Brain development

2 problems with following assumption: changing function/development is due to physiological changes/growth of brain

• Brain changes are correlated with life changes/experience

• Matching relationship between brain changes + behaviour is very complex and hard to measure

Dimensions in which the brain develops (3)

• Size

• Synaptic properties

• Myelination

Number of neurons at birth

• Approx. 100 billion (most of the neurons an individual will ever have)

Glial cells

• Non-neuronal cells that provide a range of support functions (e.g. producing myelin sheath)

Temporal lobe function

Associated with speech + language, music + emotional information

Parietal lobe function

Associated with spatial processing + sensory info integration

Cerebral lateralisation

The specialisation of different hemispheres of the brain for different modes of processing

Neurogenesis def

The proliferation of neurons through cell division

When does neurogenesis occur? (2)

• 42 days after conception to midway through gestation

• However, humans continue to develop new neurons as adults, particularly in hippocampus (memory)

Process of neuron development

• After neurons are formed, they generally migrate from centre of brain outwards towards developing neocortex

• Once reach destination, first grow axons (which elongate) + then dendrites (through arborisation)

Arborisation def

Formation of new dendritic trees + branches

Spines def

Formations on the dendrites of neurons that increase the dendrites’ capacity to form connections with other neurons

When (1→1) + where (1) does myelination occur?

• Begins prenatally + continues into adulthood

  • Most rapid few months after birth, then slows during toddlerhood, then slows more into young adulthood

• Begins deep in the brain then moves upwards + outwards into the cortex

Effect of varying rate of myelination for different brain areas (1)

• Contributes to different rate of maturation of different brain areas (e.g. sensory areas (back of brain) mature much faster than executive areas (front of brain))

What is myelination (indicated by white matter volume) correlated with? (1)

• Speed of processing → linked to cognitive abilities

Importance of white matter (WM) development (1)

• Seems to be correlated with a child’s outcome (pre-term babies with deficits/problems with WM often have cognitive difficulties (as WM increase most rapidly preterm))

Human newborns + neural development note

• Human newborns have underdeveloped neural system compared to other animals

  • Completely helpless at birth (con)

  • More potential for learning (pro)

Synaptogenesis def

The process by which neurons form synapses with other neurons, resulting in trillions of connections

When + where does synaptogenesis occur

• Most rapidly prenatally + shortly after birth

• Occurs at different rates in different brain regions (sensorimotor regions first, frontal areas last)

Synaptic pruning def

• Excess + unused synapses (up to 40%) are eliminated/’pruned’

Synaptic pruning & age (1) + note (1)

• Synapse density varies as a function of age

  • Causes decrease in cortical volume + thickness in adolescent period

• Occurs earlier in visual cortex than auditory or prefrontal cortex

Associations of thinner left + right cortices in parietal areas + note

Better global performance in the brain

• However, unsure of why this is the case

Developmental disorders associated with atypical pruning patterns (2) + why (2)

• Autism spectrum disorder (ASD)

  • Larger brain + increased cortical thickness suggests greater synaptic density → reduced/delayed pruning

• Schizophrenia

  • Excessive pruning in adolescence

Experience expectant brain-function

• Require common basic experiences to develop (e.g. visual stimulation)

• Synapses → ‘use it or lose it’

• Normal development

Plasticity def + children vs adults

• The capacity of the brain to be affected by experience

• Children have more plastic brains than adults (thus can recover from brain injury better)

Pro + con of experience-expectant plasticity

• Pro: because experience helps shape the brain, fewer genes are needed to be dedicated to normal development

• Con: vulnerability → without experience, development will be compromised

Cross-modal reorganisation def

• When brain areas typically dedicated to one sensory modality (e.g. vision) begin to process another sensory modality (e.g. audition)

Note on sensitive periods in relation to experience-expectant plasticity (1→1)

• Neural organisation that occurs (or does not occur) during sensitive periods are typically irreversible

  • E.g. if visual stimulation doesn’t occur early in life → vision impairment

Experience-dependent plasticity def

Process through which neural connections are created + reorganised throughout life as a function of an individual’s experiences

Note on experience-dependent plasticity (1)

• Normal development occurs regardless, just differently (e.g. music training → shapes brain for music)

Evidence that frontal lobe development sets humans apart from other animals (3)

• Dev. is slow + protracted over childhood

• Prefrontal cortex implicated in executive functioning

• Prefrontal regions implicated in dev. disorders

Evidence against claim that frontal lobe development sets humans apart from other animals (3)

• Not much difference in size of frontal cortex between humans + great apes

  • Organisation may set us up: may be more richly interconnected etc.

Brain size + cognitive ability correlation (1)

.44 (significant)

Brain size + intelligence (1→1)

.18 (significant)

• Within-family correlation of brain volume with intelligence

Why correlation ≠ causation for brain size + IQ (4)

• Correlation, not causation

• Within-group differences larger than between group

• Don’t know which bio. property of brain is related to intelligence

• Also correlation is small

Why it’s difficult to establish causal relationships between biology + behaviour (3)

• Just because you have gene → doesn’t mean you will develop behaviour (environmental triggers may be required)

• Linking area of brain to behaviour doesn’t explain behaviour

• Environment influences brain structure