8.3.1 olds and milner

Question 1

describe the aims of olds and milner’s study

Answer 1

• See if electrical self-stimulation of the brain acts as a reward, a punishment or a neutral stimulus
• Discover if stimulation has a reinforcing effect on behaviour
• Find structures in the brain involved in this reinforcing function

Question 2

what type of experiment did olds and milner use?

Answer 2

animal lab experiment

Question 3

what is the iv of olds and milner’s study?

Answer 3

location in the brain of an electrode delivering electrical self-stimulation

Question 4

what is the dv of olds and milner’s study?

Answer 4

number of lever presses wehn stimulation was switched on (acquisition) and switched off (extinction)

Question 5

describe the procedure used in olds and milner’s study?

Answer 5

Electrodes implanted into 9 different areas of the rats’ brains under anaesthesia, fastened to the skull using screws. Given 3 days to recover before being tested

Rats were placed in an OC chamber (skinner-type box). Box delivered an electric current to the rats’ brains whenever they pressed a lever.

The voltage used was enough to observe a noticeable effect on the rats’ behaviour (0.5-5 volts), varied between rats

Two conditions
* acquisition testing - stimulator turned on, electric current when lever pressed, 6-12 hours over whole expt
* extinction testing - stimulator turned off, no electric current when lever pressed, 1-2 hours over whole expt.

Rats tested between 2-4 days
Each day = 3 hours acquisition testing, 30 mins extinction testing

The amount of time the rat spent responding to the electrical stimulation in the acquisition phase was compared to the time responding in the extinction phase.
Response = clear lever press at least once in 30 sec (time sampling)
No response = no lever press within intervals of 30 secs
All rats killed after testing, brain structure examined under microscope

Question 6

describe the results of olds and milner’s study

Answer 6

rewarding stimulation was found in 7/15 rats tested, focused on three main brain structures:
- septal area - four rats stimulated here spent 75-92% pressing the lever in acquisition time, but only 8-21% during extinction
- mammillothalamic tract - one rat stimulated here spent 71% level-pressing during acquisiton, and only 9% during extinction
- cingulate cortex - two rats stimulated here spent 36% and 37% lever-pressing during acquisition, but only 10% and 9% during extinction

Lower scores in the acquisition condition suggest that stimulation of that part of the brain is less rewarding. Corpus callosum =6 % of acquisition time responding 3% of extinction time responding

Areas with 0% suggest there is a punishing effect when that part is stimulated. Medial Lemniscus = 0% of acquisition time responding 4% of extinction time responding. More likely to press the lever during extinction phase (no electric current)

Question 7

describe the conclusions of olds and milner’s study

Answer 7

Certain areas of the brain, if stimulated, have a rewarding effect on behaviour, particularly the septal area.

This suggests that there is a specific ‘reward centre’ in the brain which leads to the repetition of behaviour.

Question 8

olds and milner - generalisability

Question 9

olds and milner study - reliability

Question 10

olds and milner study - application

Question 11

olds and milner- ecological validity

Answer 11

P: Low ecological validity

E: The setting of the experiment and conditions they were exposed to are not natural for a rat e.g. wires attached to their skulls and being given eclectic shocks

T: May have influenced their behaviour so that what was observed was a reaction to experimental conditions rather than their behaviour being due to reinforcement

Question 12

olds and milner - internal validity

Question 13

olds and milner - ethics