The Neural Mechanisms of Learning

1. Its all physical! The Neural Mechanisms of Learning

2. Neural basis of learning • Basic structure of the nervous system 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 • http://www.youtube.com/watch?v=90cj4NX87Yk

3. Neural Basis of learning Synaptic knob Axon terminals synapse Myelin sheath Axon

4. Synapse • Synapse involves: • 1/ Synaptic gap • 2/ Presynaptic neuron • 3/ Postsynaptic neuron

5. Neural Basis of learning

6. Hebbian Learning • Learning involves the establishment and strengthening of neural connections at the synapse. • Learning results in the creation of cell assembles or neural networks • ‘neurons that fire together wire together’

7. Neurotransmitters and LTP • Drugs that enhance synaptic transmission tend to enhance learning • NMDA (N-methyl-D-aspartate) a neurotransmitter receptor found on dendrites in the hippocampal region • NMDA specialised to work with the neurotransmitter glutamate • Important role in LTP • Neurotransmitter dopamine also plays a role in learning

8. NMDA and LTP • Genetically engineered rats with more efficient NMDA receptors showed: • Better memory • Faster learning • As compared to rats with normal NMDA receptors

9. Long term potentiation and the hippocampus – rats in a water maze • LTP crucial for not only memory but also LEARNING • Richard Morris experiment (1982) • 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

10. 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

12. Neural Plasticity • Plasticity is the ability of the brain’s neural structure or function to be changed by experience throughout the lifespan. • Two types: • 1/ Developmental Plasticity • 2/ Adaptive plasticity • Unclear whether or not all brain structures are as plastic as the sensory and motor cortices

13. Rosenzweig 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 • All rats stayed in their cages for 80 days

14. Rosenzweigstudies • When their brains were dissected the rats with enriched experience had thicker, heavier cerebral cortex • Thicker bushier dendrites (LTP) • More neurotransmitter acetylcholine • Brain weight increase as much as 10% • Neural connections increase as much as 20%

15. Other Plasticity studies • The brains of university graduates have approx 40% more neural connections than those who leave school early! (2006) • Intellectual stimulation can protect against dementia! (2004) • This is even true for twins who have identical genetic make up

16. Developmental plasticity • Changes in the brain’s neural structure in response to experience during its growth and development • Synaptogenesis– new neural connections • Synaptic pruning – removal of synaptic connections that are no longer needed • Adults have 40% less neural connections than a 3 year old!

17. 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

18. Developmental plasticity • Sensitive period – time an organism more is 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

19. Genie

20. Adaptive plasticity • The brain reorganises the way neurons in different regions operate in response to a deficit • Deficits can occur from birth or as a result of brain damage • Rerouting – neurons near damaged area seek new active connections with healthy neurons • Sprouting – new dendrites grow • Allows shifting of function from damaged area to healthy area

21. 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

22. 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

23. Use of Imaging technologies to localise changes in the brain due to learning • Comparative brain scans can be conducted • fMRI, PET and SPECT effective to monitor brain function before and after learning • MRI scans of London taxi drivers show larger rear hippocampus regions (responsible for spatial navigation) as compared to London bus drivers.