The developing brain Flashcards
nature vs nurture
extent to which cognition and behaviour (and brain development) can be attributed to genes or the environment
nature
genetic blue brint
nurture
roles of experiences
Contemporary notion of environment is much broader than commonly understood
-includes biological circumstances (e.g. Exposure to toxins, diet), personal and social circumstances
galton
nature- geniuses are born, not made
first person to realise heredity could be estimated by comparing identical and non identical twins
piaget
considered development as a cyclical process of interactions between the child and his or her environment leading to a progression
through stages
Genetic contribution = developing a brain that is ready to learn in certain ways
Environment = assimilating evidence via experience and then developing new
mechanisms in light of the feedback obtained
neuroconstructivism
A process of interaction between environment and brain based constraints that leads to the mature cognitive system emerging out of transformations of earlier ones (but does not assume discrete stages)
blue print analogy
each connection in the brain is pre-determined
at some gross level must be true: human brains are similar to each other but differ from other species
-inconceivable that genome contains detailed wiring diagram of the brain, misleading that this suggests structural details of our brain are specifies at a fine level of detail
deterministic development
genes dictate the structure of the brain, which enables the particular functions of the brain, which determines the experiences we have
probabilistic development
brain structure and expression of genes can be influenced by expression of genes and visa versa
effects of genes on the brain are probabilistic- they specify approximately how many neurons will grow but not exactly how/where they will grow
human gestation period
about 38 weeks from conception
prenatal brain development
Cell division
Cell specialization
*
Neural tube formation
o Proliferative zones: neurons and
glial cells are produced
o During early development 250,000
neurons are produced per minute
o Neurons migrate to their final
location
prosencephalon to
telencephalon and diencephalon
mesencephalon to
midbrain
rhombencephalon to
metencephalon
myelencephalon
telencephalon to
cerebrum
diencephalon to
eyecup, thalamus, hypothalamus and epithalamus
metencephalon to
pons and cerebellum
myelencephalon to
medulla oblongata
prenatal brain development
Highly folded cortex is highly distinguishable feature of human brain
-visible in last few months before birth and shows further small changes over the fist 2 years of life
Folding likely to be a outcome of packing more neurones within a restricted space together with stretching the cortical surface by axonal tension
-rather than it being specified by genome
Gyri and fissures very similar for everyone
-emerges from constraints
Spontaneous waves of electrical activity emanating from the retina before birth are important in setting up synaptic pathways from the retina to the LGN and the V1 in readiness for processing of visual stimuli
-this is the beginning of individual experience/ differences
what is the beginning of individual experience/ differences?
Spontaneous waves of electrical activity emanating from the retina before birth are important in setting up synaptic pathways from the retina to the LGN and the V1 in readiness for processing of visual stimuli
hebbian learning
Spontaneous electrical activity enables networks to form
postnatal brain development
Majority of neurons formed
prior to birth
Newborn brain weights 450 g
(vs. 1400 g adult brain)
Postnatal increase in brain
size:
o Synaptogenesis
o Myelination
o Glial cell proliferation
plasticity
increased grey matter: new synapses, dendrites, axon collaterals, glia cells
synaptogenesis
-there is a characteristic rise and fall in the synapse formation
-synapses fall during the course of development because the process of fine tuning the brain to the environment renders some connection redundant
-more synapses do not necessarily reflect more efficient functioning
myelination
-increase in fatty sheath that surrounds the axons and increases speed of information transmission
-prefrontal cortex = one of the last areas to reach adult levels of myelination
plasticity
experience dependent change in neural functioning, alterations in the pattern of synaptic connections
adults who learn to juggle over a 3 moth period show increased grey matter density
assessed with MRI, in a region, V5/MT, specialized for detecting visual motion as well as the occipitoparietal region implicated in hand–eye coordination
We might expect a positive relationship between individual difference in ability and local increases in grey matter, this isn’t always the case
congenitally blind people have more grey matter in V1 than sighted people
One cant take grey matter density as a simple proxy of cognitive ability as it depends on the underlying mechanisms
-developmental pruning of synapses -thinner is better
-experience-dependent changes -thicker is better
what can increase grey matter density?
new synapses
Glia cells can divide or change in size which could contribute to changes in grey and white matter volume
More dendritic branches, synapses or axon collaterals
functional brain development
prenatal brain damage can lead to major reorganisation of tracts
extreme plasticity
In the face of major insult, the brain may be capable of reorganising itself in some fundamentally different ways
In non human animals it is possible to surgically transplant a region of the cortex or sever pathways such that novel ones emerge
AH
10 year old girl- failed to develop a right hemisphere and right eye prenatally
Only has minor visual impairment
fMRI showed visual information could be rerouted into the intact ipsilateral hemisphere
-neurons coding left and right sides of space in the same cortical map where they are normally segregated into separate hemispheres
functional brain plasticity limitations
Spontaneous patterns of activity prior to birth are already shaping neural activity and parcellating them into different networks - these connections will not be fully lost
Major reorganisation seems to be strictly time limited
Lorenz imprinting - critical and sensitive periods
Once imprinted, the gosling is unable to learn to follow a new foster parent
happens between 15h and 3 days, movement is key
Intermediate and medial of the hyperstriatum ventrale (IMHV) in chick forebrain, which may correspond to mammalian cortex, is critical for enabling imprinting
two main features of critical and sensitive periods
- Learning takes place within a limited window
o But opportunity can be extended in lack of experience - This learning is hard to reverse by later experiences
o But chicks imprinted to one object can generalize to similar objects
(colour or shape)
o Preference can be changed after sensitive period
language sensitive and critical periods
Each basic skill involved in language may have its own sensitive period rather than a fixed cut off point at puberty
e.g. Sensitive period for phonemic discriminations - occurs during infancy and is resistant to subsequent exposure
In contrast, accents are ore fluid during childhood and but become notoriously hard to change from onset of adulthood
possible explanations of critical and sensitive periods
Genetically programmed synaptogenesis (readies brain for learning),
followed by reduced plasticity (learned information is then “fossilized”)
- Closure of window could be initiated by learning itself, i.e. an environmental
cue
empiricist view
newborn mind is a blank slate
natiavist view
we are born with some knowledge
