What is learning in neuroscience?
• Learning is a relatively lasting change in behaviour or brain function
• Caused by experience
• Occurs via changes in synaptic strength and neural circuits
What is the biological basis of learning in the brain?
• Learning occurs through synaptic plasticity
• Involves strengthening or weakening of connections between neurones
• Alters prediction of outcomes
What is associative learning?
• Learning that two events or actions are linked
• Forms associations such as stimulus–stimulus or action–outcome
• Core mechanism underlying conditioning
What is Hebbian learning?
• Hebbian learning is activity-based learning
• Described as ‘neurones that fire together wire together’
• Repeated co-activation strengthens synapses
How does Hebbian learning work at the synapse?
• Repeated firing of presynaptic and postsynaptic neurones together
• Leads to long-term potentiation (LTP)
• Increases synaptic efficiency
Which receptors are central to Hebbian learning?
• NMDA receptors detect coincident activity
• Allow calcium influx
• Trigger insertion of AMPA receptors
Which brain regions rely heavily on Hebbian learning?
• Hippocampus – memory formation
• Cerebral cortex – perceptual and skill learning
Why is Hebbian learning NOT reward-based?
• It depends on neuronal co-activity, not outcomes
• No reward or punishment signal required
• Learning is correlation-based
What is unsupervised learning?
• Learning occurs without external feedback
• The system detects patterns and regularities
• No teacher and no error signal
What does the brain do during unsupervised learning?
• Groups similar inputs
• Extracts statistical structure
• Organises sensory information
What are examples of unsupervised learning in humans?
• Face recognition
• Sensory development in infancy
• Perceptual organisation
What is the neural basis of unsupervised learning?
• Hebbian plasticity
• Sensory cortex reorganisation
• Experience-dependent synaptic changes
How is unsupervised learning relevant to psychiatry?
• Autism – atypical pattern detection
• Schizophrenia – abnormal salience assignment
What is supervised learning?
• Learning guided by a teacher or error signal
• System is told what is correct or incorrect
• Learning aims to reduce error
What is the key mechanism in supervised learning?
• Error correction
• Minimising difference between expected and actual outcome
Which brain structures are associated with supervised learning?
• Cerebellum – motor learning
• Cortical feedback loops
Why is supervised learning less central in psychiatry?
• Most psychiatric learning abnormalities involve reward and salience
• Reinforcement learning is more relevant clinically
What is reinforcement learning?
• Learning driven by rewards and punishments
• Behaviour shaped by outcomes
• Central computational model in psychiatry
What question does reinforcement learning answer?
• ‘Was the outcome better or worse than expected?’
• Behaviour is updated accordingly
What is reward prediction error (RPE)?
• RPE = actual reward – expected reward
• Core signal that drives learning
How does dopamine encode reward prediction error?
• Better than expected outcome → increased dopamine firing
• Worse than expected outcome → reduced dopamine firing
Which brain systems mediate reinforcement learning?
• Dopamine neurones (VTA, substantia nigra)
• Basal ganglia
• Prefrontal cortex
Why is dopamine NOT a pleasure signal?
• Dopamine codes prediction error
• Signals unexpectedness, not enjoyment
• Pleasure can occur without dopamine
How is reinforcement learning altered in depression?
• Reduced reward sensitivity
• Blunted dopamine response
• Impaired reinforcement learning