1. Chapter 5 Movement Models Jeffrey C. Ives Copyright © 2014 Wolters Kluwer Health| Lippincott Williams & Wilkins Motor Behavior: Connecting Mind and Body for Optimal Performance

2. Objectives and Questions Copyright © 2014 Wolters Kluwer | Health Lippincott Williams & Wilkins 1.What is motor abundance and the degrees of freedom problem? 2.What is the purpose of movement models? 3.What are open- and closed-loop systems, and what models fit within these systems? 4.What do the terms generalized motor program, central pattern generator, schema, reflex model, and internal model all mean? 5.What are synergies and coordinative structures? 6.What are similarities among old and new models? 7.What are the systems model, constraints, affordances, and perception–action coupling?

3. The Need for Models Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins For any given movement, there are numerous ways the movement could be done. –This situation is called motor redundancy, which enables a wide range of options. –Redundancy also poses a problem in selecting just one solution, called the degrees of freedom problem. Determining what and how the brain and body are trying to control movement is theorized using models. Models provide a “big picture” framework to explain how the CNS and neuromuscular systems work to make movement. Objectives 1, 2

4. Models Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Models provide a general framework of the processes and physiological systems contributing to the formation and execution of motor acts. Movement models serve two main purposes. –Provide a conceptual framework by which to understand how movements are formulated and executed, and this enables prediction of change following interventions. –Provide a framework for practical use to devise more effective programs for rehabilitation, practice, and training Objective 2

5. Feedforward Versus Feedback Models Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Traditional models of motor control have been broadly described as open loop or closed loop. –Closed-loop models explain movement as an outcome of feedback-initiated reflex actions and prepatterned neural systems. Does not require sophisticated commands from higher brain centers –Open-loop models suggest a strict top–down hierarchy across CNS and neuromuscular structures in planning, executing, and initiating movement. The role of feedback in movement initiation and execution is minimized. Objective 3

6. Feedforward Versus Feedback Models (cont.) Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Objective 3 Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins

7. Contemporary Hierarchical Versus Heterarchical Models Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Hierarchical models are similar to open loop, describing a systematic command structure from top to bottom. Objectives 2, 3 Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins

8. Contemporary Hierarchical Versus Heterarchical Models (cont.) Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Heterarchical models are similar to closed loop, describing a distributed and balanced command and execution system. Objectives 2, 3 Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins

9. Closed-Loop, Feedback-Based, and Heterarchical Models Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins The simplest models of motor control are reflex models. –Movement stems from chaining together of reflex actions that provide building blocks of complex behavior. –In many animals, basic acts such as chewing, swallowing, and “fight or flight” actions are initiated by sensory feedback and executed by reflex movements. –Reflex models are based on the presence of hardwired neural circuits and produce fixed movement patterns. Objectives 3, 4

10. Closed-Loop, Feedback-Based, and Heterarchical Models (cont.) Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Hardwired circuits can also produce more complex stereotyped movements through central pattern generators (CPGs). CPGs are built-in movements initiated by CNS or sensory systems. Because they can run without complex commands or on sensory input only, they are considered closed loop. Objectives 3, 4 Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins

11. CPGs in Locust Flying Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Objectives 3, 4 Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins

12. CPGs in the Spinal Cat Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Objectives 3, 4 Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins

13. Human Limb CPGs Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Circumstantial evidence for arm CPGs suggests each arm has its own pattern generator. CPGs can be reinforced by sensory feedback, though initiated and driven by nominal supraspinal commands. Objectives 3, 4 Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins

14. Human CPGs for Walking Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Mounting evidence suggests walking CPGs in humans. CPGs may be exploited to improve walking performance in hemiparetic patients. Body-weight supported training is one therapeutic tool to engage the CPG. PBS video moving memories Objectives 3, 4 Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins

15. Complex Heterarchical Models Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Complex closed-loop models include involvement of higher brain centers but still rely on feedback loops. Brain centers provide basic command to the next lower level, which in turn modifies and “re-commands” the signals and routes them out to the next lower levels. –Modification via sensory feedback is essential to fulfill the command signals at each level. Objectives 3, 4

16. Complex Heterarchical Models (cont.) Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Theories of what constitutes the motor commands vary. –Equilibrium point hypothesis suggests the commands set stretch reflex thresholds. –Uncontrolled manifold hypothesis posits that the brain activates series of synergistic muscle actions. –The brain may only offer “suggestions” to the next lower levels. Objectives 3, 4

17. Complex Heterarchical Models and Synergies Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins New models often rely on synergistic muscle and limb actions to simplify the CNS command structure. –Synergies are ensembles or groupings of muscles and limbs that work together as a functional unit. –Actions of limbs or muscles constrain what actions can happen at other limbs or muscles. Synergies involve inherent neural pathways, muscle and limb biomechanical properties, and learned behaviors. Synergistic actions reduce degrees of freedom and simplifies CNS planning. Objectives 3, 4, 5

18. Synergies among opposite limbs during bilateral movements are called coordinative structures. Synergies in muscle activation and timing are seen in wrist out-of- phase movements transitioning into in-phase movements during rapid movements. Synergies and Coordinative Structures Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Objectives 3, 4, 5 Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins

19. Synergies and Coordinative Structures (cont.) Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins In this experiment, based on the work of Kelso and colleagues, asymmetric movements assimilated the timing of one another such that each arm arrived at the target at the same time. Objectives 3, 4, 5 Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins

20. Synergies and Coordinative Structures (cont.) Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Objectives 3, 4, 5 The experiment demonstrated here shows coupling among arms and legs.

21. Summary of Heterarchical Models and the Need for Hierarchical Control Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins There is evidence for distributed control of motor actions from the CNS to peripheral systems such as CPGs and synergies. –Yet, heterarchical models do not explain nuances that influence movement execution. –Heterarchical models cannot easily explain the widely distributed and highly complex actions of the brain that accompany movement. Thus, the need for a centralized command system arising out of brain structures: hierarchical control Objectives 3, 4, 5

22. Open-Loop and Hierarchical Models Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Hierarchical models suggest that motor skills arise from comprehensive sets of CNS commands. –Movements are considered centrally preprogrammed. –Precise manipulation of movement characteristics comes from a continually involved CNS controller. Feedback from sensory systems comes back into the brain centers but is largely used to prepare or modify the next movement. The initiation of movement is purely open loop because there has been no preceding movement to provide feedback. Objectives 3, 4

23. The Schema Theory Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins The most long-standing hierarchical model is the schema theory. Schema theory posits a generalized motor program (GMP) and schemas. –GMPs are a general representation of various motor actions, or a class of actions. –The schemas are separate memory components in which movements are recognized and recalled, essentially the decision-making and learning processes for the GMP. Objectives 3, 4

24. The Schema Theory (cont.) Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Stored in the GMP and schemata are invariant characteristics and parameters. –Invariant characteristics are features of the GMP that do not change, for example, relative force, relative timing, and sequencing. –Parameters are features that change within the GMP, for example, overall force, overall duration, and specific muscles. Objectives 3, 4 Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins

25. Schema Theory Evidence Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Blocked movement shows similar movement pattern as normal movement. Suggests preprogrammed neural commands not influenced by feedback Objectives 3, 4 Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins

26. Schema Theory Evidence (cont.) Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Other evidence for motor programs is found in bimanual transfer, for example, left and right handwriting similarities. Objectives 3, 4 Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins

27. The Rise of Internal Models Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Schema theory criticized for: –Implausibility of the brain being able to store so much information –GMPs do not explain how entirely novel movements are created. –GMPs rely on an executive controller making never- ending rapid fire decisions. –The concept of movement invariant characteristics may not be so invariant. Newer hierarchical models center on internal models. Objectives 3, 4

28. Internal Hierarchical Models Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Internal model emphasize that the brain sends commands to the PNS and itself through efference copy. –Efference copy includes the movement plan and a prediction of the sensory outcome. –Planning and initiation of the motor command are based on prediction of outcomes. –Differences between the actual movement feedback and the predicted feedback are used to refine subsequent motor commands. –Motor commands are thus based on understanding the relationship between the original motor commands and the actual output. Objectives 3, 4

29. Internal Model Schematic Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins This forward internal model shows the planner (P) somewhere in the cortex sends a plan to the controller (CT) in the motor cortex. Plans are sent to the to the controlled object (CO), for example, spinal interneurons or motor units. Objectives 3, 4 Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins

30. Internal Model Schematic (cont.) Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Efference copy goes to the forward model (FM) comparator, where it is compared to sensory feedback (FB). –Difference relayed back to the controller Visual cortex (VC) information is relayed to the controller. Plans are revised based on comparator differences. Objectives 3, 4 Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins

31. Model Consensus Points Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins All the models find consensus on three points: –The nervous system is most concerned with movement outcomes or effects than specific muscle actions. –The nervous system must take into account psychological, physiological, and biomechanical properties of the body, the movement goals, and the environmental context. –There exists hardwired, preformed, and synergistic movements that form building blocks for more complex movements. Objectives 3, 4, 6

32. The Systems Model and Approach Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins The systems model describes the production of skilled movement as a natural outcome of the person interacting with the environment. –Task goals and characteristics of the individual interact with the characteristics of the environment. –Task requirements and the environmental context cannot be separated from movement planning, initiating, and executing. Objective 7 Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins

33. The Systems Model and Approach (cont.) Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Objective 7 Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins

34. The Systems Model and Approach (cont.) Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins The individual, the task, and the environment are systems that interact and each of these systems contain multiple subsystems that also interact. –Systems are assemblies or groups of components that together have certain features or characteristics that are task specific. –The dynamic interplay among these systems identifies them as dynamic systems. Objective 7

35. Systems Model and Constraints Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins The features and characteristics of systems impose constraints to movement. –A constraint is a barrier or restriction that must be used, avoided, or overcome for effective movement to take place. Constraints may be task, environmental, or individual. –Task constraints and environmental constraints are considered external. –Environmental constraints may be regulatory or nonregulatory and physical or sociocultural. –Individual systems produce internal constraints. Objective 7

36. Behavior of Biological Systems Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Dynamic systems, working as individual units and interacting with other systems, have self-organizing properties. –The system tries to maintain a stable and patterned state of operation, called an attractor state. –The stable state is resistant to change but does naturally fluctuate within the stable state. –If knocked out of the stable state, the system will try and find a new stable (attractor) state given the new set of circumstances and dynamic properties. Objective 7

37. Behavior of Biological Systems (cont.) Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Changing from one stable state to another is called a transition phase. –Example: Walking to running demonstrates that high speeds or workloads destabilize the stable walking pattern and forces a transition to running –Speed is a control parameter, which are those factors that when they change may cause a wholesale change throughout the entire system. –The rest of the system components that follow suit are called order parameters. Coordination, gait repatterning, and vertical center of mass movement are order parameters. Objective 7

38. Transitions in Dynamic Systems Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Objective 7 The walk to run transition is marked by changes in limb velocity as a control parameter. Characteristics such as range of motion, “flight phase,” and center of mass movement are order parameters. Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins

39. Destabilizing Dynamic Systems Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Objective 7 It is often necessary to destabilize the system in order to promote better functioning at a new stable state. –Example: Strength training aims to cause tissue breakdown to promote new tissue growth. Destabilization does not always have positive outcomes. –Changing one variable, even for the “better,” may have a minimal impact on overall performance. –Sometimes, such as in overtraining syndrome, the system adapts to a poorly functioning stable state.

40. Stabilizing Dynamic Systems with Perception–Action Coupling Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Objective 7 Constraint-based information from the environment continually merges with internal sensory information. –Given a task, the system wants to find a stable movement solution. Perceptual systems determine ways to take constraints into account for movement planning and execution. –This process is known as searching for affordances. –Affordances link what is perceived and what action may take place; a process termed perception–action coupling.

41. Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Perception–Action Coupling Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Objective 7 Perception–action coupling makes precise motor programs unnecessary. Planning and action information are part of the environment and revealed when interacting with the environment. Consider the wall-climbing actions afforded each person in the picture.

42. Perception–Action Coupling (cont.) Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins This experimental setup could change the virtual reality hallway “speed” to match or mismatch treadmill speed. –Resulted in optic flow perceived by the person that he were walking faster or slower than in reality. Mismatched virtual reality hallway speed caused the person to walk faster or slower to match the environment. –Clear example of perception–action coupling Objective 7 Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins

43. Perception–Action Coupling (cont.) Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Objective 7 Permission from Mohler et al. (2007) Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins

44. Applying the Systems Approach Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Objective 7 The systems approach provides a framework from which to address movement-related problems. –How individuals interact within the environment with their own constraints and capabilities leads to individual-specific assessments and interventions. –Understanding environmental constraints enables the practitioner to bring those situation-specific constraints into the practice and training environment.

45. Summary Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins The benefit of motor abundance also brings on the problem of degrees of freedom. –Movement models attempt to explain the overarching planning, initiation, and execution process. Models fall into open- (hierarchical) and closed-loop (heterarchical) systems. –Hierarchical models include the schema theory and internal models. –Heterarchical models range from reflex models to dynamic systems.

46. Summary (cont.) Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins The systems theory and approach views movement from the perspective of what factors influence movement production. –Involves dynamic systems interacting, including individual, task, and environmental systems –Dynamic systems include synergies and other interacting components that set constraints upon one another. Interactions among the human operator and the task and the environment are worked out based on the ideas of constraints, affordances, and perception–action coupling.