The effects of digital anesthesia on force control using a precision grip

Area of Science:

• Neuroscience
• Biomechanics
• Human Motor Control

Background:

• The nervous system relies on sensory feedback for precise motor control.
• Internal models are hypothesized to predict sensory consequences of motor commands.
• The role of cutaneous sensation in refining grip force and object manipulation is not fully understood.

Purpose of the Study:

• To investigate the extent to which internal models compensate for the loss of cutaneous sensation during grasp-lift tasks.
• To determine the necessity of continuous sensory feedback for optimal internal model function.
• To analyze the impact of digital anesthesia on grip force, load force coordination, and resultant torques.

Main Methods:

• Subjects performed a grasp-lift-and-hold task with a manipulandum simulating object weights.
• Experiments were conducted with and without visual feedback, both before and after digital anesthesia (mepivacaine).
• Grip force, load force, and resultant linear/torsional forces and torques were measured.

Main Results:

• Digital anesthesia significantly increased grip force and disrupted grip-load force coordination.
• Anesthesia led to the appearance of significant linear and torsional forces/torques, particularly in horizontal and frontal planes.
• Visual feedback did not correct finger misalignment after anesthesia, suggesting reliance on tactile feedback for precise force application.

Conclusions:

• Internal models alone are insufficient to fully compensate for the loss of cutaneous sensation.
• Optimal internal model function appears to require continuous or frequent intermittent excitation from cutaneous receptors.
• Mechanoreceptors in fingertips are crucial for signaling pressure, enabling the nervous system to optimize grip forces for manipulation.