Classic Health Study: Olds and Milner (1954)

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  • Olds and Milner (1954)
    • aim
      • to explore whether electrical brain stimulation acts as a positive reinforcement in rats.
    • procedure
      • 15 male hooded rats were used, weighing around 250g
        • they were all killed after testing to have their brain structures and areas that were stimulated examined under a microscope
      • electrodes were implanted in their brains (under anaesthesia) in different parts of the brain in each rat.
        • they were given three days to recover before being tested.
        • the electrodes were connected to an electrical lead suspended from the ceiling of the cage so that they had minimal interference with the rats health and movement.
      • the rats were placed in an operant conditioning chamber similar to Skinner's box.
        • it delivered an electric shock to their brain whenever they pressed a lever.
          • voltage just high enough to have a noticeable effect - 0.5-5 volts.
      • they completed two conditions.
        • acquisition testing: lasted 6-12 hours overall, 3 hours at a time. the stimulator was turned on so an electric current passed through the rats if they pressed a lever.
        • extinction testing: lasted 1-2 hours total, 30 minutes at a time. the stimulator was turned off so no electric current passed through if they pressed the lever.
        • tested for 2-4 days, one session of each of the conditions on each day.
      • the amount of time that the rat spent responding vs not responding was compared.
        • it was a response if there was a clear behaviour shown in a thirty second time period.
    • results
      • some rats had 12 hours of acquisition but some only had 6 so the first 6 hours were the only ones used in analysis.
      • the highest scores happened when the central portion of the brain (septal) was stimulated.
        • these rats spent over 75% of the acquisition time responding.
        • they all spent less than 22% of extinction time responding, showing that the stimulation of the septal area is the primary reward.
      • areas of the brain with less response time in the acquisition stage show that the area is less rewarding.
        • areas with 0% response in the acquisition phase (medial lemniscus and medial geniculate) suggest a punishing effect when stimulated.
    • conclusion
      • certain areas of the brain, when stimulated, have a rewarding effect on behaviour.
        • as this was particularly in the septal area, it suggests a 'reward centre' within the brain.

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