M.Sc Thesis

M.Sc StudentKerzhner Marina
SubjectIndicators of Motor Learning in EEG Signals Recorded
while Practicing Motor Task
DepartmentDepartment of Biomedical Engineering
Supervisors PROFESSOR EMERITUS Hillel Pratt
PROF. Miriam Zacksenhouse



Brain recovery following injury shares similar processing with motor learning, gearing the plastic changes towards maximizing behaviorally relevant functions. Impairments in neurological patients are a result of complex patterns of reorganization, both injury-related and use-dependent. While in healthy subjects increased use of body parts in relevant tasks leads to an enhancement of the representation of those body parts in the cerebral cortex, intensive therapy in neurological patients induces use-dependent cortical reorganization that counteracts adverse brain function changes and enhances recovery-associated plastic changes. EEG measurements can contribute to our understanding of neural processes underlying motor learning, allowing electrical brain activity to be visualized as it is occurring. In this study we aim to identify and characterize EEG-based markers that indicate different stages of motor learning, while performing a motor task consisting of a sequence of four planar movements.

We hypothesize that skill acquisition will result in improved kinematic performance with emergence of more efficient movement elements and co-articulation of the co-aligned segments of the motor task. The experience-dependent modulation of the kinematic performance will be supported by changes in the sensory-motor cortical activity: changes will be evident in the amplitude of the motor- related ERP components and in the power of the EEG spectrum.

Eight healthy subjects practiced a new motor task comprised of 4 planar segments, with segments 3 and 4 being highly collinear. The task was performed with the ReoGoTM robotic system. Each subject practiced the task during 5 sessions, each comprised of 5 blocks of 50 trials.  EEG signals from 64 electrodes and hand position of the subjects were recorded while they were practicing the motor task.

Both kinematic and EEG data were analyzed. Kinematic analysis results showed that the time to perform task trial decreased with practice. Peak velocity values, as well as minima values in points B and D in the velocity profile increased with practice. 

Analysis of the EEG recordings revealed two movement-related ERP components- positive and negative. The average amplitude of the positive ERP peak significantly changed between the practice sessions in the frontal and central sites. Scalp distribution of ERP peaks showed activation in central, fronto-central sites, ipsilateral and contralateral sites.  PSD analysis revealed a trend of significantly growing power in delta, theta and gamma low bands.

The changes in motor performance, as revealed by kinematic data analysis, indicate that motor learning took place. The changes in the velocity profile peaks and minima are compatible with a beginning of the formulation of 2 new movement primitives instead of four that existed in the beginning of the practice. Changes in the amplitude of the positive peak of the motor-related potential indicate increase of activation with practice. In the frequency domain the increase in the power of delta, theta and low gamma bands can be interpreted as changes of processes related to memory and retrieval, as well as the emergence of new representation of the motor task.