deprivazione sensoriale cos'e e gli effetti sul cervello umano

Sensory Deprivation: What It Is and How It Affects the Brain

The human brain is immersed in sensoriality. It could be said that most of its work is to organize and rework sensory stimuli, so as to then produce effective strategies for action. Therefore, removing sensory input from our organ means leaving it in a unnatural silencewhich he tries to fill by self-inducing activations in the sensory areas. The result? Visual hallucinations And auditorybut also, when the deprivation is only a few hours, a deep sense of relaxation And stress reduction. Let’s see in detail what the effects of sensory deprivation on the brain are and how this particular psychophysical state can be achieved.

Effects on our brain

There are several ways to remove sensory input from the brain. One could be disconnect receptors from the central nervous system, but this is a risky operation, because it would mean acting directly on the spinal tract which carries messages from the receptors.

Another one, the simplest, is to build some closed tanksinside which we put a liquid dense enough to allow us to to float without difficulty and whose temperature both that of our body, between 36 and 37 °C approximately, so as not to make us perceive neither hot nor cold.

This is exactly what neuroscientist John Lilly invented in the 1950s to study the effects of deprivation on consciousness. At the time it was thought that once sensory messages were removed from the brain, it would stopped workingat least until he received no new messages.

What was seen instead was that the brain, when it does not receive input, creates it itself. Having hallucinations means, on a neuroscientific level, witnessing the activation of sensory areas whose inputs do not arrive from external receptors, and this is exactly what happens after several hours in a state of deprivation.

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Sensory deprivation as therapy

Once observed that the sensory deprivationtested over the course of a few hoursbrought numerous advantages, it began to be used in the field therapeutic. The REST (Restricted Environmental Simulation Therapy) is a therapeutic technique that tries to limit sensory input to a minimum, and in its Floating-REST version uses precisely this sensory deprivation tank.

A recent systematic review from the Californian Brain Institute that analyzes numerous laboratory results from 1960 to 2023 takes stock of the situation. The data tell us that sensory deprivation used as a therapy leads to a decreased perception of pain as in the case of chronic headache, stress reduction and anxiety, positive effects on sports performances It is on mental well-beingwhile a poor efficacy has been noted in the fight against addictions and sleep disorders.

On a physiological level it appears to have inhibitory effects on the level of activation of the sympathetic system (the part of the nervous system that is activated in alarm situations, associated with the fight-or-flight system), with decrease in blood pressure, Breath relaxation And lowering of cortisol levelsthe stress hormone.

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Floatation–REST. Justin S. Feinstein, Sahib S. Khalsa, Hung–wen Yeh, Colleen Wohlrab, W. Kyle Simmons, Murray B. Stein, Martin P. Paulus, via Wikimedia Commons.

Sensory deprivation as torture

But sensory deprivation also has a dark side. We know that our brain “lives” on sensory stimuli, it feeds on them continuously, and when it is short of them it produces them itself. But when this situation of deprivation is prolongedthose neural pathways that produce hallucinations both visual and auditory, and we have big impacts on the states of consciousnesswith phenomena of distorted perception of the passage of time, Out-of-body experiences and effects similar to those caused by psychedelic substances.

After a few days in a room with limited sensory input, the subjects of the experiment conducted in 1954 by Bexton, Heron and Scott, began to experience difficulty concentrating, emotional instability and long periods of emptinesssimilar to the common sensations of enchantmentbut definitely more long-lasting.

In a short time some of them have switched to vivid hallucinationssuch as “a miniature rocket that discharged pellets that kept hitting his arm”, or out-of-body experiences such as “feeling his head detached from his body like a floating ball of cotton wool”. The extreme cases encountered went as far as body schema disruption (the body map contained in our brain), delusions And psychosiswhich resolved with the interruption of deprivation and a rapid return to pre-experiment cognitive abilities.

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Sensory deprivation tank. Credit: Trogain, via Wikimedia Commons.

For these reasons, sensory deprivation has been used as a torture technique (nicknamed “white torture”, due to the absence of direct and violent action by the torturer). Today, sensory deprivation and its short-term benefits can be experienced in sensory deprivation tanks like the one shown in the photo.