Motor Planning under Unpredictable Reward: Modulations of Movement Vigor and Primate Striatum Activity

Area of Science:

• Neuroscience
• Behavioral Science
• Motor Control

Background:

• Reward probability significantly influences animal behavior.
• The neural mechanisms linking reward expectation to movement vigor (reaction time and speed) remain unclear.

Purpose of the Study:

• To investigate how the brain translates reward expectation into movement vigor.
• To identify neural correlates of reward predictability in movement control.

Main Methods:

• Two monkeys were trained on a reaction time (RT) task involving wrist movements.
• A variable reward schedule (75% reward probability) was employed.
• Single-unit recordings were conducted in the dorsal striatum.

Main Results:

• Monkeys exhibited faster reaction times and increased movement speed in trials with certain rewards.
• Dorsal striatum neurons showed firing rate modulations reflecting changes in movement vigor.
• Neural modulations were influenced by reward certainty, sensory modality, and movement direction.

Conclusions:

• The dorsal striatum plays a role in modulating movement vigor based on reward predictability.
• Neural activity in the dorsal striatum encodes changes in reward expectation.
• Sensory and motor factors interact with reward expectation in the dorsal striatum.