Motor Control and Upper-Extremity Function

Neural Contributions to Reach, Grasp, and Manipulation

• The objectives of the course are to describe upper extremity functions and neural contributions to UE Reach, Grasp, and manipulation
• The primary resource for this topic is the Shumway-Cook and Woollacott Motor control text, Chapter 17.

Introduction

• Upper Extremity (UE) function is the basis for fine motor skills and plays a role in gross motor skills.
• Recovery of function is an important aspect of retraining motor control.
• Contextual factors, including the environment and the individual, impact upper-extremity function.
• UE function is integrated into most self-care, work, and household activities.

International Classification of Function (ICF)

• The ICF framework connects health condition (disorder or disease) to body structure and function, activities, and participation.
• Activities include mobility (carrying, moving, handling objects) and tasks such as self-care (dressing, feeding) and domestic life (cooking, cleaning).

Sensorimotor Processing for Eye-Head and Hand Coordination

• Sensorimotor processing for eye-head and hand coordination involves the individual, task, and environmental constraints.
• The goal is to understand how the individual's CNS control UE movements

What is going on in the Brain?

• Visual cortex, posterior parietal association area, somatosensory cortex, prefrontal area, premotor cortex, primary motor cortex, basal ganglia, cerebellum, spinal cord, motor neurons, and sensory receptors play roles in sensory and motor processing
• Spinal pathways such as the dorsal column/medial lemniscus and somatosensory cortex are also involved

Hedmann's Model for Movement Observation Analysis

• The model outlines the stages of movement observation analysis, from initial conditions to the outcome.
• Key factors of the analysis include posture, ability to interact with the environment, stimulus identification, response selection, response programming, timing, amplitude, direction, smoothness, speed, and stability at termination

Motor Control Principles (SC&W PP 466)

• Feedforward and feedback control are key motor control principles.
• Motor program theory, equal to open and close loop control concepts are other key concepts.
• The visual system is highly involved in feedforward (anticipatory control), and somatosensation is highly involved in feedback (reactive control).
• Locating a target, and reach, and grasp kinematics are discussed in the context of motor control.

Feedforward versus Feedback Control of Movement

• Efficient reaching involves both feedback and feedforward control processes.
• Feedforward (anticipatory) control uses previous experience to predict sensory consequences.
• Feedback control compares sensory input to a reference signal to adjust movement (reactive).

Feedforward and Feedback Control (Diagrammatic)

• Feedback control: command specifies desired state; reference signal, error signal, comparator, controller, input processing, sensor, and actuator

• Feedforward control: command specifies response; feedforward controller (with memory), anticipatory command, input processing, sensor, controller, actuator, disturbance

Locating a Target (Eye-Head-Trunk Coordination)

• Vision guides hand movements of objects.
• Reaching for objects in the far visual field requires eye, head, and trunk movements.
• Interactions between eye and hand movements influence each other.
• Proprioceptive signals from eye muscles contribute to localizing targets in extrapersonal space.

Kinematics of Reach and Grasp

• Reaching ability requires adaptation.
• Task constraints and goals affect the reaching phase of movement.
• Velocity profile (arm vs time) changes based on task goal (grasp vs point).

Neural Control of Reach and Grasp

• Specific cortical regions are involved in reaching and grasping.
• The areas include the prefrontal cortex, parietal lobe, motor cortex, and somatosensory cortex.
• The brain uses visual and somatosensory information to achieve the action.

Association Cortices - Perceptions and Planning

• Association cortices (frontal, parietal, temporal, and occipital lobes) are involved in movement planning, space perception, and sensory processing.
• Key areas include the primary motor cortex, involved in moving the muscles, and the parietal lobe, for perception/space awareness, in planning and executing movements.

Sensory System

• The sensory system provides information about the environment and the body's position in space.
• Sensory information helps in proactively planning movements and in feedback to determine accuracy and correct errors.

Schematic of Visual Pathway

• Visual pathways transmit information via serial and parallel pathways including the Where Stream (dorsal pathway to posterior parietal cortex: action) and What Stream (ventral pathway to inferior temporal cortex: perception)
• The components are location in space and movement (dorsal pathway), shape and form, object recognition (ventral pathway).

Clinical Implication

• Clinicians need to assess perceptual and action components of visual reaching.
• Patients may have impairment of one or both systems.
• Understanding essential features of objects for grasping is critical, as is modifying the grasp according to the features.
• Interventions should train both perceptual and action components of the movement

Posterior Association Areas

• Spatial cognition, mediated by the Posterior Parietal Association area
• Wide variety of behaviors mediated by attention to internal and external space
• Parietal lobe damage can lead to unilateral hemispatial neglect.
• Facial Recognition is mediated by temporal association area. Damage causes prosopagnosia
• Object identification is another key function.

What is happening in the Posterior Parietal Cortex?

• Active during sensory and movement-related activities
• Involved in sensorimotor transformation, movement planning, and formation of internal models.
• Includes body representation and coordinate transformations.

Role of Sensory Information in Anticipatory (Feedforward) Control of Reach and Grasp

• Visual system: locating and determining the initial direction of the reach
• Visual information provides characteristics of the object
• Vision is crucial for referencing hand and object location.
• Somatosensory system: determining initial position and coordination of limb segments.

Role of Sensory Feedback to Reach and Grasp

• Visual feedback is essential in attaining final accuracy for reaching.
• However, visual feedback is not crucial in grasping.
• Somatosensory feedback is needed for simple and complex movements, especially when the limb deviates from the planned path.
• Continuous object manipulation relies on visual feedback to detect errors and adjust the movement accordingly.

Motor System in Reach and Grasping (Execution)

• The premotor and primary motor cortices receive input from the posterior parietal cortex.
• Intentions and goals, location and direction of movement, hand formation and orientation, and object characteristics are all processed.
• The posterior parietal cortex encodes visual spatial information and the premotor cortex encodes body spatial information.

Two Separate Descending Pathways for Reach and Grasp

• Motor development of reaching and grasping develops in different stages.
• Individuals with corticospinal tract injury can display problems with grasp/manipulation.
• The transport component of reaching involves shoulder and elbow pathways, potentially using midbrain/brainstem structures.
• The grasp (hand precision) component relies more on corticospinal pathways.

Musculoskeletal Contributions

• Neural and musculoskeletal systems have a complex relationship.
• Movement compensation occurs in relation to changes in range of motion (ROM), strength, and muscle tone.
• Examples of compensations include reaching with elbow range of motion limitations.
• Factors like scapular control (scapula role in reaching/grasping/arm movement differences) impact reaching and grasping.

Postural Support of Reaching and Grasping

• The postural system maintains upright posture during arm movement in anticipatory and feedback control.
• Includes anticipatory and reactive postural adjustments.

Motor Control Elements (Diagram)

• A hierarchical model showing postural activation, reaching, and grasping with related pathways

Grasping Patterns (Types)

• Power grip uses finger and thumb pads for forceful grasping.
• Precision grips involve using fingers and thumbs for precision (poke, pinch, and clench).
• Examples include spherical, hook, and cylindrical grasps for holding objects of various shapes.

Anticipatory Control of Grasp and Lift

• Grip formation initially occurs during transport, anticipating the grasp.
• Hand adaptations occur based on the characteristics and use of the object.
• Finger movements are timed in relation to the transport for precise movement and grip.
• The cerebellum predicts forces and regulates grip for weight and surface variations during lifting.
• Feedback loops address potential slip errors for adjusting and storing force predictions.

Coordination of Reach and Grasp

• Reach and grasp movements are kinematically coupled, which means they are physically linked.
• The movements have invariant features.
• Timing of transport and hand opening are key elements of the coordination.
• Generalized motor programs store movement information in the central nervous system.
• The elements such as reach, direction, distance, speed, and grasp type can be modulated based on initial conditions during the task.

Reaction Time (RT)

• Reaction time (RT) measures sensorimotor processing time before movement.
• It's a basic tool in research to measure tasks such as reaching
• Simple RT measures a single stimulus, while choice RT involves multiple stimuli and response options.

Fitts' Law of Movement (Speed-Accuracy Trade-Off)

• Movement time increases with distance and accuracy demands.
• Movement time depends on accuracy requirements and on visual processing constraints.

Theories of Reaching Control

• Distance programming theories hypothesize that the CNS uses perceived distances to activate agonist muscles and propel the limb.
• These theories rely heavily on visual perception to correct early movements.
• The impulse-based theory of control initiates with visual input and subsequently uses feedback for correction.
• Location programming theories propose that the CNS adjusts the stiffness of agonist and antagonist muscles depending on the target's location.

Interference Between Reaching and Cognitive Tasks

• A dual-task paradigm demonstrates how cognitive tasks can interfere with movement tasks.
• The interference often occurs due to the increased reaction time for the movement onset when a cognitive task is simultaneously performed..

Prefrontal Cortex and Limbic System Influence

• The prefrontal cortex plays a role in perception, action, stopping, and choosing an action.
• The limbic system involves emotional aspects of task execution and memory functions..
• These areas are critical in analyzing behavior within a particular goal-directed movement.

Conceptual Mapping of Neural Control of Reach and Grasp

• Create a conceptual map that shows the relationship between various systems involved in reaching and grasping.

What Might be the Elements of the Conceptual Map?

• Identifying various components of the reaching and grasping neural pathway such as the visual cortex, target location, target identification, sensory processing, Posterior Parietal Association area, prefrontal area, motor processing, premotor cortex, primary motor cortex and other required parts of the brain

Extrapolation to Other Tasks

• Research findings from reaching and grasping can be applied to other upper extremity tasks.
• Examples provided are picking up a spoon and feeding; overhead throwing.

This quiz explores critical concepts in motor control, focusing on upper-extremity function and its underlying mechanisms. Answer questions regarding the brain regions involved, motor processing, and the principles of motor control that integrate sensory and motor functions.