Classical Conditioning

Question 1

To understand classical conditioning, one form of memory in terms of systems neuroscience, what changes are we looking for?

Answer 1

• Very likely to include changes in synapses
• Long-term potentiation, where synapses become more powerful

Question 2

What is a problem with investigating changes in synapses in the brain?

Answer 2

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

Question 3

How can we make the problem more specific so that we have a chance of solving it?

Answer 3

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

Question 4

What form of simple learning is used to understand memory?

Answer 4

Classical conditioning

Question 5

Explain classical conditioning

Answer 5

Before conditioning
Food (UCS) = Salivation (UCR)
Bell = No response

During conditioning
Bell + Food (UCS) = Salivation (UCR)

After conditioning
Bell (CS) = Salivation (CR)

Question 6

What are the different types of classical conditioning?

Answer 6

1. Is US bad or good
   - Salivation CR ‘appetitive’ conditioning to food US
   - Limb withdrawal CR ‘aversive’ conditioning to painful US
2. Autonomic versus skeletal
   - Heart rate, dry mouth etc versus movement
3. Movements of different types of body
   - Limb withdrawal
   - Eyeblink
4. Eyeblink conditioning

Question 7

Explain eyeblink conditioning in humans

Answer 7

US is usually a puff of air to the eye
CS is usually a tone
CR and UR movements of eyelid

Question 8

What is a nictitating membrane?

Answer 8

Some animals have a third eyelid
NMR = nictitating membrane response - can be classically conditioned

Question 9

Why is NMR conditioning preferred to human eyelid CR?

Answer 9

No apparent interference from voluntary movements like winks, and very low level of spontaneous activity = this means it is simple

Question 10

What animals are used to test NMR conditioning and how does it work?

Answer 10

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

Question 11

What are two important features in eyeblink conditioning?

Answer 11

1. 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’
2. 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

Question 12

Which parts of the brain are involved?

Answer 12

Well known since 1950s that the hippocampus is important for memory

Question 13

How was the hippocampus discovered as an important structure for memory?

Answer 13

Hippocampus and surrounding tissue removed bilaterally to stop intractable epilepsy (patient HM)
Successful but caused anterograde amnesia - couldn’t form new memories

Question 14

What type of memory is eyeblink conditioning?

Answer 14

Long term memory

Question 15

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

Answer 15

NO
Weiskrantz and Warrington (1979) examined patients with anterograde amnesia
Clear evidence of learning even though the patients could not remember the apparatus

Question 16

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

Answer 16

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

Question 17

Is there more than one type of LTM?

Answer 17

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 18

What other possible areas of the brain could be involved in delay eyeblink conditioning?

Answer 18

Forebrain - mainly cerebral cortex
Brainstem
Cerebellum

Question 19

Could it be the forebrain?

Answer 19

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

Question 20

What was the first technique used to explore the brainstem and cerebellum in NMR conditioning? (McCormick & Thompson, 1984)

Answer 20

1. 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

Question 21

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

Answer 21

Recorded from the deep cerebellar nuclei close to cerebellum

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

Question 22

What is a limitation of electrophysiological recording?

Answer 22

Recordings do not establish cause so lesion studies are needed - correlation does not equal cause

Question 23

What was the second technique used to explore the brainstem and cerebellum in NMR conditioning?

Answer 23

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

Question 24

What were the behavioural effects of lesions in rabbits?

Answer 24

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

Question 25

How do you control for deafness in lesion studies in rabbits?

Answer 25

Effects of unilateral lesions are unilateral - not deaf because unilateral lesions only affect conditioning of the ipsilateral eye

Question 26

What do the results of lesion studies in rabbits suggest about conditioning?

Answer 26

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)

Question 27

What is the engram?

Answer 27

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

Question 28

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

Answer 28

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