TYPES OF LEARNING

Updated for 1999 Lecture Notes - Week 10
Learning - Chapter 14 TYPES OF LEARNING

1) Perceptual learning – ability to learn to recognize stimuli that have been seen before

Primary function is to identify and categorize objects and situations
Changes within the sensory systems of the brain

2) Stimulus-response learning – ability to learn to perform a particular behavior when a certain stimulus is present

Establishment of connections between sensory systems and motor systems
Classical conditioning – association between two stimuli

Unconditioned Stimulus (US), Unconditioned Response (UR), Conditioned Stimulus (CS), Conditioned Response (CR)
Hebb rule – if a synapse repeatedly becomes active at about the same time that the postsynaptic neuron fires, changes will take place in the structure or chemistry of the synapse that will strengthen it (see Figure 14.1)
Rabbit experiment – tone paired with puff of air

Instrumental conditioning – association between a response and a stimulus; allows an organism to adjust its behavior according to the consequences of that behavior

Reinforcement – positive and negative
Punishment

3) Motor learning – establishment of changes within the motor system

4) Relational learning – involves connections between different areas of the association cortex

5) Spatial learning – involves learning about the relations among many stimuli

6) Episodic learning – remembering sequences of events that we witness

7) Observational learning – learning by watching and imitation other people

LONG-TERM POTENTIATION

long-term increase in the excitability of a neuron to a particular synaptic input caused by repeated high-frequency activity of that input

hippocampal formation - specialized region of the limbic cortex located in the temporal lobe. It contains:

entorhinal cortex whose axons grow toward the dentate gyrus, forming the perforant path
dentate gyrus projects to pyramidal cells in CA3
pyramidal cells project both to CA1 and to basal forebrain

associative long-term potentiation - produced by association in time between 2 sets of synapses; weaker strengthens after being paired with stronger synapse
series of pulses delivered at a high rate all in one burst will produce long-term potentiation, but not the same number of pulses given at a slow rate

there are aftereffects which serve to prime future pulses by depolarizing the postsynaptic membrane
long-term potentiation requires two events:

activation of synapses
depolarization of the postsynaptic neuron

NMDA receptors - type of glutamate receptor, critical in long-term potentiation

found in hippocampus, mostly CA1
controls a calcium ion channel which normally is blocked by a magnesium ion
even the channel is stimulated by glutamate, calcium ions can’t get past the magnesium
but, if the membrane is depolarized, then the magnesium is ejected and the channel can admit calcium ions
therefore, need both glutamate and depolarization to admit calcium
calcium is critical for long-term potentiation - both necessary and sufficient

entry of calcium activates some calcium dependent enzymes

1) protein kinase C (PKC) - normally in cytoplasm, activated by calcium to increase synaptic transmission

2) CaM-KII - when activated by calcium it remains active even after calcium is gone, until deactivated by another enzyme

3) tyrosine kinase - also plays a role in long-term potentiation

nitric oxide - soluble gas used as a messenger in various parts of the body

produced by nitric oxide synthase in postsynaptic cell, communicates with presynaptic terminal buttons - retrograde effect

dendritic "spikes" - what are they? How do they happen? Why are they significant?

AMPA receptors - control sodium channels - involved once long-term potentiation has occurred

Long-term depression - low-frequency stimulation of the synaptic inputs to a cell can decrease their strength; opposite of Hebb rule - weak synapses not associated with strong ones become weaker

PERCEPTUAL LEARNING

Involves learning about things, not what to do when they are present
Simple perceptual learning, recognizing stimuli, takes place in appropriate regions of sensory association cortex

1) Visual Learning

inferior temporal cortex - necessary for visual pattern discrimination, receives info from visual cortex
ventral/dorsal streams - what and where
delayed matching-to-sample task - requires that stimulus be remembered for a period of time

"remembering" the stimulus involves a neuronal circuit; it is the circuits, not the individual neurons that recognize particular stimuli
lesions of inferior temporal cortex disrupts an animal’s ability to remember what it has just seen
electrical stimulation of the inferior temporal cortex during the delay causes forgetting

responses of single neurons in inferior temporal cortex recorded when pairs of stimuli shown

found that when stimuli are paired, the neural circuits responsible for recognizing them become linked together
perception of either stimulus activates both circuits

visual long-term memory involves the establishment of new circuits in the inferior temporal cortex by means of synaptic changes

2) Auditory Learning

auditory learning tasks modify response characteristics of neurons in various parts of the auditory system

study pairing tones with shock

pretraining, neuron responds best to 9.5 Hz tone
CS is 9-Hz tone, paired with shock
after training, neuron now responds best to 9-Hz tone, and less to 9.5 Hz

medial division of the medial geniculate nucleus (MGm) - important for classically conditioned emotional responses

receives info from auditory and somatosensory systems
directly connected to the central nucleus of the amygdala
which activates the nucleus basalis
nucleus basalis contains acetylcholine neurons which innervate auditory cortex, telling it to pay particular attention to the ventral division of the medial geniculate nucleus (conveys auditory information)

S-R LEARNING

1) Classical Conditioning

central nucleus of the amygdala involved in classically-conditioned emotional responses
see figure 14.29 -MGm eceives auditory and somatosensory info
pairing of tone and footshock increases responses to CS
extinction - somehow, NMDA receptors again involved - most likely due to long-term depression

2) Instrumental Conditioning and Motor Learning

2 pathways exist between sensory association cortex and motor association cortex:

1) direct trascortical connections - short-term memory, and with hippocampus involved in episodic memory

2) via basal ganglia and thalamus - used once no longer "new" learning; Parkinson's example

premotor cortex - monkeys raising arms for food; humans learning motor task
reinforcement:
reinforcing brain stimulation discovered by Olds and Milner in 1954
medial forebrain bundle - best place for self-stimulation; also involved in natural reinforcers, such as food, water, or sex
dopamine - likely serves as a neuromodulator, involved in reinforcement - receptors in nucleus accumbens

conditioned place preference - animals prefer to be where they have encountered a reinforcing stimulus
this process used to test influence of dopamine on reinforcement
if given dopamine antagonist during place training, don’t develop conditioned place preference
also involved in negative reinforcement - dopamine antagonists prevent avoidance learning
amphetamine is a dopamine agonist - animals will work to get injections of it

drug discrimination procedure - train animals to press a certain lever to receive food after it has been given a drug and to press another lever after it has been given saline
found that rats would press drug lever only if amphetamine put directly into nucleus accumbens, rather than other brain structure
they pushed the saline lever if they also had been given a dopamine receptor blocker with the amphetamine into the nucleus accumbens

REINFORCEMENT SYSTEM

must be able to first detect and then respond to reinforcement opportunities
ventral tegmentum area - reinforcing stimuli activate neurons here, which they stimulate release of dopamine in other systems

neurons activated by both natural and conditioned reinforcers
information received from 3 sites:

1) amygdala - involved in detection of CS for reinforcement - if monkeys trained that food follows a visual stimulus, then amygdala lesioned, the monkey forgets the association

2) lateral hypothalamus - neurons become active when monkeys see food, but only when hungry - neurons show sensory-specific satiety; activity related to presence of reinforcing stimuli

3) prefrontal cortex - secretes excitatory glutamate, which triggers bursts of dopamine to be released from neurons in the ventral tegmental area into the nucleus accumbens; may serve as monitor for reinforcement-seeking activity

a reinforcement system is required by instrumental conditioning

1) discriminative stimulus activates weak synapse

2) circumstance that causes animal to press lever activates a strong synapse

3) if behavior is reinforced, then neurotransmitter/neuromodulator released (dopamine), causing synaptic changes, strengthening weak synapses