Adaptive vs. Maladaptive Plasticity

• Neural plasticity


  The ability of neurons to change their function, chemical profile, and structure

  • Involved in learning and the creation of new memories
  • Observed as changes in the number of synapses or the strength of these synapses
  • Can be manifested at the systems level as alterations in neural networks and reorganization of cortical maps
  • Essential for recovery from damage to the central nervous system
• For neural plasticity to be of functional relevance, it is necessary for these changes to result in sensory, motor, or cognitive behavioral changes
• Functional recovery


  The ability to perform tasks and overall behaviors at the same level as was possible prior to the injury or disease
• Compensation


  Residual neural tissue taking over functions of damaged or lost tissue, potentially resulting in differences in motor and task performance from that which was observed prior to injury or disease
• Approaches to improving function after brain damage include interventions directed at limiting the severity of the initial injury to minimize loss of function and targeted therapies that reorganize the brain to restore and compensate for function that has already been compromised or lost

  
• Neural plasticity can be viewed as a continuum from short-term changes in the efficiency or strength of synaptic connections to long-term structural and functional changes in the organization and numbers of connections among neurons
• Neural plasticity is present from birth and continues throughout life
• There are sensitive or critical periods when neural plasticity is increased and more malleable to change
• The brain encodes experiences and learns new behaviors via neural plasticity
• Experience-dependent plasticity


  The process of repair and remodeling that is responsive to the experience of the patient following injury
• Experience-dependent plasticity can be adaptive or promoting recovery of lost function or maladaptive which prevents recovery of lost function
• Adaptive plasticity


  • Promotes recovery of lost function in response to targeted activity and training
  • Begins with active movement
  • Motor skill training improves motor function and drives restorative neural plasticity
  • Training needs to be specific to the lost function
  • Task-specific training utilizes functional activities
  • Activity must target specific movements and skills that are salient to the patient
  • The context of training is essential
  • Requires repetition at an intensity that challenges the nervous system
  • Timing of the training is critical
• Maladaptive plasticity


  Prevents recovery of lost function via use of compensatory and substitution movement patterns
• Maladaptive plasticity


  • Targets synaptogenesis within the contralesional hemisphere, expansion of the motor maps in these regions, and facilitates abnormal interhemispheric inhibition
  • Promotes substitution and compensatory movement patterns that prevent the affected side from developing motor behaviors
• Learned non-use


  The patient fails to use the paretic limb even though spontaneous recovery has occurred, and the paretic limb has greater movement ability and function
• Recovery of function


  • The reacquisition of movement skills lost through injury
  • Defined strictly as the functional goal being attained in the same manner it was performed before the injury using the same processes, or more softly as the ability to achieve task goals using effective and efficient measures which don't have to be the same as prior to the injury
  • Functional behavior emerges over time in patients via spontaneous recovery and activity-induced recovery of function
• Recovery of function can describe how functional behavior emerges over time in patients via spontaneous recovery and activity-induced recovery of function
• Recovery can describe the changes in the underlying neural structures that occur in the same time frame as the behavioral change in function
• Motor recovery


  • Reappearance of motor patterns that were present prior to the nervous system injury
• Motor compensation


  • New motor patterns appear as a result of adaptation of remaining motor elements or substitution

  
• Differences between recovery and compensation

  • At the level of the health condition
  • At the level of body structure and function
  • At the level of activity
• Motor recovery at the activity level


  Using limbs or end effectors to perform a task typically used in persons without nervous system injury
• Motor compensation at the activity level

  Using alternative limbs or end effectors to perform a task

  
• Restorative interventions


  • Directed toward remediating or improving the patient's status in terms of impairments, activity limitations, participation restrictions, and recovery of function
  • The patient has potential to change
  • Targeted at movement deficiencies using activity-based interventions and motor learning strategies
• Compensatory interventions


  • Directed toward promoting optimal function using new motor patterns
  • Can result from adaptation of remaining motor elements or substitution
  • Designed to promote early resumption of function using less-involved body segments
• Restorative interventions include repetitive and intense practice of task-oriented, functional activities, strategies that enhance active motor learning and adherence-enhancing behaviors and strategies that encourage use of the more-impaired body segments while limiting use of the less-impaired segments
• The best way to promote functional recovery and retention is to design restorative interventions based on a functional goal that is meaningful to the patient
• Compensatory interventions include altered movement strategies, assistive devices, environmental adaptation, and the use of less-involved body segments for function
• Substitution is used where changes are made in the patient's overall approach to the task where the uninvolved or less involved extremities are targeted for intervention
• A compensatory approach may be the only realistic approach possible when recovery is limited, and the patient has severe impairments and functional losses with little or no expectation for additional recovery
• Factors affecting recovery


  • Endogenous (age, lesion characteristics, preinjury neuroprotective factors)
  • Exogenous (postinjury factors)

  
• Diaschisis


  Transient loss of function controlled by intact brain regions due to the loss of input from the parts of the brain affected by the stroke
• Unmasking of previous silent neurons and pathways


  Contributes to recovery of function
• Regenerative and reactive synaptogenesis

  Generates collateral pathways to target neurons that were previously innervated by the damaged neurons
• Neurogenesis


  Potential for new cells in the motor cortex to contribute to functional recovery

  
• Alterations to cortical maps and changes in neural activation patterns

  Occur in both the affected and unaffected hemisphere

  
• Strengthening of descending brainstem pathways

  May contribute to recovery of movement, potentially exhibited as abnormal synergistic mass patterns
• Early, intense, and focused training, specifically training focused on skill acquisition, positively affected neural mechanisms associated with recovery of function shaping cortical maps
• Experience-dependent plasticity


  Occurs in response to experiences the patient has post injury