University of Otago anatomy researcher Prof John Reynolds has replicated the ‘‘Pavlov’s Dogs’’ experiment with rodents, and used a flash of light in association with a reward. PHOTO: PETER MCINTOSH Findings from a replication of the ‘‘Pavlov’s Dogs’’ experiment at the University of Otago, may have benefits for people with Parkinson’s disease. It has been more than 130 years since Russian experimental neurologist and physiologist Ivan Pavlov trained dogs to associate the sound of a bell with the imminent delivery of food. The dogs were so used to the pairing of a bell with food, that they would salivate when hearing the sound, even if they were not fed. But now, new University of Otago-led research has discovered the part of the brain that reacts during these experiments, which also shines a light on how the brain learns new things. Lead author and Otago anatomy researcher Prof John Reynolds replicated the ‘‘Pavlov’s Dogs’’ experiment with rodents, and used a flash of light in association with a reward. The flash of light previously had no inherent value to the rodents, but when they learned it has an association with a positive reward, the researchers discovered a mechanism in the brain that played a part in the learning process. Prof Reynolds said when something important and valuable happened, our brains constantly tried to discover what we did to cause it. ‘‘If we work that out, we can turn it into a habit so that we don’t have to use our scarce brain resources all the time.’’ He said they found the response in the superior colliculus sensory area of the brain when the lights flashed, and it became stronger with repetition of the experiment. They also found it stayed strengthened, unless the light flash was then repeatedly delivered without a reward. He said the process of strengthening the superior colliculus required the combined actions of two major neurochemicals — dopamine and serotonin. ‘‘We further found that once strengthened, the visual signal began to channel through the colliculus to directly drive the release of dopamine itself, into areas where the learning of actions lead to delivery of reward. ‘‘Hence, the initial formation of a strong representation of the reward value of the light through classical conditioning begins to contribute to the processes of operant conditioning, teaching the brain the actions that are required to earn the reward.’’ Despite being a century old, the neural mechanisms underlying sensory conditioning by reward, were not fully understood until now, Prof Reynolds said. ‘‘It might seem that how cues gain significance would be well-known. ‘‘However, we have discovered that it happens in a very primitive part of the brain that is the first to see the light — the superior colliculus — rather than the much bigger and more sophisticated cerebral cortex.’’ The study is believed to be the first report of a mechanism directly linking the processes of classical and operant conditioning at the cellular level. He said the findings might be helpful for scientists studying conditions like Parkinson’s disease. ‘‘Because it helps us understand the mechanism of how dopamine works in the brain to cause this conditioning, it is of importance to human learning. ‘‘It helps us understand better about how dopamine needs to be timed to make the light more meaningful, and to then drive the learning of what we need to do to get something pleasant. ‘‘The timing of dopamine is important to understand in the context of say Parkinson’s disease — when the person is taking drugs to replace the lost dopamine, the dopamine signal loses its timing relevance and can strengthen all sorts of things we don’t need to strengthen, like all movements in addition to the useful ones, resulting in dyskinesias, and even can over-reward stimuli in some people, resulting in some addictive behaviours.’’ john.lewis@odt.co.nz
