Neuro 2 exam 1

Regions of the Basal Ganglia

Striatum: Caudate Nucleus and Putamen

Globus Pallidus: Internal and External segments (GPi/GPe)

Subthalamus Nucleus (STN)

Substantia nigra- pars compacta (SNc) and pars reticulata (SNr)

Substantia nigra pars compacta

Contains dopamine producing neurons for motor control, reward, learning and enforcement

Basal Ganglia have

Strong inhibitory baseline activity

• primary modulatory areas in the motor system

Role of Basal Ganglia in movement

Synch cortical motor activity

Modulate movement by influencing which motor programs are facilitated or inhibited

Regulate initiation and execution of movement

Hypokinetic

Basal ganglia has too much inhibition

• reduced movement

Hyperkinetic

Basal ganglia has too little inhibition

• excessive, involuntary movement

Pathway of motor signals throughout the brain to the muscles

• 1) Posterior parietal cortex

  • Sensory information and target location

• 2) Prefrontal cortex

  • Plan movement and predict outcomes

• 3) Premotor cortex and supplementary motor area

  • Prepare and sequence movements

• 4) Primary motor cortex (M1)

  • Issue motor commands

In the brainstem of motor signals throughout the brain to the muscles

Axons from M1 connect to the brainstem and spinal cord

• all relevant descending motor fibers cross over at medulla

Posterior parietal cortex

Sensory information and target location to guide movements

• sensory feedback sustains movements

Prefrontal Cortex

Responds to sensory signals that lead to movement

• Calculate predictable outcomes

• Plans movements using the executive supervisory attentional system (SAS)

Premotor Cortex

Prepares and sequences movements

• Integrates information about a target in space with body information (spatial) to organize movement direction

Supplementary Motor Area (SMA)

Helps prepare and sequence movements

• Coordinating movements involving BOTH hands

Primary Motor Cortex (M1)

Controls voluntary movements through descending projections to the brainstem and spinal cord

Cerebellum

Coordinates movement, timing, accuracy, and error correction

Bimanual Coordination formed

Coordinating movements of both hands/limbs

• Supplementary motor areas

• Planning activates both hemispheres, the communication produces crosstalk (interference between movement goals)

Where in motor system does neural signal cross midline

At the level of the medulla

• where descending corticospinal motor fibers cross over (decussate)

• Contralateral control

Contralateral Control

Left primary motor cortex controls right side of body

• right primary motor cortex controls left side of body

Graziano conclusion about movement sequences

Motor cortex is specialized for controlling coordinated movements rather than individual muscles

Electrical Stimulation of portions of M1

Create complex, coordinated, multi-jointed movements that are useful

• not isolated muscle contractions

How do neurons code for movement direction

Neurons in M1 show directional tuning

• each neuron has a preferred direction of movement (responds to every range of direction)

Georgopoulos recorded neurons while monkeys moved joystick in different directions

Found that individual neurons fired most strongly for particular movement directions

• Population Vector

Population vector

Each neuron contributes based on its preferred direction and firing rate

Activity of population is averaged

Resulting population vector represents intended movement direction

Primary neurotransmitter responsible for supporting motor control and reward processing

Dopamine system in the midbrain

• Motor control, reward, learning, reinforcement

• Dopamine loss in Parkinson=disrupt basal ganglia function= difficult moving

Motor symptoms of Parkinson disease

Hypokinetic symptoms

• Delay in movement sequences with shuffling walk

• difficulty preparing movement sequences into plan

• Rigidity

• stationary tremors

Akinesia

Lack of spontaneous movement (in parkinson)

Bradykinesia

Slowness of movement (in Parkinson)

Behavioral effects in parkinson

not evident until approximately 60 percent of substantia nigra cells and 80 percent of dopamine have been lost

• treatments: L-DOPA and Deep Brain Stimulation (DBS)

Motor symptoms of Huntington’s disease

Hyperkinetic symptoms

• excessive, involuntary movements

• Rapid, jerky movements of the limbs, head, and face

• Degeneration of neurons in the striatum, in the caudate nucleaus and putamen

Chorea

Involuntary, excessive movements (huntington)

Dystonia

Contorted or abnormal postures

Four cortical regions for skilled movement

Posterior parietal cortex

Prefrontal Cortex

premotor and supplementary motor cortex

primary motor cortex (m1)

What role does the four cortical regions for skilled movement play

• 1) Posterior parietal cortex

  • guide movement

• 2) Prefrontal cortex

  • calculate movement using SAS

• 3) Premotor cortex and supplementary motor area

  • organize movement direction

  • BIMANUAL COORDINATION

• 4) Primary motor cortex (M1)

  • voluntary movements (sending descending motor signals to brainstem and spinal cord)

How did Evarts test movement coding in monkeys

Recorded activity of neurons in the wrist region of the primary motor cortex

• Found: neuronal activity tracked movement planning, exection, and force

• Motor cortex neurons endoce characteristics of movments

How did Georgopoulos test movement coding in monkeys

Recorded M1 neuronal activity while joystick moved in directions

• Neurons and directional tuning

  • Each neuron had preferred direction

Population vector

Combined activity of neurons produces, represents direction of resulted movement

Brain Computer Interface translate brain activity into robotic movements

Neural signals associated with actions such as reaching or handwriting is recorded and encoded by computer

• computer translates patterns into commands that control a device or text

Contrast brain structures affected and corresponding neurotransmitter actions disrupted by parkinson and huntington

Both affect basal ganglia

• Parkinson: degeneration of dopamine neurons in substantia nigra (striatum)

  • Disrupts balance between direct and indirect basal ganglia pathways

  • Increase inhibitory-ness and produce hypokinetic symptoms

• Huntington

  • Degeneration of striatal neurons, indurect pathway

  • Reduces suppression of unwanted movements and produce hyprekinetic symptoms

Huntington caused by

Caused by genetic HTT disease, unlike Parkinson

• Parkingson is degeneration of dopaminergic neurons

In conclusion: Parkinson is HYPOKINETIC

Affected- Substantia nigra

Neurotransmitter- decreased dopamine

Movement- slow

Symptoms- Bradykinesia, akinesia, rigidity, resting tremor

Treatment- L-DOPA and Deep Brain Stimulation

In conclusion: Huntington is HYPERKINETIC

Affected-Striatum (caudate nucleus and putamen)

Neurotransmitter-Disrupted inhibitory signaling (GABA), striatal neurons degenerate

Movement- too much

Symptoms-Chorea, dystonia, rapid movements

Cause- HTT gene

Fritsch and Hitzig

Electrical stimulation of the cortex induces movement

• motor cortex has topographic organization

Graziano

Portions of M1 evoke coordinated, multi-joint movements

• not just muscle contractions

Evart

M1 neuronal activity tracks wrist movement planning, execution, and force

Georgopoulos

M1 neurons have preferred movement directions

• population activity predicts movement direction

What is attention

Process by which certain information is selected for further processing and other information is discarded

• supports momentary awareness and affects how we analyze sensory information, encode information into memory

  • Process semantically and act on it

What is inattentional blindness

Failure to nice a visible stimulus because attention is directed somewhere else

• stimulus visible but not consciously noticed because attention is directed elsewhere

Overt attention

Directing attention towards stimulus by moving the eyes or head towards it

Covert attention

Shifting attention without moving the eyes

• Eyes fixed on center of screen, but attention is on something else in visual field

Helmholtz demonstrated that people could

perceive letters more clearly within focus of their mental attention, even if eyes are elsewhere

• covert attention

Three primary features of attention

Voluntary- attention that can be intentionally direction

Selected in nature- some information prioritized over other information

Limited capacity- brain cannot fully process every stimulus at once

How does general arousal/alertness differ from attention

One refers to the general state of wakefulness and readiness to respond

The other refers to the selective processing of a particular information while another is ignored

• selective attention

Two primary types of attention

Voluntary and Involuntary attention

Voluntary

ENDOGENOUS: Top down

• goal directed and intentional

• internally generated

• directs attention towards information

  • (search room for phone)

Involuntary

EXOGENOUS: Bottom up

• stimulus driven

• externally generated

• captures attention and reorient us to environmental information

  • (Turning towards unexpected sound)

Memory trick for attention

Top-down= goal directs attention

Bottom-up= stimulus captures attention

Essential mechanism for how the brain modulates attention processing

GAIN CONTROL

• attention network changes the excitability and responsiveness of neurons in sensory system including sensory cortex and thalamus

  • Signal: amplification of selected information

  • Noise: reduction of non-selected information

Attention does not turn sensory processing on or off

They continually process incoming information, but attention adjusts how strongly that information is represented

What is an attentional blink

Temporary limitation in the ability to detect a second target with 2 targets appear in rapid succession

In rapid serial visual presentation task (RSVP)

Participants see a fast stream of visual items and identify 2 targets

• detecting the second target is impaired when t appears 150-450 milliseconds after the first target

  • Brain limited processing capability to process first and detect second

What is Hemispatial Neglect syndrome

disorder of attention in which a person fails to attend or show awareness of the side of space opposite of a brain lesion

• neglect of the left side of space following damage to the right inferior parietal region

Behavioral evidence of Hemispatial Neglect

Ignoring stimuli or object on left side

Eating from food on the right side only

Allocentric vs egocentric neglect

Left side of object vs left side of space relative to the body

• left side of apple vs only seeing apple on right side of body

Damage to which brain region is responsible for hemispatial neglect syndrome?

Lesion: Right inferior parietal lobule

• regions associated with the temporoparietal attention network

• Right hemisphere= role in spatial attention

• Right parietal damage causes left side neglect

What evidence do we have of limited attention capacity in the visuospatial domain

Tresiman and collages

• when searching for a single feature, the target pops out, and search time is constant as the number of distractors increase

• while searching for a conjunction of features, search time increases as the number of distractors increases

  • Conjuction searches require more attention and involve sequential processing

What evidence do we have of limited attention capacity in the temporal domain

RSVP tasks

• participant identify 2 targets appearing in rapid stream of visual stimuli, the ability to detect second target is impaired when it appears 150-450 milliseconds after the first target

  • Attentional blink

  • Attention has limited processing capacity over time

Hermann von Helmholtz research approach and key conclusion about attention

Kept his eyes focused on a central location while directing his mental attention towards different locations in the visual field

• he could perceive letters in the focus of his mental attention clearly than letters outside that focus

• Covert attention (attention shift independently of eye movements)

Anne Treisman and college series studies of visual search

Feature Integration Theory

• detecting a single feature produces a pop out effect with little change in search time as number of distractors increase

• suggest parallel processing of individual features

• detecting conjunction of multiple features takes longer as number of distractors increase

  • Attention is required to combine features into a unified representation

Conjunction searches involve

Sequential or serial processing and depend on top-down attention (DLPFC and FFF)

Top down and bottom up

Top down: dorsolateral prefrontal cortex and frontal eye fields

Bottom up: primary visual cortex and posterior parietal cortex

Describe how the brain engages attention control networks

Regulate processing in the sensory cortex and thalamus

• Gain Control

• attention modulates sensory processing

Gain control in the attention control network

• neurons in this area influence the excitiability of neurons in sensory areas, enhancing responses to relevant information and reducing responses to irrelevant information

Dorsal frontoparietal network

Goal oriented and top down attention

Ventral Frontoparietal network

detect unexpected or behaviorally relevant stimuli and reorient attention

Identify top down and bottom up controllers of attention and how they interact to modulate attention

Interact to determine which information receives priority

• alter neuron excitability in sensory cortex and thalamus, increasing processing of relevant signals and reducing irrelevant noise

• Top down: Direct attention to goal

• Bottom up: respond to unexpected environmental stimuli

Top Down

Dorsolateral prefrontal cortex and frontal eye fields

• intraparietal sulcus and superior parietal lobule

• Directs attention to goals and relevant information

Bottom Up

Primary visual cortex and posterior parietal cortex

• temporoparietal junction and ventral frontal cortex

• Responds to unexpected or important environmental stimuli and reorients attention

Kinsbourne hypothesis of attentional neglect, contrasting roles of left and right hemisphere in attention processing

Compete for control of spatial attention

• Right hemisphere: direct attention towards both sides

• Left hemisphere: biased towards right side

Damage to right parietal region

Left hemisphere dominate attentional control, biasing right and neglect of left side

• Left sided neglect is more common and severe

Lack of awareness in neglect different from blindsight

Hemispatial neglect: damage to attention related regions (right pariteal cortex)

• person to fail to acknowledge stimuli on the contralateral side of space

• Can see it doesnt do anything about it

Blindsight: damage to primary visual cortex (V1)

• no conscious visual awareness in part of the visual field

• 
  

Hemispatial neglect= lack of awareness

damage to attention related regions (right pariteal cortex)

• person to fail to acknowledge stimuli on the contralateral side of space

Hemispatial neglect vs blindsight

attention and spatial awareness disorder vs loss of conscious visual perception

Attention has limited capacity as seen in

Early selection: selection occurs before sensory analysis complete

Late selection: selection occurs after sensory analysis

Multiple level selection: based on task demands, high demand favor early selection

Posner and Cohens research of exogenous attention showed 2 effects

Facilitation: when target appears after cue, detection is faster

Inhibition of return: When delay is after the cue longer, the detection is slower

• attention initially facilitates processing at a location, but longer intervals slows processing speed

O’craven, Downing, and Kanwisher investigated

whether attention to objects operate independently of spatial attention

• Fusiform face area

• Parahippocampal place area

• Mt/V5

Spatial attention vs object based attention

Fusiform face area: face

Parahippocampal place area: Houses and places

Mt/V5: motion

Results of

• Attention to a moving face increased Fusiform Face Area activity

• Attention to moving house increased PPA activity

Conclusion: object-based attention influences category specific processing independently of spatial attention

Perceptual memory

Holds sensory information (briefly) after it is received

• lasts 1-2 seconds before information fades

Working/Short term memory

Capacity to keep track of, update, and manipulate information at the moment

• 45 seconds max

• 4 CHUNKS OF INFORMATION

• In Dorsolateral prefrontal cortex

Categories of long term memory

Declarative (explicit): Information consciously remember and reported

Non-declarative (implicit) memory: Skills/ habits

Which types of memory are you consciously aware of

Declarative memory

• Episodic

• Semantic

Two categories of declarative memory (Endel Tulving)

Episodic: autobiographical memories of personally experienced events

Semantic: factual knowledge

Non-Declarative memory examples

Conditioning: Learning association between stimulus and response

Priming: previous exposure to influences how you process it later

Motor/skill/prodecual learning: improving skill through practice

What is context dependent memory

Remember information between when the context during the retrieval matches the encoding context

• encoding specificity hypothesis

Encoding specificity hypothesis

Retrieval is more effective when the cues available at retrieval overlap those present during learning

• studying in same place where test is taken

Brain region responsible for supporting working memory

Dorsolateral prefrontal cortex

• maintain information temporarily and manipulate it

Working memory test: Digit span

Repeats sequence of numbers

• Short term maintenance and capacity

Working memory test: N-Back test

Indicates whether current item matches an item presented N position either

• Updating and monitoring information

Working memory test: Delayed match to sample

Sees sample, wait through delay, selects matching object

• retaining and recognizing information after a delay

Working memory test: Delayed non-match to sample

Sees sample, waits, selects object that does not match sample

• retaining information and selecting nonmatching object

Behavioral results of testing working memory

Performance becomes difficult as memory load increases or the delay increases

• DMTS: correct response selects previously presented object

• DNMTS: correct response selects different object