Electrical Stimulation of Brain via Scalp May Ease Bradykinesia

Marisa Wexler, MS avatar

by Marisa Wexler, MS |

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Electrical stimulation given through the scalp to a brain region called the supplementary motor area may ease certain aspects of upper limb bradykinesia in people with Parkinson’s disease, a small study suggests.

The study, “Transcranial direct current stimulation of supplementary motor area improves upper limb kinematics in Parkinson’s disease,” was published in Clinical Neurophysiology.

Bradykinesia, a hallmark Parkinson’s symptom, is characterized by slow movements, delayed reaction times, and decreased amplitude of movements (that is, smaller movements). Bradykinesia “is among the most functionally debilitating symptoms of Parkinson’s disease,” the researchers wrote.

As its name suggests, the supplementary motor area, or SMA, is a part of the brain that helps to coordinate movements — specifically, it is thought to be involved in preparing for and initiating movement. Abnormally low electrical activity in this brain region has been linked to bradykinesia in Parkinson’s, implying that increasing electrical activity in the SMA might ameliorate this symptom.

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Scientists at the University of Ottawa, in Canada, tested whether providing an electrical signal to the SMA might ease patients’ bradykinesia symptoms. The electricity was administered through electrodes placed on their scalp, a process called transcranial direct current stimulation (tDCS).

The experiment’s purpose was to investigate whether applying anodal tDCS over the SMA for 10 minutes would lead to improvements in patients’ premotor reaction time and movement kinematics (the study of motion) during a simple reaction time task performed by the upper limb.

Researchers hypothesized that tDCS “would lead to increased cortical excitability [i.e., electrical activity in the brain] and result in a reduction in premotor RT [reaction time] and improved kinematic features related to bradykinesia symptoms, such as movement time, displacement and velocity.”

They enrolled 13 right-handed people with Parkinson’s, 12 men and one woman with a mean age of 63; all had a mean disease duration of eight years, and were tested while in an “on” treatment state.

In the experiments, participants waited with their right arm in a fixed position; then, upon being cued, extended their elbow in a specific manner (20 degrees) “as quickly and accurately as possible.” The scientists recorded these movements — done in two blocks of 20 cued extensions — alongside accompanying electrical activity in patients’ muscles.

These sessions took place before and after a tDCS or sham procedure (without electrical stimulation) given each patient, without them being aware of the procedure chosen, and a seven-day rest between stimulations. Results were then compared.

tDCS did not significantly affect participants’ reaction times, findings showed.

“The current RT results suggest that in individuals with PD [Parkinson’s disease], a single session of anodal tDCS applied over SMA does not increase cortical excitability enough to provide improvement in [brain electrical activity] required for faster RT,” the researchers wrote.

Despite this lack of difference in reaction times, “participants appeared to be better able to execute the elbow extension movement following anodal tDCS,” the team added.

For example, participants were generally able to complete the movement faster after undergoing tDCS — mean peak velocity was 172 degrees/second after tDCS, as compared with 155 degrees/sec after the sham procedure. Participants also were significantly faster to reach the maximum amount of movement (peak displacement) after tDCS.

“Our results suggest that anodal tDCS applied over the SMA improved time to peak displacement and overall movement time of an upper limb movement,” the researchers concluded.

“Therefore, anodal tDCS to SMA may be a viable adjunctive intervention [add-on treatment] to assist upper limb movement kinematics in individuals diagnosed with PD,” they added.

This study is limited by its small size, and its imbalance of sexes among participants, making it impossible to draw broad conclusions for this data, the researchers noted. They highlighted a need for more research into the potential benefits of tDCS — to the supplementary motor area, and potentially other brain regions — for people with Parkinson’s.

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