Motor Control and Disorders of Action, Lecture 10 Flashcards
Introduction to Motor Control
Most actions require multiple muscles, precise timing, and multiple components of movement
Higher cognitive aspects of motor control include planning, timing, sequencing, imagery, and expertise
Applications include learning motor skills, rehabilitating patients with movement difficulties, and creating artificial limbs/robots
Primary Motor Cortex (M1)
Located in the pre-central gyrus
Somatotopic organization (activation in specific parts of M1 causes movement of specific body parts on the opposite side)
Cells in M1 have a preferred direction of movement and code the direction of movement through vector coding
Two parallel systems in M1: (a) body-part specific for fine motor control and (b) somato-cognitive action network (SCAN) for integrating goals and whole-body movement
Brain Lesions
Stroke affecting one side of the brain can affect movement of the opposite side of the body
Hemiplegia is paralysis of one side, hemiparesis is weakness of one side
Supplementary Motor Area (SMA) and Lateral Premotor Cortex
SMA is involved in internally generated actions, such as well-learned sequences
Lateral premotor cortex is involved in externally generated actions, such as selecting and preparing movements
Coordinating bimanual movements requires the use of the cerebellum, SMA, and pre-motor area
These areas are more active during difficult bimanual tasks
Sequence Learning and Neural Plasticity
With practice, we produce faster and more accurate movements and transition from effortful to automatic movements
Changes involve both cortical and subcortical structures, including the dorsolateral prefrontal cortex, SMA, lateral premotor cortex, primary motor cortex, cerebellum, and basal ganglia
Activity in the dorsolateral prefrontal cortex tends to decrease, while activity in the SMA and lateral premotor cortex tends to increase as we learn a sequence
The cerebellum plays a role in fine-tuning movements, and the basal ganglia are involved in the selection and initiation of movements
These changes reflect the neural plasticity that occurs as we learn and automate a motor sequence, with important implications for motor control and rehabilitation.
Role of Supplementary Motor Area (SMA) in motor sequence learning
Gerloff et al. (1997) used TMS to investigate the role of SMA in motor sequence learning
Repetitive TMS over SMA temporarily blocked its activity
SMA disruption only interfered with the most complex motor sequence, a 12-element sequence
SMA plays a crucial role in the learning and performance of complex motor sequences
Interference effects were transient, indicating that other brain areas could compensate for the disruption
TMS can be used to study brain function and plasticity
Prefrontal cortex and its involvement in motor control
Prefrontal cortex, especially DLPFC, is involved in higher-level cognitive processes related to motor control and action selection
Prefrontal cortex is involved in choosing which action to perform, attention to action, and representation of longer-term goals and intentions
Prefrontal cortex is not specific to action and is also involved in other cognitive processes such as working memory, decision-making, and planning
Activity of prefrontal cortex is modulated by task difficulty, novelty, and long-term goals
Frith et al. (1991) demonstrated that prefrontal cortex is involved in choosing which action to perform, such as which finger to use when pressing a button
Prefrontal cortex plays a crucial role in the cognitive control of action
Effects of prefrontal lesions on motor control
Prefrontal lesions can produce perseveration, utilization behavior, disinhibition, and frontal apraxia
Perseveration: repeat the same action when it is no longer relevant
Utilization behavior: act on irrelevant (or inappropriate) objects in the environment
Disinhibition: e.g., in the antisaccade task
Frontal apraxia: not able to follow steps in routine tasks (e.g., making tea)
Antisaccades task and prepotent tendency
Antisaccade task requires participants to make a saccade (a rapid eye movement) to a location opposite to a target that appears in their visual field
This requires inhibiting the pre-potent or automatic tendency to look at the target and instead directing the gaze away from it
Norman and Shallice Model of action selection
Norman and Shallice model explains how the human brain processes information and selects appropriate actions in complex, real-world situations
Two key mechanisms are involved in the selection of actions: contention scheduling and the supervisory attentional system (SAS)
Contention scheduling resolves conflicts between different schema (i.e., pre-existing action plans or routines) that are activated by the environment or by internal cues
Supervisory attentional system (SAS) is responsible for monitoring and regulating the operation of lower-level schema
SAS is particularly important when dealing with novel or less automatic actions, which require more conscious attention and control
Norman and Shallice model provides a framework for understanding how the brain selects and executes actions in complex, real-world situations, highlighting the importance of both lower-level contention scheduling and higher-level SAS mechanisms in this process
Action Errors
Action errors occur when there is a breakdown in the normal processes involved in selecting and executing appropriate actions.
Two common types of action errors are perseveration and utilisation behaviour, which are both related to the activation of inappropriate schema.
Perseveration refers to the tendency to continue using a schema or action plan even when it is no longer appropriate or effective.
Utilisation behaviour refers to the activation of inappropriate schema in response to environmental cues.
Understanding these types of action errors can help in designing interventions and strategies to address them and improve overall performance in complex, dynamic environments.
Perseveration
Perseveration is a type of action error where a person becomes fixated on a particular strategy or fails to update their schema in response to changing circumstances.
This can lead to continuing to use a particular tool or technique even when it is no longer effective or persisting in pursuing a goal that is no longer achievable.
Difficulties in adapting to changing circumstances and selecting appropriate actions are related to perseveration.
Utilisation Behaviour
Utilisation behaviour is a type of action error where a person’s SAS is unable to suppress the activation of schema that are not relevant or appropriate to the current situation.
This can lead to automatically reaching for a tool or object that is irrelevant to the task at hand or performing an action that is socially inappropriate in response to a particular cue.
Difficulties in adapting to changing circumstances and selecting appropriate actions are related to utilisation behaviour.
Apraxia
Apraxia is the inability to perform skilled purposeful movement.
Ideomotor apraxia is a type of apraxia where the idea and execution of an action are disconnected, but the person retains knowledge of the action.
People with ideomotor apraxia can recognise actions performed by others but may fail in pantomiming actions or performing components of a sequence.
Subcortical Motor Areas
The subcortical motor areas are regions of the brain that are involved in the planning, initiation, and control of movement.
Two important subcortical motor areas are the basal ganglia and the cerebellum.
Damage to the cerebellum can lead to action tremor, dysmetria, deficits in coordinating across joints, and difficulties with motor learning and timing.
