Unit 3 COG Neuro

Amplitude

The ____ of a sound wave is its intensity.

Frequency

The ____ of a sound is the number of compressions per second, measured in Hz. 

Relavant frequencies

Caps at around 8k Hz

Cochlea

Responsible for separating out specific frequencies of sound

• Deep inside the inner ear

• When sound waves cause fluid in the cochlea to move, they create a traveling wave on the basilar membrane.

  • The location of the highest amplitude vibration determines the perceived frequency.

Hair cells

____ are located in the cochlea.

• Fluid runs through these cells, with the hair causing the fluid to move.

• The location of the highest amplitude vibration determines the perceived frequency.

Would the absence of hair cells cause deafness?

No, I do not think that someone would be able to hear without hair cells present in the cochlea.

• The fluid would have nothing to travel through, thus not creating vibrations in the cochlea that can be translated into vibrations/ frequencies.

Motion deafness

Occurs when an individual has damage to the superior temporal cortex of the auditory system.

• Individuals with motion deafness can hear sounds, but they cannot detect that the source of the sound is moving.

How can motion deafness be compared to motion blindness?

Both are associated with localized brain damage in the primary areas responsible for visual or auditory function.

• Individuals with motion blindness have damage to their MT

• Individuals with motion deafness have damage to they superior temporal cortex

Both cannot detect that motion is occurring

• Motion blindness views moving objects as a stutter

• Motion deafness cannot tell that the source of the sound is moving

Damage to the A1

 Does not cause deafness.

• Individuals with damage have trouble interpreting speech and music, but can identify and localize sounds reasonably well.

• Thus, there are deficits in their hearing but they are not entirely deaf.

A1 damage vs V1 damage

A1 damage does not entirely cause deafness but V1 usually causes some form of blindness.

Imagined sounds

Cause A1 to activate - not just actively heard sounds

Tonotopic map

A spatial arrangement of how different sound frequencies are mapped in the auditory system. 

• High frequencies are processed in specific areas and low frequencies in others

Nerve deafness (inner ear deafness)

Results from damage to the cochlea, the hair cells, or the auditory nerve.

• Results in ringing in the ears, extreme sensitivity to noise, or impaired hearing

  • Tinnitus

Tinnitus

Results from nerve deafness

• A1 is not inactiveduring a tinnitus experience

  • rather, it is typically hyperactive leading to constant ringing sounds.

Place theory

Argues that pitch is determined by where the cochlea's basilar membrane vibrates

• (high pitch = base, low pitch = tip)

Frequency Theory

Argues that pitch is determined by how fast neurons fire in sync with sound waves.

What three factors are used to determine the source location of sounds

• Phase difference between ears 

• Difference between intensity in each ear 

• Time of arrival at the two ears

Thermoreceptors

Response is relative

• At constant temps, receptors continuously active

• does not code absolute temp vsalues

• conveys info on changes vs body temp

  • alters firing rate when temp changes

Thermoreceptors only operating in specific temperature ranges

• Lower limit below 10 c

• Upper limit of warm receptors is 45 c

• Outside of these ranges, pain receptors dominate

Thermoreceptors can also be activated by specific chemicals

• For example, mint and cooling feeling

  • Not actually changing the temperature but giving the illusion that it is

Nociceptors (aka free nerve endings)

Sensation of pain signaled by ___

• All over body (skin, organs, joints) except for in brain

  • Example of open brain surgery - don’t apply anesthetic to the actual brain

Touch receptors

• Touch

• Temperature

• Nociception (Pain)

• Proprioception (one’s muscle movements)

  • Depth in skin indicates type of stimuli each receptor is geared for

Mechanoreception

• Touch receptors depolarize due to mechanically-gated ion channels being “squished open”

• Receptors close to skin surface have small receptive fields & respond to light touch

• Receptors deeper in skin have large receptive fields & respond to stronger, deeper pressure

Fast adapting receptors

Respond at onset of stimulus, stop firing if stimulus continues (adapted)

• Useful for high-frequency vibrations

Slow adapting receptors

Fire more consistently throughout long lasting stimulus

• Useful for rough textures, coarser low-frequency vibrations

Silent nocireceptors

Responds to the bodies own chemical signals

• Can play a role in increased sensitivity to stimulation following injury such as sunburn

  • Ex. Sunburn is the skin undergoing apoptosis. Without this we may develop skin cancer.

Different types of nocireceptors

• Thermal - activated by very high or very low temperatures

• Mechanical - activated by physical damage (needle)

• Chemical - activated by caustic chemicals

• Polymodal - responsive to more than one type of stimuli mentioned above

Perception of pain and emotionality

We learn to avoid pain

• When brain receptors are activated, so are negative emotion regions

  • That is what pain is

    • We have encoded emotions onto pain

• Pain is not always physical

  • Top down influences

    • Psychological stuff influencing how we perceive the world

      • Research showing that if people get financial gain, will reduce the pain their feeling and vice versa

Perception of pain

Pain is only felt if nociceptors can signal the brain and if a person is conscious and not brain dead

• Pain perception regulated by various brain regions

• Can still feel emotional feelings of pain

  • Such as loss

Congenital insensitivity to pain

Mutation In pin fibers prevents them from firing

• Do not feel pain on the extremities of the body

• Will not detect damage

  • Bad becsause often will not get help if hurt because they cannot tell if something goes wrong (indicator of something being wrong is pain)

    • Thus often do not live long

Propioception

• Sense of position and movement of our own body parts

• Receptors located in muscles, tendons, and joints

• Can detect length of muscle, speed of stretching, and muscle tension. Last one limits contractions to prevent injury

Somatosensory Pathways

• Info from head and face sent via cranial nerve (not spinal cord)

• Info from each dermatome of body sent into dorsal horn of spinal cord, crosses to contralateral side in brainstem, and sent to primary somatosensory cortex

• Recall reflex arc – motor response started in spinal cord before pain signal gets to brain

Somatosensory cortex

Each skin area/ dermatome (and some internal organs) has a dedicated piece of S1

• More sensitive parts cover more brain area

  • More cortical representations/ cortical magnification

• S1 contains somatotopic map

• S2 builds complex representations (objects, texture, size)

Somatosensory Homunculus

Corticature of cortical representations re-mapped into humanoid features

• Shows which body parts are more sensitive than others

  • So the largest body parts on figure is how sensitive each body part is

Body ownership

Sight converges with other senses

• Can give false somatosensory information without any touch input

  • Example: the rubber hand experiment

Sensation

detecting stimuli in the world, using our senses

Perception

Sensory stimulation processed by the mind/ brain

Attention

Selection process filtering sensation from perception; process by which the mind chooses from among various stimuli

• what gets into our conscience experience and what does not

Arousal

Global physiological and psychological state that can gate sensation from perception

• Sleepiness vs alertness

• Attention can occur at any level of arousal

  • Attention does not equal arousal

Voluntary attention

Goal-directed (e.g looking for a restaurant when hungry, searching for a friend in train station)

• Also can be referred to as consciousness, endogenous, top-down

Involuntary attention

• Bright objects, objects moving quickly or towards you, loud sounds

  • Automatic, unconscious, reflexive, exogenous, bottom-up

Pros and cons of different types of searching

Single feature search is relatively easy

1. Analyzed and compared in parallel

2. No need to search entire array

3. Distractors matter less

Finding multiple features is much harder; depends on the # of distractors; requires a serial search

Feature integration theory

Type of searching

• Individual features (color or size) perceived quickly and automatically

• Recognizing objects and shapes is slower and requires combining features

Feature pop out search

Relies on discriminating between obvious features

Conjuction search

Target shares one more features with distractors

Guided search theory

Expands upon feature integration theory

• States that all searches have two stages: parallel stage and serial stage

Parallel stage:

Activation map of all possible locations based on simple most salient features

• Gives next stage the most likely locations for goal

Activation map assigns activation values to specific locations

• Based on likelihood of containing the goal/target

Serial Stage

Sequentially evaluates these “pre-screened” high-activation locations

Change blindness

We are relatively unaware of some features awe do to clearly actively attend to

• Thus we do not perceive shifts in these features if our attention is elsewhere

  • Some people detect the change more easily than others

• Attention is overall required for awareness

Attentional capacity

• Prior examples suggest limited capacity of attention systems

• Is the brain capable of processing all incoming sensory inputs nearly simultaneously to create a representation of the world, then applies attention later to filter down to important targets?

  • This assumes attention does not influence sensory processing

Biased competition model

Objects compete for attention based on relevance to situation (searching for signs on the road), salience of features (signs that are colorful engage attention more), and/or what is already being attended to

Dorsal Stream

Where stuff is

• Parieletal lobe

Ventral stream

What something is

• Temporal lobe

Endogenous attention

Voluntary and goal driven

• consciously focus on stimuli based on internal goals or knowledge.

Exogenous attention

Involuntary and stimuli driven.

• Very intense stimuli redirects your attention in terms of exogenous attention.

The ventral right attention network

Activated by novel stimuli

• Exogenously driven

The dorsal frontal parietal network

The dorsal frontal parietal network involves intentionally searching for objects and stimuli.

• The search is endogenously driven.

Inhibition of return

Produced by the superior colliculus

• Prevents our attention system from returning to a point that does not involve our target.

• This is to ensure that our attention does not get stuck on something that has already been ruled out.

What is the general idea of how the DMN might be part of the cause of hallucinations in schizophrenia?

There is cross wiring between the DMN and other brain networks hence, the internal monologue associated with the DMN can get confused as external monologue

How does it make sense that dopamine-boosting medications can aid the deficits in ADHD, despite such medications being known for causing hyperactivity?

The theory is that the brain will perform a certain amount of actions until it reaches sufficient levels of dopamine. Hence, inhibiting dopamine through medication ensures that extra actions are not needed to be performed and that individuals can focus on one action at hand.

What is some important context for any time that someone indicates, “These two groups have significantly different XYZ brain area sizes.”?

How vast is this difference in this size? Is it simply a 10% (which is quit negligible) difference in size or a 50% difference in size

Balints syndrome

Experience simultagnosia

• Individuals are unable to recognize multiple objects presented simultaneously.

  • Can only see one object or the other, not both.

Hemispatial neglect (aka contralateral neglect)

Individuals unable to see visual stimuli that lies in one side of their environment

• Typically cannot see stimuli on the left side of their environment

If we ask someone with contralateral neglect to draw a clock, what kind of clock will they draw?

They would draw a partial clock with all 12 numbers crammed onto the right side. 

Contralateral neglect is not due to sensory problems, such as partial blindness. How do we know that?

Because these patients can still detect attention-grabbing features that fall within their “deficient” visual field.

• Hence, it is simply an inability to respond to the other hemisphere of their brain. 

Attentional capacity

• Prior examples suggest limited capacity of attention systems

• Is the brain capable of processing all incoming sensory inputs nearly simultaneously to create a representation of the world, then applies attention later to filter down to important targets?

  • This assumes attention does not influence sensory processing…

Biased competition model

Objects compete for attention based on relevance to situation (searching for signs on the road), salience of features (signs that are colorful engage attention more), and/or what is already being attended to

Posner orienting paradigm

Participants fixate on a center point while cues indicate potential target locations on the left or right.

• Cues that correctly orient participants to target give participant reaction time bonus

• Cues that orient participants away from target give participant reaction time cost/deficit

Oddball paradigm

Any setup involving the following aspects

• Stimulus train which has several similar stimuli and one oddball mismatching “oddball” stimulus

• Some way of measuring brain activity (EEG, MEG, fMRI)

Can discriminate between voluntary and involuntary attention

• Involuntary attention tested with new oddball that is very different from regular stimuli and prior oddball

Example: Regular stimuli: cars, Regular oddball: schoolbus, Novel oddball: a face

Brain activity of attention

Cues going to pop up on either side. Will attend to when the target pops up. (example, attend to left or attend to right)

• When they fail to move their attention, the amplitude is less

• Attention to target results in stronger (better?) encoding of inputs and degradation of unattended inputs (P1, N1, N2, amplitude)

• Spatial selection happens early

Content dependent nature of attention processing

In some cases feature attention may precede spatial attention

• For example, when we do not know the location of the target in advance

• Or, when the task is too difficult (a lot of distractors/ competition for attention)

  • Example: guided search theory

Features may guide subsequent shifts of attention to locations of those features so that higher resolution “mechanisms” can process and identify conjunction targets

• In line with feature integration theory & guided search

Masking

We can make things intentionally disappear so that it is not processed further and does not reach awareness

• Put between distorter stimulus to holds the brain attention so that the target “masked word” is not noticed

  • Also shown for shorter period of time

Why we use attention

Attention modulates perception such that it leads to

• Quicker and more accurate target detection (seen behaviorally and in EEG)

• Better sensitivity to the features

• Enhance neural processing (reflected in the amplitude of ERP’s and in increased neuronal firing rate of cortical cells)

• Enhanced responses of relevant cortex

  • When we engage in something we get more processing power

Attention involves a widespread network

•  subject not attending to particular stimulus, activation does not spread beyond sensory areas.

• If subject aware of stimulus, activity spreads beyond sensory areas, into frontal and parietal areas

What is happening neurologically in attention masking?

• Example to right is fMRI activity

• Conscious perception of word involved amplified/enhanced activity in same areas as unconscious word perception

• Conscious percept activates a distributed & higher order network

• This filtering occurs in the N2 and P3 ERP events – later stage processing

Simple motor hierarchy

Structured in reverse of the senses

• Higher order regions coordinate abstract plans

  • Less associated with specific muscle activation

  • Many movements lead to the same result

• Lower order regions/neurons more directly control output behaviors & movements

Motor controls in the brain

• Conscious decision to start a motor action begins in prefrontal cortex, then is conveyed to the back parts of the frontal lobe 

  • Right next to somatosensory cortex in the parietal lobe

• Translating motivation to action happens in basal ganglia (including accumbens)

• Some parts of basal ganglia also control impulses, habits, “tics”

Skeletal muscles

 Muscles that attach to our skeletons via tendons and cartilage.

• They are also muscles which we can consciously control via the somatic nervous system.

Smooth muscles

Internal organ musculature such as the digestive tract

• Do not have conscious control over

Cardiac muscles

The heart tissue

• Do not have conscious control over

Why is it important that we do not utilize our voluntary movement control systems on things like digestive organs or the heart?

It would distract from our attention systems which need to focus more on the surrounding world.

• Also, it poses the issue of life threatening situations.

  • For example, if we become conscious of our heart beating leading it to stop, this would pose a life threatening issue.

The automatic nervous system regulates its functioning instead. 

Briefly describe how muscles move (exclude neuromuscular junction - that’s asked about below).

The autonomic nervous system directs the muscles when it is time to contract. Then, neuromuscular junction occurs where a neural signal is converted into a mechanical output.

Name three features that the neuromuscular junction has that make it similar to the connection between two neurons.

1. They both have neurons that send  a message to a recipient (another neuron or a muscle fiber).

2. Both neurons and muscle fibers have neurotransmitter receptors.

3. Both neurons and muscle fibers can depolarize in response to neurotransmitters

Flacid paralysis

There is no contraction

• Completely inhibited

• Limp

Rigid paralysis

Everything contracts and is locked up

• Canot relax

M1 - Primary motor path

Corticospinal Tract - output of concious movement

a.k.a. Pyramidal tract

• Starts with motor cortex, projects far through spinal cord, then synapses onto more local “lower” motor neurons

  • Most connections go contralateral in brainstem

  • Upper neurons coordinate complex movement, lower neurons contract specific muscle fibers

Damage to the corticospinal tract

• Causes paralysis

  • “locked-in” syndrome - conscious and cannot willingly move

    • Global shutdown of entire motor cortex

    • Your locked into your body

Different pathways for voluntary vs involuntary movement of same muscle groups

• Voluntary tract controls posed smiles, involuntary tracts control genuine emotional smiles 

  • Emotional cortical areas (cingulate, amygdala) coordinate with reticular formation

Cortical motor representation

Brain has dedicated regions for controlling all skeletal muscles -  motor cortex in frontal lobe

• Similar to somatosensory homunculus

M1 map of movements

One upper motor neuron coordinates multiple muscles

• Further, multiple M1 neurons coordinate movement direction (rather than final movement target)

  • Population coding

  • Single neurons have broad/vague directionality

  • Groups of neurons code for much more precise movements

Map may be more complex than the homunculus

Longer stimulation evokes complete movements, like moving hand to mouth and opening mouth

• There is no obvious population coding of direction with longer stimulation

• Suggests combination of population AND rate coding to add flexibility

How does botox work?

Destroy the synaptic vesicle “machinery” inside acetylcholine-sending nerve terminals that exist near the muscles.

• Thus, people have localized muscle paralysis in the injected area. 

How do certain war toxins work

Act on an enzyme in the body called cholinesterase, causing acetylcholine to build up and triggering contraction in the muscles.

• This prevents the muscles from being able to release or change from a constantly contracted state. 

Pre Motor Cortex (PMC)

Externally guided actions

• How do we react to external stimulus

Supplementary Motor Area (SMA)

Internally guided actions

Posterior Parieletal Cortex

Representation of space, how body is situated, coordinates body movement

Cingulate area

Emotionally-tied movement

• Duchenne smile from before

What does the knee-jerk reflex tell us about opposing muscle groups?

It confirms that your nerves and muscles are working properly

Why distinction between flaccid and rigid paralysis matters

Important because treatment for one might make the other worse in terms of severity of paralysis. 

What is still required for CPGs to execute their movement patterns successfully?

Sensory feedback to know how to change the pace.