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Control strategies correcting inaccurately programmed fingertip forces: model predictions derived from human behavior
Anders Fagergren1, Orjan Ekeberg, Hans Forssberg
1Neuropediatrics Q2:07, Department of Woman and Child Health, Astrid Lindgens Childrens Hospital, Karolinska Institutet, S-171 76 Stockholm, Sweden. anders.fagergren@ks.se
Journal of Neurophysiology
|June 5, 2003
Summary
The brain adjusts motor commands to prevent objects from slipping when friction changes unexpectedly. This study reveals how grip-load force delay and motor command timing are key to maintaining a stable grip.
Area of Science:
- Neuroscience
- Biomechanics
- Motor Control
Background:
- The central nervous system (CNS) predetermines motor commands for object manipulation based on expected friction.
- Unexpected decreases in friction can lead to object slippage, triggering sensory feedback.
- Understanding the CNS's corrective strategies for altered frictional demands is crucial for motor control research.
Purpose of the Study:
- To investigate the motor system's correction strategies in response to unexpected frictional changes during object lifting.
- To estimate motor commands to the motoneuron pool using a novel combination of behavioral recordings and neuromuscular modeling.
- To identify key factors influencing the efficiency of grip force adjustments to prevent slippage.
Main Methods:
- Developed a mathematical model of muscles, hand mechanics, and object lifting.
- Utilized a control system simulation to send motor commands and receive sensory signals.
- Combined behavioral recordings of fingertip forces (grip and load) and position data with neuromuscular modeling to estimate motor commands.
- Analyzed data from 200 lifts with experimentally reduced friction.
Main Results:
- Identified three critical factors for correction efficiency: motor command time development, grip-load force delay (GF-LF-delay), and lift speed.
- Sensitivity analysis indicated that GF-LF-delay and rapid motor command adjustments are effective in preventing or arresting slip.
- Experimental data confirmed that subjects utilized GF-LF-delay to prevent slip, and a sharp increase in grip force motor command (NGF) efficiently arrested slippage.
- Estimated motor commands suggest a control system employing a limited set of corrective commands and leveraging GF-LF-delay for efficient strategies.
Conclusions:
- The CNS employs efficient strategies combining motor command adjustments and grip-load force delay to manage unexpected friction changes.
- The selection of a specific correction strategy is influenced by the timing and magnitude of tactile sensory information.
- The developed technique for estimating motor commands offers a valuable tool for studying the central control of the motor system during precision grip tasks.