Olfactory Brain

The olfactory bulb is a neural structure of the vertebrate forebrain involving in olfaction; the sense of smell. It sends olfactory information to be further processed in the amygdala; the orbitofrontal cortex (OFC) and the hippocampus where it plays a role in emotion, memory, and learning. The bulb is dividing into two distinct structures: the main olfactory bulb and the accessory olfactory bulb.

The piriform cortex

Therefore the main olfactory bulb connects to the amygdala via the piriform cortex of the primary olfactory cortex; directly projects from the main olfactory bulb to specific amygdala areas. So the accessory olfactory bulb resides on the dorsal-posterior region of the main olfactory bulb and forms a parallel pathway. But the destruction of the olfactory bulb results in ipsilateral anosmia; while irritative lesions of the uncus can result in olfactory and gustatory hallucinations.

How sensory perception in the brain affects learning and memory processes is far from fully understood. But two neuroscientists of Ruhr-Universität Bochum (RUB); have discovered a new aspect of how the processing of odors impacts memory centers. They showed that the piriform cortex a part of the olfactory brain has a direct influence on information stored in our most important memory structure; the hippocampus. Dr. Christina Strauch and Professor Denise Manahan-Vaughan report about their findings in the online edition of the magazine.

To find out how odors affect memory formation; the researchers triggered an artificial perception of an odor in the brains of rats. To do this, they stimulated the piriform cortex with electrical impulses. “They very surprised to see that the hippocampus directly responds to stimulation of the piriform cortex,” remarked Christina Strauch. The hippocampus uses sensory information to create complex memories.

Transmission across synapses

Therefore the basis of these processes is its ability to increase the efficacy of information transmission across synapses; thereby store memory contents. This process is called synaptic plasticity. So Manahan-Vaughan and Strauch the first to show that stimulation of the anterior piriform cortex triggers synaptic plasticity in the hippocampus.
In a second step, the researchers examined to what extent the piriform cortex competes with the entorhinal cortex in driving hippocampal synaptic plasticity. This structure sends information about activity in all sensory modalities to the hippocampus. Activating the afferent pathway of this structure, called the perforant path, triggered completely different reaction patterns in the hippocampus, to those generated by the piriform cortex.
“The study gives us a theoretical basis for understanding how olfaction plays such a special role in memory formation and retrieval,” commented Denise Manahan-Vaughan. But the two scientists have to work together since 2010 to investigate how odors cause memory formation.