Experience Dependent Plasticity in the Developing Brain

Hebb’s Postulate

Coordinated activity of presynaptic and postsynaptic neuron strengthens the synaptic contact between the two

Neurons that fire together, wire together

Activity dependent plasticity

Postnatal Life

During the first month and years of life there are a lot of changes to the brain

Brain continues to grow after birth, more synapses and connections

Connections increase during early development (first year) after that the number of synapses decreases (synaptic pruning)

Activity Dependent Plasticity

Early life experiences shape activity dependent plasticity

Compensation for deficits

If an eye is lesioned early enough then the other will compensate and be overly sensitive

Sensory Tuning

Becoming more sensitive to a biological relevant stimulus

In humans sounds in 2-5 kHz

In birds sounds of their song

Critical Periods

Maximal effect of experience on learning, animals can still learn skill after critical period however it will not be as good

During embryonic: When nervous system is formed

After birth: language

Critical Period in Songbirds

Aquisition of song must occur during the first two months or learning impaired

Initially sensory acquisition, listening to the song

Sensory Motor Learning: similar to babbling in humans, correcting for mistakes in song

Crystallized song: Song is learned and bird keeps it for life

Critical Period in Language

Children with deaf parents or that are deaf will start to babble with hands around 7 months

Babbling at 7 months important for development of language

Fluency in learning new language declines with age

Critical periods for tuning to phonemes

Learning a language activates different brain region in children and adults (could be why learning a language as a kid is easier)

Synapse Addition and Elimination In Critical Periods

In early life there is an increase in synapses and then there is a decline until it stabilizes

Motor skills stabilize slower because motor skills are acquired much later in life

Changes in amount of Gray and White Matter

Gray Matter: Area of brain where cell bodies are located

Decrease in gray matter over years

Increase in white matter over the years

Why does gray matter decline with age

Result of synaptic pruning

Born with more neurons than needed as an adult, neurons that are not needed die off or synapse with other neurons

Why does white matter increase with age

More connection and strengthening of connection

Building myelin over the years

Why is there a sex difference

Males are physically bigger than females, this could be why there is a difference in the brain

Gray Matter and ADHD

Difference in amount of gray matter in child with ADHD and without

Childrens with ADHD do not have as much gray matter as those that do not have ADHD, decrease follows the same trend

Critical Periods in Visual System

Closing of one of the eyes during early development causes increased activity for the opposite eye (eye never became functional)

If closing of eye happens later in life, there is a weaker response but still process information

Peripheral input and Cortical Organization

In rodents, whiskers are really important and they have a representation in the thalamus

Lesioning of trigeminal nerve removes organization

Changing of receptors will also see changes in pattern

Calcium’s Role

Drives changes in gene expression and plasticity

Calcium dependent signaling involved in NMDA receptors

Triggers removal and addition of AMPA receptors

Changes in neuronal structure

Activates kinase that induce gene expression via CREB