Classical Conditioning Flashcards
To understand classical conditioning, one form of memory in terms of systems neuroscience, what changes are we looking for?
- Very likely to include changes in synapses
- Long-term potentiation, where synapses become more powerful
What is a problem with investigating changes in synapses in the brain?
There are trillions of synapses in the brain, whose plasticity underlies all sorts of different behaviours
Some of these behaviours are very complex e.g., those mediated by the hippocampus
How can we make the problem more specific so that we have a chance of solving it?
Solution = choose a form of learning that is as simple as possible (simple learning)
The hope is that only a small number of synapses are involved
This gives us a chance of identifying them and finding out how they work
If the same forms of synaptic plasticity underlie both simple and complex learning, understanding simple tasks will help with complex behaviour
What form of simple learning is used to understand memory?
Classical conditioning
Explain classical conditioning
Before conditioning
Food (UCS) = Salivation (UCR)
Bell = No response
During conditioning
Bell + Food (UCS) = Salivation (UCR)
After conditioning
Bell (CS) = Salivation (CR)
What are the different types of classical conditioning?
- Is US bad or good
- Salivation CR ‘appetitive’ conditioning to food US
- Limb withdrawal CR ‘aversive’ conditioning to painful US - Autonomic versus skeletal
- Heart rate, dry mouth etc versus movement - Movements of different types of body
- Limb withdrawal
- Eyeblink - Eyeblink conditioning
Explain eyeblink conditioning in humans
US is usually a puff of air to the eye
CS is usually a tone
CR and UR movements of eyelid
What is a nictitating membrane?
Some animals have a third eyelid
NMR = nictitating membrane response - can be classically conditioned
Why is NMR conditioning preferred to human eyelid CR?
No apparent interference from voluntary movements like winks, and very low level of spontaneous activity = this means it is simple
What animals are used to test NMR conditioning and how does it work?
Rabbits
CS (tone) comes on about 0.5s before the UCS (shock/puff of air) but both terminate at the same time
Day 1 = response to US only
Day 3 = evidence of eyelid movement before US arrives
Day 5 = CR clear to see
In effect the eyelid closes in anticipation of the US
What are two important features in eyeblink conditioning?
- The US overlaps with the CS - termed delayed conditioning - if the gap between the end of the CS and the start of the US, termed ‘trace conditioning’
- The US is usually a brief mild shock delivered to the skin around the eye (periorbital shock) - this means that closing the eye has no effect on the US, classical conditioning defined as CR does not affect the US, otherwise it is avoidance learning
Which parts of the brain are involved?
Well known since 1950s that the hippocampus is important for memory
How was the hippocampus discovered as an important structure for memory?
Hippocampus and surrounding tissue removed bilaterally to stop intractable epilepsy (patient HM)
Successful but caused anterograde amnesia - couldn’t form new memories
What type of memory is eyeblink conditioning?
Long term memory
Does damage to the hippocampus and surrounding tissue prevent eyeblink conditioning?
NO
Weiskrantz and Warrington (1979) examined patients with anterograde amnesia
Clear evidence of learning even though the patients could not remember the apparatus
What more recent evidence from Gabrieli et al. (1995) proves that the hippocampus and surrounding tissue does NOT prevent learning?
More subjects plus a control group
Examined conditioning of the eyeblink response (UCR) to a tone CS paired with an airpuff (UCS) in the delay paradigm
7 amnesic and 7 control participants
Verified radiologically that the amnesic patients had damage to the medial temporal lobe (area of hippocampus)
Amnesic patients exhibited normal baseline performance compared to control group
These results indicate that in humans, as in rabbits, brain structures critical for declarative memory (i.e., hippocampus) are not essential for the acquisition of elementary CS–UCS associations
Is there more than one type of LTM?
Yes, LTM is divided
Squire et al. (1993)
“major distinction is between conscious memory for facts and events and… nonconscious memory, including skill and habit learning, simple classical conditioning, the phenomenon of priming.. expressed through performance rather than recollection”
What other possible areas of the brain could be involved in delay eyeblink conditioning?
Forebrain - mainly cerebral cortex
Brainstem
Cerebellum
Could it be the forebrain?
NO
Delay NMR conditioning still possible in rabbits lacking either hippocampus or cerebral cortex
Also possible in rabbits with forebrain separated from brainstem and cerebellum
What was the first technique used to explore the brainstem and cerebellum in NMR conditioning? (McCormick & Thompson, 1984)
- Electrophysiological mapping during conditioning - systematically record multiple units in cerebellar cortex and the deep cerebellar nuclei
Unpaired: a control condition in which CSs and USs are presented as frequently as in the training condition but unrelated
Here no neuronal response
When paired units increase responding as CR develops
Where did McCormick & Thompson (1984) localise the brain activity to?
Recorded from the deep cerebellar nuclei close to cerebellum
Found that almost all cerebellar output goes through these deep cerebellar nuclei
What is a limitation of electrophysiological recording?
Recordings do not establish cause so lesion studies are needed - correlation does not equal cause
What was the second technique used to explore the brainstem and cerebellum in NMR conditioning?
Lesions of entire cerebellum plus output nuclei (Thompson, 1983)
CR is completely abolished - cannot be relearnt
Similar effect with smaller lesions, confined to deep cerebellar nuclei
Yeo et al. (1985) - In fact lesions confined to the front portion of the middle (interpositus) nucleus are effective so we can localise the crucial output for CC to this area
What were the behavioural effects of lesions in rabbits?
After lesion there is selective loss of the CR but UR is not affected
Important in showing that the lesion does not produce a simple motor deficit, it shows we are not just paralysing the nictitating membrane because it still moves perfectly well
- this is a type of implicit control we get from lesion studies
How do you control for deafness in lesion studies in rabbits?
Effects of unilateral lesions are unilateral - not deaf because unilateral lesions only affect conditioning of the ipsilateral eye
What do the results of lesion studies in rabbits suggest about conditioning?
The lesions did not cause paralysis because unconditioned blinks are still present and not deaf because unilateral lesions only affect conditioning of the ipsilateral eye
== Therefore, loss of the conditioned responses appears to be loss of the memory trace (the engram)
What is the engram?
The neural substrate for storing memories
Refers to the enduring offline physical and/or chemical changes that were elicited by learning and underlie the newly formed memory associations
How much do we know about where in the brain are the plastic synapses that mediate this conditioning?
Humans- medial temporal lobe damage prevents formation of new long-term memories, but has little effect on eyeblink conditioning
Rabbits- forebrain not needed for delay NMR conditioning
But both electrophysiological and lesion studies implicate the cerebellum
