Facilitatory non-invasive brain stimulation in older adults: the effect of stimulation type and duration on the induction of motor cortex plasticity

• Published in: Experimental brain research Vol. 234; no. 12; pp. 3411 - 3423
• Main Authors: Puri, Rohan, Hinder, Mark R., Canty, Alison J., Summers, Jeffery J.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.12.2016; Springer; Springer Nature B.V
• Subjects: Aged; Aging; Analysis of Variance; Biomedical and Life Sciences; Biomedicine; Biophysics; Brain research; Brain stimulation; Electromyography; Evoked Potentials, Motor - physiology; Functional Laterality; Humans; Locomotion; Male; Middle Aged; Motor Cortex - physiology; Muscle Contraction; Muscle Strength; Neurology; Neuronal Plasticity - physiology; Neuroplasticity; Neurosciences; Older people; Psychological aspects; Pyramidal Tracts - physiology; Research Article; Time Factors; Transcranial Direct Current Stimulation; Transcranial Magnetic Stimulation - methods; Young adults; Australia; Non-invasive brain stimulation; Theta burst stimulation; Transcranial magnetic stimulation; Transcranial direct current stimulation; Older adults; Plasticity
• ISSN: 0014-4819; 1432-1106
• DOI: 10.1007/s00221-016-4740-3

Despite holding significant promise for counteracting the deleterious effects of ageing on cognitive and motor function, little is known of the effects of facilitatory non-invasive brain stimulation (NBS) techniques on corticospinal excitability (CSE) in older adults. Thirty-three older adults (≥60 years) participated in four NBS sessions on separate days, receiving 10- and 20-min anodal transcranial direct current stimulation (atDCS), and 300 and 600 pulses of intermittent theta burst stimulation (iTBS) over the left M1. Motor-evoked potentials measured in the contralateral hand served as a measure of CSE before and for 30 min following each NBS intervention. At the group level, generalized post-stimulation CSE increases were observed ( p  < 0.001) with no significant differences between the two durations of each stimulation type (atDCS: p  = 0.5; iTBS: p  = 0.9). For individuals exhibiting overall facilitatory change to atDCS (‘responders’, n  = 10), 20-min atDCS resulted in longer lasting CSE facilitation than 10 min. No such difference was observed between the two iTBS protocols. Considerable variability was observed inter -individually, where 52–58 % of the cohort exhibited the expected facilitation after each of the NBS protocols—as well as intra -individually, where 45–48 % of the cohort maintained consistent post-stimulation responses across the varying durations and types of stimulation. In conclusion, as shown previously in young adults, older adults demonstrate substantial variability in response to different facilitatory NBS protocols. Studies to assess the intra-individual reliability of these protocols are critical to progress towards translation of appropriate protocols (i.e. those that elicit the greatest response for each individual) into clinical practice.