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It’s a testament to the strength and versatility of the human brain that anyone with at least half of one tends to assume that their senses give them direct access to objective reality. The truth is less straightforward and much more likely to induce existential crises: the senses do not actually provide the brain with a multifaceted description of the outside world. All that the brain has to work with are imperfect incoming electrical impulses announcing that things are happening. It is then the job of neurons to rapidly interpret these signals as well as they can, and suggest how to react.

This neurological system has done a pretty good job of modelling the world such that the ancestors of modern human beings avoided getting eaten by sabre-toothed tigers before procreating, but the human brain remains relatively easy to fool. Optical illusions, dreams, hallucinations, altered states of consciousness, and the placebo effect are just a handful of familiar cases where what the brain perceives does not correspond to whatever is actually occurring. The formation of a coherent model of the world often relies on imagined components. As it turns out, this pseudo-reality in one’s imagination can be so convincing that it can have unexpected effects on the physical body.

Back in the 1980s, the future of computing⁠—and pretty much everything else⁠—was thought to lie in virtual reality. Although few modern homes actually contain immersive, multi-sensory 3D virtual reality machines, some devices along these lines can be found in medical facilities. Virtual reality therapy (VRT) has often targeted neuropsychological conditions such as phobias and post-traumatic stress disorder; however, since everything we experience has a lot to do with the brain, the range of the potential applications of VRT is much wider than this.

One creative use of VRT has come out of the University of Washington in Seattle, where researchers Hunter Hoffman, David Patterson, and Sam Sharar have been employing VRT since 1996 to address the excruciating pain of severe burn victims. Pain is a neurological response that is very sensitive to psychological factors. For instance, pain is particularly susceptible to the placebo effect, which depends merely on the expectation that a particular treatment will work. Burn victims frequently have flashbacks to the scenes of their accidents, and this intensifies their discomfort. The novel insight of the Seattle researchers has been that these patients experience much less pain from their burns if they imagine being cold. To that end, the researchers have collaborated on a virtual reality game called SnowWorld in which the player uses a headset and joystick to explore glaciers and icy caves full of animated snowmen, penguins, snowballs, and so on. Particularly during wound care⁠—for instance, when bandages are being replaced⁠—patients have reported substantially less pain and preoccupation with their burns while playing SnowWorld than while playing everyday Nintendo 64 games. In other words, SnowWorld owes its effectiveness not simply to being a distraction from the pain, but to convincing the brain that whatever heat it senses from the replay of the burn experience is being nullified by the cold suggested by the virtual environment. Studies based on functional MRI (fMRI) imaging are also beginning to show evidence for the utility of virtual reality in providing relief from pain.

SnowWorld

In fact, mental exercises of all kinds⁠—not just those supported by persuasive video games⁠—can have a considerable effect on brain activity. One example is a type of mental arithmetic practised in Japan. Physical abacuses⁠—counting devices relying on rows of beads⁠—are common in the country, but a valued skill is anzan, or quick and accurate calculation by means of a mental abacus. Anzan propelled 22-year-old Naofumi Ogasawara to first place at the 2012 Mental Calculation World Cup in Germany. It is also featured in a competition called ‘Flash Anzan’, in which fifteen three-digit numbers are rapidly flashed on a screen and participants use mental abacuses to add them up. Using these imagination-based calculating tools, the most skilled participants can sum fifteen three-digit decimals in less than two seconds. Contestants begin using the mental abacus so immediately that afterwards they cannot remember any of the individual three-digit numbers.

Skills that can rely on mental practise are also familiar to those who need to practise physical motions regularly, such as musicians and athletes. For instrumentalists, having an actual instrument to play is pretty handy, but it turns out that having a mental copy of one can be almost as good. The musical community in general has been aware of this for decades or more. Noted pianists Vladimir Horowitz and Arthur Rubinstein both employed the technique of mental rehearsal⁠—playing pieces on an imaginary piano in their minds⁠—and for different reasons. Horowitz was uncomfortable practising on any piano other than his favourite Steinway; Rubinstein simply disliked spending hours at a time sitting at a physical piano. A similar story is recounted by Matthew and Sandra Blakeslee in their 2007 book The Body Has a Mind of Its Own: a violinist spent seven years in jail without his instrument, but practised mentally every single night. On the very night he was released, the violinist gave an impeccable real performance on his violin. The imaginary motions that the violinist engaged in during his stint in jail were able to build, or at least maintain, his fine motor skills.

These days, neuroscience is beginning to catch up to musicians who practise mentally. Although the details are still somewhat elusive, the key to the success of mental imagery as a rehearsal technique is that most of the same neurological regions are invoked by mental practise as by real practise. Research led by Alvaro Pascual-Leone of Harvard Medical School has found that this is true even in individuals who do not have prior musical training. Pascual-Leone and his associates taught two groups of non-musicians a basic finger exercise on the piano keyboard; they then had one group practise in the ordinary way and the other practise in their minds, for two hours per day, five days in a row. At the end of the study, the mapping of the rehearsal pattern in the brains of participants from both groups had changed in the same ways. Essentially, the brain can only barely tell the difference; a strong mental simulation of motion is, neurologically speaking, an excellent substitute for the counterpart real motion. Data from a 2004 fMRI study conducted by a team of researchers in Germany corroborates this conclusion; while activation is indisputably stronger and a little more widespread during actual music performance, mental rehearsal covers most of the same basic ground. This finding adheres to a general pattern that imagining a given action or sensation is likely to be neurologically analogous to physically carrying out that action or experiencing that particular stimulus.

A comparison of the frontal and parietal activation in music performance (left) and music imagery (right)

Very similar, but even more striking, is the evidence from athletic training. As with rehearsing a piece on the piano, practising a complex physical task in the mind alone is nearly as effective a learning strategy as actually physically doing it. But it doesn’t stop there. In a 2004 study, a group of researchers from the Cleveland Clinic Foundation decided to find out whether mental practise of a minor exercise routine could actually result in physical changes to the target areas of the body. One group of subjects performed a regular exercise involving moving a finger sideways; a second group regularly imagined doing the same exercise but did not go through the physical motions; and a third (control) group did nothing unusual with their fingers at all. After 12 weeks of training, the physical finger-workout group showed an increase of 53% in finger strength; the control group did not show any changes in finger strength; and the mental-finger-stretching group showed an increase of 35%. In other words, the mental-exercise group physically increased the strength of one of their fingers by imagining, repeatedly, over the course of about three months, that they were exercising it. They didn’t have to lift a finger in order to convince their brains that they were, in fact, lifting a finger.

This result is not unique. A 2007 Canadian study targeting hip muscles had the same outcome: a group of college students using weightlifting increased their hip-muscle strength by 28.3%, a control-group doing nothing to their hip muscles exhibited no change in strength, and a group working on the muscles only via mental imagery showed an increase in the strength of those muscles by 23.7%. What this means is that imagining was almost as good as going to the gym, and probably cheaper as well. One can lie on the couch and build muscle just by thinking about doing those 200 push-ups or running those five kilometres, as long as one is careful and thorough.

Neuroscientists are still working on the enigma of why this might be. Clearly the brain has been tricked⁠—motor neurons in the brain are receiving enough of a signal from the mental exercise to send out their minions to strengthen muscles⁠—but the details are currently somewhat nebulous. Nonetheless, it is clear that the human imagination alone is capable of doing things that are certainly more than imaginary in their results. For that reason, anyone who has found the above insights to be “mind-blowing” are cautioned against repeatedly envisioning a literal take on this description.

Update 31 October 2019: Zokaei et al. (2019) in the Proceedings of the National Academy of Sciences reported that mere memories of bright lights caused the size of their participants’ pupils to change automatically.