Microanatomical Changes Following Odor Learning

This book describes the effect of odor learning on brain circuitry. For the research described in this book, rats learned to distinguish between pairs of odors. The results show that olfactory-discrimination learning in the rat is accompanied by a transient increase in dendritic spine density along apical dendrites of the primary olfactory cortex (the Piriform cortex) and hippocampal neurons. The learning-related increase in spine density in neurons from trained rats probably reflects a net increase in the number of excitatory synapses in the piriform cortex and hippocampus following olfactory rule learning. This increase is accompanied by a series of modifications in the geometrical parameters of dendritic spines in the piriform cortex and by biochemical changes in cell adhesion molecules. These changes may reflect synaptic remodeling or creation of new neurons that could underlie the establishment of odor rule-learning. The modifications described here combine to create a state in which the rat remembers to associate specific odors with a reward.