SMA and PMA Functions in Motor Control

Supplementary Motor Area (SMA)

• Has a 10% direct projection to the spinal cord.
• Connects to M1 and other key cortical areas.
• Direct projections to the spinal cord terminate on alpha-motoneurons, which control hand muscles.
• Implicated in sequence-specific and internally generated (self-initiated) movements.
• Heavily involved in complex movements.
• Active during both real and imagined movements, which is useful for mental rehearsal.
• Involved more in the planning phase of movement rather than execution.
• SMA activity increases with the complexity and sequencing of a movement.
• Mirror neuron activity is present, meaning that imagining a movement activates the SMA similar to actual movement.
• Motor imagery and execution share overlapping activation patterns in the SMA, which aids in skill acquisition.

Premotor Cortex (PMA)

• Positioned just anterior to M1, but more laterally compared to the SMA.
• Has fewer direct connections to the spinal cord (10%) compared to the SMA.
• Characterized by strong subcortical connections.
• Triggered by external sensory events and delayed actions.
• Crucial for obstacle avoidance and preventing perseveration behaviors (repetitive, ineffective behaviors).
• Has less direct control over movement compared to the SMA.
• Many PMA neurons connect to the cerebellum to coordinate movement.
• Supports pantomime tasks (delayed actions).
• Perseveration is doing the same action repetitively, even if it's ineffective.

M1, SMA, and PMA Activation Study

• Monkeys were tested with external visual stimuli and internally generated movement tasks.
• Raster plots were recorded neuron firing rates in M1, SMA, and PMA.

Findings for M1 (Primary Motor Cortex)

• Visual cues increased neuron activity.
• Internal cues also increased neuron activity.

Findings for SMA

• Visual cues resulted in no major activity change.
• Internal cues led to significant activity before and during movement.

Findings for PMA

• Visual cues resulted in activity before, during, and after movement.
• Internal cues showed minimal activity change.
• M1 is involved in both externally and internally cued movements.
• SMA is primarily for internally driven movements.
• PMA is highly influence by external stimuli and preparatory activity.

Mirror Neurons

• Accidentally discovered when recording single-cell activity in monkeys.
• Neurons activate both when watching an action and when performing it.
• Support for imitation, learning, and social interaction.
• Three conditions that activate mirror neurons: seeing another monkey grasp food, seeing a human pick up food, and picking up food itself.
• Support the "monkey see, monkey do" theory.

Functions of Mirror Neurons

• Plays a key role in understanding the actions and emotions of others.
• Is vital for learning through imitation.
• Might be linked to autism due to autism-linked differences in mirror neuron activity.
• SMA is active in internally generated and complex movements.
• PMA responds to external sensory cues and plays a role in delayed actions.
• M1 is involved in both externally and internally driven movements.
• Mirror neurons facilitate learning, imitation, and social behavior.
• Motor imagery and real movement activate SMA similarly, which aids in motor learning.
• The regions, in order, are SMA, PMA, VPMA (Ventral Premotor Area), S1 (Primary Somatosensory Cortex), IPC (Inferior Parietal Cortex).

Hemispheres

• The brain has two hemispheres (right and left).
• The hemispheres are identical on the microscopic level, but have very different functions.
• The left hemisphere controls speech, language (lateralized), and movement praxus.
• Most right-handed people (95%) are specialized in the left hemisphere.
• Damage to the left hemisphere leads to apraxia.
• The right hemisphere controls haptics (sensory), visual spatial processing, musical abilities, and numeracy.
• The lobes have a crossed nature of control (left controls right, right controls left).

Speech Perception and Production

• Broca was interested in people who have lost the ability to speak.
• Broca performed a post-mortem dissection of the brain.
• He determined that a stroke or syphilis in the left, frontal hemisphere (Broca's region) caused speech issues.
• Wernicke was interested in why people suddenly lose the ability to understand language.
• Wernicke performed a post-mortem exam.
• He determined that an injury occurred in the left temporal lobe region (Wernicke's area).

Communication Disorders

• Broca's Aphasia: Individuals exhibit slow and laborious speech, and are unable to articulate speech.
• Individuals know what they want to say but cannot express it.
• Speaking in a sing-song voice can bypass the Broca's region and engage the right hemisphere, which skips the damaged area.
• Wernicke's Aphasia: characterized by non-meaningful language, with a lost rule, meaning, and structure.
• Individuals are not conscious of their mistakes and think that their speech has meaning.
• The right hemisphere controls automatic language production (memorized, deeply ingrained language).
• This can still be produced, including swearing and counting.

Disconnection Syndrome and Conduction Aphasia

• Broca's region and Wernicke's area are connected by the arcuate fasciculus.
• The arcuate fasciculus is a "superhighway" of axon bundles that send info between Broca's region and Wernicke's area.
• Diffusion tension imagery (water molecules) are used to see this area
• Disconnection: a cut to this area leads to speech and processing effects.
• Disconnection: There is no awareness of speech production, but the automatic remains unaffected.
• Conduction aphasia: caused by a deficit from disconnection.
• Individuals understand what is being said but can only produce one word.

The Split Brain

• The two hemispheres are connected through the corpus callosum (a bundle of fibers).
• The two hemispheres are connected through the corpus callosum (a bundle of fibers).
• The split-brain procedure separates the corpus callosum to alleviate epilepsy severity.
• Prevents communication between the two hemispheres, limiting the spread of epileptic seizures so the seizures are less severe.
• Theoretically, this is good, but it can cause adverse effects by not allowing communication.
• The right and left brain work independently of each other, which shows specialization.

Apraxia

• Apraxia: a high-level impairment of learned, skilled purposeful movement that cannot be explained by language, comprehension, motor or sensory deficits.
• Diagnosis involves excluding other deficits and evaluating speech and limbs.
• There is always a speech, language, and motor deficit present.
• Ideomotor Apraxia: Inability to translate movement knowledge into innovatory apraxia.
• Analogous to Broca's aphasia: individuals know what they want to do but cannot produce the movement.
• However, they possess the engrams (instructions) for the movements.
• Ideational Apraxia: Inability to recall a movement from memory.
• A lesion impacts the engrams, and the patient forgets how to perform simple movements.
• A stroke causes Ideational apraxia, and is analogous to Wernicke's area.
• Conceptual Apraxia: Inability to understand the relationship between a tool and an object (how to use it).

Dyspraxia

• Used in a developmental context, typically seen in clumsy children.
• A developmental cognitive disorder.
• Involved with global problems with movement timing (cortical and cerebellum).
• Articulations for speech are in an organized but incorrect order.

Down Syndrome

• Down syndrome is a genetic disorder caused by the triplication of chromosome 21 (trisomy 21).
• People with Down syndrome are shorter than their age-matched peers.
• People with Down syndrome experience cognitive challenges and developmental delays.
• Their brains are smaller than those of age-matched individuals without Down syndrome.
• Brain size appears proportional to their shorter height.
• The corpus callosum in individuals with Down syndrome is thinner and has fewer fibers.
• Individuals with Down syndrome are more likely to be left-handed.
• Dominant hand preference is strongly linked to the lateralization of the brain.
• The increased left-handedness may relate to how receptive language is lateralized.
• Dichotic Listening Task: a task developed by Doreen Kimura that helps to identify receptive language lateralization.
• In the general population there is a right ear advantage for recalling auditory stimuli because the right ear connects directly to the left hemisphere, which is specialized for receptive language.
• In individuals with Down syndrome there is a left ear advantage.
• This suggests their right hemisphere is specialized for receptive language.

Cerebral Specialization in Down Syndrome

• It was previously thought that people with Down syndrome had a reverse model of cerebral specialization.
• Reverse model of cerebral specialization: functions typically lateralized in the left hemisphere of the general population were lateralized in the right hemisphere in Down syndrome.
• Instead, studies indicate speech production and movement praxis (planning and coordination of movement) are also lateralized to the left hemisphere.
• The main difference is in speech perception, which is lateralized to the right hemisphere in Down syndrome.

Model of Biological Dissociation

• Right hemisphere specialization for receptive language in Down syndrome.
• Speech production and movement praxis remain left hemisphere functions.
• Between-hemisphere communication is problematic in individuals with Down syndrome.
• Individuals with Down syndrome struggle with verbal instruction but perform better when given visual instruction because this bypasses interhemispheric communication.

Pyramidal Tract

• The pyramidal tract involves upper motor neurons and originates in M1, SMA, PMA, and partial cortex.
• Contains over 1 million axons, most of which are myelinated (fast signal conduction).
• Primarily innervates facial, axial, and intrinsic musculature.
• Divided into corticobulbar and corticospinal tracts.
• Corticobulbar Tract: Connects the cortex to the brainstem.
• Primarily controls facial muscles.
• Corticospinal Tract: Controls axial and distal muscles.
• Further divided into lateral and ventral corticospinal tracts.
• Humans have the most advanced descending motor pathway
• 50-60% of fibers originate in M1 (primary motor cortex)

Corticobulbar Tract (Facial Motor Control)

• Any descending fiber originating in M1 and traveling to the midbrain is considered the corticobulbar tract.
• Upper motor neurons: The descending tract originates in the cortex and synapse at the midbrain, where they interface with lower motor neurons.
• It innervates the face, neck, and head (no oculomotor).
• Lower motor neurons: Considered alpha motor neurons as they directly cause movement by sending signals to muscles, causing muscle contraction.
• Rostral innervates upper facial musculature bilaterally.
• Caudal innervates lower facial musculature contralaterally.

Beating Heart Illusion

• Blurred Boundaries & Perception: The brain constructs an image of an the boundary of an object at any given time.
• If there is no sharp boundary, V1 neurons will attempt to differentiate the edges, and the changing activation of V1 neurons creates heartbeat illusions.
• Visual illusions trick perception, but they don't affect vision for action.

Corticobular Tract Injury

• Upper Motor Neuron Injury (Stroke) causes selective paralysis.
• Cannot move muscles on lower left side, but they are able to move elsewhere.
• The deficit is selective to only these lower muscles.
• Lower Motor Neuron Injury (Bell's Palsy) causes paralysis on one side of the face.
• The lower motor neurons are inflamed and cannot communicate to the muscles.
• Ventral Corticospinal Tract originates in M1.
• This extends to the spinal cord
• Most fibers descend uncrossed and primarily innervate axial musculature.
• There are very few monosynaptic connections (fine motor control).
• There are many fibers allowing for coordinated movement of many muscles, also known as propriospinal neurons.
• Lateral Corticospinal Tract originates in M1.
• 70-80% of fibers decussate (cross over) at the pyramids in the medulla.
• Primarily innervates intrinsic muscles.
• Has many monosynaptic connections, supporting fine movement and independent digit control.
• Controls precision precision grip due to precise depolarization of axons.

Alpha (α) Motoneuron

• A motor Unit: A neuron innervating power-producing extrafusal muscle fibers
• Larger than gamma (γ) motoneurons.
• Innervation Ratio
  • Large muscles - high ratio (one neuron controls many fibers)
  • Small muscles - low ratio (one neuron controls few fibers)

Gamma (γ) Motoneuron

• Gamma (γ) Motoneuron: fusimotor neuron that innervates intrafusal muscle fibers.
• These fibers are proprioceptive.
• Smaller than α-motoneurons
• Oriented parallel to extrafusal fibre
• Controls muscle spindle sensitivity to stretch
• Important for reflexes and muscle tone regulation
• The type of muscle fiber determines the types of movement someone can do.

Types of Motor Units

• Fast Twitch, Fatigable (FF) – Fast Motor Unit features the highest conduction velocity (100 m/s) because of large diameter and a large fiber diameter
• Innervates fast-twitch muscle fibers, e.g. Type II X, for rapid, powerful movements (extrafusal muscle fibers).
• Fast Twitch, Fatigue-Resistant (FR) has a medium conduction velocity (60 m/s) and a medium fiber diameter.
• Innervates fast and/or slow-twitch muscle fibers (Type II A).
• Slow Twitch, Fatigue-Resistant (SR) – a slow motor unit that has the lowest conduction velocity (40 m/s) and has a small fiber diameter.
• Innervates slow-twitch muscle fibers (Type I) for endurance-based activities.
• Those with more fast motor units will perform better in short term athletics, where those with less fast motor units will perform better in long term athletics.
• Those with less fast motor units will perform better in long term athletics, where those with more fast motor units will perform better in short term athletics.
• Spinal cord injuries eliminate sustained movement, leading to an abundance of FF fibers.

Recruitment of Muscle Fibers

• The muscle unit will recruit from smallest to largest.
• Size of motor units increases with the size of force production.
• Henneman Size Principle: ordered recruitment of motor units and the associated muscle fibers from smallest to largest.
• Leading causes of falls in older adults: incorrect weight shifting.
• Selective loss of fast twitch fibers (Type II X) can occur, which are smaller and less populated
• Demyelination mostly in fast motor units (Type II X) can cause them to be more susceptible to loss of action efficiency
• Fast twitch fibers allow for quick movement to stop falls, an absence of these increases risks for older adults with quick postural innervation
• To prevent falls, there needs to be exercise that is both physically and cognitively engaging
• Square Stepping: walking on a pattern of squares and promotes weight transferring and social engagement
• Wobble Board: balancing on a board that's been found to show long lasting results for a decrease in falls

Oculomotor Control

• Retinotopic Map: a map of the superior colliculus which can show neural distribution through LED lights and help scientists identify and study disorders in M1
• Retinotectal Pathway: involves involuntary prosaccade: involuntary draw to the target
• The primate visual pathway prosaccades consist of a stimulus that moves from retina, superior colliculus, BS Nuclei, and then eye detects deficits in executive function, more specifically voluntary antisaccades
• Geniculostirate Cortex defects- Detects deficits in executive function – voluntary antisaccades
• Antisaccades are part of The Primate Visual Pathway: stimuli moving from retina, to thalamus, to LGN, V1, parietal cortex, DLPFC, and then eye

Executive Function

• DLPFC is critical for executive function and activated for antisaccades (inhibitory control)
• Damage (stroke) affects a humans ability to producing antisaccades due to the DLPFC being a major assistance for helping to prevent that disorder Schizophrenia: makes it hard to tell the difference between real and fake stimuli
• The sufferer must also think cleanly, have normal emotional response, and adhere to standards
• Sufferers often have different brain structure with the same larger lateral ventricles connected to the same fluid filled area
• They are also linked to cortical atrophy as well as smaller DLPFCs that make it harder to preform EF tasks and cannot perform antisaccades or inhibitory actions

Inhibitory Dysfunction

• Persons with SZ produce more antisaccade directional errors (30- 70%) than healthy controls
• Using the antisaccade task as a phenotype for genetic studie can allow them to benefits form SZ families
• Siblings diagnosed with schizophrenia shared a similar pattern
• The test can be a biomarker that detects gene carriers in to improve detections and empower connection
• More movements and actions occur in to many location activity wise for those preforming tasks, which in not how it suppose to perform for the test.
• This introduces composition because these active regions can't inhibit unwanted activity in the brain
• People with schizophrenia have difficulty regulating cortical active that is appropriate for a task

Foveal vision

• the center part of the retina (known as the fovea), has high density of retinal ganglion cells
• the area is also known to promote high spatial resolution because of everything that is available
• It allows retina detailed and sharp vision for tasks like reading and object recognition

Peripheral Vision

• more specialized for motion detection and spatial awareness than fine details
• The eye exhibits structural asymmetry because different parts of the retina were mapped onto specific regions of the primary visual cortex (V1)
• Cortical Magnification: the foveal region is represented by a greater area in the V1 that assist the brain in more processing of information
• Cortical Magnification not only occurs here but is in the retina itself

Processing in the Hemiretinas

• Lower visual field (LVF) information is processed by the superior hemiretina
• Upper Visual Field (UVF) information is processed by the inferior hemiretina
• the superior hemiretina ha more retinal ganglion cells than the inferior, leading to greater cortical magnification in V1 for the lower visual field
• When people fixate on Fixation 1, responses for accurately improve with the target appearing in their lower visual field
• People fixate on targets where the movements and reactions are more slower and less precisely and can be due to the upper visual field

"Lead in the Cloud" Phenomenon

• When people look up at an engaging complex task, they do so do engage with the upper visual field that is more capable for cognitive and better at processing information
• Movements can be critical for physical awareness and spacial reactions to engage with the lower visual field

Goals of Science

• To understand, describe, explain, predict, correlational vs. cause-effect
• Verification that must be verified via observation

Hypothesis Testing

• Made based on evidence that acts as a starting point to provide for further investigation made from an empiricism experiment
• Independent Variables: variables that must be manipulated to observe and be effected by the dependent variable
• Dependent Variables: measured outcomes that depend on the independent value

Task Organization

• Discrete Skill: organized where actioned can be brief and well defined
• Serial Skill: actions can connected and linked in a order to act as a successful sequence

Motor Skills

• Continuous Skill: actions work without beginning or end, that goes on repeating itself constantly
• Motor Skill: ability of the motion working to perform certain movement tasks
• Cognitive Skill: abilities in quality to assist in performer to decide
• Environmental Predictability: an organized environment that acts predictably
• Level of Environmental Predictability- a skill or state that's known advance
• In an Unpredictable that requires reactions to be adapt to dynamic properties of the certain environment

Measures of Time

• Measuring reaction time in response to some stimulus
• Measuring the way time works and what that can mean
• How it affects functions in the nervous sytem

Reactions and Times

• Reactions are efficient to those who can accomplish and complete actions in less time Reaction Time: from signal, stimulus and response with that comes a initiation Simple reaction time (SRI): A time set respond to a Expected/ Single stimulus: 250-350 ms
• Basic to Measure Info Processing Multiple Respones w/ response: Stimuli that takes time
• High for cognition w/ EF
• Effects must unknown

Measuring the Nervous system

• Task Inhibition w control
• Higher errors with certain lesions Increasing the number of SRI will show a increase in time response: provides a sign that randomized before signal occurs Times with that effect emotions
• Reaction Time is set to 80% to detect it, the remainder (20%) for muscles activation without starting moments

Injury Reaction

• Electromyography (EMG) shows muscle activation before visible movement. Upper Motor Neuron Injury - Increased time Motor Neuron can delay

Measurements

• Movements with constant or bias due trails
• Errors w/ sum vs division
• Movements w/ measure or division
• Tasked/Mirrored images are viewed different

Measuring and Interpreting Motion

• Analyzes motion w/ Qualitative and verbal description

Motion Kinematics: Quantitative

• Spatial/Arm position (Displacement)
• Velocity the Speed
• Velocity Change:acceleration
• Positive Skew: Time spent after peak velocity
• Velocity increases w/ Displacement: higher velocity that causes the increase

Nuerological Issues

• Apraxia by injury effecting wrist and elbow