M.Sc Thesis

M.Sc StudentGottlieb Sigal
SubjectElectroencephalographic Responses during a Motor Task with
Healthy Subjects and Stroke Patients
DepartmentDepartment of Mechanical Engineering
Supervisor PROF. Miriam Zacksenhouse
Full Thesis textFull thesis text - English Version


Error-related potentials (ErrPs) have been explored extensively in the context of cognitive tasks as a window for investigating error monitoring and information processing in the brain and assessing cognitive impairment. More recently, there is a growing interest in ErrPs that are evoked during motor tasks, both for investigating motor learning and for potential applications to brain-computer interfaces. Motor errors are classified as either execution errors, reflecting deviations between the observed and planned movements, or outcome errors, reflecting failure to perform the task. Previous work with healthy subjects in our laboratory revealed that execution errors elicit the two subcomponents of P300, P3a-like component and P3b-like component, time locked to disturbance onset while, in line with other research, outcome errors elicit error related negativity (ERN) time locked to the response. In contrast with investigations of ErrPs in healthy subjects, investigations of ErrPs in stroke patients (SPs) were restricted to cognitive tasks and even in that domain were not conclusive. ErrPs evoked in SPs in response to motor errors are especially interesting to assess their error monitoring and whether their internal models are updated to reflect the resulting motor deficiency. 

The purpose of the present study was to investigate ErrPs evoked when stroke patients fail to perform a movement task with the affected hand, and compare them with the ErrPs evoked when they fail to perform the task with the unaffected hand, and with ErrPs evoked in healthy subjects. For that purpose we designed a simple computer game, inspired by a common rehabilitation game. Disturbances were introduced to induce errors for healthy subjects and one of those disturbances was also introduced when SPs used their unaffected hand. Thus, the main objectives of this study were: (i) Characterize ErrPs evoked in response to execution and outcome errors during a video-game. (ii) Compare ErrPs evoked by natural or imposed outcome errors. (iii) Characterize ErrPs evoked in stroke patients when using their affected versus unaffected hand.

In healthy subjects, different execution errors elicit statistically different front-central positivity (P3a-like component) and parietal positivity (P3b-like component). Moreover, two positive components were also detected in the potentials locked to the end of unsuccessful trials, and were statistically stronger for natural, rather than imposed, failures. Hence, it might be concluded that natural and imposed outcome errors were perceived differently in healthy subjects. In SPs, a significant positive component was evoked when failing to perform the task with either the affected or the unaffected hand, while disturbance elicited only a negative component.