Lecture 8 Flashcards
(24 cards)
Overview of the adult brain?
- Composed of billions of neurons
- Neurons are information-processing cells
- Make connections with other neurons to create networks
- Each neuron can connect with 1000 other neurons = 60 trillion neuronal connections in adult brain
What are the composition of neurons?
- Dendrites are the where neuron receives incoming signals
- Cell body and axon at the end = signal is propagated to axon terminal where it connects with other neurones or effector cells
- Synapse: chemical in brain not electrical = usage of neurotransmitters in vesicles into synaptic cleft to bind to post-synaptic membrane
What are terms for the brain?
- Grey matter - cell bodies (neuron)
- White matter - nerve fibres (axons) - myelinated = insulated layer
- Gyri - ridges
- Sulci - depressions/folds
What is fetal and post-natal brain development size?
- Biggest growth spurt is from around 7mo prenatally to 2yo postnatally
- Basic structure of brain is formed from week 8 from conception
- Adult neurons present in utero
- Brain grows so much postnatally because of connections made between neurones and links between dendritic trees
- Neurones appear at birth and then migrate and specialise
What is the timecourse of maturation of different regions?
Development is so sensorimotor cortex develops first, then parietal and temporal association cortex, and then prefrontal cortex
What is the study looking at grey matter?
- Looked at children every 2 years from 5-20
- By age 5, regions are mature (developed and pruned) = visual cortex and motor
- By age it spreads into parietal and temporal
- Dorsolateral pre-frontal cortex is last
What happens in the first 1-2 years?
- Brain doubles in volume
- Cortical thickness and SA increase
- Complexity of neurons and no. of synapses
- Myelination begins before birth but continues beyond adolescence
How does face perception develop?
- Genetic: have genetic program and will have face processing system
- Innate: present at birth = do we have a precursor system and we develop and finetune it
- Experience-dependent: experience needed to develop
What are the genetic contributions to face perception?
- Twin study of face-specific recognition ability, face inversion effect, and composite face effect
- All more highly correlated in monozygotic than dizygotic twins = suggests something heritable about face perception
- Developmental prosopagnosia is a lifetime inability in recognising faces = runs in families
- No heritability for inverted faces or houses
- Face heritability seems to be independent of general cognitive abilities
What perceptual abilities are present in newborns?
- Face detection: face vs non-face
- Preference for faces
- Face recognition - discriminate between identities
- Face recognition across viewpoint changes
- Special face-processing related effects e.g inversion effect
What was a study about face detection and attention in newborns?
- Tested newborns within hour of birth
- Babies lying over caregivers lap and paddles either had schematic of face, features/scrambled face, and nothing
- Measured the head and eye turning for each paddle
- Face had the most response, then scrambled, and then low levels to the blank paddles = idea of innate system
- Could just be the template = more structure on top than bottom = sufficient for a face
- Newborns can detect faces and preference to faces within an hour
What was a study looking at recognition in newborns?
- 1-3 day old infants recognise the identity of non-familiar faces = babies like looking at new things, habituate quickly and new things grab their attention
- Present babies with identity during habituation phase, and then 2 other images, one of which has a different identity. If baby looks more at new identity = recognise its different as its new
- When presented babies with a 45 degree viewpoint change = still preferred to look at new face vs one they had seen, but could not differentiate with a full 90 degree change
- Face recognition abilities early on
What was a study looking at specific facial recognition (inner/outer features of face) in newborns?
- Had a full features condition, inner features and outer features
- Each condition provides sufficient cues for face recognition
- Inversion disrupted recognition of inner features condition = suggests that infants have a lot of signatures associated with face perception
What is an overview of face perception in development?
- By age 4, children have adult-like signatures of face perception
- Lots of tasks have no evidence of children under 3yo as not performed
- Lots of evidence of presence in birth and not much development across age
What are critical periods for face perception?
1) Cases of early visual deprivation due to congenital cataracts: typically show normal recognition of same-image faces later in life BUT impaired recognition across viewpoint changes
- No composite face effect = indicates some critical periods for viewpoint changes etc. and others do not need input.
2) Patient MM, blind 3-46 and some experience of brightness, got corneal transplant and monocular vision restored at 46, tested following surgery and 10y later
- No evidence for experience-depending recovery of function, neither behaviourally nor neurally = function cannot be recovered = aspects of face perception need to occur early in life = need external input for perceptual system to develop
What is perceptual narrowing in face perception?
- Infants are better discriminating at their native language than foreign ones after 6mo
- After 6 mo they hone in on faces they know, and lose this ability (can discriminate between monkey faces also) = experience seems to be eliminating ability to discriminating monkeys
What was controlled rearing in monkeys? (study)
- Monkeys were reared about exposure for faces for 6,12 or 24 months (neither monkey or human faces)
- A week before deprivation ended, monkeys showed preferential looking to faces vs other ovjects and could discriminate monkey and human faces equally well
- Face discrimination with adult-like accuracy
- After deprivation happened, monkeys either exposed to monkey faces only or human faces only for a month
- There was selective discrimination of exposed species, difficulty discriminating non-exposed species = suggests experience need for perceptual narrowing = but also had an innate way of discriminating
What is the development of face perception in the brain?
- By age 5, most of face specific regions are evident
- Put 4-6mo infants in a mri scanner looking at faces and houses
- Orange regions respond to faces more than houses and blue is vice versa: identifies FFA etc. BUT these regions are less selective than adult FFAs = spatial layout of face-specific regions apparent
What was a longitudinal study of monkeys?
- From birth to first year of life: scanned them every month and showed them with faces and scrambled faces and object to see how brain regions develop
- Some functional organisation of IT apparent at 30 days
- Prior to 170 days (6mo), no evidence for face-specific patches (face vs object)
- From day 200, face-selective response is stable
- Is it due to experience - no because of prior study with monkeys - could be innate/pre-programmed
Is seeing faces necessary for development of face-domain?
- Monkeys reared without ever seeing a face (controlled rearing)
- Monkeys could hear and smell other monkeys had social contact and visual experience but not faces
- At 90 days old, during MRI scans they saw faces = by 252 days in control there are face patches, but in exp there is no face patches = no exposure = no face patches = experience is necessary = cannot be preprogrammed and requires input
What was the link between connectivity and function of a region?
- Surgically removed connections in ferrets and rewired them so the auditory cortex receives input from retina
- When presented with visual stimuli there is an auditory cortex response - developed to process visual input = long-range connections that are in place when the system begins to take in information determines what function that region will have
- Even orientation columns develop in auditory cortex = looks like a visual cortex
- Ferrets do not hear things but see things = clear link between connections and functions of a region BEFORE function is exposed to stimuli
What is the link between connectivity and selectivity of faces?
- Looked at FFA and connectivity fingerprints from that region = tracking nerves to other areas of the brain from FFA to create probability maps of where things connect to = linked to individual differences of activity of each regions
- Could predict on connections = how strongly area could respond to faces
What is evidence from early brain damage?
- Adam had a stroke when he was 1 day old and had damage to occipital lobe
- Tested at 16, visual acuity was not great and object recognition was not good
- Profound prosopagnosia
- Stroke destroyed his long range connections to FFA
What is further development through adolescence?
- Hard to assess children as tasks are not designed for them = most abilities are present and adult like at ages 4-5
- Ffa grows in size and selectivity due to myelination affecting cortex, and those that were limb selective have been taken over by face selectivity
- Facial expression perception is not seen properly before 7mo = emotion recognition develops well into adolescence
