Essential Tremor (ET) and Parkinson’s disease (PD) are tremor-related disorders that affect the execution of fine controlled movements such as handwriting. Smooth handwriting involves a complex combination of motor tasks and attentional demands that must be undertaken in parallel, or switched between in series. The present thesis used electroencephalography (EEG) to address the neural processes associated with handwriting and related attentional processes in ET and PD groups compared to an age-sex matched control group (CO). Specifically, we aimed to indirectly investigate the activity in the cerebellum (implicated in ET) and basal ganglia (implicated in PD) during the manipulations of task-switching demands and feedback. Participants were asked to perform two tasks. The first task was a handwriting task (using ET and control groups) to record cursive switch (el, le) and no-switch (ee, ll) handwriting under visual, countback (counting backwards in threes), non-visual and repeated visual condition. Behavioural performance was assessed using various temporal and spatial variables of letter pairs. EEG was used to analyse spectral power and calculate event related spectral perturbation (ERSP) in alpha (8-12Hz) and beta (13-30Hz) frequency bands. The second task was an attention task (using ET, PD, CO groups) to record postural tremor while holding a cell phone to maintain position of a ball within a target under different manipulations in attentional engagement. Behavioural performance was assessed by recording spectral power of postural tremor of the left and right hand in the frequency bands 3-8Hz, 4-7Hz (theta), 8-12Hz (alpha), 13-30Hz (beta). EEG was used to analyse spectral power and calculate ERSP in the theta, alpha and beta frequency bands.
The key findings of the handwriting task partially supported the hypotheses in our temporal measures. There was more variable and longer time to write letter pairs in the countback condition for the ET group compared to the CO group. For the attention task, the hypotheses were partially supported in the behavioural and neural measures. There was larger spectral power of postural tremor in the ET group compared to the PD group at 3-8Hz, 4-7Hz, 8-12Hz and compared to the CO group at 3-8Hz. Across groups, there was more synchronous theta activity in the countback condition compared to the small target condition at electrode sites Cz and Pz, and compared to the medium and large target conditions at electrode sites Fz, Cz, and Pz. Between groups, there was more synchronous theta activity in the least attention demanding condition (large target condition) in the ET group compared to CO group at electrode site Fz. This same effect was found in the right hand compared to the left. There was also more desynchronous alpha activity at electrode sites Cz and Pz in the medium and large target conditions compared to the countback condition across groups. The results of these tasks suggest that individuals with ET are not impaired in motor switching but are impaired in tasks that affect allocation of attentional resources, specifically in least attention demanding tasks.
