4. The developing brain

Piaget- development

* considered development as a cyclical process of interactions between child and their environment leading to a progression through the stages

Genetic contribution - Piaget

developing a brain that is ready to learn in certain ways

Environment - Piaget

assimilating evidence via experience and then developing new mechanisms in light of the feedback obtained

Neuroconstructivism

* interaction between environment and genetic factors
* cognitive system matures as brain goes through developmental changes

Blueprint analogy of the brain

* each connection in the brain is predetermined

deterministic development

structures of the brain are the same for everyone

Probabilistic development- modern dominant view

creation of brain in stages- each stage influence each other

* genes, brain structure, brain function, experience

Prenatal brain development

* cell division occurs
* then cell specialisation
* few weeks in- nervous system starts to form
* neural tube formation - frontal part develops as brain, back end develops as spinal cord- proliferative zones: neurons and glial cells are produced


* during peak stages, 250,00 neurons produced p/m
* neurons migrate to their final location

where other structural features of the brain emerge from

* folded cortex emerges from having lots of neurons (surface shape of brain)
* axons connect forming white matter tracts
* Hebbian learning: spontaneous electrical activity enables networks to form (e.g. electric activity from retina forms visual pathways)
* can start shaping individual experiences from the womb

postnatal brain development

* majority of neurons formed prior to birth
* postnatal increase in brain size-
* synaptogenesis:
* Myelination
* Glial cell proliferation

Synaptogenesis

* formation of synapses between neurons in the NS
* synaptic density increases after birth, then levels out, different for each brain areas 
* more synapses doesn’t mean more efficient processing- fine tuning happens over time 

Myelination

* myelin sheath thickens after birth- resulting in quicker information processing
* Pfc is the last area to develop myelin sheath- Pfc associated with adult functioning

Glial cell proliferation

* helps to increase brain size

Plasticity- PNBD

* experience dependent change in neural functioning
* experience alone can lead to small but observable structural changes e.g. juggling
* increased grey matter: new synapses, dendrites, axon collaterals, glial cells - not due to neurogenesis
* more grey matter doesn’t mean better cognitive ability

Functional brain development

* functional brain plasticity : prenatal brain damage can lead to major reorganisation of tracts
* case study: AH- no right hemisphere
* found plasticity: left hemisphere processed visual info from both visual fields

Functional brain plasticity limits

* spontaneous electrical activity enables networks to form intrauterine - these connections won’t be fully lost
* opportunities for major reorganisation are time limited= critical or sensitive periods

Filial imprinting

* Lorenz
* process by which young animals learn to recognise parent
* happens between 15h- 3 days
* movement is crucial

Critical and sensitive periods- 2 main features

1. learning takes place within a limited window - but window can be extended in lack of movement
2. learning is hard to reverse by later experiences - but chicks imprinted to one object can generalise to similar objects, preference can be changed after sensitive period

imprinting in humans

* phonemic discrimination e.g. between r and l - if doesn’t exist in native language- won’t be able to differentiate sounds later in life
* accents- infant brain familiarises itself w the sounds in native language

2 explanations for existence of critical period

1. after birth- Alot of synapses formed- plasticity drops after and learned information is fossilised, brain removes weaker connections
2. closure of window initiated by learning itself e.g. an environment cue - particular gene playing a role in filial imprinting that is switched off after exposure

Innate knowledge - philosophy

Empiricism- newborn mind is blank slate

nativist- born w some knowledge

innate knowledge- modern view

* we have innate knowledge= readiness to learn (e.g. imprinting)
* knowledge or behaviour that arises in absence of appropriate experience - development of cat visual cortex
* or presence of experience- e.g. infants liked sweet flavour

Prenatal ultrasound

* structural: diff types of tissue have diff physical properties
* used to create STATIC maps
* can identify diff structures

Prenatal MRI

* to study development of brain in the womb
* only tells us about structure of brain

Behavioural methods

* we can infer brain development from their behaviour:
* preferential looking paradigm - looking chamber
* habituation paradigm

preferential looking- form perception

* 1 week old- 3.5 months olds
* differntial interest within pairs was based on pattern differences
* able to perceive forms and differentiate them - innate knowledge

preferential looking- visual acuity threshold

* the width of the stripes of the finest pattern that was preferred to grey would provide an index to visual acuity
* the width of the finest stripes could be distinguished decreased w increasing age (0-6 months)
* the eye, the visual nerve pathways and the visual part of the brain are poorly developed at birth

Modern use of preferential looking

* video camera
* stimuli presented on screen
* babies stay w caregiver- who doesn’t interfere

Modern use of preferential eye tracking

* uses infrared (non collimated) light to measure where the p is looking at the screen at any moment
* fixations and saccades
* more precise measurement of looking times and fixations

problems w preferential looking

* if infants looking equally to screen 1 and 2 either: failed to discriminate 1 and 2 or finds one and two equally interesting

Habituation paradigm

* infants prefer novelty
* showed pairs of stimuli simultaneously: one pair remained constant and one changed across trials
* found decreasing fixation to the familiar pattern and increasing fixation to the novel pattern

Modern use of Habituation paradigm

* makes infant bored w one stimuli then pair it w another - if interested in new one then they can differentiate

Functional neuroscience methods

* Functional: temporary changes in brain physiology associated w cognitive processing e.g. fMRI
* problem: usually ask p’s to perform some kind of task or sit still and look at images- infants can’t do

Functional neuroscience methods that can be used with infants

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EEG/ERP- quick installation, infant friendly stimuli and more breaks during study

fMRI and fNIRS 

Infant ERP peaks

* some adult ERP peaks are present in infants but delayed e.g. visual ERPS
* N290 in infants= N170 in adults
* same perceptual and face specific component/ networks

Infant ERP’s

* can compare visual processes in adults and infants
* if processes are similar (similar ERP) then we can assume that the underlying brain networks and/or processing mechanisms are also similar e.g. face processing

some ERP components only present in infants 

* NC- negative central peak
* peaks between 300-700 ms after stimulus onset
* larger peak reflect higher attention
* larger Nc for mothers face compared to strangers face- infant can process mothers face and differentiate it from other faces

fMRI

* not ideal to use w infants
* highly sensitive to motion artifacts
* loud restrictive environment
* there are some attempts- using headphones

fNIRS

* measures BOLD signal
* unlike fMRI, uses near infrared spectrum of the light
* skin tissue and bone are mostly transparent to NIR light
* HB and deoxyHB absorb NIR
* emitter emits NIR light, detector detects
* HB and deoxyHB absorbs NIR- from difference between emitted and detected NIR, we can compute BOLD
* measures concentration changes of oxy and deoxy, related to brain activity
* only scans surface

fNIRS pros and cons

* NIRS can be appropriate substitute for fMRI for studying brain activity related to cognitive tasks 

cons

* fNIRS has lower spatial resolution 
* only surface of cortex imaged 
* only few sensory used above a certain brain areas 

pros

* portable 
* more tolerant of movement