Flashcards in 211 Learn Mem. L16 W10 Deck (20)
What is Learning
Learning refers to the process by which experiences change our nervous system. Learning can:
- involve specific relations between stimuli in the environment
- involve recognition and categorisation of objects and situations
- involve information about events in the world.
- involve skilled actions
What is memory
Memory refers to the process that encodes, stores and retrieves the learning experience. Memories:
- can be transient or durable.
- can be consciously (explicitly) declared or involve implicit
- have a personal frame of reference
- permits a form of time-travel
- are not equally vulnerable to disease and disruption
Habituation is a simple form of learning,
Aplysia sea slug ex.
▪ The aplysia is an invertebrate sea slug with a simple nervous system (20,000 neurons).
▪ The Aplysia has a large gill for respiration, and a siphon through which it expels water.
If the siphon is lightly touched, the gill withdraws reflexively.
Repeated touching with a tactile stimulus reduces the magnitude of the reflex until the Aplysia ignores the touch stimulus.
This waning of sensitivity to repeated stimulation is known as habituation.
aside: fan, clock tick, havituates to variety of stimuli on enviro.
Due to no significant consequence. No waste energy to respond.
What is Associative learning?
▪ In associative learning, the experimenter arranges a relationship between two events.
▪ Learning is the ability to learn to perform a behaviour in the presence of a particular stimulus.
▪ This type of learning involves connections between circuits involved in perception and those involved in movement.
▪ The resulting behaviour can be a reflexive response (e.g. salivation or eyeblink) or a complicated sequence of previously learned movements.
▪ Two major categories of associative learning:
- Classical conditioning
- Instrumental conditioning
Associative Learning: Classical Conditioning
▪ In classical (Pavlovian) conditioning, a stimulus that previously had no effect on behaviour becomes able to evoke a reflexive ‘conditioned’ response.
▪ The procedure involves the repeated pairing of two stimuli.
Neural Circuit of Classical Conditioning?
▪ We assume:
- The UCS is detected by a
single neuron in the somatosensory system.
- The CS is detected by a single neuron in the auditory system.
- The CR is controlled by a singe neuron in the motor system.
▪ When action potential reaches synapse T, the EPSP is too weak to make the neuron fire.
▪ Synapse P is a strong synapse because a blink is a defensive reflex.
- For conditioning, the CS must be followed almost immediately by the UCS.
The Hebb Rule (D.O. Hebb, 1949)
▪ The Hebb Rule states that the cellular basis of learning involves the strengthening of a synapse that is repeatedly active when the postsynaptic neuron fires
Associative Learning: Instrumental Conditioning
▪ In instrumental (operant) conditioning, the animal adjusts its behaviour according to the consequences of that behaviour.
▪ If the learned behaviour is followed by favourable consequences, it will be be strengthened (more likely to occur). If it the behaviour is followed by negative consequences, it will be weakened (less likely to occur).
▪ The procedure involves the association between a stimulus and a response (but also the response and the outcome/reward).
Neural model of operant conditioning?
The process of reinforcement strengthens a connection between neural circuits involved in perception (sight of the lever) and those involved and those involved in movement (the act of lever pressing).
What is Perceptual Learning?
▪ Perceptual learning is the ability to learn to recognise stimuli that have been seen before.
▪ The primary function of perceptual learning is to recognise and identify objects (including members of our own species) and situations.
▪ If we cannot recognise something, we are unable to behave in response to it.
▪ We learn to recognise by visual appearance, sounds, smells, movements. Variety of stimuli
▪ Learning to recognise complex visual or auditory stimuli involves changes in the visual and auditory association cortices, respectively.
What is Motor Learning?
Relate to operant conditioning.
▪ Motor learning involves learning to make a new response. It cannot occur without sensory guidance from the environment.
▪ Most skilled movements involve interactions with the environment: bicycles, rackets, knitting needles, etc.
▪ Movements that we make ourselves (e.g. dance steps) involve feedback from joints, vestibular system, eyes and contact between the feet and the floor.
Learning Involves Perceptual, Associative and Motor Components
See slide diagram, just. Summary of interaction!
Relational Learning is?
Hint: Space and time
▪ Learning about the relationships among different stimuli is relational learning.
▪ Spatial learning allows us to learn about relations among stimuli located in space.
▪ Episodic learning enables us to remember sequences of events (episodes) that we witness.
Synaptic Plasticity is?
▪ Synaptic plasticity refers to the changes in the structure or biochemistry of synapses that alter their effects on postsynaptic neurons.
Aside on sleep consoIdation
▪ The hippocampus is an important structure involved in learning and memory and shows remarkable plasticity.
This plasticity is manifested through the phenomenon of long- term potentiation (LTP).
-LTP can cause the long-term strengthening of the synapses between two neurons (i.e. Hebb Rule in action).
The Hippocampal Formation includes?
▪ The hippocampal formation (complex) is a collection of structures which include the hippocampus proper (CA1-CA4 fields), the dentate gyrus and the subicular complex.
▪ The hippocampal formation is located in the temporal lobe.
▪ The hippocampal formation has a complex, orderly 3D shape; a slice taken anywhere perpendicular to its long axis contains the same circuit.
Intrinsic Anatomy of the Hippocampal Formation
Neurons of the dentate gyrus send axons to the CA3 field and form synapses with dendrites of pyramidal cells.
Granule cells of the dentate gyrus receive information from the entorhinal cortex via the perforant path.
One branch of the axons of CA3 pyramidal cells travel through the fornix to reach areas of the basal forebrain. Another branch of axons synapse with the pyramidal cells of the CA1 field.
CA1 pyramidal cells provide the main output of the hippocampus to the subiculum, entorhinal cortex and basal forebrain.
The entorhinal cortex channels the major neocortical inputs and outputs.
Inducing LTP, how to?
▪ A stimulating electrode is placed among the axons in the perforant path.
▪ A recording electrode is placed near the granule cells of the dentate gyrus.
▪ A single pulse of electrical stimulation is delivered to the perforant path.
▪ This produces a population EPSP which is recorded in the dentate gyrus.
▪ Population EPSP is a measurement of the EPSP’s produced by many synapses of the perforant path axons that connect with the dentate granule cells.
▪ The size of the ‘first’ population EPSP indicates the synaptic strength ‘before’ LTP has taken place.
▪ We can induce LTP if we stimulate the perforant path with high intensity, high frequency stimulation.
In LTP, many axons are stimulated rapidly
▪ A rapid rate of stimulation causes the EPSP’s to summate which depolarises the postsynaptic membrane.
▪ Slow rates of stimulation fail to depolarise the membrane.
What is ltd, just as important but different mechana
Long-term depression (LTD) is a weakening of the synaptic strength that lasts from hours to days.
▪ It occurs following slow rate of low-frequency stimulation of the synaptic inputs to a cell.
▪ LTD also play an important role in learning and memory; some
memory circuits are established by strengthening some synapses while weakening others.
Review textbook part of this!
What is the Role of NMDA Receptors in ltp(d)?
In the CA1 field of the hippocampus, N-methy-D-aspartate (NMDA) glutamate receptor plays a significant role in LTP.
NMDA receptors control calcium ion channels that are normally blocked by magnesium ion (mg2+).
Glutamate must be present and
Synaptic membrane must be depolarizer, if clacium ions are to enter cell. Central step in ltp!
Note: Drugs that block NMDA receptors (e.g. AP5) prevent calcium entering the dendritic spines and block LTP.
Role of AMPA Receptors in ltp is?
▪ The synaptic strength during LTP is due to AMPA receptors (AMPA is a glutamate receptor).
▪ AMPA receptors control NA+ channels.
▪ They are located in clusters at the base of the dendritic spine.
▪ When LTP is induced, the AMPA receptors flood into the dendritic spines of CA1 neurons (the postsynaptic density).
▪ The movement of AMPA is caused by a calcium dependent enzyme called type II calcium-calmodulin kinase (CaM-KII).
▪ CaM-KII can autophosphorylate; it can attach a phosphate group to a particular location on the molecule. This allows CaM-KII to remain active by itself without the need for calcium.
Peefent autophos... Prevent ltp. So that enzyme is very imp.
More ampa, more epsp more glutamate.