Learning and memory
- Learning allows to acquire new information and refers to the process by which experiences change our nervous system and our behaviour.
- Long term changes in the nervous system following learning are referred to as memories
- Memories persist over time and are formed when something is learned. Learning something new and creating a memory physically changes the structure of the nervous system, altering neural circuits that participate in perceiving, thinking, planning and behaving
Types of learning
- Stimulus-response learning
- Motor Learning
- Perceptual Learning
- Relational Learning
Stimulus-response learning
- Stimulus-Response learning is the ability to learn to perform a particular behaviour when a particular stimulus is present. This involves conditioning.
- Conditioning is learning from exposures to a stimuli to produce a lasting behavioural change by establishing connections between circuits involved in perception and movement. There are two types of conditioning:
- > Classical Conditioning
- > Operant Conditioning
Classical conditioning
- Classical conditioning is a learning procedure where a stimulus that initially produces no particular response is followed several times by an unconditioned stimulus that produces as defensive or appetitive response (unconditioned response).
- The first stimulus (now called a conditioned stimulus) then itself evokes the response (now called a conditioned response)
Hebb learning rule
- Donald Hebb proposed the Hebb Learning Rule to explain how neural connections are shaped by experience during learning.
- the cellular basis of learning involves the strengthening of a synapse that is repeatedly active when the postsynaptic neuron fires.
- So, in the “air-puff” example, the audio tone causes the weak synapse between the auditory and motor neuron to become active. If the air puff happens straight after this, the somatosensory neuron is active, and makes the motor neuron fire (strong synapse). The act of firing then strengthens any synapse with the motor neuron that has just been active
Operant conditioning
Operant Conditioning is a learning procedure where the effects of a particular behaviour in a particular situation increase (reinforce) or decrease (punish) the probability of that behaviour.
Reinforcers = increase likelihood of repeating a behaviour
Punishers = decrease likelihood of repeating a behaviour
Motor learning
- Establishes changes (responses) within motor systems following a stimulus
- Requires sensory guidance from the environment
Perceptual learning
- Ability to learn to recognize stimuli that have been perceived before
- Primary function is to identify and categorize objects and situations
- Accomplished primarily by changes in the sensory association cortex for each sensory system
Relational learning
- Learning the relationships among individual stimuli
- Relative locations of objects
- Episodic learning involves remembering sequences of events that we witness
Types of memory
- Sensory Memory
- Short Term Memory
- Long Term Memory
Sensory memory
A brief period of time that the initial sensation of environmental stimuli is initially remembered
• Length ranges from fractions of a second to a few seconds
• Occurs in each of the senses
Short term memory
- Contains information from sensory memory only if it is meaningful or salient enough
- Length ranges from seconds to minutes
- Rehearsal
- Capacity is limited to a few items
- Chunking
Long term memory
• Contains information from short-term memory that is
consolidated
• Relatively permanent
• Last for minutes, hours, days, or decades
• Strengthened with increased retrieval
• Two major categories: Nondeclarative memory and
Declarative memory
Long term memory - nondeclarative
- Also called implicit memory
- Includes memories that we are not necessarily conscious of
- Operates automatically and controls motor behaviours
- Such as riding a bike, throwing a ball, dancing
Long term memory - declarative
• Also called explicit memory
• Memory of events and facts we can think and talk about
• Not simply verbal, but like a video
• Includes episodic memories (context) and semantic
memories (facts)
Conditioned emotional responses: role of the amygdala
• Information about the CS arriving from the sensory cortex (e.g. site of the fence) and US arriving from the somatosensory cortex (e.g. the shock) converge in the lateral nucleus of the amygdala.
• Synaptic changes responsible for learning could occur here
*look up image
Conditioned emotional responses: long term potentiation
- Long-term potentiation (LTP) is a series of synaptic changes, synaptic connections become stronger when frequently activated
- LTP among glutamate synapses in the lateral amygdala help establish conditioned emotional responses
- Synaptic changes in the glutamate system increase the excitatory post synaptic potential (EPSP) to the postsynaptic cell
Role of basal ganglia in operant conditioning
• Circuits responsible for operant conditioning begin in
the sensory association cortex (perception) and end
in the motor association cortex (movements)
• Two major pathways:
1. Direct transcortical connections
2. Connections via the basal ganglia and thalamus
Direct transcortical connections
- Connections from one area of the cerebral cortex to another
- Involved in acquiring episodic memories and complex behaviours that involve deliberation or instruction
- A memorized set of rules provides a script to follow
Basal ganglia pathways
- As learned behaviours become automatic and routine, they are transferred to the basal ganglia
- Frees up the transcortical circuits
- No longer need to deliberately think through each step
In depth, basal ganglia pathways
• The neostriatum (caudate and putamen) of the basal
ganglia receives sensory info from all regions of the
cerebral cortex, as well as info about planned
movements from the frontal lobes
• The neostriatum projects to another part of the basal
ganglia called the globus pallidus
• The globus pallidus projects to the premotor and and
supplementary motor cortex (movement planning) and
then to the primary motor cortex (movement execution)
*look up image
Reinforcement
• Dopaminergic neurons play an important role in reinforcement:
1. The mesolimbic system: begins in the ventral tegmental area (VTA) of the midbrain and projects to several regions including the amygdala, hippocampus
and nucleus accumbens (NAC)
2. Mesocortical system: begins in the VTA and projects to the prefrontal cortex, limbic cortex and the hippocampus.
*look up VTA and NAC
Role of dopamine in reinforcement
• Activity in the nucleus accumbens (NAC) and the dopamine released there are responsible for reinforcement:
- Cocaine or amphetamine administration = dopamine release in the NAC
- Reinforcers such as water, food, sex partner, receiving money = dopamine release in the NAC
A reinforcement system must:
- Detect the presence of a reinforcing stimulus
- Strengthen connections between neurons that detect a specific stimulus (e.g. sight of a lever) and neurons that produce a response (a lever press)
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