Spampinato, Danny, and Pablo Celnik. "Multiple motor learning processes in humans: defining their neurophysiological bases." The Neuroscientist 27.3 (2021): 246-267.

June 8, 2023

Introduction

• Humans are capable of learning and acquiring knowledge for performing new motor tasks.
• Multiple learning processes have been identified as contributors to this learning process:
  • Error-based learning (EBL)
  • Use dependent learning (UDL)
  • Reinforcement learning. (RL)
  • Cognitive strategies (CG)
• These processes are posited to have distinct neural substrates and computations, involving the cerebral cortex, cerebellum, and striatum.
• The current challenge for motor learning research is to confidently disentangle each form of learning and their respective physiological mechanisms.
• Behavioural manipulations can be used to potentially weight these different forms of learning differently to isolate them; although this is not always possible.
• Techniques like TMS and tDCS can be used for probing the neural substrate to identify the circuits that might be involved in the different forms of learning.

Error-based learning

• One of the most basic forms of learning; plays a major role in motor adaptation, which allows us to perform accurate movements in the face of changing environments and our bodies.
• Short-term form of learning.
• Operates through a predictive mechanism, in particulate sensory-prediction error, which gives the details of how an expected movement has failed.
• Sensory predictions are produced by forward models (motor activation in, the expected limb kinematics out), and sensory prediction error (SPE) can be used to calibrate the internal models.
• Learning happens on a trial-by-trial basis, and learning is evident even in a single trial.
• The cerebellum plays a critical role in error-driven, forward internal models, generating sensory predictions and encoding the sensory prediction errors for updating the forward (and also inverse?) internal models.
• Individuals with cerebellar pathology exhibit significant impairment in EBL.
• Animal models have shown that the Purkinje cells of the cerebellum might be involved in forward model learning; one study found that the Purkinje cell activity was related to the arm kinematic rather than the actual motor command sent to the arm.
• Human Neurophysiological Studies of EBL
  • Paired TMS is used to measure changes in connectivity between the cerebellum and the M1 cortex - “cerebellar inhibition”.
  • Cerebellum (Purkinje cells in lobule VII and VIII) $\longrightarrow$ Inhibitory connection to the deep cerebellar nuclei (DCN) $\longrightarrow$ Excitatory connection to the M1.
  • CBI reflects the normal inhibitory tone that the cerebellum exhibits over M1 via that thalamus.