Lecture 10 - Perception to Action

Introduction

Course: KIN 255 – Fundamentals of NeuroscienceInstitution: University of Waterloo, Faculty of Health - Kinesiology and Health Sciences

Course Outline

Topics Covered:

  • Sensorimotor transformations: Understanding how sensory information is converted into movement actions.

  • Primary motor cortex: Exploration of the structure and function of the M1 region in motor control.

  • Descending motor pathways: Investigation of the various neural pathways involved in transmitting motor commands from the brain to the spinal cord.

  • Motor planning: Supplementary and premotor cortex: Analysis of how higher brain areas contribute to planning movements before execution.

  • Cortical contributions to sensorimotor integration: The role of different brain regions in coordinating sensory inputs with motor outputs.

Overview of Perception to Action

  • Basic task example: Reaching and grasping an object illustrates the complexity of motor tasks.

  • Complexity in the brain’s problem-solving: This task involves intricate processes including:

    • Sensory information processing: Gathering relevant visual and tactile information.

    • Motor planning: Creating a strategy for movement execution.

    • Movement execution: The physical act of reaching and grasping the object.

Primary Motor Cortex (M1)

  • Organization:

    • Research through single-cell recordings has evidenced broad somatotopic organization within M1, indicating how different body regions are represented in the cortex.

  • Motor Homunculus:

    • Illustrates disproportionate representation of body parts, highlighting areas involved in precise motor control such as fingers and facial muscles, as opposed to larger limbs which are represented less distinctly.

  • Neuron complexity:

    • Many neurons in M1 encode movement properties (e.g., direction, speed) rather than isolating individual muscle activity.

Descending Projections from Motor Cortex

  • Pyramidal neurons' role:

    • These neurons project from M1 to different brain stem and spinal cord regions, crucial for facilitating voluntary movement.

  • Key tracts:

    • Corticobulbar tract: Projects from cortex to brain stem, influencing motor neurons.

    • Corticospinal tract: Connects the cortex to spinal gray matter, affecting both motor neurons and interneurons.

  • Modulatory functions of other tracts:

    • Corticorubral: Influences rubrospinal tract aimed at regulating muscle tone.

    • Corticoreticular: Works with reticulospinal tract for postural adjustment.

    • Corticopontine: Coordinates motor function by projecting to the cerebellum.

    • Corticostriate: Provides inputs to basal ganglia, essential for movement coordination.

Corticobulbar Tract

  • Projections:

    • Motor cortical pyramidal neurons send projections to various brain stem motor neurons, allowing for the volitional control of diverse muscle groups.

  • Muscle innervation:

    • Innervates facials, head, eye, neck muscles, tongue, and larynx via several cranial nerves.

  • Cranial nerves and their functions:

    • Oculomotor (III): Eye movement control.

    • Trochlear (IV): Controls the superior oblique muscle of the eye.

    • Trigeminal (V): Sensation in the face and motor functions such as biting and chewing.

    • Abducens (VI): Controls lateral eye movement.

    • Facial (VII): Controls muscles of facial expression.

    • Vagus (X): Controls functions of the heart, lungs, and digestive tract.

    • Spinal Accessory (XI): Controls shoulder and neck muscles.

    • Hypoglossal (XII): Controls tongue movements.

  • Decussation:

    • Approximately 50% of corticobulbar tracts decussate at various levels; ~75–90% of corticospinal tracts decussate, indicating crossing over for contralateral control of muscles.

Corticospinal Tract

  • Projects from upper motor neurons:

    • These neurons communicate to contralateral lower motor neurons and interneurons, directly influencing voluntary muscle movement.

  • Lower motor neurons:

    • Located primarily in the ventral horn of the spinal cord, critical for muscle contraction.

  • Interneurons:

    • Found in the intermediate and ventral regions, assist in integrating sensory inputs and motor outputs.

  • Origins:

    • Primary motor cortex (~30%), premotor cortices (~30%), parietal/cingulate gyri (~40%).

  • Decussation:

    • Most prominently occurs at the medulla, crucial for contralateral control.

Motor Cortex Output Influences

  • Input variety to M1:

    • Inputs stem from diverse cortical regions and subcortical structures, indicating a broad range of influence.

  • Input types:

    • Distinction between predictive motor planning (anticipating future movements) versus feedback adjustments (correcting ongoing movements based on sensory updates).

Premotor Areas and Motor Planning

  • Premotor and Supplementary Motor Cortex:

    • Both areas are critical in motor planning, selection of actions, and successful execution of movements.

  • Roles of premotor areas:

    • They contribute significantly to corticospinal tract axons, with 30% of their origins traced back to premotor areas.

  • Consequences of voluntary movements:

    • Stimulation of pyramidal neurons typically initiates muscle contractions, essential for actions like postural control.

Premotor vs. Supplementary Motor Areas

  • Supplementary Motor Areas (SMA):

    • Crucial for converting intentions of actions into specific sequences, particularly activated when recalling movements from memory.

  • Premotor Cortex:

    • Responsible for coordinating movement anticipation, associating visual cues to actions, and ensuring appropriate limb kinematics during execution.

Neuron Analysis in Motor Cortex

  • Analysis of neuron activity:

    • Investigates the engagement of specific neurons during reaching tasks, contrasting visually guided actions versus actions generated from internal cues.

  • Specific contributions to movement execution:

    • Focuses on how certain neurons influence the direction and control of movements.

Neuron Types in SMA

  • Three types of neurons:

    • Sequence selective: Respond to specific sequences necessary for action completion.

    • Movement selective: Engage depending on particular actions being performed.

    • Rank-order selective: Important for defining the timing of different elements of an action.

  • Function overview:

    • The SMA orchestrates the conversion of experienced intentions into well-defined movements.

Sequence Selective Neurons

  • Functionality:

    • These neurons specifically code for sequences essential to obtaining desired outcomes, e.g., responding specifically to the Pull-Turn-Push action sequence necessary for certain tasks.

Rank-Order Neurons

  • Functionality:

    • These neurons establish the overall timing of various elements within an action, focusing on the order rather than the precise spatial locations.

Movement Selective Neurons

  • Functionality:

    • Focus on specific stages within action sequences, such as Pull movements, during task performance.

Dorsal Premotor Cortex

  • Functionality:

    • Codes the spatial vectors of movements based on the location of target objects, emphasizing how body posture adjusts to different reaching tasks.

  • Activity patterns:

    • Show substantial variation based on the direction of movement, distinguishing between targets on the left versus right sides.

Ventral Premotor Cortex

  • Functionality:

    • Codes the orientations required of effectors in relation to target objects, essential for grasping.

  • Responses:

    • Exhibits preference in response to specific objects, while showing diminished responses for visually similar objects, indicating a focus on specific grasping techniques.

Parietal Cortex Functions

  • Transformative role of the posterior parietal cortex:

    • Acts as a convergence zone that integrates diverse sensory inputs, vital for actionable planning.

  • Intraparietal sulcus role:

    • Key to converting visual information into body-centered coordinates essential for movement execution.

Specific Areas of the Intraparietal Sulcus

  • Roles:

    • These areas contribute to the mapping of visual information to body-centered coordinates for varying actions:

      • Medial IPS (MIP): Involved in reaching movements.

      • Anterior IPS (AIP): Critical for grasping actions.

      • Lateral IPS (LIP): Essential for eye movement control.

      • Parietal reach region (PRR): Coordinates hand-eye interactions during reaches.

From Vision to Motor Plan

  • Projections:

    • From the ipsilateral sulcus to premotor cortex that guide diverse actions through precise mapping:

      • Dorsal PM: Utilized for mapping stimulus-response rules relevant to intended actions.

      • Caudal PM: Analyzes body-relative information necessary for planning kinematics of movements.

      • Ventral PM: Determines grip type based on object characteristics, crucial for mirror neuron activity that influences social and observational learning.

Summary of Supraspinal Control

  • Recap:

    • Summarizes the pathways involved in various motor planning and session execution aspects discussed throughout the course content, emphasizing integration among neural circuits.

Revisiting Initial Questions

  • Encourage exploration:

    • Students should discern key brain areas that activate during simple tasks like reaching and grasping, reflecting the interconnected nature of the motor system.

Final Summary of Fundamental Topics

  • Core concepts recap:

    • Emphasizes the relationship among sensorimotor