Week 6-Behind the scenes of classical conditioning.

In the last post, we discussed about the theory of classical conditioning. So in this post, let's see the -behind the scenes- on what goes inside the brain during this phenomena.

let's understand the neural correlates with the help of an experiment, where the US is an air-puff to eye and UR is closing eye. Now the US is paired with a CS, which is a light bulb. The behavioral result is even when the light is not paired with the airpuff, we close eye by predicting an airpuff to follow. This is also an aversive conditioning.

Now let's check what is happening in the behind the scenes; the neural correlates. The cerebellum deep cerebellar nuclei and different fiber pathways, which makes the learning(classical conditioning) possible. There are two pathways; the US pathway and the CS pathway. When an airpuff is given, the inferior olive nuclei receives the signal, which then travels to the inter positus nuclei and purkinje cells through climbing fibers. The purkinje cells also makes an inhibitory connection with the inter positus nuclei which mediates the CR a the output of the circuit. One thing to note is that inter positus also makes an inhibitory connection with inferior olive (we will come to this part later).

The second pathway is the CS pathway, where pontine nuclei receives the signal of the CS presentation. The pontine nuclei have specific receptors for different signals such as light, sound or sound of different frequency. The signal thus received by the pontine nuclei then travels to the interpositus and the purkinje cells through the mossy fibers, which then connects to the interpositus and mediates the CR.

When a US is present alone: The siganl received by inferior olive reach purkinje cells and mediates the CR by passing through the interpositus.

When US is paired with a CS: with enough trials the learning occurs.

When CS present alone after learning: the signal received by the pontine nuclei travels through the mossy fibers to reaches interpositus and mediates the CR, but when US is also present with CS, then the the inhibitory connection at the interpositus and inferior olive inhibits the inferior olive activation, so that the CS itself is enough to mediate a CR.

References

Gluck, M. A., Mercado, E., & Myers, C. E. (2008). Learning and memory: From brain to behavior. Worth Publishers.