On the Similarity of the Mechanisms of Processing Olfactory, Auditory, and Visual Information in the CNS: A Hypothesis

A possible mechanism for processing odors in a neural network that includes the olfactory bulb, the piriform cortex, the olfactory tubercle, which is the part of the ventral striatum, the ventral pallidum, the mediodorsal thalamic nucleus, and the orbitofrontal cortex, has been proposed. According to this mechanism, dopamine released by midbrain neurons in response to odor and reinforcement, as well as adenosine receptor antagonists, in a certain way modulates the efficacy of excitatory synaptic inputs to spiny cells of the olfactory tubercle projecting into the ventral pallidum. As a result, the neurons of the olfactory bulb are disinhibited by the ventral pallidum and contrasting odor representations are formed on them, as well as on their target cells in the piriform cortex. Simultaneously, there is a disinhibition of neurons in the mediodorsal nucleus and their target cells in the orbitofrontal cortex, which excites the neurons of the piriform cortex. This promotes the induction of LTP of the inputs from the olfactory bulb to the piriform cortex and the memorization of odor representations. It is pointed out for the first time that the mechanism for odor processing is similar to the mechanisms we earlier proposed for processing of auditory and visual information in topographically organized cortico-basal ganglia-thalamocortical loops, which include the primary and higher areas of the auditory and visual cortex, as well as the prefrontal cortex. It is proposed that the mechanism for olfactory processing is similar in vertebrates at different stages of evolution, including lampreys, due to the similarity of the functional organization of the basal ganglia and their interactions with other structures. It follows from the proposed mechanism that in cases where dopamine drugs are not effective in restoring odor perception, it is desirable to use adenosine A2A receptor antagonists. An improved odor perception in patients with COVID-19 treated with A2A receptor antagonists is evidence that supports this prediction.