"Maintaining unnecessary association pathways requires energy for the brain. The researchers believe that this is the reason for the brake mechanism – even though in this case it happened to be a little too powerful." see Neuroscience news
“Purkinje cell activity during classical conditioning with different conditional stimulus explains central tenet of Rescorla–Wagner model” by Anders Rasmussen, Riccardo Zucca, Fredrik Johansson, Dan-Anders Jirenhed, and Germund Hesslow in PNAS. Published online October 26 2015 doi:10.1073/pnas.1516986112
A central tenet of Rescorla and Wagner’s model of associative learning is that the reinforcement value of a paired trial diminishes as the associative strength between the presented stimuli increases. Despite its fundamental importance to behavioral sciences, the neural mechanisms underlying the model have not been fully explored. Here, we present findings that, taken together, can explain why a stronger association leads to a reduced reinforcement value, within the context of eyeblink conditioning. Specifically, we show that learned pause responses in Purkinje cells, which trigger adaptively timed conditioned eyeblinks, suppress the unconditional stimulus (US) signal in a graded manner. Furthermore, by examining how Purkinje cells respond to two distinct conditional stimuli and to a compound stimulus, we provide evidence that could potentially help explain the somewhat counterintuitive overexpectation phenomenon, which was derived from the Rescorla–Wagner model.
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