Post Midterm Content Part 2 Flashcards
What model was produced to show that dopamine was associated with ‘reward prediction error’?
- showed that recordings of dopamine neurons reveal ‘reward prediction error’ (RPE) signals.
- RPE is the difference between what was predicted and what actually occured.
-> positive error: better than expected
-> negative error: worse than predicted - RPE signals are critical for learning
- Dopamine might regulate Hebbian plasticity by strengthening connecting between simultaneously active neurons.
Dopamine
- dopamine system innervates many brain regions
- James old & Peter Milner found that the rats will self-stimulate the medial forebrain bundle, causing release of dopamine in the nucleus accumbens
- led to suggestion that dopamine = pleasure (involved in reward and enjoyment)
- distinction between
-> Liking (enjoyment)
-> Wanting (drive to pursue) - dopamine mediates wanting but opioids regulate liking.
What are key brain regions in executive functions?
-> ‘Executive Functions’ or ‘control system’ adapt cognitive functions to the current environment &/or internal state of the individual
-> Various related functions have been linked to regions of the prefrontal cortex
Orbitofrontal cortex & reward
- OFC (orbitofrontal cortex) is implicated in estimating the value of reward based on past & present information
- reward value is subjective
- example: favourite snack, candy we like, water when you are thirsty, food that gave you food poisoning, wine that costs a lot of money.
What plays a role in decision making?
- OFC and ventromedial prefrontal cortex (vmPFC) may calculate a ‘common currency’ that informs decision making
- OFC/vmPFC neurons show firing changes when the value of reward options are maintained in short-term memory
What happens if there is a lesion in vmPFC/OFC?
- impair ability to weigh different options e.g. buying a new car
- OFC lesions also impair the ability to learn about which stimuli reliably predict reward and punishment
What does the dorsal anterior cingulate cortex (dACC) & ventral striatum contribute to?
- maintaining and comparing reward values
What is the role of dorsolateral prefrontal cortex?
1) dIPFC -> suports flexible, oriented behaviour
- dIPFC makes other groups of neurons more or less responsive to inputs & feedback to produce different responses in different contexts
2) also implicated in keeping information in mind to guide behaviour (works in short term memory)
- firing of dIPFC neurons increase when information is held in short-term memory
- E.g. monkey trained to observe a stimulus after a delay
- dIPFC neuron firing maintains the stimulus information over the delay
3) Rule encoding
- implicated in learning task rules
- dIPFC neuron firing varies with current rule in a monkey match- non-match task
- dIPFC patients have deficits in rule switching in the wisconsin card sorting task indicating difficulty in adapting to changing circumstances
What are the functions of the dorsolateral prefrontal cortex?
1) Learning task rules
2) Firing of dIPFC neurons increase when information is held in short term memory
3) dIPFC makes other groups of neurons more or less responsive to inputs and feedback to produce different responses in different contexts
What is the anterior cingulate cortex (ACC) involved in?
- evaluating the outcome of decisions & updating the connections between stimulus inputs & behavioural outputs
- ACC is activated by errors that reduce rewards (disappointment)
- ACC tracks the value of outcomes that were not selected to influence the appraisal of the selected outcome
- ACC activated by surprise & other stimuli that rapidly change behaviour (e.g. pain)
- ACC detects the need to change the behaviour, the dIPFC executes the change
- ACC also activated by conflict
- Stroop test (it is more difficult to read a colour word where the colour of the text conflicts with the word)
- ACC activity is enhanced during cognitive conflict suggesting that resolving the conflict requires extra cognitive control that recruits the ACC
What happens if there is atypical activity in the ACC?
- associated with obsessive compulsive disorder
- overly sensitive to stimuli e.g. dirt, clutter
- self-doubt (e.g. did I turn the oven off?)
- compulsion to perform illogical acts
- inability to control these acts
- surgical ablation of ACC can be effective in server cases of OCD
- suggestion that individuals with OCD have hyperactive ACC that makes them hypersensitive to error signals
- Disconnecting the ACC may reduce this error sensitivity, allowing adaptive behaviour to proceed
What is the function of the ventrolateral prefrontal cortex?
- self-control
- supports the ability to withhold behavioural responses i.e. restrict impulses
- individuals with vIPFC damage respond more quickly but with less accuracy in timed tasks
- In real life, associated with poor decision making marked by impulsivity and lack of self- control in social situations
- vIPFC transcranial magnetic stimulation increases the ability to suppress undesired responses in lab task e.g.
-> suppressing behaviour in a repeated response task
-> Task switching - Experimental use of vIPFC TMS in OCD patients (area that we can reach and use so thats why we chose it, and there is a connection from this area to ACC)
What is the function of the Anterior Insula?
- internal context
-information about internal body states regulates decision making (hunger, thirst, heart rate)
- anterior insula receives information about bodily states via subcortical brain regions & is associated with emotional awareness
- anterior insula relays this information to cortical and subcortical areas
- anterior insula often co-activated with AAC
- also linked to attention, time perception, love, mood, speech, and music
What is the function of the posterior cingulate cortex?
- self-awareness
- high order complex functions
- PCC is linked to our awareness of ourselves as part of a larger world
- PCC is most active during distraction from a task or daydreaming
- part of the ‘default mode network’ (networks in brain that are engaged when we are not doing anything actively - need to be disengaged when we are doing something actively)
- PCC activated when thinking about oneself in the future and thinking about others in relation to ourselves
- suggest a role in representing the self in relation the larger world
What specifies fundamental frequency in speech?
Vibrating vocal fold specify fundamental frequency (100 to 400 Hz). Gender, size, age and speaker decide F0.
What is the basic speech sounds called?
Basic Speech sounds called phones and the percept they elicit and phonemes. Phonemes divided to vowels and consonants.
What is the natural resonance of layrnx called?
-> formants!
F1 around 500Hz
F2 around 1500
F3 around 2500 Hz
What is shown with Vowel Formant Chart?
A Vowel Formant Chart shows the positions of vowel sounds based on their acoustic characteristics, represented by the frequencies of the first two formants. It helps linguists and phoneticians analyze and compare vowel sounds in different languages or dialects.
Each language we have F1 and F2 Formant Chart and by knowing the formant of those, we can say where we are.
Where is language located? What about in congenitally deaf individuals?
- language is located in the left hemisphere
- in congenitally deaf individuals, sign language functions are located in similar cortical areas suggesting the language centres are specialized for symbolic representation and communication rather than hearing & speech.
What areas of the brain are critical for language?
- left frontal and temporal association cortices are critical for language
- language functions are strongly lateralized
- representations of language is distinct from sensory and motor control of speech production and auditory and visual perception
What is the primary function of cortical language centres?
-> symbolic representation for communication.
grammar: set of rules for use of symbols
syntax: ordering of symbols to create meaning
prosody: providing emotional valence by varying intensity, pitch, rhythm
Where is language processed in the brain?
- clinical evidence demonstrates the ability to produce or perceive spoken language can be compromised without effecting the ability to use language to communicate e.g. deafness
- damage to specific brain regions can compromise essential language abilities while leaving the sensory & motor control mechanisms intact
- aphasias diminish or abolish the ability to understand and/or produce language as a means of communication, while sparing the ability to perceive the relevant stimuli & produce intelligible words
- the fundamental deficit is the ability to recognize or use the symbolic value of words correctly
What did Broca discover?
- that language was localized to the ventroposterior region of the frontal lobe
- observed that the loss of ability to produce meaningful language (distinct from the ability to move the mouth & produce words) was usually associated with damage to the left hemisphere
What did Wernicke distinguish?
- difference between patients who had lost the ability to understand language and those who had lost the ability to produce language.
- patients with deficits in wernicke area can produce language and understand it, but the language they say may not be coherent or meaningful.
Where did Wernicke patients have damage?
- in the left posterior and superior temporal lobe.
- observed aphasic patients who could still produce grammatical, syntactically fluent utterances but that these lacked meaningful content.
Broca’s aphasia
- motor or expressive aphasia
- difficulty producing language efficiently
- associated with left frontal lobe ‘Broca Area’
- must be distinguished from dysarthia, the inability to properly move the muscles of the mouth, tongue & larynx that mediate speech
- involves deficiencies of motor planning, consistent with the complex motor functions of the posterior frontal lobe & its proximity to the primary motor cortex
Wernicke’s aphasia
- sensory or receptive aphasia
- affects the ability to understand spoken language
- deficits of reading & writing (alexias & agraphias) are separate disorders arising from damage to distinct but related brain regions although most aphasics also have difficulty with these
- generally associated with damage to the auditory association cortices in the posterior lobe ‘Wernicke’s area”
Conduction aphasias
- arise from lesions to the pathways that connect the relevant frontal and temporal regions e.g. the arcuate fasiculus in the subcortical white matter that links broca’s & Wernicke’s area
- results in the inability to produce appropriate responses to a heard communication, although the communication is understood
How was language lateralization confirmed?
1) Until 1960s, the primary evidence for the localization of language came from lesion studies. Roger Sperry’s work using ‘split-brain’ patients.
2) As a treatment for severe, intractable epilepsy in a subset of patients, the anterior commisure & corpus callosum are severed
3) In such patients, it is possible to independently assess the function of the left and right cerebral hemisphere
4) Such studies confirmed that language is highly lateralized
-> to evaluate the function of each hemisphere, the patient is asked to use each hand independently to identify objects without visual cues. Somatic information from the right hand is processed by the left hemisphere and vice versa.
-> The subject is then asked to describe the item that they are manipulating in one hand or the other to test the language capacity of each hemisphere.
-> using the left hemisphere, split-brain patient could easily name objects held in right hand.
-> using the right hemisphere, most split-brain patients failed to produce any verbal account or could produce only an indirect description (e.g. a round thing, rather than a ball)
What are left-hemisphere functions?
- analysis of right visual field
- stereognosis (right hand)
- lexical and syntactic language
- writting
- speech
what are right-hemisphere functions?
- analysis of left visual field
- stereognosis (left hand)
- emotional colouring of language
- spatial abilities
- rudimentary speech
In 1960s, what did Geschwind identify?
- identified an asymmetry in the superior aspect of the temporal lobe known as the ‘planum temporale’
- larger on the left side in 2/3 of humans (also in apes)
Is there anyone who is right hemisphere dominated for language?
Yes! So before surgery, they need to check just to make sure.
How many people have language that dominates in left and how many in right?
- 2/3 97% in left, the rest in right
What method is used to map language functions?
- Wada method, short-acting anesthetic is injected into patients left carotid artery to transiently anesthetize the left hemisphere.
- if the language is dominant for language, then the patient will become transiently aphasic. (if they are counting, they can no longer count anymore)
- but this test is a bit invasive
What are less invasive tests of hemispheric lateralization?
- Positron emission tomography (PET)
- Functional magnetic resonance imaging (fMRI)
- Transcranial magnetic stimulation
- Tachistoscopic stimulus presentations
What did Dr. Wilder Penfield do?
- used electrical mapping techniques developed from animal neurophysiology research to delineate language areas in the cortex prior to surgery fro tumours or epilepsy
- this kind of intraoperative mapping was essential to ensure the cure was not worse than the disease
- this came after hemispheric localization was discovered
Sign Language
- cortical organization of language is not just about specialization for hearing & speaking
- language regions are broadly specialized for processing symbols of social communication
- sign language also have grammar, syntax and emotional tone
- studies of congenitally deaf patients with lesions to either the left or right hemisphere showed that damage to the left-hemisphere lead to deficits in sign production & understanding
- damage to the right hemisphere leads to deficits in the emotional tone of signing
Dyslexia
- written language involves the production and interpretation of visual symbols for language
- dyslexia is a learning disorder that involves difficulty reading due to problems identifying speech sounds and learning how they relate to letters and words.
- normal or above-normal intelligence
- often extends to problems with writing, spelling and marked by errors of transposition.
- runs in families (possible genetic basis)
- in normal people: we have Visual Word Form Area (VWFA) in the left hemisphere is activated selectively by written language. But we have reduced activation of VWFA in individuals with dyslexia.
What are the critical periods for language?
- language fluency requires early language exposure
- this is an example of a ‘critical period’ i.e. a period of increased sensitivity of natural plasticity that supports behaviour
- learning a second language earlier than 7 years old leads to native-speaker fluency
