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An experimental technique used to boost brain performance with electrical pulses can actually cause people to perform less well in some tasks, scientists have found.

The technology, known as transcranial direct current stimulation, is already being marketed in commercial products as a way of helping computer game players and athletes improve their focus. 

However, new research from the University of Oxford suggests that the benefits of this technique, which stimulates activity in the brain with an electrical current, may be limited by personality as it appears to only be helpful to people who are stressed about performing a task.

Brain stimulation devices have been used by researchers to study a range of brain functions but they do not believe the technology is understood well enough to be available for use by the general public

They found that while electrical stimulation helped those who lacked confidence or were anxious about performing a series of sums, it caused those who did not fear mathematics to decline.

A follow up study that examined how volunteers fared at spotting which way an arrow was pointing on a screen when confronted with distracting information showed that all those who received stimulation performed more poorly. 

Early experimental studies using transcranial direct current stimulation have suggested that the simple devices can boost memory and cognitive performance.

This has led to some DIY enthusiasts who have attempted to build their own equipment at home.

However, Dr Roi Cohen Kadosh, a lecturer in experimental psychology at Oxford University who led the latest study, urged people not to attempt using the technology at home.

He said: 'The central finding is that stimulation may be beneficial to some populations but detrimental to others, rather than merely less effective, depending on the trait. 

'Such research is essential given the increasing academic and public enthusiasm over transcranial direct current stimulation, including do-it-yourself stimulation. 

'These tendencies may overlook the importance of identifying traits and situations that respond to stimulation as costs with no demonstrable gains, as with our low mathematics anxiety participants.'

Previous research has shown that transcranial direct current stimulation can improve mathematical ability when applied to part of the prefrontal cortex. 

Safe? Some transcranial direct current stimulation devices are already being sold commercially to the public

This area is known to play a role in regulating emotion, so Dr Cohen Kadosh and his colleagues tested the technique on 25 students who found mental arthimetic stressful and 20 who had no problem with sums.

According to their findings, which are published in the Journal of Neuroscience, participants who were anxious about performing maths gave correct answers faster after receiving brain stimulation.

Experimental results showing transcranial direct current stimulation can boost brain activity has led some to attempt to build their own devices at home, but new research suggests this harms cognitive performance

These participants also had lower levels of the stress hormone cortisol in their saliva. The findings suggest that the brain stimulation may have helped the students control their anxiety.

Another study by Dr Cohen Kadosh, published in Frontiers in Systems Neuroscience earlier this year, also showed that people's response to electrical stimulation varied by age, gender, hormone levels and the pre-existing activity of their brain. 

Dr Cohen Kadosh is now pushing for new regulations to control the sale and use of these brain stimulation devices.

Speaking to the Guardian, he said: 'It's not something people should be doing at home at this stage.

'I do not recommend people buy this equipment. At the moment it's not thereapy, it's an experimental tool.'

A transcranial device that uses a smartphone is already been developed by a US company called Thync as a way of altering a users mood.

Other commercial companies have been marketing similar devices to help computer gamers react faster. 

In a recent article for the Journal of Law and Biosciences, Dr Cohen Kadosh's colleague Dr Hannah Maslen argued: 'Recently, it has become very easy for individuals to purchase devices which directly modulate brain function.

'For example, transcranial direct current stimulators are increasingly being produced and marketed online as devices for cognitive enhancement. 

'Despite posing risks in a similar way to medical devices, devices that do not make any therapeutic claims do not have to meet anything more than basic product safety standards. 

'We present the case for extending existing medical device legislation to cover CEDs.'

Dr Nick Davis, an expert in brain stimulation at Swansea University added that the science underpinning the affects of such techniques were still too poorly understood to be available to the public.