An international team led by researchers from the Research Center of the Brain and Spinal Cord Institute (CNRS/Inserm/UPMC) has successfully increased the visual capacities of a group of healthy volunteers thanks to transcranial magnetic stimulation (TMS). After stimulating a cerebral area of the right hemisphere - linked to orientation of spatial attention and perceptive awareness - the volunteers were more able to perceive a target appearing on a screen. This research, which has just been published in the journal PLoS ONE, could be used to develop new rehabilitative techniques for certain sight disorders. What’s more, it could also help to improve the capacities of people carrying out tasks calling for very high precision.
TMS is a non-invasive technique involving the delivery of a magnetic impulse on to a given area of the brain. This activates the cortical neurons located within the magnetic field’s radius of action, and changes their activity temporarily and painlessly. For a few years now, scientists have been interested in the possibility of improving certain cerebral functions in healthy volunteers using this technique.
The latest research by Antoni Valero-Cabré’s team on the stimulation of a region of the right cerebral hemisphere, called the frontal eye field (FEF), falls into this context. The FEF is not a primary visual area strictly speaking, but it does play a part in planning eye movements as well as directing each person’s attention in the visual space. In an initial experiment, a group of healthy volunteers had to try and perceive a target with very low contrast appearing on a screen for 30 ms. For some tests, before the target appeared, the volunteers received a magnetic impulse on the region for 80 to 140 ms. Success was found to be greater after use of TMS, with the visual sensitivity of the healthy volunteers temporarily increasing by around 12%. In a second experiment, the volunteers received a brief visual clue telling them where the target may appear. In this setup, the increase in visual sensitivity - which was the same - only occurred when the clue pointed out the actual location of the target.
Although such brain functions as conscious sight are highly optimized in healthy adults, these findings show that there is significant room for improvement and that this can be “increased” by TMS. This technique might be tested for the rehabilitation of patients with damaged cortices, due to a CVA for example, as well as patients suffering from retina problems.
The second experiment suggests that rehabilitation based on both TMS and visual clues could be more selective than using stimulation on its own. The researchers want to look into this option further through repetitive TMS which, this time, would enable a sustainable change to cerebral activity to be brought about.
Moreover, according to the researchers, TMS may also, shortly, be able to improve the attention capacities of people carrying out tasks that require considerable visual skill.
These experiments were supported by the European initiative ERANET NEURON BEYONDVIS, partly financed by the ANR.
"Manipulation of pre-target activity on the right Frontal Eye Field enhances conscious visual perception in humans"
Lorena Chanes, Ana B. Chica, Romain Quentin, Antoni Valero-Cabré
PLoS ONE. May 15th 2012
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