Neural suppression in odor recognition memory

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.

fNIRS a novel neuroimaging tool to investigate olfaction, olfactory imagery, and crossmodal interactions: a systematic review

Olfaction is understudied in neuroimaging research compared to other senses, but there is growing evidence of its therapeutic benefits on mood and well-being. Olfactory imagery can provide similar health benefits as olfactory interventions. Harnessing crossmodal visual-olfactory interactions can facilitate olfactory imagery. Understanding and employing these cross-modal interactions between visual and olfactory stimuli could aid in the research and applications of olfaction and olfactory imagery interventions for health and wellbeing. This review examines current knowledge, debates, and research on olfaction, olfactive imagery, and crossmodal visual-olfactory integration. A total of 56 papers, identified using the PRISMA method, were evaluated to identify key brain regions, research themes and methods used to determine the suitability of fNIRS as a tool for studying these topics. The review identified fNIRS-compatible protocols and brain regions within the fNIRS recording depth of approximately 1.5 cm associated with olfactory imagery and crossmodal visual-olfactory integration. Commonly cited regions include the orbitofrontal cortex, inferior frontal gyrus and dorsolateral prefrontal cortex. The findings of this review indicate that fNIRS would be a suitable tool for research into these processes. Additionally, fNIRS suitability for use in naturalistic settings may lead to the development of new research approaches with greater ecological validity compared to existing neuroimaging techniques.

Disgust sensitivity and psychopathic behavior: A narrative review

Humans live under constant threat from pathogenic microorganisms and minimizing such threat has been a major evolutionary selective force in shaping human behavior and health. A particular adaptive mechanism against the harm caused by parasites and their infectiousness is disgust sensitivity, which has evolved to detect and avoid poisonous foods as well as bodily secretions harboring virulent microorganisms. This ubiquitous and reflexive behavior requires the integration of several internal and external sensory signals between the brain, the autonomic nervous system (ANS), and the gastrointestinal tract. Although the emotional expression of disgust is experienced by almost all individuals, the neural mechanisms of sensory signals underlying disgust sensitivity may differ in certain psychiatric conditions. Psychopathy, for instance, is a personality disorder in which disgust sensitivity to contagious bodily secretions is apparently absent or downregulated from its atypical personality temperament. In this review, we provide convergent behavioral, anatomical, and cellular evidence to suggest that a fractured experience of disgust sensitivity might be an additional feature of psychopathic behavior. First, we discuss the neural networks of certain brain regions mediating the emotional states of disgust and then discuss the intersection of the ANS and gastrointestinal tract in the processing of disgust and its relevance to aberrant antisocial behavior. Together, this work highlights the interconnections between the brain and the bilateral body plan as an integrated cell network that is relevant for understanding common principles underlying function and dysfunction of disgust levels in psychiatric domains.