Lectures and seminars Cognitive Neuroscience Club with Alkis M. Hadjiosif: "Post-stroke biases in arm resting posture reveal separable control of reaching vs. holding still"
The Cognitive Neuroscience Club is hosting monthly webinars on the topic Cognitive Neuroscience. The webinars usually takes place during the last week of the month. On Tuesday 29 March 2022, we welcome Dr. Alkis Hadjiosif, Postdoctoral Fellow, Johns Hopkins University, United States. Join us via Zoom.
"Post-stroke biases in arm resting posture reveal separable control of reaching vs. holding still"
Dr Alkis M. Hadjiosif, Postdoctoral Fellow, Johns Hopkins University, United States.
Abnormal resting postures are one of the most common and widely recognizable motor symptoms after stroke. For example, the typical hemiparetic arm posture consists of flexion at the fingers, wrist, and elbow. This pattern appears to parallel the abnormal muscle synergies during active movement, such as the abnormal coupling of muscles that move the shoulder vs. the elbow joint.
Whether these synergies are generated by the same mechanism as abnormal resting postures remains an open question; it might instead be that resting abnormalities are inactive during movement. Also unknown is the degree to which resting postural abnormalities influence active moving and holding. Here we systematically assessed resting postural abnormalities in stroke patients.
We found that patients exhibited abnormal postural force biases at rest, which mirrored characteristics of abnormal synergies: for example, postural abnormalities were markedly lower when the arm was supported against gravity, and, critically, strongly related to the Fugl-Meyer scale, a measure based on abnormal synergies.
These findings suggest a shared mechanism between resting abnormalities and abnormal synergies after stroke. We then examined whether these resting postural abnormalities affected the motor control of active reaching in the same workspace. We did not find any systematic effects of resting postural forces either across patients with different resting posture magnitudes, nor between high- vs. low-resting postural force regions for the same patient. Bizarrely, however, we found evidence suggesting that resting postural abnormalities influence the control of actively holding still after the reach is complete.
This set of findings not only suggests separate mechanisms behind deficits in movement vs. posture after stroke, but also suggests separate mechanisms for the control of active reaching vs. holding still in general.