Functional Mapping of Human Brain in Olfactory Processing: A PET Study

Abstract

This study describes the functional anatomy of olfactory and visual naming and matching in humans, using positron emission tomography (PET). One baseline control task without olfactory or visual stimulation, one control task with simple olfactory and visual stimulation without cognition, one set of olfactory and visual naming tasks, and one set of olfactory and visual matching tasks were administered to eight normal volunteers. In the olfactory naming task (ON), odors from familiar items, associated with some verbal label, were to be named. Hence, it required long-term olfactory memory retrieval for stimulus recognition. The olfactory matching task (OM) involved differentiating a recently encoded unfamiliar odor from a sequentially presented group of unfamiliar odors. This required short-term olfactory memory retrieval for stimulus differentiation. The simple olfactory and visual stimulation resulted in activation of the left orbitofrontal region, the right piriform cortex, and the bilateral occipital cortex. During olfactory naming, activation was detected in the left cuneus, the right anterior cingulate gyrus, the left insula, and the cerebellum bilaterally. It appears that the effort to identify the origin of an odor involved semantic analysis and some degree of mental imagery. During olfactory matching, activation was observed in the left cuneus and the cerebellum bilaterally. This identified the brain areas activated during differentiation of one unlabeled odor from the others. In cross-task analysis, the region found to be specific for olfactory naming was the left cuneus. Our results show definite recruitment of the visual cortex in ON and OM tasks, most likely related to imagery component of these tasks. The cerebellar role in cognitive tasks has been recognized, but this is the first PET study that suggests that the human cerebellum may have a role in cognitive olfactory processing as well.

Brain activation when hearing one's own and others' names

“…The authors suggested that the participants used a strategy involving mental imagery to achieve the task. In a PET study of the cognitive component of olfactory processing, left cuneus was activated when participants named the odors (Qureshy et al, 2000). The authors suggest that the task involved some imagery to ascertain the name of the odor and indicated that the visual cortex is involved in mental imagery tasks (see also Kosslyn, 1988;Royet et al, 1999).…”

Modulation of Olfactory Perception by Visual Cortex Stimulation

“…Analogously, neuroimaging studies have reported activation of visual cortical areas during the performance of various purely olfactory tasks (Royet et al, 1999;Qureshy et al, 2000;Zatorre et al, 2000;Dade et al, 2002). One possible explanation for these visual-olfactory interactions is that subjects decide upon the identity of the stimulus, based entirely on processing within olfactory brain regions, after which they visualize the corresponding object.…”

Olfactory Impairments in Patients with Unilateral Cerebellar Lesions Are Selective to Inputs from the Contralesional Nostril

“…Although the cerebellum is not traditionally considered part of the olfactory system, cerebellar activity has been consistently observed in functional imaging studies of olfaction (Small et al, 1997;Yousem et al, 1997;Sobel et al, 1998;Qureshy et al, 2000;Savic et al, 2000;Zatorre et al, 2000;Cerf-Ducastel and Murphy, 2001;Ferdon and Murphy, 2003). Despite this, the pathways through which olfactory information reaches the cerebellum and the functional role of the cerebellum in olfaction remain unknown.…”