Coding of digit displacement by cell spiking and network oscillations in the monkey sensorimotor cortex

Area of Science:

• Neuroscience
• Motor Control
• Sensory Processing

Background:

• Beta-band oscillations (β-band) are observed in motor and sensory cortices and muscle activity, particularly after movements.
• These oscillations suggest a potential role in representing or probing the limb's final sensory state post-movement.

Purpose of the Study:

• To investigate whether β-band oscillations and neuronal firing rates encode finger displacement information after a movement.
• To compare the timing and amount of information conveyed by oscillatory activity versus single-unit firing rates.

Main Methods:

• Two macaque monkeys performed a cued finger flexion task with four possible displacements, held without visual feedback.
• Local field potentials (LFPs) and single-unit spiking were recorded from primary motor cortex and parietal areas.
• Information theoretic analysis quantified displacement coding in both LFP β-band power and unit firing rates.

Main Results:

• Both β-band LFP oscillations and unit firing rates significantly encoded finger displacement in all recorded areas after movement cessation.
• Unit firing rate carried more information (0.07 bits) and peaked earlier (0.73 s post-movement) than β-band LFP oscillations (0.05 bits, 0.95 s post-movement).
• Significant heterogeneity was observed, with some units showing delayed maximal information encoding and 30% of cells exhibiting rate information lagging LFP oscillation information.

Conclusions:

• Finger displacement is represented in the cortex through multiple mechanisms, including both non-oscillatory feedback/efference copy immediately post-movement.
• Oscillatory processing, specifically β-band oscillations, may contribute to sensory representation with increasing delay after movement cessation.