Some studies on olfactory conditioning in rodents have shown that long term memory of the conditioned odor depends on neurogenesis, while other studies did not detect such a dependence on neurogenesis. In their paper entitled „Involvement of Newborn Neurons in Olfactory Associative Learning? The Operant or Non-operant Component of the Task Makes All the Difference“, Mandairon et al. make the interesting discovery that neurogenesis in the olfactory bulb is dependent on the procedure by which experimental animal learn to distinguish two odors, providing a potential explanation for the discrepancy between the previous studies. The authors set up an operant conditioning paradigm where the animals could explore two differently scented boxes, only one of which contained a sucrose reward. In the non-operant or classical experiment, the animals were trained with only one box and one odor that alternatingly either contained odor A and no sucrose or odor B and sucrose. While the operant animals received sucrose throughout the 5 days of training, the classical animals were presented with a choice of two boxes each with one of the two odors on the final day. The choices of both animal groups were then tallied and compared. Each of these two groups had a matched ‘pseudo-conditioned’ group in which there was a random association between odor and sucrose, such that no odor was predictive of the sucrose.
The authors then sacrificed the animals after the final experimental day and used BrdU staining to screen for newborn neurons in the olfactory bulb. The functionality of these neurons was tested by detecting the immediate-early gene Zif. The authors found a higher density of BrdU-stained neurons in the olfactory bulb of operantly trained neurons compared with their pseudo-conditioned control group, while there was no such difference between the two classical groups. However, presumably because the trial duration was set to be higher in the classical conditioning paradigm, both classical groups had a higher density of BrdU-stained neurons than their respective operant groups. The percentage of active newborn neurons was also larger in the operant vs. its control group, while no such difference was found in the classical groups. This difference in functional neurogenesis was not due to generally higher activation in the experimental vs. the pseudoconditioned groups, as overall activation was similar across all groups.
Finally, the authors found higher brain activation levels in the orbital cortex for the operant group and in the infralimbic cortex for the classical group, further supporting the different behavioral requirements in the two conditioning procedures.
These results not only could potentially help explain the varying results when the necessity for neurogenesis is tested in olfactory conditioning experiments, but could also pave the way for studies into why operant learning is always more effective than classical conditioning (learning-by-doing, generation effect), despite the fact that both groups are learning he same thing.
Mandairon, N., Sultan, S., Nouvian, M., Sacquet, J., & Didier, A. (2011). Involvement of Newborn Neurons in Olfactory Associative Learning? The Operant or Non-operant Component of the Task Makes All the Difference Journal of Neuroscience, 31 (35), 12455-12460 DOI: 10.1523/JNEUROSCI.2919-11.2011
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Am 22. March 2012 um 02:38 Uhr
I find it interesting that operant conditioning is more effective than classical conditioning. I can see how behavior is more likely to be shaped by consequences rather than using a stimulus to cause an already existing behavior. The animals that were positively reinforced with sucrose, were the ones who were able to pick from the correct box at the end of five days. Since learning occurred in the operant group, it makes sense that newborn neurons were found in larger portions in these animals, compared to the controlled group.
Am 22. March 2012 um 18:59 Uhr
Both groups learned, but we cannot assess if one group learned better than the another, because the authors didn’t use the same measure (even though they easily could’ve). We can only assume that the shorter trial duration in the operant case means they learn more quickly.
One reason for the ‘learning-by-doing’ effect that can be found even in the very old literature of almost a hundred years ago, is that in classical conditioning, there’s nothing that helps the animal to find out which stimuli to pay attention to and so it takes time to identify CS and US. The operant control is thought to speed this process up. To my knowledge, there exist no tests of this hypothesis, despite its age.
Am 23. March 2012 um 19:42 Uhr
When discussing operant and classical conditioning in my pyschology class, I was a little surprised that operant conditioning worked better than classical conditioning. Operant conditioning seems like it would take more time for the animal to adjust to, whereas when a reward is constantly being giving for the recognition in a classical conditioning experiment, it motivates the animal more. It makes sense to me that if the animal has to work harder for the reward (the operant experiment), that their neurogensis would also be greater than the animals in the classical experiment.
Am 24. March 2012 um 03:31 Uhr
I thought this article was very interesting in the fact that it explains that operant conditioning is much more effective than classical conditioning when dealing with distinguishing odors using the olfactory bulb in rats. The reason for this differentiation is because of the larger production of new brain cells, during a process called neurogenisis, when a rat is subjected to operant, rather than classical conditioning. Both groups learned with the sucrose, but the operant group learned the best. One interesting contradiction can be made though. The same measure was not used throughout. The operant group was conditioned for five days, while the classically conditioned group was only conditioned on the last day. It can be pointed out that the results may be skewed toward the operant group because of the four extra days the rats had to learn the expected behavior.
Am 24. March 2012 um 12:19 Uhr
@Jen: The main difference between classical and operant conditioning is that there precisely is no “reward” in classical conditioning. The food is presented irrespective of whether the animal has done any “recognition” – that’s the definition of classical. If reward is contingent on the animal’s behavior, it’s operant. I think, with that in mind, learning-by-doing may not seem so surprising any more?
@Lisa: Because the authors used different measures when evaluating the behavior of their animals in the choice situation and because the operant animals were fed in this stage, it is impossible to tell if one group was ‘better’ than the other. Also, the classical group received four days of training and one day of test, nont the other way around. Thus, there only was one day of difference in terms of training/test between the groups.