Anodal Transcranial Direct Current Stimulation Shows Minimal, Measure-Specific Effects on Dynamic Postural Control in Young and Older Adults: A Double Blind, Sham-Controlled Study

Abstract

We investigated whether stimulating the cerebellum and primary motor cortex (M1) using transcranial direct current stimulation (tDCS) could affect postural control in young and older adults. tDCS was employed using a double-blind, sham-controlled design, in which young (aged 18–35) and older adults (aged 65+) were assessed over three sessions, one for each stimulatory condition–M1, cerebellar and sham. The effect of tDCS on postural control was assessed using a sway-referencing paradigm, which induced platform rotations in proportion to the participant’s body sway, thus assessing sensory reweighting processes. Task difficulty was manipulated so that young adults experienced a support surface that was twice as compliant as that of older adults, in order to minimise baseline age differences in postural sway. Effects of tDCS on postural control were assessed during, immediately after and 30 minutes after tDCS. Additionally, the effect of tDCS on corticospinal excitability was measured by evaluating motor evoked potentials using transcranial magnetic stimulation immediately after and 30 minutes after tDCS. Minimal effects of tDCS on postural control were found in the eyes open condition only, and this was dependent on the measure assessed and age group. For young adults, stimulation had only offline effects, as cerebellar stimulation showed higher mean power frequency (MPF) of sway 30 minutes after stimulation. For older adults, both stimulation conditions delayed the increase in sway amplitude witnessed between blocks one and two until stimulation was no longer active. In conclusion, despite tDCS’ growing popularity, we would caution researchers to consider carefully the type of measures assessed and the groups targeted in tDCS studies of postural control.

Comparison of Transcranial Direct Current Stimulation of the Primary Motor Cortex and Cerebellum on Static Balance in Older Adults

“…In line with the present findings regarding the effects of cerebellar stimulation on balance, other studies showed that a-tDCS of the cerebellum could improve stability parameters in AP and ML directions (8), peak-to-peak sway amplitude, and mean power frequency of sways (7) in older adults. Some motor and cognitive disorders in older adults are associated with age-related changes in the cerebellum (17).…”

“…The present findings also showed that a-tDCS of M1 could improve balance in older adults. Similarly, Craig and Doumas (7) found that M1 stimulation had positive effects on the sway amplitude of older adults. In line with studies on older adults, it was reported that M1 facilitation could improve balance in young adults (7,30,31) and patients with Parkinson's disease (32), chronic low back pain (33), and stroke (34).…”

“…a-tDCS of the cerebellum had no significant effects on balance (25)(26)(27). These controversial findings show that age is a factor, which may affect the outcomes of brain stimulation techniques (7,28,29).…”

“…Most published studies used the cerebellum or primary motor cortex (M1) as the target areas for tDCS. They reported that 20 minutes of cerebellar tDCS in older adults could improve their stability indices in the anteroposterior (AP) (7,8) and mediolateral (ML) directions (8). Craig and Doumas (7) also showed that M1 tDCS with an intensity of 2 mA could decrease the peak-to-peak sway amplitude in older adults.…”

“…They reported that 20 minutes of cerebellar tDCS in older adults could improve their stability indices in the anteroposterior (AP) (7,8) and mediolateral (ML) directions (8). Craig and Doumas (7) also showed that M1 tDCS with an intensity of 2 mA could decrease the peak-to-peak sway amplitude in older adults. cols in these studies vary in terms of intensity, electrode setup, and type of balance task (4).…”