• memory
• Learning
• structural plasticity
• parvalbumin interneurons

This work is focused on the study of mechanism underlying learning and memory, on a mouse animal model. I used fear conditioning as a behavioral paradigm to investigate the involvement of different cortical and subcortical areas at different stages of the learning process.
Fear conditioning is a form of reinforce learning, in which the animal learns to predict the occurrence of an aversive (or positive) stimulus by associating it to the context in which this happens. This context/stimulus association is supported by the hippocampus, which has a central role in the spatial representation of the environment.
As a consequence of fear conditioning, structural changes occur in both excitatory and inhibitory circuits of recruited areas. In particular, previous studies had shown that learning can induce an increase in feed-forward inhibition through a corresponding increase of excitatory synapses onto fast-spiking interneurons in the hippocampus, and this is required for memory precision. This class of interneurons can be distinguished from the others on the base of the expression of the Ca2+ binding protein parvalbumin (PV) and his high frequency firing pattern. Moreover, parvalbumin is not expressed at the same level in all PV interneurons, but there are cells expressing it at low, intermediate or high levels; upon fear conditioning, there is an increase of the percentage of cells that express high levels of PV in the hippocampus, and this seems to correlate with an increase of excitation onto these cells.
Using this phenomenon as a read-out for structural plasticity, I’ve analyzed the intensity of PV expression, through immunohistochemistry and confocal microscopy, in entorhinal and perirhinal cortices, which are key regions linking hippocampus to neocortex, and the primary and secondary visual cortices; PV intensity was measured both one day and one month after fear conditioning.
The results show an increase inthe percentage of cells expressing PV at high levels in Perirhinal, entorhinal and primary visual cortex one day after fear conditioning, whereas one month after there are no differences with control mice. In the secondary visual cortex instead, no difference is detected after one day.
The early recruitment of the primary visual cortex may be linked to expectation: prior expectations about the visual world may act a sort of filter of perception and allow the animals to quickly detect relevant information from the all set of sensory inputs that are perceived, and to behave accordingly.
Tofurther investigate the relative role of hippocampus and primary visual cortex, I silenced the hippocampus by injecting muscimol just before fear conditioning and I’ve analyzed PV intensity in primary visual cortex:in this case, no changes in the read out were detected. This would suggest that, although the primary visual cortex is recruited at an early stage of learning, the hippocampus is essential for these structural changes to occur.