Holding the arm still through subcortical mathematical integration of cortical commands

Mapping Intimacies ◽

10.1101/556282 ◽

2019 ◽

Author(s):

Scott T. Albert ◽

Alkis M. Hadjiosif ◽

Jihoon Jang ◽

John W. Krakauer ◽

Reza Shadmehr

Keyword(s):

Corticospinal Tract ◽

Subcortical Structure ◽

Adaptive Feedback ◽

Trial Basis

A period of holding still follows every movement. It has been assumed that for the arm, moving and holding are functionally independent: movement is via an adaptive, feedback-dependent controller that generates commands to transport the arm, while holding is via setting of reflexes that produce a postural field at movement endpoint. This assumption predicts that commands that move the arm should not affect the postural field at movement termination. Surprisingly, we found that as the reach commands changed, so did the ensuing postural field. The postural commands depended on mathematical integration of the reach commands. Following damage to the corticospinal tract, despite severe reach impairments, the holding system faithfully integrated the imperfect reach commands on a trial-by-trial basis. Together, these findings suggest that holding the arm still is accomplished via a separate, likely subcortical structure that acts as a mathematical integrator of the commands generated by the cortical reach controller.

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Postural control of arm and fingers through integration of movement commands

eLife ◽

10.7554/elife.52507 ◽

2020 ◽

Vol 9 ◽

Cited By ~ 2

Author(s):

Scott T Albert ◽

Alkis M Hadjiosif ◽

Jihoon Jang ◽

Andrew J Zimnik ◽

Demetris S Soteropoulos ◽

...

Keyword(s):

Postural Control ◽

Corticospinal Tract ◽

Target Location ◽

Hold Period ◽

Trial Basis ◽

Limb Posture

Every movement ends in a period of stillness. Current models assume that commands that hold the limb at a target location do not depend on the commands that moved the limb to that location. Here, we report a surprising relationship between movement and posture in primates: on a within-trial basis, the commands that hold the arm and finger at a target location depend on the mathematical integration of the commands that moved the limb to that location. Following damage to the corticospinal tract, both the move and hold period commands become more variable. However, the hold period commands retain their dependence on the integral of the move period commands. Thus, our data suggest that the postural controller possesses a feedforward module that uses move commands to calculate a component of hold commands. This computation may arise within an unknown subcortical system that integrates cortical commands to stabilize limb posture.

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Effects of Monetary Incentives on Task Switching

Experimental Psychology (formerly Zeitschrift für Experimentelle Psychologie) ◽

10.1027/1618-3169/a000146 ◽

2012 ◽

Vol 59 (4) ◽

pp. 216-226 ◽

Cited By ~ 36

Author(s):

Thomas Kleinsorge ◽

Gerhard Rinkenauer

Keyword(s):

Task Switching ◽

Temporal Dynamics ◽

Reward Processing ◽

General Level ◽

Monetary Incentives ◽

Switch Costs ◽

Expectancy Effect ◽

Reward Expectancy ◽

Trial Basis

In two experiments, effects of incentives on task switching were investigated. Incentives were provided as a monetary bonus. In both experiments, the availability of a bonus varied on a trial-to-trial basis. The main difference between the experiments relates to the association of incentives to individual tasks. In Experiment 1, the association of incentives to individual tasks was fixed. Under these conditions, the effect of incentives was largely due to reward expectancy. Switch costs were reduced to statistical insignificance. This was true even with the task that was not associated with a bonus. In Experiment 2, there was a variable association of incentives to individual tasks. Under these conditions, the reward expectancy effect was bound to conditions with a well-established bonus-task association. In conditions in which the bonus-task association was not established in advance, enhanced performance of the bonus task was accompanied by performance decrements with the task that was not associated with a bonus. Reward expectancy affected mainly the general level of performance. The outcome of this study may also inform recently suggested neurobiological accounts about the temporal dynamics of reward processing.

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