Classical Conditioning

Question 1

What is an important issue in systems neuroscience?

Answer 1

Understanding the changes in the brain that underlie memory

Question 2

What changes in the brain are we looking to examine?

Answer 2

Likely to be changes in synapses

e.g. in LTP where synapses become more powerful

Question 3

What is an issue with examining synapses?

Answer 3

There are trillions of synapses in the brain that underlie many different behaviours
- some behaviours are complex e.g. those mediated by the hippocampus where LTP has been demonstrated

Question 4

What is a good strategy for studying the neural basis of memory?

Answer 4

Picking a simple task to start with

Question 5

Why is it best to pick a simple task?

Answer 5

Hopefully only a small number of synapses are involved here
–> 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

Question 6

What simple form of learning is easiest to study?

Answer 6

Classical conditioning

Question 7

How does classical conditioning work?

Answer 7

Before training
UCS produces UCR

During training
Pair CS + UCS

After training
CS produces CR

Question 8

What are the different types of CC?

Answer 8

1. A good (e.g. food) or bad (e.g. shock) UCS
   -Produces either salivations or limb withdrawal
2. Autonomic vs skeletal
   -Heart rate, dry mouth vs movement
3. Movements of body parts
   -Limb withdrawal, eyeblink

Question 9

What type of CC has been proven the easiest to study?

Answer 9

Eyeblink conditioning

Question 10

How is eyeblink conditioning studied in humans?

Answer 10

UCS = puff of air to the eye
CS = tone
CR and UCR = movement of eyelid

Question 11

What is the nictitating membrane?

Answer 11

Some animals e.g. cats or birds, have a third eyelid

This nictitating membrane can be clasically conditioned

Question 12

Why is the nictitating membrane CR preferred over an eyelid CR?

Answer 12

Eyelid responses have interference from voluntary movements like winks and spontaneous activity which don’t affect the nictitating membrane
-NMR is an autonomic response

Question 13

What is the preferred animal of choice for the NMR ?

Answer 13

Rabbits- easy to train, have a nictitating membrane, responses cause little-to-no distress

Question 14

What happens in an NMR rabbit experiment?

Answer 14

Typically 100 trials per day for the rabbit

CS (tone) comes on about 0.5s before the UCS (shock/puff of air) but both terminate at the same time

Day 1: response on UCS only

Day 3: Evidence of the nictitating membrane moving before the UCS (somatosensory stimulus) comes on i.e. shows a CR

Day 5: CR clear to see - effect= eyelid closes in anticipation of the US

Question 15

What are two important features of eyeblink conditioning?

Answer 15

1. The UCS overlaps with the CS - this is called ‘delay conditioning’
   -if there’s a gap between the end of the CS and the start of the UCS its called ‘trace conditioning’ (invovled more structures so is less simple-not the case for NMR)
2. The UCS is usually a mild brief shock delivered to skin around the eye (‘periorbital shock’)
   -means that closing the eye have no effect on the UCS, this is as it should be because CC is defined in this way- the CR does not affect the UCS otherwise its avoidance learning, a form of instrumental learning

Question 16

How do we know which parts of the brain are involved?

Answer 16

Anterograde amnesia studies

Accidental finding from HM who had a surgery resulting in the bilateral removal of the temporal lobe – this was successful in stopping his epilepsy but unexpected side effect = his new memories now only lasted for 1 minute

Question 17

What did patient H.M. demonstrate about STM and LTM?

Answer 17

H.M’s STM was intact but LTMs could not be formed

Question 18

What type of memory is eyeblink conditioning?

Answer 18

LTM

Question 19

Does damage to the hippocampus and surrounding tissue prevent eyeblink conditioning?

Answer 19

No

Question 20

What is the evidence from Weiskrantz and Warrington (1979) that damage to the hippocampus and surrounding tissue does NOT prevent eyeblink conditioning?

Answer 20

Examined patients with anterograde amnesia
Evidence of normal learning, even though the patients could not remember the aparatus that was delivering the UCS

Question 21

What more recent evidence from Gabrieli et al. (1995) proves that the hippocampus and surrounding tissue does NOT prevent learning?

Answer 21

More recent report

More subjects and control groups
It was verified radiologically that there was damage to the medial temporal lobe
Again, the rates of conditioning were the same in both groups

So we can be sure this type of learning is not due to the hippocampus

Question 22

Is there more than one type of LTM?

Answer 22

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”

Question 23

What potential brain regions could eyeblink conditioning depend on?

Answer 23

Forebrain (cerebral cortex mainly)
Brainstem, pons and medulla
Cerebellum

Question 24

What is the evidence against the invovlement of the forebrain?

Answer 24

Delay NMR conditioning still possible in rabbits lacking either hippocampus or cerebral cortex

Also possible in rabbits with forebrain separated from brainstem and cerebellum (‘decerebrate’ preparation)

Mauk & Thompson (1987)

Question 25

Who researched the brainstem & cerebellum’s involvement?

Answer 25

Thompson’s group

Ref: Thompson (1983)
McCormick & Thompson (1984)

Question 26

What two techniques were used to examine the involvement of the brainstem and cerebellum?

Answer 26

Electrophysiological recording
Lesions

Question 27

Explain the electrophysiological recording research methodology. (McCormick & Thompson 1984)

Answer 27

Carried out electrophysiological mapping during conditioning
- they systematically record from multiple units in cerebellar cortex and the deep cerebellar nuclei

Control group- unpaired CS and UCS presented as frequently as in the training condition but they were unrelated

Experimental group- paired CS and UCS

Question 28

Explain the findings from electrophyiological reocrdings. (McCormick & Thompson (1984)

Answer 28

Recording MUA from the cerebellum

Control group- no response before the UCS but NMR to the shock in the CR

Experimental group- even on day 1 there is a little NMR which is very strong by day 3

Question 29

Where did McCormick & Thompson (1984) localise the brain acitivty to?

Answer 29

Recorded from the deep cerebellar nuclei close to cerebellum

Found that almost all cerebellar output goes through these deep cerebellar nuclei

Question 30

What is a limitation of electrophysiological recording?

Answer 30

Recording does not establish a central role- this correlation does not equal causation

Question 31

What did Thompson (1983) find with lesions?

Answer 31

Large lesions of the entire cerebellum plus the output of the deep cerebellar nuclei

These lesions abolish any previously learned CR and they can never be relearned -> in-activating this part of the brain makes conditioning impossble

So, this area seems to be central to classical conditoning

Question 32

What did Yeo, Hardiman & Glickstein (1985) find from lesion studies?

Answer 32

Even small lesions confined to the deep cerebellar nuclei produced a similar effect of abolishing the CR

Lesions confined to the anterior portion of the interpositus nucleus are effective - so we can localise the crucial output for CC to this area

Question 33

What are the important controls from these lesions as discussed in Yeo (1987) that are assessed in behaviour?

Answer 33

After lesion = selective loss of CR but the UCR is not affected

This is 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

Lesions do not make the animals deaf (can still hear the tone)- we know they are not deaf because unilateral lesions only affect conditioning to the eyes on the same side of the head , we can still get the CR on the ipsilateral side of the head

Question 34

What is the conclusion therefore from lesion studies?

Answer 34

That loss of the conditioned response appears to be genuine loss of the memory trace (the ‘engram’)

Effects we have observed are because we have reached the synapses in the brain where the memory trace is stored

Question 35

How much do we know about where in the brain are the plastic synapses that mediate this conditioning?

Answer 35

Humans- medial temporal lobe damage (hippocampus, amygdala & parahippocampal regions) 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