Sensorimotor Control: Internal Models and Motor Function

Sensorimotor Control

Introduction to Sensorimotor Control

Sensorimotor control refers to the processes by which the brain converts sensory information into purposeful movement. This involves integrating both stored and real-time sensory data to generate and adjust motor commands that guide the body’s actions.

• Key Point: The brain must determine which muscles to activate to achieve a desired movement.

• Internal Representation: To generate an initial movement trajectory, the brain requires an internal representation of body geometry and the interaction of the motor system (e.g., arm, eye) with the environment.

• Development: These representations likely develop through experience, forming connections between brain areas involved in motor behavior.

• Example: Infants learning to reach for objects gradually develop accurate internal models through trial and error.

Internal Models for Motor Control

Types of Internal Models

Internal models are neural mechanisms that predict and control motor behavior. There are two main types: forward models and inverse models.

• Forward Model: Predicts the behavior of the motor system in response to a command and estimates the current and future state of the effector (e.g., arm, leg).

• Function: Forward models can predict sensory consequences from efference copies of issued motor commands.

• Example: When reaching for a cup, the forward model predicts the position of the hand based on the motor command.

• Inverse Model: Calculates the necessary feedforward motor commands from desired motor output information, using an 'inverse model' of the musculoskeletal system.

• Function: Inverse models determine which muscles to activate to achieve a specific movement goal.

• Example: To move the hand to a target, the inverse model computes the required muscle activations.

Comparison of Forward and Inverse Models

Model Type	Function	Example
Forward Model	Predicts sensory consequences of motor commands	Anticipating hand position during reaching
Inverse Model	Calculates motor commands needed for desired movement	Determining muscle activations to reach a target

Information Processing Model in Motor Control

Stages of Information Processing

The information processing model describes how sensory input is transformed into motor output through several stages:

• Stimulus Identification: Recognizing relevant sensory information.

• Response Selection: Choosing an appropriate motor response.

• Movement Programming: Planning and executing the motor command.

Role of Internal Models in Information Processing

• Inverse Model: Involved in response selection and movement programming, learned through experience.

• Forward Model: Provides anticipated feedback during movement execution.

Neural Basis of Internal Models

Brain Regions Involved

Internal models are supported by specific brain regions that contribute to procedural learning and movement monitoring:

• Parietal Cortex: Involved in integrating sensory information and spatial awareness.

• Premotor Cortex: Plays a role in planning and selecting movements.

• Cerebellum: Critical for fine-tuning movements, error correction, and updating internal models.

Models of Motor Function: Integration of Forward and Inverse Models

Combined Use in Movement Control

Motor control often requires both forward and inverse models working together:

• Initial Movement: Motor target and current position are input into the inverse model to determine necessary muscle activations.

• During Movement: Forward model estimates movement end-point based on sensory inflow and efference copy.

• Error Correction: Discrepancies between desired and actual movement lead to modification of ongoing motor commands.

Feedback and Adaptation

• Adaptation Component: Updates the internal model based on differences between desired and actual motor output.

• Example: Learning to throw a ball accurately involves continuous updating of internal models based on feedback.

Summary

• Forward and inverse models combine to govern voluntary movements.

• Brain regions related to procedural learning and movement monitoring are key neural components of these internal models.

Additional info: Internal models are fundamental to understanding motor learning, adaptation, and rehabilitation in psychology and neuroscience.