Biology subjects

Iravani, B.

Publications and source records attributed to Iravani, B..

9 recordsLinked to original sources

bioRxiv2023

The how, when, and what of odor valence communication between the olfactory bulb and piriform cortex

A core function of the olfactory system is to determine an odors valence. The central processing of odor valence is initiated in the olfactory bulb, but the neural mechanisms by which this important information is communicated to, and from, the olfactory cortex (piriform cortex) in humans are not known. To assess communication between the two nodes, we simultaneously measured odor-dependent neural activity in the olfactory bulb and piriform cortex from human participants while obtaining trial-by-trial valence ratings. We determined when valence information was communicated, what kind of information was transferred, and how the information was transferred (i.e., in which frequency band). Support vector machine learning on the coherence spectrum and frequency-resolved Granger causality were used to identify valence-dependent differences in functional and effective connectivity between the olfactory bulb and piriform cortex. We found that the olfactory bulb communicates odor valence to the piriform cortex in the gamma band shortly after odor onset, while the piriform cortex subsequently feeds valence-related information back to the olfactory bulb in the beta band. Decoding accuracy was better for negative than positive valence, suggesting negative valence superiority. Critically, we replicated these findings in an independent dataset using other odors across a larger perceived valence range. Combined, these results demonstrate that the olfactory bulb and piriform cortex communicate levels of odor pleasantness across multiple frequencies, at specific time-points and in a direction-dependent pattern in accordance with the two-stage model of odor processing. It also provides further evidence that odor valence should be viewed as two perceptual dimensions and not one continuous.

neuroscience↗

bioRxiv2023

Metabolic state modulates neural processing of odors in the human olfactory bulb

The olfactory and endocrine systems have recently been shown to reciprocally shape the homeostatic processes of energy intake. As demonstrated in animal models, the individuals metabolic state dynamically modulates how the olfactory bulb process odor stimuli using a range of endocrine signals. Here we aimed to determine whether the neural processing of odors in human olfactory bulb is modulated by metabolic state. Participants were exposed to food-associated odors, in separate sessions being hungry and sated, while neural responses from the olfactory bulb was obtained using electrobulbogram. We found significantly higher gamma power activity (51-100Hz) in the OBs response to odors during the Hunger compared to Sated condition. Specifically, EBG gamma power were elevated while hungry already at 100ms after odor onset, thereby suggesting intra-bulbar modulation according to metabolic state. These results demonstrate that, akin to other animal models, hunger state affects OB activity in humans. Moreover, we show that the EBG method has the potential to measure internal metabolic states and, as such, could be used to study specificities in olfactory processing of individuals suffering from pathologies such as obesity or anorexia.

neuroscience↗

bioRxiv2023

Whither unisensory olfactory cortex: processing of visual and auditory stimuli in olfactory cortex, independently of odor associations

Primary sensory cortices have been demonstrated to process sensory input from non-preferred sensory modalities, e.g. primary visual cortex reacting to auditory stimulation, bringing their presumed sensory specificity into question. Whether this reflects processing of the non-preferred stimulus per se or originates from cross-modal associations is debated. Visual/auditory objects typically have strong reciprocal associations; hence, it is difficult to address this question in these modalities. Here, we attempt to dissociate between the two competing hypotheses of whether this form of activation in primary cortices is caused by unisensory processing or cross-modal associations by turning to the olfactory system where cross-modal associations are generally weaker. Using unisensory visual and auditory objects with odor associations ranging from none to strong, we show that the posterior piriform cortex, an area known to process odor objects, is activated by both sounds and pictures of objects. Critically, this activation is independent of the objects odor associations, thereby demonstrating that the activity is not due to cross-modal associations. Using a Floyd-Warshall algorithm, we further show that the amygdala mediate condition-relevant information between the posterior piriform cortex and both the auditory and visual object-oriented cortices. Importantly, we replicate past findings of clear crossmodal processing in the visual and auditory systems. Our study demonstrates processing of non-olfactory input in olfactory cortices that is independent of cross-modal associations and contributes to a more nuanced view of modality specificity in olfactory, auditory, and visual cortices.

neuroscience↗

bioRxiv2021

ODOR IDENTITY CAN BE EXTRACTED FROM THE RECIPROCAL CONNECTIVITY BETWEEN OLFACTORY BULB AND PIRIFORM CORTEX IN HUMANS

Neuronal oscillations route external and internal information across brain regions. In the olfactory system, the two central nodes--the olfactory bulb (OB) and the piriform cortex (PC)--communicate with each other via neural oscillations to shape the olfactory percept. Communication between these nodes have been well characterized in non-human animals but less is known about their role in the human olfactory system. Using a recently developed and validated EEG-based method to extract signals from the OB and PC sources, we show in healthy human participants that there is a bottom-up information flow from the OB to the PC in the beta and gamma frequency bands, while top-down information from the PC to the OB is facilitated by delta and theta oscillations. Importantly, we demonstrate that there was enough information to decipher odor identity above chance from the low gamma in the OB-PC oscillatory circuit as early as 100ms after odor onset. These data further our understanding of the critical role of bidirectional information flow in human sensory systems to produce perception. However, future studies are needed to determine what specific odor information is extracted and communicated in the information exchange.

neuroscience↗

bioRxiv2021

The human olfactory bulb process odor valence representation and initiate motor avoidance behavior

Determining the valence of an odor to provide information to guide rapid approach-avoidance behavior is thought to be one of the core tasks of the olfactory system, yet little is known of its initial neural mechanisms or subsequent behavioral manifestation in humans. In two experiments, we measured the functional processing of odor valence perception in the human olfactory bulb (OB)--the first processing stage of the olfactory system--using a non-invasive method as well as assessed subsequent motor avoidance response. We demonstrate that odor valence perception is associated with both gamma and beta activity in the human OB. Moreover, we show that negative, but not positive, odors initiate an early beta response in the OB, a response that is linked to a preparatory neural motor response in motor cortex. Finally, in a separate experiment we show that negative odors trigger a full-body motor avoidance response, manifested as a rapid leaning away from the odor, in the time period predicted by the OB results. Taken together, these results demonstrate that the human OB processes odor valence in a sequential manner in both the gamma and beta frequency bands and suggest that early processing of unpleasant odors in the OB might underlie rapid approach-avoidance decisions.

neuroscience↗

bioRxiv2021

Acquired olfactory loss alters functional connectivity and morphology

Removing function from a developed and functional sensory system is known to alter both cerebral morphology and functional connections. To date, a majority of studies assessing sensory-dependent plasticity have focused on effects from either early onset or long-term sensory loss and little is known how the recent sensory loss affects the human brain. With the aim of determining how recent sensory loss affects cerebral morphology and functional connectivity, we assessed differences between individuals with acquired olfactory loss (duration 7-36 months, n=20) and matched healthy controls (n=23) in their grey matter volume, using multivariate pattern analyses, and functional connectivity, using dynamic connectivity analyses, within and from the olfactory cortex. Our results demonstrate that acquired olfactory loss alters grey matter volume in, among others, posterior piriform cortex, a core olfactory processing area, as well as the inferior frontal gyrus and angular gyrus. In addition, compared to controls, individuals with acquired anosmia displayed significantly stronger dynamic functional connectivity from the posterior piriform cortex to, among others, the angular gyrus, a known multisensory integration area. No significantly stronger connectivity in healthy control participants were demonstrated. When assessing differences in dynamic functional connectivity from the angular gyrus, individuals with acquired anosmia had stronger connectivity from the angular gyrus to areas primary responsible for basic visual and taste processing. These results demonstrate that recently acquired sensory loss alters both cerebral morphology within core olfactory areas and increase dynamic functional connectivity from olfactory cortex to cerebral areas processing multisensory integration.

neuroscience↗

bioRxiv2020

Differentiating ADHD subtypes and simulation of in silico therapeutic neuronal excitation in a whole-brain nonlinear dynamic modelling frame-work

Recent advances in non-linear computational and dynamical modelling have opened up the possibility to param etrize dynamic neural mechanisms that drive complex behavior. Importantly, building models of neuronal processes is of key importance to fully understand disorders of the brain as it may provide a quantitative platform that is capable of binding multiple neurophysiological processes to phenotype profiles. In this study, we apply a newly developed adaptive frequency-based model of whole-brain oscillations to resting-state fMRI data acquired from healthy controls and a cohort of attention deficit hyperactivity disorder (ADHD) subjects. As expected, we found that healthy control subjects differed from ADHD in terms of attractor dynamics. However, we also found a marked dichotomy in neural dynamics within the ADHD cohort. Next, we classified the ADHD group according to the level of distance of each individuals empirical network from the two model-based simulated networks. Critically, the model was mirrored in the empirical behavior data with the two ADHD subgroups displaying distinct behavioral phenotypes related to emotional instability (i.e., depression and hypomanic personality traits). Finally, we investigated the applicability and feasibility of our whole-brain model in a therapeutic setting by conducting in silico excitatory stimulations to parsimoniously mimic clinical neuro-stimulation paradigms in ADHD. We tested the effect of stimulating any individual brain region on the key network measures derived from the simulated brain network and its contribution in rectifying the brain dynamics to that of the healthy brain, separately for each ADHD subgroup. This showed that this was indeed possible for both subgroups. However, the current effect sizes were small suggesting that the stimulation protocol needs to be tailored at the individual level. These findings demonstrate the potential of this new modelling framework to unveil hidden neurophysiological profiles and establish tailored clinical interventions.

neuroscience↗

bioRxiv2019

Dynamic synergetic configurations of resting-state networks in ADHD.

Attention deficit hyperactivity disorder (ADHD) is characterized by high distractibility and impaired executive functions. Notably, there is mounting evidence suggesting that ADHD could be regarded as a default mode network (DMN) disorder. In particular, failure in regulating the dynamics of activity and interactions of the DMN and cognitive control networks have been hypothesized as the main source of task interference causing attentional problems. On the other hand, previous studies indicated pronounced fluctuations in the strength of functional connections over time, particularly for the inter-network connections between the DMN and fronto-parietal control networks. Hence, characterization of connectivity disturbances in ADHD disorder requires a thorough assessment of time-varying FCs. In this study, we propose a dynamical systems perspective to assess how the DMN over time recruits different configurations of network segregation and integration. Specifically, we were interested in configurations for which both intra- and inter-network connections are retained, as opposed to commonly used methods which assess network segregation as a single measure. From resting-state fMRI data, we extracted three different stable configurations of FC patterns for the DMN, namely synergies. We provide evidence supporting our hypothesis that the ADHD brain differs in both recruitment rate and the topology of specific synergies between resting-state networks.

neuroscience↗

bioRxiv2019

Non-invasive recording from the human olfactory bulb

Current methods can, in a non-invasive manner, assess neural activity in all areas of the human brain but the olfactory bulb (OB). The OB is intimately involved in a long list of olfactory tasks, has been suggested to fulfill a role comparable to that of V1 and the thalamus in the visual system, and have been closely linked to a wide range of neuropathologies. Here we present a method for non-invasive recording of signals from the human OB with millisecond precision. We demonstrate that signals obtained via recordings from EEG electrodes at the nasal bridge represent responses from the olfactory bulb - recordings we term Electrobulbogram (EBG). The EBG is localized to the OB, is reliable, and follows response patterns demonstrated in non-human animal models. The EBG will aid future olfactory-related translational work but can also easily be implemented as an everyday clinical tool to detect pathology-related changes in human central olfactory processing in neurodegenerative diseases.

neuroscience↗