Primary Motor Cortex (M1): Historical Perspective

Introduction to Psychomotor Behavior: Primary Motor Cortex (M1) - A Historical Perspective

• Edouard Hitzig, a German neurologist, experimented on dogs and observed a hind leg twitch after sending a mild electrical current to a specific part of the cortex.
• The location of the twitch varied depending on the location of the brain stimulated.
• Hitzig created the first idea of a motor map.
• David Ferrier, a Scottish physician, experimented on non-human primates and expanded on Hitzig's research.
• Ferrier conceptualized that specific regions of the cortex cause twitching in particular parts of the body.
• Ferrier created lesions of the cortex to observe the effects on movement, noting what movement was allowed or inhibited.
• Ferrier was the first person charged with animal cruelty in research.
• John Hughlings Jackson was an English neurologist interested in epilepsy, which is characterized by random and unorganized electrical activity in the neurons.
• Jackson identified Jacksonian march, a systematic progression of a seizure that starts in the shoulder and progresses down the arm, after his wife had epilepsy.
• Jackson determined that the brain is organized systematically and that seizures spread throughout, affecting different regions.
• Wilder Penfield, an American/Canadian neurosurgeon, used brain surgery methods to understand the M1 organization.
• Penfield expanded brain surgery methods and techniques.
• Penfield was the first to map M1 systematically and found areas in the brain that cause epilepsy in various people.

Neurosurgery and Brain Mapping

• Neurosurgery focuses on diagnosing and treating nervous system disorders through surgery, including the removal of tumors, brain tissue, skull, and implantations.
• Brain mapping is used in neurosurgery to study brain function by identifying the locations of different cognitive and motor activities.
• Brain mapping reduces surgical risks by identifying regions of the brain with essential functions and preserving that area.

Brain Topography and Projections to Spinal Cord

• The brain has distinct regions responsible for specific functions that are mapped orderly.
• Neurons descend from the regions to the spinal cord.
• 50% of these projections originate from M1 (600,000) and descend through the brain stem to the direct path of the lateral cortical spinal tract, a very important region.
• The most important area for producing movement is the IDC (Independent Digit Control).
• A lesion to M1 would cause issues performing fine motor control movements.

The Human Homunculus

• The human homunculus is a classic organization mapped by Wilder Penfield which shows cortical magnification.
• Cortical Magnification shows neuron amount reflected in size.
• More neurons are needed in some body parts because of fine motor demands.
• The homunculus shows a body with exaggerated eyes, ears, nose, lips, fingertips, and genitals.
• Classic view: the proximal leg is next to the proximal arm, with fingers next to the forehead.

Short Burst Electrical Stimulation

• Short Burst Electrical stimulation is rapid, repetitive electrical pulses applied to the motor cortex which identifies functional areas in the brain.
• Wilder Penfield used short burst electrical stimulation to create the motor homunculus during brain surgery.

Independent Digit Control Impairment

• Independent Digit Control (IDC) refers to the brain's ability to move individual fingers separately rather than as a whole, which is important for fine motor movements and precision.
• Next to speech, this is the most complicated task that depends on input from M1.
• Precision Grip uses the fingertips to manipulate small objects with fine control and is controlled by the contralateral side.
• Power Grip uses the entire hand to generate strong force for object stability and is controlled by both ipsilateral and contralateral sides.
• Hemiparesis Lesions impair IDC, Precision grip, impairs power grip, remains intact.
• Hemiparesis is impairment on one side that affects the power and precision grasp on the opposite side.
• Lesions are challenging to fix because they require a lot of neuroplasticity for healing.

Historical View of Organization and Control

• The historical view of M1 is mainly derived from the writings of Wilder Penfield.
• Mapping: the precentral gyrus (M1) contains a discrete, topographic map of the body.
• Neurons: each point in the map specifies “tension” in a single muscle, where one neuron controls each muscle.
• Pathway: Cortical motor areas are organized hierarchically, and M1 is the final common pathway to action (a strict, step-by-step order is followed).
• Neuroplasticity: The organization is invariant (not plastic) so there is no chance for recovery.
• People have been adhering to these views for 60 years, however, contemporary neuroscience research contrasts these views.

Rethinking the Classic View - Neuroplasticity and Mapping

• Kindled Rats are laboratory rats used in epilepsy research, in which repeated subthreshold electrical or chemical stimulation is applied to specific brain regions to induce seizures.
• Over time, the rat's brains would show a motor map change.

Mapping

• The only individuals that Wilder Penfield mapped had a long-term chronic condition that caused uncontrolled brain activity.
• Brains may have been changed by the effects of epilepsy.
• The original map is not correct, is jumbled and more expansive.

Neuroplasticity

• Wilder Penfield assumed that motor maps could not be changed, but when kindled, the rats motor map underwent a significant shift.
• The brain is capable of neuroplasticity and change.
• M1 is highly plastic and adapts after experience.

Phantom Limb Syndrome

• A phantom limb is the perception of sensations (including pain, movement, or touch) in a limb that has been amputated or is missing.
• Amputees experience phantom sensations because neurons in M1 and S1 still retain the representation of the missing limb.
• Mapping: Amputees show remapping– M1 and S1 are not fixed , they can reorganize after limb loss.
• Orientation is also wrong, with the chin being closer to the hand.
• The brain remaps after amputation - reorganization can lead to phantom pain when adjacent brain areas "take over" the limb's activity.

Mirror Box Therapy – Helping Phantom Pain

• Mirror Box Therapy uses visual feedback to "trick" the brain into believing the limb is moving, reducing pain.
• This therapy works by retraining the brain's motor-sensory maps to reduce phantom pain.

Rethinking the Classic View – Mapping, Neurons, and Pathway

• The historical view is that M1 is the final common pathway to action (a strict, step-by-step order)
• Historically it was believed that M1 just sent information to the spinal cord.
• It was also assumed that each neuron had a distinct area with no overlapping in the brain.
• Overlapping occurs with multiple neurons in different spaces.
• Schieber & Hibbard were the first to show that Wilder Penfield wasn't completely right about the strict topographic map.

Overlapping Representations (Animal Model)

• A recording was used from the M1 hand representation of a single neuron, with each digit represented using differently colored spheres.
• Sphere size relates to intensity and frequency of firing.

Overlapping Representations (Human Model)

• When S & H studied, there wasn't proper technology to study fully.
• In the early 2000's, fMRI emerged enabling the measurement of activity in the brain.
• S1 = posterior and adjacent to M1 and is more discreet and stricter in arrangement.
• S1 makes up the somatosensory map.

Rethinking the Classic View – Pathway

• Wilder Penfield proposed an idea that M1 is a connector, not a coder, an idea that is wrong.
• WP studied epileptic people using short, mild stimulus, which always results in twitching.
• A short burst is not enough to produce a functional movement.

Functional Movement

• Functional movement is achieved applying a ½ second shock on M1 (longer stimulus)
• Movement, such as hand-to-mouth feeding, demonstrates that M1 is more than a final common pathway and has complex neurons that code for complicated, purposeful movements.

Rethinking the Classic View – Neurons and Pathway

• Georgopoulos (1998) stipulated M1 neurons act like arrows (vectors) pointing in different directions that the brain then combines these signals to determine movement direction (population vector).
• Movement in a particular direction is determined by a population of neurons.
• Vector length equals level of activity for a particular movement direction.
• Georgopoulos' perspective focuses on the direction of M1 encoding movement rather than muscle activity.
• Georgopoulos recorded the activity of a single neuron in M1- tracked when it is active during a motor task.

Raster Plots

• These plots are used to visualize neural activity over time.
• Each row represents a single trial or repetition of a task.
• Each dot represents a spike (action potential) from a recorded neuron.
• Plots are aligned to an event (movement onset) to show firing patterns.
• Raster plots help show how M1 neurons fire for different movement directions.
• More spikes appear in the preferred direction of the neuron.
• Denser spike patterns mean higher firing rates.

Directional Tuning

• M1 neurons fire in relation to movement direction.
• Each neuron has a preferred direction where it fires most.
• Movement direction is determined by neurons working together (population coding).

Visual Motor Rotation

• Visual motor rotation is a change in the relationship between hand movement and visual feedback.
• A shift of visual stimuli is where population vectors are rotated from the direction of the stimulus to the direction of the movement, determined by estimating an angle based on rotation.
• Neurons in motor and sensory areas adapt their firing patterns to compensate for the visual perturbation.
• The neuron responsible for the direction will activate and then will become inactive as the next neuron activates which will continue until the right one is hit.
• Visual motor rotation shows neuron plasticity and predictive behaviors in M1.

Rethinking the Classic View – Pathway

• M1 was not thought of as a coding region by Wilder Penfield and was thought to be only conducting signals.
• Muir and Lemon showed that muscle activity is different for tasks – indicating complex coding in M1.
• Muir and Lemon performed 2 tasks including a precision grip and power grip.
• Precision grip had lots of neuronal activity while power grip had almost none, even while using the same muscles.
• Muir and Lemon's findings proved that M1 codes for complex movements.

Movement Specificity

• Motor learning and neural adaptations are specific to the practiced movement.
• Demonstrates how M1 codes for complex movements.
• Precise motor mapping is needed to understand all ranges of movement that M1 codes for.

Why Understanding Organization is Important

• Understanding organization is important for prosthetics, learning about how the coding of neurons relates to the movement of non-body parts.
• It involves theoretical and neuroscience combined to fit and control the device.
• Prosthetics are controlled by an implanted electrode that can pick up activity of neurons that is then sent to a computer to be interpreted as movement.

Neuroplasticity

• Neuroplasticity: The brain's ability to reorganize itself by forming new neural connections.
• Neuroplasticity allows adaptation to learning, experience, injury, or environmental changes.
• Neuroplasticity generally diminishes with age and peak cortical volume is reached in our mid 20s before pruning (loss of unused neurons).
• Lesions take a long recovery because of diminished neuroplasticity.
• There is a more positive outlook for rehabilitation in a young child.

Neuroplasticity and Movement Practice

• Draganski's study showed how practice can influence cortical density.
• A group of people practiced how to juggle for 6 months and showed an increase in cortical volume in the occipital lobe (hand-eye coordination), bilateral V5/MT and Left intraparietal sulcus.
• When these people did not practice for 6 months, the density returned to baseline.
• This shows the first principal evidence of neuroplasticity – "Don't use it, lose it!"

Dysmelia

• Dysmelia is a general term used for congenital limb abnormalities, where a person is born with malformed or missing limbs and can involve complete absence, shortening, or abnormal development of limbs.
• Dysmelia is caused by thalidomide (a drug given to pregnant women), which is teratogenic (prevents development).
• Dysmelic limbs representation on M1 is smaller and redistributed, which is developmental neuroplasticity.

Supplementary Motor Area (SMA)

• The SMA has direct projections (10%) to the spinal cord.
• It connects to M1 and other cortical areas.
• Direct projections to the spinal cord terminate on a-motoneurons, which control hand muscles.
• The SMA is involved in sequence-specific movements.
• It is active during internally generated movements (self-initiated).
• There is more SMA activity with complex movements.
• The SMA is active for both real and imagined movements, which is important for mental rehearsal.
• The SMA is involved in movement planning rather than execution.
• The more complicated and sequenced a movement, the more SMA activity.
• Mirror neuron activity is observed here; imagining movement activates the SMA similarly to actual movement.
• Motor imagery and execution have overlapping activation patterns in the SMA, which helps in skill acquisition.

Premotor Cortex (PMA)

• The PMA is located just anterior to M1, and positioned more laterally compared to SMA.
• The PMA has fewer direct connections to the spinal cord (10%) compared to SMA.
• There are strong subcortical connections.
• The PMA is triggered by external sensory events and delayed actions.
• It is important for obstacle avoidance and perseveration behaviors (repetitive, ineffective behaviors).
• PMA has less direct control over movement than SMA.
• Many PMA neurons connect to the cerebellum for movement coordination.
• Pantomime tasks (delayed actions) are supported by PMA activity.
• Perseveration behavior involves doing the same action repetitively even if it's ineffective.

M1, SMA, and PMA Activation (Neurophysiology Study)

• Monkeys were tested with external visual stimuli and internally generated movement tasks.
• Raster plots recorded neuron firing rates in M1, SMA, and PMA.
• Findings for M1 (Primary Motor Cortex): visual cue increased neuron activity, internal cue also increased neuron activity.
• Findings for SMA: visual cue showed no major change, internal cue showed significant activity before and during movement.
• Findings for PMA: visual cue was active before, during, and after movement, internal cue showed minimal change.
• M1 is involved in both externally and internally cued movements.
• The SMA is primarily for internally driven movements.
• The PMA is influenced by external stimuli and preparatory activity.

Mirror Neurons

• They were found accidentally while recording single-cell activity in monkeys.
• Neurons activate when watching an action as if the observer was performing it.
• Mirror neurons support imitation, learning, and social interaction.
• 3 conditions where mirror neurons fire in all three cases: a monkey sees another monkey grasping food, a monkey sees a human picking up food, and a monkey picks up food itself.
• This supports the "monkey see, monkey do" theory.
• Functions of Mirror Neurons involve understanding others' actions and emotions.
• They're important for learning through imitation.
• Mirror neurons are possibly linked to autism (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 help with learning, imitation, and social behavior.
• Motor imagery and real movement activate SMA similarly, aiding in motor learning.
• Relevant areas: SMA (Supplementary Motor Area), PMA (Premotor Cortex), VPMA (Ventral Premotor Area), S1 (Primary Somatosensory Cortex), and IPC (Inferior Parietal Cortex).

Lecture 10: Cerebral Asymmetries: Hemispheres

• The brain has 2 hemispheres (right and left) that are identical on the microscopic level but have very different functions.
• Left hemisphere: speech and language (lateralized) and movement praxus (control), and is more likely to be specialized in right-handed people (95% of the population).
• Lesions to the left cause Apraxia.
• Right hemisphere: Haptics (sensory), visual spatial processing, musical abilities, and numeracy.
• These lobes have a crossed nature of control (left controls right, right controls left).

Speech Perception and Production

• Broca was a French man interested in people who have lost the ability to speak.
• Broca performed a post-mortem dissection of the brain and found a stroke or syphilis in the left, frontal hemisphere (Broca's region).
• Wernicke was interested in why people suddenly lose the ability to understand language.
• Wernicke performed a post-mortem exam and found injury in the left temporal lobe region (Wernicke's area).

Communication Disorders

• Broca's Aphasia involves slow and laborious speech, where individuals are unable to articulate the speech that the person wishes to produce, knowing what they want to say but cannot express it.
• Speaking in a sing-song voice can help bypass the Broca's region and engage the right hemisphere, skipping damage.
• Wernicke's Aphasia generates non-meaningful language and lost rule, meaning, and structure, where people are not conscious of their mistakes and think that it has meaning.
• The Right Hemisphere controls automatic language production (memorized, deeply ingrained language).
• The right hemisphere can still produce language, including swearing and counting.

Disconnection Syndrome and Conduction Aphasia

• Broca's region and Wernicke's area are connected by the arcuate fasciculus, which is a superhighway of axon bundles that send info between the two.
• To see this area, use diffusion tension imagery (water molecules).
• Disconnection. a cut to this area can be devastating and leads to speech and processing effects, where there is no awareness of speech production, but the automatic remains unaffected.
• Conduction aphasia is caused by a deficit from disconnection.
• These people can understand what is being said, but can only produce one word.

The Split Brain

• The 2 hemispheres are connected through the corpus callosum, a bundle of fibers.
• People with untreatable epilepsy experience many large seizures throughout the day.
• Split brain procedure separates the corpus callosum and can be a safe way to alleviate epilepsy severity.
• This procedure doesn't allow the 2 hemispheres to communicate, effectively limiting the spread of epileptic seizures, making them less severe.
• Theoretically, this is good, but not allowing communication can have some adverse effects.
• The right and left work independently of each other, which shows specialization.

Lecture 11: Cerebral Asymmetries

• Apraxia is high-level impairment of learned, skilled purposeful movement that cannot be explained by a language, comprehension, motor or sensory deficits.
• To diagnose, you have to exclude other deficits and evaluate speech and limbs.
• A speech, language, and motor deficit is present.
• Ideomotor Apraxia is the inability to take a movement knowledge and translate it into innovatory apraxia.
• Ideomotor apraxia is analogous to Broca's aphasia because the person knows what they want to do, but is unable to produce the movement.
• People with ideomotor apraxia still possess the engrams (instructions) for the movements.
• Ideational Apraxia is an inability to recall a movement from memory.
• A lesion impacts the engrams, and they forget how to perform simple movements.
• Ideational Apraxia arises because of a stroke and is analogous to Wernicke's area.
• Conceptual Apraxia is the inability to understand the relationship between a tool and an object (how to use it).

Dyspraxia

• Dyspraxia is used in a developmental context for clumsy children and as a developmental cognitive disorder.
• Children have 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

• The dichotic listening task, developed by Doreen Kimura, helps 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: a left ear advantage is found, suggesting 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 meaning that functions typically lateralized in the left hemisphere of the general population would be lateralized in the right hemisphere in Down syndrome.
• Studies have shown instead that speech production is lateralized to the left hemisphere, similar to the general population, that movement praxis (planning and coordination of movement) is also lateralized to the left hemisphere and that 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.
• Individuals with Down syndrome struggle with verbal instruction, but perform better when given visual instruction because it bypasses interhemispheric communication

Lecture 12: Descending Motor Pathways: Pyramidal Tract

• This tract involves upper motor neurons and originates in M1, SMA, PMA, and partial cortex.
• It contains over 1 million axons, most of which are myelinated (fast signal conduction).
• It primarily innervates facial, axial, and intrinsic musculature.
• The pyramidal tract is divided into corticobulbar and corticospinal tracts.

Corticobulbar Tract

• The corticobulbar tract connects the cortex to the brainstem and primarily controls facial muscles.

Corticospinal Tract

• This tract controls axial and distal muscles divided further into lateral corticospinal tract as well as ventral corticospinal tract.
• Humans have the most advanced descending motor pathway where 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 the corticobulbar tract.
• Upper motor neurons are the descending tract that originates in the cortex and synapse at the midbrain, where they interface with lower motor neurons.
• They innervate face, neck and head but not the oculomotor.
• Lower motor neurons are considered alpha motor neurons and directly cause movement by sending signals to muscles which causes muscle contraction.
• Rostral innervates upper facial musculature, providing bilateral innervation.
• Caudal innervates lower facial musculature contralaterally.

Beating Heart Illusion

• Blurred Boundaries & Perception: Our brain constructs an image of an object's boundary at any given time.
• When there is no sharp boundary, V1 neurons attempt to differentiate the edges and the changing activation of V1 neurons creates the illusion that the heart is pulsating.
• Visual illusions trick our perception, but they do not affect vision used for action.

Corticobulbar Tract Injury

• Upper Motor Neuron Injury (Stroke): causes selective paralysis, so the deficit is selective to only the lower muscles.
• Lower Motor Neuron Injury (Bell's Palsy) causes paralysis on one side of the face, and lower motor neurons are inflamed and cannot communicate to muscles.

Ventral Corticospinal Tract

• This tract originates in M1 and extends to the spinal cord.
• Most fibers descend uncrossed and primarily innervate axial musculature.
• There are very few monosynaptic connections (fine motor control) meaning that there might be many fibers allowing for coordinated movement of many muscles - propriospinal neurons.
• Lateral Corticospinal Tract originates in M1 and 70-80% of fibers decussate (cross over) at the pyramids in the medulla.
• It primarily innervates intrinsic muscles.
• It has many monosynaptic connections, which supports fine movement and independent digit control.
• The lateral corticospinal tract controls precision grip as well through precise depolarization of axons.

Lecture 13: Motor Units: Alpha (α) Motoneuron

• Alpha (a) Motoneuron serves as the Motor Unit.
• A neuron innervating power-producing extrafusal muscle fibers and is larger than gamma (y) motoneurons.
• Innervation Ratio: a high ratio for large muscles (one neuron controls many fibers) and a low ratio (one neuron controls few fibers) for small muscles.
• Gamma (γ) Motoneuron serves as the Fusimotor Neuron.
• Small neurons innervating intrafusal muscle fibers (proprioceptive).
• They are smaller than a-motoneurons and are oriented parallel to extrafusal fibers.
• They control muscle spindle sensitivity to stretch.
• These neurons are important for reflexes and muscle tone regulation.
• The different type of muscle fiber plays an important role in postural and movement control and the types of movement someone can do are determined by the motor unit type the individual has.

Types of Motor Units

• Fast Twitch, Fatigable (FF) acts as a Fast Motor Unit.
• This unit has the highest conduction velocity (100 m/s) because of the large diameter.
• This unit has a large fiber diameter and innervates fast-twitch muscle fibers (Type II X) for rapid, powerful movements, referring to extrafusal muscle fibers.
• Fast Twitch, Fatigue-Resistant (FR).
• This Fiber has medium conduction velocity (60 m/s) and medium fiber diameter,.
• This unit innervates fast and/or slow-twitch muscle fibers (Type II A).
• Slow Twitch, Fatigue-Resistant (SR) has the function of Slow Motor Unit.
• This fiber has the lowest conduction velocity (40 m/s) and Small fiber diameter,.
• This fiber innervates slow-twitch muscle fibers (Type I) for endurance-based activities.
• There are more fast motor units in short term athletics but less in long term.
• In spinal cord injuries, there is no sustained movement so there is an abundance of FF.

Recruitment of Muscle Fibers

• The muscle unit is invariant from smallest to largest
• Recruitment of muscle fibers increases with the size of force production
• Henneman Size Principle: ordered recruitment of motor units and the associated muscle fibers which leads to a linear progression from smallest to largest.
• The leading causes of falls in older adults is found to be due to incorrect weight shifting.
• This occurs because of the selective loss of fast twitch fibers (Type II X) because they are smaller and less populated.
• There is also demyelination mostly in fast motor units (Type II X) that causes them to become less efficient.
• Fast twitch fibers allow for quick movement to stop falls and in the absence of these, there is an increased risk in older adults (quick postural innervation).

Training Programs

• To prevent falls, there needs to be exercise that is both physically and cognitively engaging.
• Square Stepping: involves walking on a pattern of squares and promotes weight transferring and social engagement.
• Wobble Board: balancing on a board 5 times a week has long lasting results for a decrease in falls.

Lecture 14: Oculomotor Control: Retinotopic Map

• A map of the superior colliculus that shows neural distribution through LED lights.
• This can help scientists identify and study disorders in M1.

Retinotectal Pathway

• Involuntary prosaccade: involuntary draw to the target.
• The primate visual pathway is prosaccades.
• Stimulus, Retina, SC, BS Nucelli, Eye.
• Geniculostirate Cortex: Detects deficits in executive function from voluntary antisaccades.
• The primate Visual Pathway – Antisaccades, Stimulus, Retina, Thalamus, LGN, V1, Parietal Cortex, DLPFC, Eye.

Executive Function

• DLPFC: critical for executive function and is activated for antisaccades (inhibitory control).
• If there is damage (stroke), humans will have difficulty producing antisaccades and the DLPFC is very important in the process of antisaccade generation.
• Schizophrenia is a mental disorder that makes it hard to tell the difference between real and fake, think clearly, have normal emotional response, and adhere to social norms.
• People with schizophrenia often have a different brain structure, where FEP = larger lateral ventricles.
• These are fluid-filled and linked to cortical atrophy.
• There is also a smaller DLPFC, making it harder to preform EF tasks.
• Patients cannot perform antisaccades or inhibitory actions.

Inhibitory Dysfunction

• Persons with SZ produce more antisaccade directional errors (30- 70%) than healthy controls. Genetic studies may benefit from using the antisaccade task as a phenotype within SZ families
• Siblings had a similar pattern to siblings diagnosed with schizophrenia.
• This can be a biomarker and improve detection of gene carriers and the power to detect linkage enhanced. Individuals with schizophrenia, when they perform EF tasks, there is much more activity in the frontal lobe, which implies it is harder to inhibit unwanted active regions .
• People with schizophrenia have difficulty regulating cortical active that is appropriate for a task.

Foveal vs. Peripheral Vision

• Foveal Vision: The center part of the retina, with a high concentration of retinal ganglion cells.
• Because of this high density of ganglion cells, foveal vision has very high spatial resolution.
• This part of the retina allows for detailed and sharp vision, essential for tasks like reading and object recognition.
• Peripheral Vision: The peripheral retina has a lower concentration of retinal ganglion cells.
• This results in low spatial resolution, making peripheral vision less detailed.
• Peripheral vision is more specialized for motion detection and spatial awareness rather than fine details.

Structural Asymmetry of the Eye and Cortical Representation

• The eye exhibits structural asymmetry, meaning different parts of the retina are mapped onto specific regions of the primary visual cortex (V1).
• Cortical Magnification: The foveal region is represented by a much larger area in V1 compared to the peripheral vision enabling the brain to devote more resources to processing central visual information than peripheral vision.
• Cortical Magnification occurs not only in the visual field but also in the retina itself where the retina plays an important role in movement control through its magnification process.

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 has more retinal ganglion cells than the inferior hemiretina, leading to greater cortical magnification in V1 for the lower visual field.
• Visual Field Processing.
• When people fixate on Fixation 1, they respond faster and with more accuracy because the target appears in their lower visual field.
• If they fixate on another point where the target falls into the upper visual field, their response time is slower and movements are less precise.
• The "Head in the Clouds" Phenomenon involves people tending to look up when engaging in complex cognitive tasks.
• This is because the upper visual field is better at processing abstract and cognitive information.
• Movement-related tasks engage the lower visual field, which makes it critical for physical actions and spatial awareness.

Lecture 15: Scientific Method

• The Goals of Science are to Understand, Describe, Explain, Predict, and determine Correlational vs. cause-effect.
• Empiricism refers to Verification via observation.
• Hypothesis Testing involves a supposition or proposed explanation made based on limited evidence as a starting point for further investigation.
• A well-done experiment must have a prediction based on empiricism.
• Independent Variables are the variables that researchers manipulate to observe their effect on the dependent variable.
• Dependent Variables are the measured outcomes that depend on the independent variable.

Lecture 16: Classifying Motor Skills: Task Organization

• Discrete Skill: A skill organized such that the action is usually brief and has a well-defined beginning and end.
• Serial Skill: A skill characterized by serial discrete actions connected in a sequence.
• The order of the actions is critical to performance success.
• Continuous Skill: A skill that unfolds without a recognizable beginning or end, in an ongoing and often repetitive fashion.

Motor and Cognitive Elements

• Motor Skill: Primary determinant of movement success is the quality of the movement.
• Cognitive Skill: Primary determinant of success is the quality of the performer's decision making.
• Level of Environmental Predictability.
• Closed Skill: Skill performed in an environment that is predictable or stationary and that allows individuals to plan their movements in advance.
• Open Skill: Skill performed in an unpredictable or in motion environment, requiring individuals to adopt their movement in response to the dynamic properties of their environment.

Lecture 17: Measuring. Evaluating, and Interpretation in the Movement Neurosciences

• Levels of Analysis: Performance outcome, Describing the movement, and Measuring activity of the central nervous system (CNS).
• Performers who accomplish an action in less time are more efficient.
• Reaction Time: The interval between the onset of a signal (stimulus) and the initiation of a response.
• Simple reaction time (SRT): The time taken to respond to a single, expected stimulus with a single response (250-350ms), which is basic and measures the base speed of information processing.
• Choice reaction time (CRT): The time taken to respond to one of multiple possible stimuli, each requiring a different response.
• CRT requires Higher level of cognitive and EF control.
• Discriminant reaction time (DRT): The time taken to respond only to a specific stimulus while ignoring others.
• DRT requires Specific task inhibitory control and allows high degree of errors if there is a lesion.
• Increasing the number of SR options will increase the RT.

Measuring Reaction Time

• Provide a warning signal and a randomized foreperiod before a "go" signal.
• Fractionating Reaction Time.
• Premotor Time (80%): Time taken to detect, process, and send information to the alpha motor neurons and majority of the reaction time.
• Motor Time (20%): when Muscles begin activation, but movement hasn't started yet. Electromyography (EMG) shows muscle activation before visible movement.
• Injuries and Reaction Time:
• Upper motor neuron injury increases premotor time reflecting difficulty planning movement.
• Lower motor neuron injury increases motor time reflecting difficulty executing movement.
• Time from the initiation to completion of a movement is the Movement Time (MT).
• Total Response Time (TRT) = RT + MT.
• Real-World Application of Reaction Time.
• The International Amateur Athletic Federation (IAAF) defines a false start as any movement in less than 100 ms after the starter's gun.
• Prosaccades are Fast, reflexive eye movements used in daily life with a short neural network that is unable to react in less than 150 ms.

Lecture 18: Measuring. Evaluating, and Interpretation in the Movement Neurosciences

• Measures of Accuracy.
• Constant Error (∑(X1 – T)/N): the average signed error score providing a measure of bias (under or overshooting).
• The sum of where you ended up and where the target is divided by the number of trails.
• Variable Error ( ∑ X 1 − T 2 /N): a measure of consistency (or variability) across a series of trials.
• Absolute Error (Σ|X 1 – T|/N): the average unsigned error score.
• Continuous Task.
• Root mean squared error: the average unsigned error for a continuous task (SD). Done in mirror so everything is opposite and As time goes on, performance improves. Measuring, Evaluating, and Interpreting Movement (Qualitative Description).
  • Uses verbal descriptions and time-lapse photography to analyze movement.

Movement Kinematics (Quantitative Analysis)

• Displacement: Spatial position change of an effector (an arm). Velocity: Speed of movement.
• Acceleration: Change in velocity over time.
• Characteristics of Velocity Profiles. Slight positive skew: More time spent after peak velocity.
• Peak velocity increases with displacement: Larger movements = Higher peak velocity.
• Peak acceleration scales with peak velocity.

Neurological Control of Movement

• Parietal Cortex Lesions: Can cause apraxia (movement disorder). Disrupts coordination between wrist and elbow movement.