Brain response to odors presented inside the nose, directly in front of the nose or with ambient air

Naturalistic approach to investigate the neural correlates of a laundry cycle with and without fragrance

Advancements in brain imaging technologies have facilitated the development of "real-world" experimental scenarios. In this study, participants engaged in a household chore - completing a laundry cycle - while their frontal lobe brain activity was monitored using fNIRS. Participants completed this twice using both fragranced and unfragranced detergent, to explore if fNIRS is able to identify any differences in brain activity in response to subtle changes in stimuli. Analysis was conducted using Automatic IDentification of functional Events (AIDE) software and fNIRS correlation-based signal improvement (CBSI). Results indicated that brain activity, particularly in the right frontopolar and occasionally the left dorsolateral prefrontal cortex, was more pronounced and frequent with the unfragranced detergent than the fragranced. This suggests that completing tasks in an environment where a pleasant and relaxing fragrance is present might be less effortful compared to an odourless environment.

Differential connectivity of the posterior piriform cortex in Parkinson's disease and postviral olfactory dysfunction: an fMRI study

Olfactory dysfunction is a common feature of both postviral upper respiratory tract infections (PV) and idiopathic Parkinson's disease (PD). Our aim was to investigate potential differences in the connectivity of the posterior piriform cortex, a major component of the olfactory cortex, between PV and PD patients. Fifteen healthy controls (median age 66 years, 9 men), 15 PV (median age 63 years, 7 men) and 14 PD patients (median age 70 years, 9 men) were examined with task-based olfactory fMRI, including two odors: peach and fish. fMRI data were analyzed with the co-activation pattern (CAP) toolbox, which allows a dynamic temporal assessment of posterior piriform cortex (PPC) connectivity. CAP analysis revealed 2 distinct brain networks interacting with the PPC. The first network included regions related to emotion recognition and attention, such as the anterior cingulate and the middle frontal gyri. The occurrences of this network were significantly fewer in PD patients compared to healthy controls (p = 0.023), with no significant differences among PV patients and the other groups. The second network revealed a dissociation between the olfactory cortex (piriform and entorhinal cortices), the anterior cingulate gyrus and the middle frontal gyri. This second network was significantly more active during the latter part of the stimulation, across all groups, possibly due to habituation. Our study shows how the PPC interacts with areas that regulate higher order processing and how this network is substantially affected in PD. Our findings also suggest that olfactory habituation is independent of disease.

The Effect of Olfactory Training on Olfaction, Cognition, and Brain Function in Patients with Mild Cognitive Impairment

BACKGROUND

The olfactory system is affected very early in Alzheimer's disease and olfactory loss can already be observed in patients with mild cognitive impairment (MCI), an early stage of AD.

OBJECTIVE

The aim of this randomized, prospective, controlled, blinded study was to evaluate whether olfactory training (OT) may have an effect on olfactory function, cognitive impairment, and brain activation in MCI patients after a 4-month period of frequent short-term exposure to various odors.

METHODS

A total of 38 MCI outpatients were randomly assigned to OT or a control training condition, which were performed twice a day for 4 months. Olfactory testing, comprehensive neuropsychological assessment, and magnetic resonance imaging were performed before and after training.

RESULTS

The results suggested that OT exhibited no significant effect on olfaction and cognitive function. However, OT exhibited a positive effect on frontal lobe activation (left middle frontal gyrus and orbital-frontal cortex) but exhibited no effect on grey matter volume. Moreover, the change of olfactory scores was positively associated with the change of frontal activation.

CONCLUSION

OT was found to have a limited effect on olfaction and cognition in patients with MCI compared to a non-OT condition but increased their functional response to odors in frontal area.