Cog Neuro Exam 3

Semantic memory

Your knowledge about the world, knowledge about what things are and how they work

Embodied cognition

Close ties between knowledge and our perceptual/physical interactions with the environment

Meaning of concepts is composed of different types of features including…

Perceptual, functional, lexical, encyclopedic

Modality specific

Different types of features are stored in different brain regions

How are different types of features stored in the brain?

Distributed manner

Sensory-Motor model

* Different areas of the brain have different functions
* Modality-specific nodes are distributed throughout the brain

Concepts emerge through…

co-activation

Location of nodes are tied to…

Primary perceptual and motor systems

Evidence for Sensory-Motor Model

* Condition 1: Participants were in a scanner and were asked to do things like wiggle their finger, move their tongue, move their lips, etc.
* Condition 2: Participants were in a scanner and were asked to say words, related or unrelated
* fMRI evidence generally shows close correspondence between brain activity when people are thinking about an object and when they are perceiving or using an object (Hauk et al., 2004)

Evidence for Sensory-Motor Model has lead to the idea that…

Conceptual knowledge in the semantic memory system is distributed throughout all of these legality specific cortical areas 

Frontotemporal Dementia includes the loss of…

Semantic memory

Frontotemporal Dementia

* An umbrella clinical term that encompasses a group of neurodegenerative diseases characterized by progressive deficits in behaviour, executive function, or language
* All tied together through the nature of the pathology 

How common is Frontotemporal dementia?

FTD is common in middle aged individuals, most common form of dementia in individuls aged 45-65, \~20/100,000

What is the survival time for FTD?

Around 8 years

As FTD progresses, it affects what areas of the brain?

Affects the temporal lobes and the frontal lobes 

Various sources of neuropathological change that invariably result in the…

Selective degeneration of the frontal and temporal cortices

In most cases, FTD is lateralized to the…

Left hemisphere

Common symptoms of FTD

* Problems with executive control
* Cannot easily inhibit tendency to say or do something
* Stealing can be common
* Loss of knowledge of what is and is not appropriate

Video 1 shown in class FTD

* Stephanie Godder, shown yelling and exclaiming how much she loved everybody
* Clapping
* Cannot inhibit sharing her feelings with the world

Semantic dementia

Progressive and profound degradation of semantic memory with relative sparing of most other cognitive functions (*e.g.*, Episodic memory, problem solving, speech, perception)

Semantic dementia includes a loss of blank, not blank

Loss of what things are not who they are

SD includes the idea of spreading activation, meaning …

Once one area lights up from a concept, it can light up other areas as well to make semantic connections

Semantic impairment is selective early in the disease, but progresses to what else as atrophy spreads?

Other cognitive functions as atrophy spreads

SD initially affects what part of the brain?

Anterior temporal lobe, mostly in the left hemisphere

Video 2 on SD

* Couldn’t describe who “Millie” was, only could say she was just Millie even though Millie is her daughter
* Would be asked to point out the scissors, would point out a pen and vice versa
* Some semblance of knowledge there, just a breakdown of the knowledge concepts

Original case study on SD

* In Ireland by Carol Heishnen 
* Wife complained about husband not being able to regonize sheep as they drove by because he had been a farmer his entire life 

Semantic Dementia: Impaired Picture Categorization Task

* Particpants were asked to describe the image below by asking several questions: 
* Is this an animal? GENERAL
* Is this a dog? BASIC
* Is this a Great Dane? SPECIFIC

Results of Impaired Picture Categorization Task

* Showed a dramatic decline in patients with SD, especially within the level of detail given
* General level showed little decline 
* Basic level showed some decline
* Specific level showed the most decline

Semantic Dementia: Impaired Picture Naming

* Single-case study
* Assessed longitudinally
* One participant followed up on for several years, in September and March every 6 months 
* “+” means the correct name was given
* Picture naming

Results of Impaired Picture Naming Task

Progessive loss of specificity and conceptual knowledge (*e.g.,* Swan → Bird → Bird → Animal)

Semantic Dementia: Impaired Drawing

* Individuals with semantic dementia can copy a drawing
* Cannot draw from memory (All drawings are basically the same)
* Serious loss of animal specific knowledge after delay
* *Ex*. Camel lost its hump, duck lost its webbed feet, but main features of animals stay like habing four legs and a body

Why do individuals with SD have impaired drawing skills?

No long-term memory representation of the features that make each animal unique

Tool Use in SD

* Condition 1: Had individuals use real tools, they have had a lifetime experience with
* *Ex*. A comb
* Condition 2: Had individuals use novel tools, haven’t used it before but can use previous life experience to figure it out 

Results of SD Tool Use

* Found that those with semantic dementia still performed just fine with the novel tools but performed poorly with the real tools 
* When there is no requirement that they must tap into this long term representation of what things are used for or typically maniupluated they perform fine

* If semantic knowledge is distributed across a network of modality-specific nodes, why would damage to the anterior temporal lobe cause such profound deficits for modalities that are NOT represented in the anterior temporal lobes?
* Reframed: Why would someone that has damage to the anterior temporal lobe not be able to tell you how to use a tool, despite the fact that the primary motor cortex and motor areas are working just fine? 

Alternative option is the Hub and Spoke model

Hub and Spoke Model of Semantic Memory

* Information from modality-specific regions (spokes) converges in the temporal pole (hub)
* Idea is that rather than conceptual knowledge emerging through coactivation of all of those different nodes (spokes), the actual concept is represented in the anterior temporal lobe where all of that modality specific cortical information is converging 
* Information is going from the primary motor cortex to the anterior temporal lobe etc.
* Hub integrates information into an abstract representation that is activated according to task demands


* You don’t lose your hearing, or your perception, or your senses, you lose everything 
* Still not well understood!

Why is the Hub and Spoke Model not well understood?

* Really difficult to get good fMRI data out of this area of the brain, its right behind the sinuses
* Anytime you have an air cavity near tissue you have a hard time getting quality, reliable fMRI signals

Simulating Semantic Dementia with TMS

* 10 neurologically healthy participants
* Experiment 1: TMS applied to left temporal pole
* Experiment 2: TMS applied to right temporal pole
* Particpants had to choose which word (shown below) closest resembled the word interesting
* Control had to choose which number (shown below) is closest in magnitude to 17

TMS

Electromagnetic field over the scalp, showing action potentials in the brain 

Results of Simulating Semantic Dementia with TMS

Results showed stimulation to the anterior temporal lobe, regardless of what hemisphere, increased reaction time on synonym judgment tasks 

How does TMS Applied to the Temporal Poles Affects Semantic Memory?

* TMS increased reaction times in the synonym task but not the number task
* The effect was comparable across the left and right hemisphere

How is SD different from aphasia?

Semantic dementia is not just a language problem, separating it from aphasia, its a loss of conceptual knowledge

Change Blindness video

Car commercial, don’t even notice everything changing in the video unnoticed

Who coined the term attention?

James, 1980

James, 1980 definition of attention

Everyone knows what attention is. It is the taking possession by the mind, in clear and vivid form, of one out of what seem several simultaneously possible objects or trains of thought. Focalization, concentration of consciousness are of its essence. It implies withdrawal from some things in order to deal effectively with others, and is a condition which has a real opposite in the confused, dazed, scatterbrain state.

Taking possession by the mind

* Can be voluntary
* You have voluntary control of what you attend to

Several simultaneously possible objects or trains of thought

* Involves selection (or gating)
* Attention involves selection

Withdrawal from some things in order to deal effectively with others

* Limited capacity
* You do not have the capacity to attend to everything

Do we really know what attention is?

No

Attention as a Gating Mechanism

* Only a limited amount of information is going to cross the threshold into the conscious mind
* Attention allows us to select which information will be processed

Our brain has an ___ on the amount of information that can be processed within a particular amount of time

Inherent Limitation

Selective attention allows us to what?

Prioritize targeted thoughts or perceptions while ignoring those that are irrelevant

How do we view the processing stage where attentional gating occurs?

* Use EEG data
* High temporal resolution

Early selection models

* Sensory information is being processed by multiple different systems 
* Sensory inputs that can enter higher levels of the brain for processing are screened early in the information-processing stream
* Only the most important information passes through for perceptual processing

Main idea of early selection models

Idea of these early selection models is that there is some sort of mechanism to filter or gauge that removes the majority of the information being received by the sensory systems before any processin takes place 

Evidence in Favour of Early Auditory Gating

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* Dichotic listening task
* In one ear one thing is playing while in the other theres another sentence being played
* Participant is given some direction of which one to pay attention to, creating some biastoward processing information in the left or the right ear 
* Condition 1: Attend to the left ear
* When there is a tone in the left ear and the participant is paying attention to the left ear, versus the right ear, there is an increase in amplitude in the N1 response, thought to reflect the earliest notion of a response (precognitive processing, nothing high level right now)
* Exact opposite in the right ear
* Condition 2: Attend to the right ear
* Results suggest that directed attention modulates sensory processing \~80-100 ms after stimulus presentation
* Modulating the nature of the brain response very early on 

Dichotic listening

Different tones played simultaneously to different ears

What is N1?

N1 is an ERP component that reflects auditory event detection

Evidence in Favour of Early Visual Gating

* Participants instructed to keep their eyes fixated on the center of the screen, attending to either an image on the left or right side of the screen while still actively looking at the middle
* Fixate eyes on a centrally presented cross while stimuli are flashed to the left or right visual field
* Instructed to covertly attend to either the left or right of the display (still fixating on the center)
* Shows a very early response to visual stimulus, response is much greater when told to attend to the left side and a stimulus is presented on the left side as well 

What does early visual gating suggest?

Suggests that there is some sort of filtering going on very early on in the hierarchy of stimulus processing 

Evidence Against Early Selection Models

* Cherry (1953) created the dichotic listening task to study attention
* Participant listens to different auditory streams (different stimulus played in each ear) and repeats information from just one ear, *i.e.,* attention is biased to one ear
* Particpant asked to verbally repeat the stimulus from the left or right ear, can’t repeat it, not paying attention to it
* Participants were unable to report any details about the speech in the unattended ear
* Could, however, report whether the unattended speaker was male or female
* Some information is still getting through the filter while some is ignored
* Cocktail party effect

Cocktail party effect

* Idea that you can be in a very busy room and have an individual conversation and not be able to attend to any other background conversations
* If you hear your name, you immediately pay attention to that instead of the person in front of you 

Time Course of Attentional Selection: Late Selection Models

* Suggests that all of the early perceptual processing that takes place that represent the external 
* Perceptual systems first process all information equally before selection takes place at higher stages
* General agreement that there are early and late selection mechanisms

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What are early and late filters meant to do?

Early filters are meant to break down information into channels, whereas the late filters allow you to process the broken down information more deeply 

Hemineglect Class Video

* Woman asked to draw a clock and put the numbers on it accordingly
* Compression of space, she has the numbers but only around ½ to ⅔ of the clock

What causes Hemineglect?

* Typically caused by a unilateral stroke that affects the brain’s attention network
* Affects one of the two cerebral hemispheres

Which cerebral hemisphere does hemineglect usually effect?

Most typically on the right 

What is hemineglect characterized by?

* Characterized by an inability to attend to the side of space that is contralateral to their lesion (more frequent consequence of brain damage in the right hemisphere)
* Inability to attend to half of the visual field 
* Typically relative to the midline of the body
* Contralteral 
* The ignored space is most often defined relative to the midline of the patient’s body

Are patients who have heminegelct aware of their problem?

Patients are unaware of their problem and behave as though one side of space does not exist

What does hemineglect research reveal about attention?

Reveals that attention is not something that we should be thinking of as a system that can be mobilized to a specific part of the brain 

Lesion Profiles in Cases of Hemineglect

* Inferior parietal cortex
* Temporo-parietal junction
* Ventrolateral prefrontal cortex
* Superior/middle temporal area
* Underlying white matter tracts that connect these areas

Where is the most common place of hemineglect?

Inferior parietal cortex

Neglect symptoms most likely reflect …

A functional breakdown at the level of attentional networks rather than individual regions

* Neglect also reveals that the pattern of impairment, regardless of the location of the lesion, have the same outcome

Can symptoms of hemineglect lessen over time and give example

* Severity of the impairment sometimes lessens over time

*Ex*. An artist who had a stroke did a series of self portraits after said stroke, slowly was able to fill in more of the face and improved over time

Evidence for Hemineglect: Line Bisection

Participants were asked to look at a line and cut it in half, results shown below, actual patient image on the right

Evidence for Hemineglect: Drawing

* Drawing a clock reveals intact semantic knowledge
* Face is round, all numbers are typically included
* Result is the same for copying and drawing from memory
* Not losing their semantic knowledge or concepts, just attending to the visual field itself 

Eye Tracking Data in heminegelct

* Participants were shown an array of “t” and “x” and were asked to point of the “x” 
* Blue trace: Path that the eyes are taking
* Green trace: What is happening in between trials 
* In the neglect patients, their eyes are not even going to the left side of the field 

Is neglect a sensory deficit?

No

Neglect Is Not A Sensory Deficit: Extinction

* Patient with right hemisphere damage/lesion
* Can detect salient and isolated stimuli in the left visual field
* Extinction of left visual field occurs when there is competition across hemifields

Extinction experiment

Experimenter holds up their fingers, one hand with two fingers and the other with none, the participant says there are two fingers. They then switch hands, the participant will again say two fingers are being held up. When both hands are held up with two fingers, the participant will say jut two fingers are being held up because they cannot attend to the other side

Extinction

They can see stimuli, but you cannot have information in the background as it will distract and create competition 

Neglect Is Modulated By Attention

Line bisection improves when patient is given a simple cue that ‘pushes’ attention to the neglected hemifield

Line bisection task

Faces are shown looking forward, to the left, or to the right. This gives a cue to the participant of where to look as well and where to bisect the line 

Hemineglect in Memory-Based Imagery

* Patient is asked to imagine standing in a well-known plaza in Milan and what they see and surrounding landmarks 
* Impoverished ability to describe things in one hemifield even when just imagining it 
* Memory is intact, patient has impaired ability to attend to information represented in the left side of space

What would you see if you were facing the cathedral?

They do not report an awareness of anything on the left side of the cathedral 

What would you see if you were standing on the steps of the cathedral?

They do not report an awareness of anything on the right side of the cathedral 

Class video about Encephalitis

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* Lonni Sue Johnson used to be an artist and a pilot 
* No memory of her 10 year marriage, but can tell you how to fly a plane or paint watercolors
* Inability to remember facts certain to her career domains, but able to remember relevant facts for performing tasks in these domains shows that we store different types of knowledge in different areas

what is encephalitis and what is is caused by?

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* Encephalitis: Swelling of the brain 
* Can be caused by infections, such as a cold
* Can be caused by the body’s immune system overreacting and attacks itself

class video 2 with Clive wearing

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* Has no short term memory, worst case of amnesia ever known 
* Only regonizes his wife Deborah
* Memory lasts from 7-10 seconds

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Encoding

Process of establishing a memory trace from incoming information and experiences

Consolidation

Post-encoding process that stabilizes otherwise labile memory traces

Storage

Retention of a memory trace over a delay

Retrieval

Involves accessing stored memory traces in a manner that influences cognition and/or behavior

Karl Lashley 1929

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* Sought to find engrams in the brain
* Trained rats to run a maze then removed a part of its cortex and observed what effect this would have on its memory of the maze
* He removed 10 - 50% of the cortex on different trails
* Subsequent maze performance was unaffected by the location of the lesion, instead it was the size that mattered
* Experiments with induced brain damage in rats showed that memory is widely distributed rather than localized anywhere in the cortex
* Lashley used carefully controlled induced brain damage in the cortex of rats that were trained to run through a maze

Law of Mass Action (*a.k.a.* ______)

equipotentiality

Law of mass action

All brain regions contribute equally to all cognitive functions

Prevailing view until 1962

Memory is a broadly distributed function

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Amnesic Syndrome

* Impaired episodic memory
* Impaired semantic memory
* Intact working memory
* Intact implicit memory
* Intact procedural memory

Brenda Milner and patient HM

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* Had uncontrollable seizures, had surgery in 1953 that almost completely removed his hippocampus, amygdala and surrounding cortex on either sides of the brain 
* Found that he had retained the ability to form non declarative memories, this system relied on the basal ganglia and the motor cortex which were not removed during surgery  
* Surgery was partially succsessful in controlling his seizures but he developed severe anterograde amnesia 
* "Right now, I'm wondering, have I done or said anything amiss? You see, at this moment everything looks clear to me, but what happened just before? That's what worries me. It's like waking from a dream. I just don't remember.“ - H.M. (Milner et al., 1968)