Thursday February 3 2011
Simply stimulating any brain region will not improve performance
“Zapping the brain with an electrical current” can help people solve puzzles reported The Daily Telegraph. The newspaper said volunteers who received electrical stimulation of the brain's “anterior temporal lobes” were three times more likely to be able to figure out an unfamiliar puzzle than those who did not get zapped.
The theory underlying this research is that a technique called transcranial direct current stimulation (tDCS) alters the activity of brain cells in specific areas of the brain. In tDCS an electrical current is applied directly to the head above the anterior temporal lobes of the brain. The aim of the research was to investigate whether stimulating the brain with tDCS affected volunteers’ performance at solving puzzles.
The researchers found that three times as many students solved the puzzles within a time limit when the electrical current was applied from the right side of the brain to the left side, causing increased activity on the right and decreased activity on the left.
This was preliminary research and the method will need to be tested in further experiments. Imaging studies of the brain while people are receiving tDCS would help to test the researchers’ theories further.
Where did the story come from?
The study was carried out by researchers from the Centre for the Mind at the University of Sydney. The authors do not report any sources of funding. The study was published in the open access journal PLoS ONE.
The Daily Mail and The Daily Telegraph both reported the detail of this study accurately. The Daily Mail included relevant quotes from researchers in the field and mentioned that a similar technique was shown last year by Oxford University researchers to improve the mathematical ability of students.
What kind of research was this?
The aim of this experimental study was to investigate whether non-invasive stimulation of the brain with a very low electrical current affected volunteers’ performance at solving puzzles. The technique, called transcranial direct current stimulation (tDCS), was applied to the anterior temporal lobes (ATL), just under the temple areas of the skull. The effects were compared with a sham procedure where no current was applied.
The researchers explain their belief that people usually have difficulty “thinking outside the box”. They suggest that once people have learned to solve a problem using a particular method, they often find it difficult to think of other ways of solving the problems. There is evidence that people with certain types of brain damage are more resistant to these “preconceptions” and this prompted the researchers to look into the issue further.
The researchers say that previous studies have suggested that tDCS can change the underlying activity of the brain surface (cortex) directly under the electrodes. The technique involves applying a weak direct current to the scalp via two sponge electrodes soaked in salt water. This polarises the underlying brain tissue with electrical fields, one side of the brain becoming positive and one negative.
In this study, the researchers wanted to see whether they could replicate this resistance to preconceptions or “mindset” in healthy people by temporarily inhibiting or disinhibiting certain areas of the brain with a weak electrical current.
What did the research involve?
The researchers recruited 67 healthy, right-handed students aged between 18 and 38 years from their university. Participants were not recruited if they were pregnant, had a history of drug use, had mental health issues or were taking any type of medication for neurological conditions. Seven of the volunteers were found to have previous experience of the task or could not complete it and were also excluded. This left 60 people to study, 29 of whom were female.
The puzzles involved tests called “matchstick arithmetic”, in which the students were asked to correct equations written as sums in Roman numerals constructed from matchsticks. They were asked to do this by moving only one stick from one position to another position without adding or discarding any of the sticks. They repeated the puzzle 27 times to ensure the participants became set in the way of answering the puzzles.
The experiment was conducted in a quiet room with no distractions. Each of the participants was fitted with the same tDCS equipment.
The participants were randomly assigned to one of three types of stimulation before the start of the experiment:
- negative electrode on the left side together with positive electrode on the right
- positive electrode on the left side together with negative electrode on the right
- control “sham stimulation”
In the experimental groups, the current was applied to the volunteers’ scalps for five minutes after the initial practice test. Depending on the polarity of the current flow, the underlying brain activity could be increased (positive, anodal stimulation) or decreased (negative, cathodal stimulation). In the sham control procedure the device was switched off, but the control knob remained at ‘on’. The researchers say the participants could not have known if they were receiving current or not (reliably blinded).
The current was applied directly after the first part of the experiment had been completed and then there was a further five-minute delay until the second test began. Both active and sham groups were then given up to six minutes to solve two new types of matchstick test while the current was applied. The participants were tested to see how long they took to complete the two new puzzles accurately.
The results were then analysed. The researchers’ main outcome of interest was the proportion of volunteers who had completed the puzzle within six minutes.
What were the basic results?
Only 20% of participants who received sham stimulation (control) solved an insight puzzle within the six minutes.
Of those who received negative electrode stimulation (decreased excitability) on the left side together with positive electrode stimulation (increased excitability) on the right side, 60% solved the problem within six minutes. This was statistically significant (p = 0.011).
The students who were given the reverse stimulation (negative current on the right side and positive on the left) did not perform differently from those in the sham group for solving either problem within the six-minute period.
How did the researchers interpret the results?
The researchers say that the findings strongly support their prediction that stimulating the anterior temporal lobes with positive electrode stimulation on the right side would enable people to be better at solving insight problems. They say they were surprised by the three-fold increase in the likelihood of solving the problems and argue that the results suggest strong hemispheric differences. They say these differences mean that simply stimulating any brain region will not improve performance.
This carefully conducted study used healthy volunteers and has further tested the theories of how some regions of the brain are involved in complex puzzle solving tasks. The different effect found when the electrodes were reversed over the brain will cause some controversy. This is partly because, as the researchers say, they were not able to look at the effect of left cathodal stimulation and right anodal stimulation in isolation to discover which has a stronger effect. This problem could be resolved if one-sided stimulation were used (not placing the electrodes across the head). However, they say this is not possible.
Further studies, including imaging studies of the brain while people are receiving transcranial direct current stimulation, would help to test the researchers’ theories further.