Charging Up the Inner GPS

A team of psychological scientists from Tufts University and the US Army may have found one way to improve a shaky sense of direction: applying an electric current to the brain.

The research team, led by Tad T. Brunyé, found that volunteers who started the experiment with poor navigation skills showed a significant improvement after receiving a dose of low-current electricity delivered to the scalp, a technique known as transcranial direct current stimulation (tDCS).

Previous studies using tDCS have shown that it can temporarily cause varying effects in people that include improved memory, creativity, and attention, and even relief from depression symptoms.

Although psychological scientists do not understood exactly how tDCS works, they think that low doses of electrical stimulation can increase the excitability of neural circuits, making it easier for neurons to fire.

Decades of research have identified specific structures in the right hemisphere of the brain as being particularly important for navigation and spatial memory, including the hippocampus and parahippocampus. Brunyé and his colleagues hypothesized that delivering tDCS to these right temporal brain regions could enhance navigation skills, helping people improve their sense of direction and spatial memory.

For the study, a group of 32 male university students volunteered to undergo tDCS while their navigation skills were tested. Half of the participants received tDCS stimulation only over the right temporal lobe, an area associated with acquiring and retrieving spatial knowledge, while the other half received tDCS only over the left temporal lobe.

During the first visit to the lab, the volunteers completed a series of measures of their spatial reasoning skills and sense of direction. They then completed a navigation task without tDCS in which they were asked to make their way through a virtual town on a computer screen while attempting to navigate between a sequence of 10 landmarks, such as finding their way from the bank to the library. During two additional sessions, volunteers completed the navigation task while receiving either a very low “ineffective” dose of electrical stimulation or a higher “working” dose of anodal tDCS (positive stimulation) in a counterbalanced order (0.5 versus 2.0 mA).

To test for changes in spatial memory, volunteers were asked to complete various tasks, including sketching a map of the virtual town on a blank piece of paper after completing the task.

As expected, volunteers who received the very low dose of tDCS stimulation — on the left side of the brain — showed no significant improvements in their sense of direction or their spatial memory. Individuals with a poor sense of direction at baseline who received a working dose of electrical stimulation — on the right side of the brain — showed significant improvement, navigating between landmarks much more efficiently.

“Brain stimulation in individuals with a low sense of direction may result in reduced excitatory thresholds in neural networks responsible for acquiring spatial knowledge during navigation, enhancing otherwise suboptimal performance,” the researchers wrote. It could be the case that activating these brain regions promotes allocentric strategies for spatial learning (encoding the location of objects relative to each other rather than relative to yourself), a strategy typically adopted by individuals with a highly accurate sense of direction.

But volunteers who already possessed a particularly good sense of direction showed worse navigational skills after receiving tDCS. The researchers suspected that stimulating an otherwise optimized navigational neural network may actually have decreased the neural network’s performance.

The researchers note that additional research using larger samples is needed to find out more about tDCS, such as how it affects particular areas of the brain in specific tasks. In fact, some researchers currently debate whether tDCS does anything at all: A meta-analysis of dozens of studies, conducted by Jared Cooney Horvath and colleagues at the University of Melbourne, Australia, failed to find significant effects of stimulation. This finding has been debated by other psychological scientists (see Price & Hamilton, 2015).

References

Brunyé, T. T., Holmes, A., Cantelon, J., Eddy, M. D., Gardony, A. L., Mahoney, C. R., & Taylor, H. A. (2014). Direct current brain stimulation enhances navigation efficiency in individuals with low spatial sense of direction. NeuroReport, 25, 1175–1179. doi: 10.1097/WNR.0000000000000214

Horvath, J. C., Forte, J. D., & Carter, O. (2015). Evidence that transcranial direct current stimulation (tDCS) generates little-to-no reliable neurophysiologic effect beyond MEP amplitude modulation in healthy human subjects: A systematic review. Neuropsychologia, 66, 213–236. doi: 10.1016/j.neuropsychologia.2014.11.021

Price, A. R., & Hamilton, R. H. (2015). A re-evaluation of the cognitive effects from single-session transcranial direct current stimulation. Brain Stimulation, 8, 663–665. doi: 10.1016/j.brs.2015.03.007