Primary Supervisor: Dr Ned Jenkinson, School of Sport, Exercise and Rehabilitation Sciences
Secondary supervisors: John Brittain
PhD project title: Understanding and improving non-invasive brain stimulation to improve motor function throughout the lifespan
University of Registration: University of Birmingham
Understanding how the human brain controls behaviour has always been hampered by the lack of techniques that allow direct interrogation of its function. Historically, neuropsychologists have studied patients following brain-injury to investigate the role of specific brain regions. Imaging techniques broadened our ability to observe brain function during behavioural tasks, though these results provide only correlational evidence of the associations between brain regions, activity, and behaviour.
Non-Invasive Brain Stimulation has shown great promise in helping us better understand the brain as it can be utilised to directly influence brain activity, which allows causal inferences between brain activity and behaviours. Much of this work has been performed using Transcranial Magnetic Stimulation, however more recently, Transcranial Direct Current Stimulation (TDCS) has become increasingly popular. TDCS is a form of neuromodulation induced by passing small direct currents to the brain via electrodes attached to the scalp. TDCS is known to modulate brain activity, as monitored by imaging techniques including fMRI and EEG. TDCS has also been shown to improve or inhibit (depending on how it is applied) many types of behaviour, including perception, cognition, mood and motor function. It therefore promises much as a non-invasive technique, both to address causality of brain processing in the healthy brain, and modulation of function, which in turn may promote recovery (i.e. rehabilitation) or retention of function (i.e. ageing).
Due to its low cost and simplicity of application TDCS is increasingly popular. However, this rise in use has seen an increase in studies reporting negative findings and replication failures. Our contention is that the rise in popularity, combined with limited understanding of the underlying mechanisms have produced these diverse set of results. As such, a better understanding of the mechanisms of action and application of TDCS is urgently needed.
For example, current thinking suggests that there is little need for spatial or temporal specificity when applying TDCS. Indeed, it is thought that the effects of TDCS are generally long lasting and spatially diffuse. However, recent work in our labs has suggested that this may represent only a limited application of the technique. We recently demonstrated a double dissociation of TDCS site with the movement being made: stimulation of the motor cortex improves motor adaptation with the hand but not the arm, whereas cerebellar stimulation specifically improves motor adaptation with the whole arm, but not the hand (Weightman et al. 2020, 2021). In these studies, we also investigate how performance changes in older adults and how brain stimulation can be used to reverse these age-related deficits.
We have also obtained date that show a temporal relationship between stimulation and the task, with short duration stimulation delivered only during the period of movement enhancing learning above the level seen in the traditional long-term stimulation protocol. Indeed, the importance of timing is in keeping with historical electrophysiological evidence that shows instantaneous responses to TDCS at a neural level as well as Hebbian (coincidence) principles of neural plasticity.
Our PhD project will investigate the principles of TDCS in both a young and an old cohort through a combined experimental and modelling approach. Specifically, we will probe behaviour using TDCS, TMS, high-density EMG to elucidate fine-grained motor control, and translate these principles into computational models capable of capturing the observed behaviours, how they differ between the ages and how brain stimulation might reverse the changes seen in old age. These models have the potential to allow us to quickly identify the most effective (bespoke) form of stimulation for further experimental manipulations, with the potential to inform future applications.
Weightman, M., Brittain, J.-S., Punt, D., Miall, R. C. & Jenkinson, N. Targeted tDCS selectively improves motor adaptation with the proximal and distal upper limb. Brain Stimulation 13, 707–716 (2020).
Weightman, M., Brittain, J.-S., Miall, R. C. & Jenkinson, N. Direct and indirect effects of cathodal cerebellar TDCS on visuomotor adaptation of hand and arm movements. Scientific Reports 11, 4464 (2021).
BBSRC Strategic Research Priority: Understanding the Rules of Life: Neuroscience and behaviour & Systems Biology & Integrated Understanding of Health: Ageing
Techniques that will be undertaken during the project:
- Behavioural testing
- Brain Stimulation
- HD EMG
- Computational modelling
Contact: Dr Ned Jenkinson, University of Birmingham