Year: 2009

Sensory deprivation lasting only 15 minutes is enough to trigger hallucinations in healthy members of the public, according to a new study published in the Journal of Nervous and Mental Disease.

The researchers were interested in resurrecting the somewhat uncontrolled research done in the 50s and 60s where participants were dunked into dark, silent, body temperature float tanks where they subsequently reported various unusual perceptions.

In this study the researchers screening a large number of healthy participants using a questionnaire that asks about hallucinatory experiences in everyday life. On the basis of this, they recruited two groups: one of ‘high’ hallucinators and another of ‘low’ hallucinators.

They then put the participants, one by one, in a dark anechoic chamber which shields all incoming sounds and deadens any noise made by the participant. The room had a ‘panic button’ to stop the experiment but apparently no-one needed to use it.

They asked participants to sit in the chamber for 15 minutes and then, immediately after, used a standard assessment to see whether they’d had an unusual experiences.

After a twenty minute break, they were asked again about perceptual distortions to see if there were any difference when normal sensation was restored.

Hallucinations, paranoid thoughts and low mood were reported more often after sensory deprivation for both groups but, interestingly, people already who had a tendency to have hallucinations in everyday life had a much greater level of perceptual distortion after leaving the chamber than the others.

This study complements research published in 2004 that found that visual hallucinations could be induced in healthy participants just by getting them to wear a blindfold for 96 hours.

However, my attention was grabbed by the researchers use of a ‘panic button’. The effect of having a panic button in sensory deprivation experiments was specifically studied in 1964 by psychologists Martin Orne and Karl Scheibe. They also asked about hallucinations and compared two groups of people.

One group was met by researchers in white coats, given a medical examination and told to press a ‘panic button’ if they wanted out. The other was met by researchers in causal clothes, weren’t given medical checks, and told to knock on the window if they wanted the experiment to stop.

The actual sensory deprivation part was the same, but the group with the panic button reported many more hallucinations, likely owing to ‘demand characteristics’, or, in other words, their expectations of what might happen.

We also know that an increase in anxiety also increases the likelihood of hallucinations, and having a ‘panic button’ during an experiment, I suspect, is likely put most people a little more on edge.

So we can’t be sure that the effect was purely due to sensory deprivation, but it does chime with various other studies showing that when we reduce our normal sensations, the brain has a tendency to ‘fill in’ with hallucinations.

Link to PubMed entry for sensory deprivation study.

An interesting case study from a 2002 edition of The Lancet of a man who suffered paralysis from drinking too much Earl Grey tea owing to the toxic effects of huge doses of bergamot oil – taken from orange rind and used as flavour:

A 44-year-old man presented in May, 2001, with muscle cramps. He had no medical history of note, but volunteered the fact that he had been drinking up to 4 L of black tea per day over the past 25 years. His preferred brand was GoldTeefix (Tekanne, Salzburg, Austria). Since this type of tea had given him occasional gastric pain, he changed to Earl Grey (Twinings & Company, London, UK), which he thought would be less harmful to his stomach. 1 week after the change, he noticed repeated muscle cramps for some seconds in his right foot. The longer he drank Earl Grey tea, the more intense the muscle cramps became. After 3 weeks, they also occurred in the left foot…

Earl Grey tea is composed of black tea and the essence of bergamot oil, an extract from the rind of bergamot orange (Citrus aurantium ssp bergamia), which has a pleasant, refreshing scent. Bergamot oil contains bergapten (5-methoxypsoralen), bergamottin (5-geranyloxypsoralen), and citropten (5,7-dimethoxycoumarin), which can be found in grapefruit juice, celery, parsnips, and Seville orange juice. Bergamot oil is a well-known UVA-induced photosensitiser with a strong phototoxic effect, and is used therapeutically in psoriasis, vitiligo, mycosis fungoides, and cutaneous lymphoma. Because of this side-effect, bergamot oil has been widely banned as an ingredient in cosmetics and tanning products. Bergamot oil also has a hepatotoxic effect and may cause contact-allergy. The adverse effects of bergamot oil in this patient are explained by the effect of bergapten as a largely selective axolemmal potassium channel blocker, reducing potassium permeability at the nodes of Ranvier in a time-dependent manner. This may lead to hyperexcitability of the axonal membrane and phasic alterations of potassium currents, causing fasciculations and muscle cramps.

In other words, it disrupts the way chemical flow through the membrane of the nerve fibre, causing the neurons that connect to the muscles to malfunction.

Link to DOI entry for the case study.

Not Exactly Rocket Science covers a fantastic study on how the structure of the brain changes as illiterate adults learn to read and write. The research was conducted on rather a novel group of participants. Most were ex-members of guerilla forces in Colombia that had recently put down their weapons to re-integrate in society.

Colombia has a sizeable program to rehabilitate ex-paramilitary ‘reinsertados’ that includes social support and education, as many have never attended school. As the researchers note, this sets up an interesting natural experiment:

After decades spent fighting, members of the guerrilla forces have begun re-integrating into mainstream Colombian society, introducing a sizeable population of illiterate adults who have no formal education. Upon putting down their weapons and returning to society, some had the opportunity to learn to read for the first time in their early twenties, providing the perfect natural situation for experiments investigating structural brain differences associated with the acquisition of literacy in the absence of other types of schooling or maturational development.

The researchers, led by neuroscientist Manuel Carreiras, recruited a group of ex-paramilitaries who could read less than five simple words on a Spanish reading and writing test, and compared them to a similar group who learnt to read and write from an early age.

The research team use MRI scans to compare differences in brain structure between the two groups to allow an insight into how brain anatomy changes to accommodate reading and writing.

While it is possible to do this with children, it is almost impossible to separate out which are the brain changes due specifically to acquiring literacy and which are just part of the massive changes that constantly take place as children develop.

The images above show the areas of the brain (in orange) where the structure was significantly different between literate and illiterate adults.

Rather neatly, these are also areas that have been identified in brain activation studies of reading and writing, and are known to be associated with visual perception, processing word sounds and dealing with the meaning of words.

Subsequent analyses showed that pathways the angular gyrus, a key language area, across each hemisphere were less developed in illiterate adults and were less active when the participants were asked to name objects.

A brilliantly innovative study, a good write-up from Not Exactly Rocket Science and perfectly timed for my arrival in Colombia.

Link to NERS on guerilla reading.
Link to summary of scientific paper.

There are a couple of excellent posts on Neurophilosophy covering recent studies that demonstrate the powerful effect of vision on the perception of physical sensations in our body.

The first covers an interesting study that found that looking directly at your hand reduces laser-induced pain compared to a condition where you are only looking at a visual substitute created with a mirror reflection of the other hand (akin to a mirror box set up).

The second post discusses the possibilities of taking advantage of the ‘rubber hand illusion‘ to allow us to feel like we’re physically inhabiting virtual bodies.

Numerous experiments have shown that we look at a rubber hand being touched simultaneously and in the same way as our real hand, the sensation seems to be located in the fake.

This new experiment attempted something similar but in virtual reality, demonstrating that a synchronised ‘touch’ could be perceived as arising from an avatar hand in a 3D computer generated environment.

While the same research team had demonstrated this effect before this new study showed how the effect could transfer, albeit more weakly, to a virtual arm controlled by a brain-computer interface driven solely from EEG readings.

Both of these studies demonstrate how vision is integrated with tactile information from the body to create our sense of body image, ownership and sensation and both get a great write-up from Neurophilosophy.

Link to Neurophilosophy post visual pain reduction.
Link to Neurophilosophy on the ‘virtual hand illusion’.