Think about a situation in the past few years where your mind was at its very best. A situation where you felt immune to distractions, thinking was easy and non-strenuous, and you did not feel information-overloaded. If you take a moment, you can probably recall one such situation. As you think about it, you may even experience it actively right now and get a sense that you could be in that state again.
You have just read a suggestion. A suggestion is a piece of information that guides your thought in a particular direction. In the above, you thought about your past and then the present. You could have thought about ice cream or the US election, but you did not.
Hypnotic suggestion is a particular kind of suggestion, usually involving a heightened response to the suggestion itself, some degree of involuntariness, and a deviance from reality. Hypnotic suggestion can change our thinking in very fundamental ways, e.g. by de-automatizing psychological processes that were hitherto thought to be automatic. For this reason, neuroscience has recently seen a surge in interest in hypnosis, e.g. following the finding that the brain can be made indifferent to pain stimulation (analgesia) and that this effect can be reversed as well: that pain processing in the brain can be induced in the absence of stimulation. Hypnosis research seems to push the boundary for what processes can be moderated by top-down processing.
For this reason, researchers have been quite creative in their use of hypnosis, particularly in the early days of hypnosis research. A 1964 study by Fromm and colleagues suggested to healthy participants that they had suffered an organic brain injury. These “brain injured” participants were then subjected to a blinded neuropsychological assessment and a group of observing neuropsychologists were asked to rate, for each participant, whether they were brain-injured. The “brain injured” participants had a much higher organicity rating than non-hypnotized controls. Fromm concluded by speculating that this effect could be reversed: that brain-injured patients could be hypnotized to believe that they were not brain injured and that they should perform better under such conditions.
Now, 53 years later, this study has been carried out to specifically target working memory, the impairment of which is one of the most prevalent and invalidating sequelae following acquired brain injury across a wide range of lesion sites, severities, and durations since incidence. An impaired working memory probably feels the opposite of the situation you thought of in the beginning of this article. Such a feeling of distractibility, that thinking is unreliable and strenuous is well known to many of us at times, but many brain injured persons experience it chronically and to such a degree that work and social relationships cannot be maintained. Unfortunately, working memory has hitherto proven quite resistant to training and rehabilitation efforts so these sequelae are regarded as chronic.
As expected, patients scored much lower than the healthy population at baseline on two measures of working memory. However, after four sessions of hypnosis, they improved on both outcome measures to slightly above the population mean. In other words, as a group, they did not behave like brain injured patients anymore – at least not on these outcome measures.
Using active and a passive control groups as well as a cross-over, we identify that a large portion of this effect can be attributed to the contents of the suggestion rather than other factors involved, including hypnosis per se, retest effects, expectation effects, an unequal sampling of groups, spontaneous recovery, etc. That is, it makes a difference what suggestions are delivered. Also, the improvement in working memory performance did not deteriorate during a seven-week break, suggesting that it is long-lasting. Finally, the magnitude of the patient’s improvement was not affected by their age, type of injury, time since injury (1-48 years), educational level, and other factors. In other words, the data implies that hypnotic suggestion works equally well for everybody with an acquired brain injury.
These are obvious reasons for excitement. But, more importantly, there are many reasons to be skeptical. I have presented what can be concluded and what cannot be concluded from the paper itself elsewhere. With respect to clinical significance, the experiment only indirectly suggests that the effect is clinically relevant outside the laboratory, i.e. in everyday life. This remains to be shown directly.
With respect to belief, the theoretically deducted probability is very low that hypnotic suggestion improves working memory in a lesioned brain in just four weeks given our knowledge about brain injuries, neural plasticity, and the fact that many studies have used suggestion-like interventions in neurorehabilitation without observing this magnitude improvement. The effect of this low prior probability can be quantified. If you thought that the chance of success was one in a thousand (which could be justified), the experiment changes that belief to between one in three, and one in 25. In other words, if you were a very strong pessimist, you would not be convinced now. Extraordinary claims do, after all, require extraordinary evidence. But you may now be more curious and hopeful. If you were less skeptical a priori, you may feel more convinced by now. More data from replications and extensions will determine whether pessimism or optimism holds out in the long run.
The potential implications are large. Brain injuries constitute the second and third largest health care costs in the world, a large portion of which can be attributed to cognitive impairments. Furthermore, the results suggest that “chronic” cognitive impairment following acquired brain injury, although very real, is not as fixed as the name implies.