Stimulating motor skills learning in healthy ageing Getting old is no fun and age-related loss of learning and retention of motor skills don’t make it any easier. EU research investigates one possible therapy, non-invasive brain stimulation (NIBS). Health © cowardlion, Shutterstock Despite being a promising therapeutic solution, surprisingly little is known about NIBS and the way it boosts motor-related neuroplasticity. Through funding from a Marie Skłodowska-Curie Individual Fellowship, the Stim-Plast-O project has investigated a form of neurostimulation, transcranial direct current stimulation (tDCS). The team used multiple magnetic resonance imaging (MRI) and analytic techniques to identify the neural processes underlying tDCS-induced modulations in behaviour in healthy older adults who are over 55 years. “We viewed this as a critical step before approaches such as tDCS are more widely implemented as viable interventions to not only minimise ageing- but also pathology-related impairments,” explains Dr Bradley King, fellow of the Stim-Plast-O project. Right or left hemisphere stimulation is critical When tDCS was applied to the primary motor cortices of healthy older adults, results showed that any influence on the motor learning-related processes depended on which brain hemisphere received stimulation. Critically, stimulation of the right motor cortex actually degraded, as opposed to boosted, performance. This particular result has widespread implications for the use of stimulation approaches. As a neurorehabilitative tool following neurological injuries that are predominantly unilateral such as a stroke, direction of the observed stimulation effects may be hemisphere-specific in these populations. Interestingly, for brain activity during performance of the motor task, tDCS did indeed modulate activity in task-relevant brain regions. Moreover, this was the case even in regions that are subcortical and therefore not directly below the area of the brain that received the stimulation. Key role for GABA Previous research in young adults has indicated that decreases in the concentration of gamma-aminobutyric acid (GABA), the primary inhibitory neurotransmitter in the central nervous system, are critical for learning and memory processes and that tDCS is an effective tool to decrease GABA concentration. “Our results, however, indicated that in healthy older adults, tDCS did not alter the concentration of GABA in the stimulated motor cortex,” notes Dr King. This potentially suggests that an inability to modulate GABA in the ageing brain could contribute to known ageing associated deficits in learning and memory behaviours, an interpretation the group is following up on. Following on from Stim-Plast-O Participants completed an extensive neuroimaging protocol that has generated a lot of data for analysis that will be finalised in the coming months. “This will allow us to examine motor learning- and stimulation-induced changes in brain activity, functional connectivity and neurometabolite concentration, and how these processes are modulated by individual variations in brain structure,” explains Dr King. More long term, the team is working on a follow-up experiment that will enable assessment of the boundary conditions required for tDCS-induced behavioural improvements. Although brain stimulation approaches such as tDCS can certainly be a powerful tool, their effectiveness depends on many such boundary conditions, including stimulation parameters and even individual variations in brain structure and functional organisation. “Additional research is necessary to fully elucidate these conditions before such stimulation approaches are more widely implemented,” concludes Dr King. Keywords Stim-Plast-O, tDCS, GABA, ageing, motor skills, motor learning, non-invasive brain stimulation, neuroplasticity
