Exam 2 Study Guide

8: Attention

• Affordance Competition Hypothesis

  • affordances - opportunities for actions

    • the brain uses the constant stream of sensory information arriving from the environment through sensorimotor feedback loops to continuously specify and update potential actions and how to carry them out

  • competition

    • our internal state, longer-range goals, expected rewards, and anticipated costs provide information that can be used to asses the utility of the different actions

    • one option wins out the other competitors

  • proposes that the processes of action selection (what to do) and specification (how to do it) occur simultaneously within an interactive neural network, and they evolve continuously

  • even when we are performing one action, we are performing the next

    • parallel processing of multiple actions

    • develop multiple plans in parallel

• Alpha Motor Neuron

  • “innervate muscle fibers and produce contractions”

  • pyramidal tract

  • The neurons that terminate on muscle fibers, causing contractions that produce movements

  • Originate in the spinal cord and exit through the ventral root of the cord

  • action potential in apm releases neurotransmitter acetylchloline

    • makes muscle fibers contract

  • provide a physical basis for translating nerve signals into mechanical actions, changing the length and tension of muscles

  • apms can be activated by cortex or spinal interneurons

  • peripheral input from muscle spindles

    • sensory receptors embedded in the muscles that provide information about how much the muscle is stretched

    • axons of spindles form an afferent nerve that enters the dorsal root of the spinal cord and synapses on spinal interneurons that project to the apm

    • stretch reflex

      • if the stretch is unexpected, the apms are activated, causing the muscle to return to its original length

      • reflexes allow — postural stability and protective functions

        • reflexes can contract a muscle to avoid a painful stimulus well before pain is consciously perceived

        • helps maintain balance without control from the brain

• Apraxia

  • a disorder in which the patient has difficulty producing coordinated, goal-directed movement, despite having normal strength and control of the individual effectors

  • NOT due to loss of muscle control

    • observed with premotor, prefrontal, or parietal lesions

      • usually in the left hemisphere

• Associative Stage

  • intermediate stage of skill acquisition

  • errors in the initial understanding detected and eliminated

  • association between movement are increased — movements become smoother as the associations between correct movements are strengthened

    • new and efficient motor programs (composition)

      • new, more efficient motor programs begin to emerge

      • movements begin to become less reliant on conscious thought

  • declarative knowledge (explicit facts) transforms into procedural knowledge

    • skill can be executed with less cognitive effort

• Ataxia

  • A movement disorder associated with lesions or atrophy of the cerebellum

  • ataxic movements are clumsy and erratic, even though muscle strength is normal

  • impairment of coordination despite intact knowledge of appropriate action

  • associated with damage to cerebellum

    • other regions as well

  • due to failure in motor timing

• Autonomous Stage

  • expert stage of skill acquisition

  • motor programs become increasingly automatic

  • speed and efficiency improve

    • adjust parameters in procedures (without disrupting performance)

    • speed, force, trajectory

  • procedural knowledge (dominates)

    • skill is performed without relying on verbal instructions

    • verbalization decreases

    • movements are controlled by implicit, well-learned motor programs

  • focus shifts to conceptual goals rather than the mechanics of movement

• Basal Ganglia

  • involved in motor control and learning

  • reciprocal neuronal loops project from cortical areas to the basal ganglia and back to the cortex

  • five subcortical nuclei

    • input: two nuclei form of striatum

    • output: internal segment of GP, part of SN

    • modulate activity: rest of SN, STN, external segment of GProle

      • Striatum

        • (1) Caudate

        • (2) Putamen

      • (3) GP: Globus Pallidus

        • GPe — external segment

        • GPi — internal segment

      • (4) SN: Substantia nigra

        • SNc pars compacta

        • SNr pars reticulata

      • (5) STN: Subthalamic Nucleus

      • Direct Pathway

        • Inhibits GPi/SNr

        • Decreases inhibition on Thalamus

        • Increases activity of thalamocortical circuit

      • Indirect Pathway

        • Inhibits GPe

        • Decreases inhibition on GPi/SNr and STN

        • Increases GPi/SNr activity

        • Increases inhibition on Thalamus

        • Decreases activity on thalamocortical circuit

      • pathways work in opposition

      • produce tonic inhibition on thalamocortical circuit

      • direct pathway faster

        • excites thalamocortical circuit first

        • inhibits thalamocortical circuit second

  • Parkinson’s and Huntington’s disease

• Basal Ganglia and Cognition

  • role of BG are also deeply connected to prefrontal cortex (responsible for higher-order cognitive processes)

  • Executive Function

    • suppress inappropriate responses and enhance relevant actions

    • planning, decision making, cognitive flexibility

    • dysfunction in these circuits is linked to impulsivity and difficulty switching between tasks

      • ADHD, Parkinson’s

  • Reinforcement Learning and Habit Formation

    • Dopaminergic system (especially in the striatum) is crucial for reward-based learning

    • BG help encode reward prediction errors

      • help brain learn from feedback (successes and mistakes)

      • repeated behaviors become automatic habits as the BG reinforce patterns of behavior

  • Working Memory and Attention

    • BG contributes to working memory

      • through connections with the dorsolateral prefrontal cortex (DLPFC)

    • selective attention, BG ensures that relevant stimuli are prioritized while distractions are suppressed

    • disruptions in BG can lead to difficulty maintaining focus or filtering out relevant info

  • Cognitive Flexibility

    • ability to shift between thoughts or patterns

    • BG plays a role in helping individuals adapt to new rules or changing environments

    • damage to BG can lead to difficulty adapting to changes and inflexible thinking in Parkinson’s disease

  • disorders in BG and cognition

    • Parkinson’s

    • Huntington’s

    • ADHD

    • OCD

• Bradykinesia

  • Slowness in the initiation and execution of movements

  • prominent symptom in Parkinson’s

• Brain-Machine Interface

  • A device that uses the interpretation of neuronal signals to perform desired operations with a mechanical device outside the body

  • signals recorded from neurons or EEG can be used to move a prosthetic arm

• Caudate Nucleus

  • part of the striatum

  • controls movement

    • works with BG to start and adjust movements so they are not too slow or too jerky

    • walking

  • helps u learn and make decisions

    • learn from experience and make better choices

    • finding a shortcut

  • forms habits

    • turns repeated actions into automatic habits

  • regulates emotions and behavior

    • works with other brain areas to control impulses and repetitive behaviors

    • in OCD, caudate doesn’t stop certain thoughts or behaviors, leading to compulsive actions

  • Huntington’s

    • caudate shrinks

    • uncontrollable movements and memory loss

  • Parkinson’s

    • caudate doesn’t get enough dopamine

    • causes slow movement and trouble making decisions

  • OCD

    • caudate overreacts

    • makes people repeat behaviors

      • checking the door a bunch of times

  • ADHD

    • caudate doesn’t control attention well

    • leads to impulsivity and distractibility

• Central Pattern Generators

  • networks of neurons in the spinal cord or brainstem can generate rhythmic, coordinated movements without needing continuous input from the brain

  • CPGs allows movements to be repeated in a coordinated and rhythmic manner

  • CPG can continue functioning without the brain micromanaging each movement

  • CPGs are found in lower neural centers

  • CPs work even if the brain is not actively controlling them

  • sensory input helps adjust and refine the movement

  • two main neurons in a CPG

    • excitatory neurons

      • activate muscle contraction

    • inhibitory neurons

      • temporarily suppress opposing muscle groups, creating alternate movements

• Cerebellum

  • critical roles

    • motor coordination

    • balance and posture

    • motor learning

    • error correction

    • timing of movements

      • Cerebellum and Cognition

        • prefrontal cortex (decision-making and problem-solving)

        • attention and focus

          • helps sustain attention and shift focus between tasks

        • working memory

          • assists in short-term storage and manipulation of information

        • language processing

          • involved in word retrieval and sentence construction

        • executive functioning

          • aids in planning, organizing, and adapting to new information

      • Cerebellum and Error Correction

        • receives sensory feedback

          • cerebellum compares intended movement (from the motor cortex) with actual movement (sensory feedback)

        • detects errors

          • if movement is incorrect cerebellum recognizes discrepancy

        • adjusts movements

          • sends signals to the motor cortex and spinal cord to correct movement for next time

      • Cerebellum and Timing

        • biological clock

        • motor timing

          • synchronize movements

          • playing the piano and hitting the required keys

        • speech timing

          • ensures smooth transition between words

        • perception of time

          • helps estimate durations and predict events

          • knowing when to jump over an obstacle while running

• Chorea

  • movement disorder

  • involuntary, unpredictable, and irregular muscle movements

• Cognitive Stage

  • beginning stage of skill acquisition

  • Declarative knowledge

    • consists of our conscious memory for both facts we have learned (semantic memory) and events we have experiences (episodic memory)

    • facts are memorized and rehearsed

  • high working memory and attentional demands

    • learner is consciously thinking through every moment

  • errors are frequent, movements are slow and uncoordinated

  • instructions and demonstrations effective

    • learner is actively trying to learn skill

  • what type of motor programs exist here?

    • motor programs are not well developed

    • movements are largely guided by verbal instruction and feedback

• Conceptual Level

  • highest level of movement planning

  • at the top of the skilled action hierarchy

  • goals and intentions are formed before an action is executed

  • corresponding to a representation of the goal of the action

• Corticospinal Tract

  • important for control of voluntary movements

  • bundle of axons that originate in the cortex and terminate monosynaptically on alpha motor neurons and spinal interneurons

  • many of these fibers originate in the primary motor cortex, although some come from the secondary motor areas

  • also pyramidal tract

• Direct Pathway

  • facilitates movement by removing inhibition from the thalamus

  • motor cortex —> striatum —> Globus Pallidus (internal) —> Thalamus —> motor cortex —> movement

  • neurotransmitter: Dopamine (D1 receptors activate this pathway)

  • increases movement

• Dystonia

  • involuntary muscle spasms and twisting of the limbs

• Extrapyramidal Tract

  • originate from subcortical nuclei

  • terminate in both contralateral and ipsilateral regions of the spinal cord

  • control posture, balance, tone, fine movements

  • a collection of motor tracts that originate in various subcortical structures, including the vestibular nucleus and the red nucleus

• Forward Model

  • the idea that the brain generates predictions of expected events

  • in motor control, the prediction of the expected sensory consequences of a movement

  • helps with error correction

• Gamma Motor Neuron

  • part of the proprioceptive system, important for sensing and regulating the length of muscle fibers

  • regulate muscle tone and reflexes by controlling spindle sensitivity

  • they work with alpha motor neurons to ensure smooth, coordinated movements

  • dysfunction can cause spasticity, poor posture control, or weak reflexes

• Globus Pallidus

  • structure within BG that plays a crucial role in motor control

  • Globus Pallidus Internus (GPi)

    • direct output to the thalamus, primarily inhibits movement

  • Globus Pallidus Externus (GPe)

    • indirect pathway relay, modulates movement suppression

  • together they regulate movement by balancing excitation and inhibition in motor circuits

  • regulates voluntary movement

  • suppresses unwanted movements

  • plays a role in the Direct & Indirect pathways

  • influences muscle tone

• Hemiplegia

  • paralysis of the contralateral limb(s)

  • lesions of the primary motor cortex that lead to loss of voluntary movements on the contralateral side of the body

• Hemiparesis

  • weakness, impaired control of contralateral limb(s)

  • partial paralysis on one side of the body, unilateral weakness

• Huntington’s Disease

  • hereditary neurodegenerative disorder

  • Degeneration of striatum (part of BG)

    • cell death up to 90%

  • symptoms

    • clumsiness, balance problems, restlessness

    • Chorea: abnormal involuntary movements, often involving multiple major muscle groups

• Hypokinesia

  • reduced ability to initiate voluntary movement

  • symptoms in Parkinson’s

• Implementation Level

  • at the bottom of skilled actio hierarchy

  • executes the movement through muscles

  • specific motor actions to achieve goal

  • converts motor plans into actual muscle contractions

• Indirect Pathway

  • prevents unwanted movements by inhibiting the thalamus

  • motor cortex —> striatum —> Globus Pallidus (external) —> STN —> GP (internal) —> Thalamus —> motor cortex

  • neurotransmitter: Dopamine (D2 receptors inhibit this pathway, allowing movement)

  • decreases movement

• Mirror Neurons

  • neuron that shows similar responses when an animal is either performing an action or observing that action produced by another organism

  • a mirror neuron responds when you pick up a pencil and when you watch someone else pick up a pencil

  • hypothesized to provide string link between perception and action, perhaps providing an important basis for the development of conceptual knowledge

  • essential for comprehending and anticipating actions

  • expert dancers vs novice watching performance

  • yawning

  • crossing arms

• Motor Program

  • a full set of commands to perform an action

  • commands can be executed without feedback

  • commands are abstract

  • same program can be used under different conditions

  • same programs can be used for different effectors (limbs)

• Negative Symptoms

  • the loss or reduction of normal behaviors

    • loss of motivation

    • movement

• Parietal and Motor Control

  • spatial awareness and body positioning

    • helps the motor system understand limb position

  • sensory motor integration

    • combines sensory input to guide movement

  • planning goal-directed movements

    • works with the premotor cortex to prepare actions

    • object interaction and grasping control

      • helps coordinate hand movements when reaching for objects

• Parkinson’s Disease

  • also a degenerative disorder

  • degeneration of Substantia Nigra Compacta

    • reduced dopamine levels up to 90%

  • Positive Symptoms

    • resting tremor: decreases or disappears with volitional movement

    • rigidity: stiffness due to simultaneous activity of agonist and antagonist muscles

  • Negative Symptoms

    • disorders of posture and equilibrium

    • Bradykinesia — slowness of movement execution

    • Hypokinesia — absence of voluntary movement

• Perception Action Cycle

  • continuous loop in which the sensory input (perception) influences movement (action), and movement provides new sensory feedback, which then refines future actions

  • fundamental for adaptive motor control, learning, and decision making

• Population Vector

  • a representation of movement direction, calculated from activity of multiple neurons

  • groups of neruonsencode movement as a collective signal

  • sum of the preferred directions of individual neurons within a group that represents the activity across that group

  • reflect the aggregate activity across the cells, providing a better correlation with behavior than that obtained from the analysis of individual neurons

• Positive Symptoms

  • the addition of abnormal behaviors or experiences

  • hallucinations

  • tremors

• Preferred Direction

  • property of cells in the motor pathway, referring to the direction of movement that results in the highest firing rate of the neuron

• Prefrontal and Motor Control

  • planning and initiating movements

    • decides when, how, and why to move

  • executive function and decision making

    • evaluates different movement options before execution

  • inhibition of unwanted movements

    • suppresses reflexive or inappropriate actions

  • learning and adapting movements

    • involved in motor learning and habit formation

• Premotor Cortex

  • secondary motor area that includes the lateral aspect of Brodmann area 6, just anterior to the primary motor cortex

  • although some neurons in the premotor cortex project to the corticospinal tract, many terminate on neurons in the primary motor cortex and help shape the forthcoming movement

  • plans, coordinates, and prepares voluntary movements

• Primary Motor Cortex (M1)

  • region of the cerebral cortex that lies along the anterior bank of the central sulcus and pre-central gyrus, forming Brodmann area 4

  • some axons originating in the primary motor cortex form the majority of the corticospinal tract

    • others project to cortical and subcortical regions involved in motor control

  • contains a prominent somatotopic representation of the body

  • executes and refines voluntary movements

• Putamen

  • large, rounded structure in BG, near caudate nucleus

  • part of striatum

  • movement control

    • regulates voluntary movement

  • motor learning

    • habit formation

    • repetition based learning

  • sensory motor integration

    • receives sensory input and helps translate it into coordinated motor commands

  • cognitive functions

    • motivation

    • decision making processes

• Pyramidal Tract

  • mass of axons resembles a pyramid as it passes through the medulla oblongata

  • also CST where axons that exit the cortex and project directly to the spinal cord

  • originate from the cortex (M1)

    • 90% contralateral

    • some are more than 1 meter long

  • primary control of muscles

• Response System Level

  • intermediate level in the hierarchical skill of action

  • organizes motor programs and selects the best movement strategy

  • determines how to execute movement (sequence, force, timing)

  • motor system to achieve goal

• Sensory Prediction Errors

  • involved in forward model

  • the difference between the predicted sensory input and actual sensory input received from the environment

• Skill Acquisition and The Brain

  • learning how to perform actions with increasing efficiency, precision, and automaticity

  • Stages of Learning

    • Cognitive Stage

    • Associative Stage

    • Autonomous Stage

• Stretch Reflex

  • helps maintain balance without control from brain

  • muscle contraction that occurs in response to muscle stretch, providing a feedback mechanism to help the muscle resist overstretching and maintain posture

  • monosynaptic reflex

    • involves a direct connection between a sensory neuron and a motor neuron

• Striatum

  • largest component of BG

  • consists of putamen and caudate nucleus

  • motor control

    • helps coordinate voluntary movements

    • processed both sensory and motor signals

  • reward and motivation

    • reward-based learning, motivating movement based on rewards

  • cognitive control

    • decision making

    • habit formation

  • action selection

    • works with other BG structures to choose the best action and inhibit inappropriate ones

• Subthalamic Nucleus

  • lens-shaped structure located beneath the thalamus

  • part of indirect pathway in the BG circuit

  • movement inhibition

    • inhibit unnecessary movement by activating GPi

  • error detection and correction

    • STN detects errors and helps adjust motor plans accordingly

  • regulation of motor pathways

    • influence the direct and indirect motor pathways

    • balancing movement initiation and suppression

• Supplementary Motor Area

  • medial surface of frontal lobe

  • involved in planning, initiating, and coordinating voluntary movements

  • important role in sequential actions and bilateral movements

• Identify the direct and indirect pathways of the basal ganglia with their excitatory or inhibitory connection on the adjacent figure (2). Imagine you typing a word on your keyboard. Describe how direct and indirect the pathways work together to ensure you type each letter in the correct order (2). Describe the deficit in this system in patient with Parkinson’s disease and how it leads to negative symptoms (2). Describe the deficit in this system in patients with Huntington’s disease and how it leads to chorea or dystonia (2).

9: Memory