|Ph.D Student||Dahan Anat|
|Subject||In Search of Motor Biomarkers for Attention-Deficit/|
|Department||Department of Education in Science and Technology||Supervisor||Professor Miriam Reiner|
|Full Thesis text|
There is a growing body of evidence pointing at motor abnormalities found in ADHD. In this study, we review findings stemming from different paradigms, and classify reported motor impairments associated with ADHD, into four motor stages: Attention to the task, motor planning, motion execution and motion monitoring.
It has been well established that individuals with ADHD show unique kinematic characteristics. Whether they are associated with reduced online motor control or with an immature motor plan, is still an open question. Hence, we further focus our research in the motor planning stage.
In the current study, we compare motor planning mechanisms of ADHD and control subjects based on their effect on later observed kinematic characteristics. We monitor hand movement following planning conditions that differ in preparation time, and evaluate the differences across conditions and participants with/out ADHD. The study was conducted on a total of 25 subjects, 12 control subjects, and 13 ADHD subjects.
Our findings show that when there is sufficient planning time, people without ADHD seem to have a motor plan ready, and immediately initiate a planned movement after a ‘GO’ cue, with a bell shaped velocity profile, towards a target. When planning time is not sufficient, they start the movement in a delayed time, possibly indicating that they needed to complete a movement plan. However, people with ADHD, did not start the movement immediately after the cue, even when provided with a long preparation time, possibly indicating that even for this planning interval they did not have a motion plan ready. The movement was not only delayed but also its velocity profile was not bell shaped and had several peaks. We further found differences between control and ADHD participants in the velocity, velocity profile, variability and jitter of movements. Our results suggest that ADHD motion characteristics are associated with an immature motor plan. This points at a neural underpinning difference between ADHD and not, that is rooted in the motor network. Based on the results we propose a paradigm to evaluate deficiencies in motor planning.
In light of the results of the motor planning experiment, we extended our question to understand the underlying mechanism of planning of object reaching movements. In this experiment we measured movement onset time, after different planning intervals, with a target appearing in one of four possible locations.
When the planning intervals were short, the movements’ onset were delayed. This may be the time needed for the visual target stimuli, to be attended, and for the data to be propagated to the relevant population of cells encoding the relevant action, so that its activity will surpass a certain threshold. When planning time was sufficient, the onset movement time was minimal. However, when the interval between target and Go cue was further extended, the movement onset was once again delayed, overall, resulting in a U-shaped pattern, with an optimal window of time for action between target and GO cue. Accordingly, we suggest an extended model for object reaching with involvement hippocampus and working memory processes.