The Neural Mechanisms of Learning Its all physical!
Feb 23, 2016
The Neural Mechanisms of Learning
Its all physical!
Neural basis of learing
Basic structure of the NS is set before birth
Neurons are however flexible living cells that can grow new connections
The ability of the brain to reorganise the way it works is referred to as plasticity
Neural Basis of learningAxon terminals
Myelin sheath
Axon
Synaptic knob
synapse
Neural Basis of learning
Hebbian theory
Learning results in the creation of cell assembles or neural networks
‘neurons that fire together wire together’
When a neurotransmitter is repeatedly sent across the synapse this can effect the strength of these connections
Neurons that do not fire together weaken their connections
Long term potentiation
Long term Potentiation New Receptor Formation
Long Term MemoryNew Synapse Formation
Late LTP
Long term potentiation and the hippocampus – rats in a water maze
Pool of milky water with platform to stand on (just under the surface)
3 groups of rats- Group 1 – frontal lobe damage- Group 2 – hippocampus damage- Group 3 – no damage
Long term potentiation and the hippocampus – rats in a water maze
Results display the importance of the hippocampus in allowing LTP
- Group 3 – no damage – located platform more quickly each trial
- Group 1 – frontal lobe damage – performed about as well as group 3
- Group 2 – hippocampus damage – never got better, showed no evidence of learning
Neurotransmitter and LTP Drugs that enhance synaptic
transmission tend to enhance learning
NDMA (N-methyl-D-aspartate) a neurotransmitter found on dendrites in the hippocampal region
NDMA specialised to work with the neurotransmitter glutamate
Important role in LTP
MDMA and LTP
Genetically engineered rats with more efficient MDMA receptors
Better memory Faster learning As compared to rats with normal
NDMA receptors
Neural Plasticity The brain is adaptive It changes as a result of experience (learning)
Remember LTP? New connections New neural networks Genes govern overall brain structure
Unclear whether or not all brain structures are as plastic as the sensory and motor cortices?
Developmental plasticity Babies born with all 100 billion nerve cells Each cell at birth synapses with around 2500
other neurons By late childhood the number of connections
increases to around 15,000 per neuron By adulthood this number decreases to around
8,000 as unused connections are destroyed
Children’s brains show greater plasticity than adults, this might explain why children learn languages faster than adults
Rozenweig studies
Lab rats placed in 3 different environments after birth with different opportunities for learning
- 1 – standard environment – simple communal cage with food and water
- 2 – impoverished environment – simple small cage housed alone
- 3 – enriched environment – large, social, with lots of stimulus objects
Rozenweig studies
All rats stayed in their cages for 80 days
When their brains were dissected the rats with enriched experience had thicker, heavier cerebral cortex
Rozenweig studies
Differences were largest in the occipital lobes and smallest in the somatosensory cortex
Also showed new synapse formation Thicker bushier dendrites More neurotransmitter acetylcholine
Later studies showed changes in adult rat brains also placed into different environments
Later studies Brain weight increase as much as 10%
Neural connections increase as much as 20%
Being raised in enriched environment can increase problem solving ability
Humans raised in isolation from proper stimulation can become severely retarded
genie & victor – the wild children
Genie
Later studies
The brains of university graduates have approx 40% more neural connections than those who leave school early!
Intellectual stimulation can protect against dementia!
This is even true for twins who have identical genetic make up
Developmental plasticity
Changes as a result of experience and maturation
Synaptogenesis – new neural connections
Synaptic pruning – removal of synaptic connections that are no longer needed
Adults have less neural connections than a 3 year old!
Developmental plasticity Sensitive period – time an organism more
responsive to certain stimulation Lack of stimulation can lead to long term deficit E.g. closed eye from birth leads to later
blindness even when eye eventually opened Language acquisition has a sensitive period (0 –
12) remember genie!
Learning a new language in teen years can lead to the development of a second Broca’s area!
Adaptive plasticity
The brain reorganises the way neurons in different religions operate in response to a deficit
Deficits can occur from birth or as a result of brain damage
Damage from birth - congenital
Congenital – E.g. People who are blind from birth may have occipital lobes that are used for senses other than vision
this may explain why people who are blind from birth have very good hearing or tactile sensitivity
Damage from injury
When a particular brain area is damaged e.g. stroke other brain areas can ‘take up the slack’
This is what happens when people ‘recover’ from brain damage
Nerve cells do not regrow, rather other neurons take over the functions of the damaged cell
Damage from injury
Rerouting – neurons near damaged area seek new active connections with healthy neurons
Sprouting – new dendrites grow May occur near damaged area of in
other parts of brain Allows shifting of function from
damaged area to healthy area ‘Relearning’ tasks like walking,
eating etc. helps these new connections form
Adaptive plasticity and experience Musicians motor and sensory areas Taxi drivers parietal lobes Dancers motor areas
Other bits -The Basil Ganglia Well learned responses
Neural network ‘transfers’ to the basil ganglia
Other bits - The Dopamine Reward System Relevant to operant conditioning
Behaviours that produce a positive consequence make us ‘feel’ good
Release of dopamine at a neural level