The cerebellar role in olfaction

University Of California-Berkeley, Berkeley CA

Investigators

Abstract

This research addresses a fundamental aspect of sensory processing, that is, the active nature of sensation. The term "sensation" itself appears inherently passive, and conjures images of sensory stimuli projected onto the sensory surface, as if it were a photodiode, microphone, or chemically sensitive polymer. The sensing mammal, however, actively seeks sensory input, and nowhere is this more evident than in olfaction, where the sensory search presents itself as a clearly noticeable sniff. This sniff is constantly and accurately modulated in accordance with the sensory input -- a strong odor is greeted with a weak sniff and a weak odor is greeted with a strong sniff. Recently, whole-brain imaging techniques have opened up a new look at the olfactory system. Although the cerebellum has never been considered as part of the olfactory system, nearly every olfaction imaging study to date has reported odorant-induced activity in the cerebellum in both humans and monkeys. The role of the cerebellum in olfaction, however, remains unknown. With NSF funding, Dr. Sobel is testing the hypothesis that the role of the cerebellum in olfaction is control of the olfactomotor response. Specifically, sniffs are modulated in accordance to odorant content: high intensity odorants are met with small sniffs, and low intensity odorants are met with large sniffs. This implies a neural feedback mechanism that measures odorant intensity and modulates sniff vigor accordingly. It is proposed that control of this mechanism is the cerebellar role in olfaction. To test this two different methods are being applied, 1) psychophysics in patients with cerebellar lesions, and 2) functional magnetic resonance imaging (fMRI). In cerebellar lesion patients, the question will be tested whether the well-documented inverse relation between odorant intensity and sniff volume breaks down. This would be predicted if the cerebellum indeed controls the olfactomotor response. With fMRI, the neural path from the nose to the cerebellum will be probed, specifically whether this link is ipsilateral or contralateral. This effort promises to elucidate both a fundamental component of olfactory processing, as well as shed light on cerebellar function in general. The results of this project promise to further the understanding of basic mechanisms underlying sensory perception. Understanding of these mechanisms may open doors towards both improved treatment of sensory impairments, as well as incorporation of the elucidated mechanisms into devices aimed at mimicking sensory perception. This is especially true in olfaction, considering the increased interest in technologies aimed at sensing air-borne markers in applications ranging from disease diagnostics to landmine and biological-agent detection.