Learning, memory and plasticity Flashcards
neural plasticity
- Changes that are caused by previous experience can be observed at the level of
- Behaviour (actions, emotions, knowledge)
- Neurons (neural network activity)
- Synapses (interactions between individual neurons)
what is learning?
the process of acquiring new information
what is memory?
the ability to store and retrieve information
types of learning
- Non-associative learning: habituation, sensitisation
- Associative learning
- Imprinting
types of learning and LTM
non-declarative (procedural)
declarative
non-declarative learning
- Conditioning
- Priming
- Skill learning
declarative memory
- Knowledge of facts (semantic memories)
- Episodic memories (what happened when and where)
duration of memory
- Short-term (STM)
- Long-term (LTM)
- Middle-term/Intermediate
hypothesised memory processes - encoding, consolidation and retrieval
- Incoming info
- Sensory buffers (e.g. iconic memory)
- STM/WM
- Consolidation
- LTM
- Retrieval –> STM –> Perf
- Loss
DIAGRAM
where are memories stored in the brain?
- Karl Lashley’s search for the memory ‚engrams’ (1929, 1950)
- Lesion studies with rats
- Lashley concluded that memory is not located in particular area of the rat cortex
Hebb synapse
- Santiago Ramón y Cajal (1893) first proposed the idea that the site of contact between neurons could play a role in memory formation.
- Foster & Sherrington (1897) termed these sites ‘synapses’ (Charles Sherrington - nobel prize laureat 1932).
- “When an axon of cell A is near enough to excite a cell B and repeatedly or persistently takes part in firing it, some growth process or metabolic change takes place in one or both cells such that A’s efficiency, as one of the cells firing B, is increased.”
- Furthermore, Hebb emphasised that there are likely to be many Hebb synapses in distributed networks
synaptic plasticity - what does change?
Assume presynaptic Neuron A very often transmit a signal that is 10 Hz (10 spikes per second) causing an EPSP in the postsynaptic Neuron B that is enough to transmit a signal by B.
how can the dynamics of signal transmission be altered?
by changing synapse efficiency over time
what might change in neuron A? (might need to look at slides)
- Temporal filtering (change in selectivity for the frequency range of spikes arriving in the axon terminal)
- Gain control (change in the amount of neurotransmitter that is released for a given signal)
- Presynaptic facilitation or depression
- Increased ntm, membrane size and/ sensitivity and pre- and post synapse size = increases PSP
- Something could also change in neuron B
- Evidence from studies that investigated mechanisms of associative learning
memory engrams - physiological and anatomical changes in the brain
Kandel and his team made important discoveries measuring changes in pre- and postsynaptic cells during learning and memory
developed mechanistic models of synaptic plasticity which are widely used in neuroscience and medicine.
habituation
Response weakens with repeated stimulus presentation due to repetition but not due to adaptation of senses or fatigue
Not an extinction of associations acquired through learning.
dishabituation - siphon example
The repeated tactile stimulation of the siphon leads to a reduced gill withdrawal response
The response is reinstated after stimulation by a different stimulus (dishabituation).
the abdomen ganglion of Aplysia
L7 - one of the motor neurons that innervates gill muscles and controls gill withdrawal
presynaptic depression as a form of synaptic plasticity - siphon example
- When the siphon is first stim by squirt water, Aplysia retracts gill, protecting it in case animal under attack
- Reflect mediated by sensory neurons synapsing directly upon motor neurons that withdraw gill
- Many sensory and motor neurons
- If siphon squirted repeatedly over hr, animal soon habituates to stimulus
- No longer retracts gill
ST habituation results as sensory neurons release less ntm on motor neurons - If siphon squirted repeatedly over days, animal habituates faster each day and eventually shows almost no response
- LT habituation due to retraction of some synaptic terminals from sensory neurons onto motor neurons
what is LTM formation characterised by?
Structural changes in neurons
what is another type of non-associative learning?
sensitisation
when a strong tail shock precedes the tactile stimulation, the gill response is much stronger
presynaptic facilitation
- Changes involving interneuron modulation
- Interneuron modulation causes increased transmitter release = increases PSP
other synaptic changes that may store memories
The neural mechanisms underlying associative learning, i.e. classical (also called pavlovian) conditioning have been studied in Aplysia, Drosophila melanogaster (fruit fly) and Apis mellifera (honeybees)
associative learning - classical conditioning learning tasks
- When a dog receives food, it starts to salivate (UR - unconditioned response).
- Pavlov noticed that his experimental dogs were already salivating before given food.
- If a sound (CS) always shortly precedes food (US), then a dog will learn that sound predicts food and will start to salivate on hearing the sound (CR)
- Coincidence of US and CS determine learning outcome
