Investigating the mechanisms of non-invasive brain stimulation
We are also using the saccadic system to investigate how transcranial direct current stimulation modulate plasticity in the brain.
To make accurate movements regardless of the changes imposed on our bodies by factors such as fatigue, aging, injury or growth the brain continuously calibrates our motor output. One of the mechanisms that that keeps our movements accurate is called motor adaptation.
The quick eye movements we make to move our gaze from one point of interest to another are called saccades. These are the most common movements made by man; on average we make three a second. We can manipulate saccades in the laboratory to cause motor adaptation to take place over a short period of time, using a protocol called saccadic adaptation. This makes saccadic eye movements an ideal system to study motor adaptation.
We have techniques in neuroscience that allow us to manipulate the excitability of the brain. The techniques are temporary, harmless and painless and can be used on humans. The stimulation is accurate and specific enough to allow us to alter the activity in a small part of the brain to investigate whether that area is involved in adaptation.
We use two techniques i) transcranial magnetic stimulation (TMS) and ii) transcranial direct-current stimulation (TDCS). TMS can be used to temporarily interfere with a small region of the brain. We use this technique to probe sites in the brain during saccadic adaptation. At present we think that there are several that are involved in the process, both the cortex and an area at the back of the brain called the cerebellum.
Depending on the polarity of stimulation TDCS can be used to excite or inhibit brain activity, and by doing so we can to modulate adaptation. We do this not only to explore the mechanisms of adaptation, but also because think that TDCS may help increase motor adaptation in people who do not adapt well – see our other project on Motor Adaptation in Parkinson’s disease.
People: Muriel Panouilleres, Ned Jenkinson
Collaborators: Chris Miall
Current Funders: The Medical Research Council
Jenkinson, N., Miall, R.C. Disruption of saccadic adaptation with repetitive transcranial magnetic stimulation of the posterior cerebellum in humans, (2010) Cerebellum, 9 (4), pp. 548-555.