge hands and lips that each of us has in his head. The explanation for all this is everyday life: one thing to pierce a lip, another a leg where you feel less pain because the nerves involved in the transport of painful impulses, the so-called nociceptive nerves, which go from here to the homunculus are much less of those connected to the lip. The same goes for the impulses of normal sensitivity that travel parallel to the painful one: what you can perceive with a finger is much more precise than what you perceive on the skin of the legs because there are much more sensory nerve branches in the fingers. Think of how they are used, for example, by a watchmaker or a precision goldsmith.
Tactile discrimination
The researchers measured the tactile perception of the study subjects based on their tactile discrimination between two points, possible thanks to the skin receptors (Meissner, Merkel, Pacini and Ruffini corpuscles). The ability to feel a punctiform object is an integral part of the normal neurological examination and is carried out with the needle of the gavel, the clinical instrument symbol of the neurologist. The needle can be used from the pointed or blunt side on the patient’s face, trunk and limbs by asking him if he feels a prick or a touch and if he feels the same on both sides of the body, always trying to use the thick pressure and advising him to give an approximate answer because the doctor is not a machine and may not apply the same pressure every time.
I study
In the study by the German researchers this problem did not exist both because they used an automated mechanism and because the patients’ responses were verified instrumentally by means of EEG and SSPE. In fact, the subjects had to keep their forefinger in a device where two needles repeatedly touched it in a painless but perceptible way. If the needles were far enough apart, the patients easily distinguished two points of contact, but if they were very close, they felt the touch in only one point. This is normal because the homunculus’ tactile discrimination threshold (from 10.2 to 131.6 millinewtons per square millimeter of skin) is limited and stable: when the contact points are too close, it cannot distinguish them, with minimal variations from person to person. person. Instead, researchers have shown that, using particular techniques of hypnotic persuasion, this variability can even be changed in the same subject. They have in fact induced patients to imagine that their index finger was five times bigger, in practice making the virtual one of their sensory homunculus enlarge. And then conversely that it was five times smaller, thus making the finger of the homunculus smaller.
With suggestion and without suggestion
The hypnosis technique without suggestion and the stronger one with suggestion were used. The former was not enough to change the perception of the contact, while with the latter the discrimination threshold improved and the subjects who had mentally enlarged the homunculus index finger were able to feel two needles, even when they were closer together. Conversely, by decreasing it, tactile discrimination gets worse because by shrinking the homunculus’ finger becomes sensitive like the legs or the rest of the body where it is more difficult to distinguish two points that are too close together. Hypnosis alone cannot change the homunculus – the authors say – but if we manage to induce a conviction in someone through verbal suggestion, we change his perception.
Homunculus oemostatico
The concept of perennial stability of the homunculus discovered a hundred years ago by Brodman therefore has a definitive reworking that already in 2021, even without the need for hypnosis, had been hypothesized by researchers at the University of London directed by Dollyane Muret who in Current Opinion in Neurobiology who proposed the concept of homeostatic homuncules, i.e. capable of adapting to new situations. In the event of the loss of a limb in adulthood, the homunculus in fact demonstrates adaptive capacities and neuronal plasticity aimed at maintaining the stability of the entire sensory-motor system, a discovery that paves the way for the most recent models of both motor and sensory prostheses. similar to the bionic limb of Star Wars hero Luke Shywalker. By combining hypnosis techniques with the suggestion of the German study, the use of these prostheses will no longer be science fiction and we could imagine a homunculus with a bionic limb. We’ll see if his virtual bionic fingers will be five times bigger or smaller.
July 1, 2023 (change July 1, 2023 | 2:47 pm)
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