Pointing to One's Moving Hand: Putative Internal Models Do Not Contribute to Proprioceptive Acuity.

Area of Science:

• Sensorimotor neuroscience
• Human motor control
• Proprioception research

Background:

• Proprioception, or kinesthesia, classically relies on sensory input processing by the central nervous system (CNS).
• Internal model theories suggest motor commands also contribute to proprioceptive limb localization.
• The precise contribution of motor command-based predictions to proprioception remains debated.

Purpose of the Study:

• To investigate the role of internal models in proprioceptive accuracy.
• To determine if motor command estimates enhance limb position sensing.
• To compare active versus passive limb movement contributions to proprioception.

Main Methods:

• Nineteen subjects performed index finger-to-finger apposition tasks under three conditions: vision allowed (active), vision blocked (active), and vision blocked (passive).
• Target limb movements encompassed a wide range of directions.
• Accuracy was measured by the mean and variable errors in finger apposition distance.

Main Results:

• Proprioceptive localization accuracy was high across all conditions, with errors averaging less than 2 cm.
• Minor improvements in accuracy were observed with vision compared to eyes-closed active movement.
• No significant difference in accuracy was found between active and passive movements when vision was blocked.

Conclusions:

• Proprioceptive localization of a moving limb is highly accurate, comparable to visually guided movements.
• The study's findings challenge the necessity of internal model-derived kinematic estimates for enhancing proprioceptive accuracy.
• Sensory feedback appears to be the primary determinant of accurate limb position sense in this context.