Artin Arshamian

The functional neuroanatomy of odor evoked autobiographical memories cued by odors and words

Behavioral evidence indicates that odor evoked autobiographical memories (OEAMs) are older, more emotional, less thought of and induce stronger time traveling characteristics than autobiographical memories (AMs) evoked by other modalities. The main aim of this study was to explore the neural correlates of AMs evoked by odors as a function of retrieval cue. Participants were screened for specific OEAMs and later presented with the odor cue and its verbal referent in an fMRI paradigm. Because the same OEAM was retrieved across both cue formats (odor and word), potential cue dependent brain activations were investigated. The overall results showed that odor and word cued OEAMs activated regions typically associated with recollection of autobiographical information. Although no odors were presented, a verbal cuing of the OEAMs activated areas associated with olfactory perception (e.g., piriform cortex). However, relative to word cuing, an odor cuing of OEAMs resulted in more activity in MTL regions such as the parahippocampus, and areas involved in visual vividness (e.g., occipital gyrus and precuneus). Furthermore, odor cues activated areas related to emotional processing, such as limbic and tempopolar regions significantly more. In contrast, word cues relative to odor cues recruited a more widespread and bilateral prefrontal activity. Hippocampus activity did not vary as function of the remoteness of the memory, but recollection of OEAMs from the 1(st) vs the 2(nd) decade of life showed specific activation in the right OFC, whereas the 2(nd) reflected a higher activation in the left inferior frontal gyrus.

A spatiotemporal comparison between olfactory and trigeminal event-related potentials

The present study compared the temporal and spatial aspects of human olfactory and trigeminal processing. A relatively selective trigeminal stimulus, CO2, and a relatively selective olfactory stimulus, H2S, were delivered with an olfactometer to young, healthy volunteers. The analysis was performed in a classical (5-electrode, main ERPs peaks) and modern approach (high topographical resolution, inverse solution, source localization). Results of microstate segmentation highlighted 5 maps that generally described the two processes at cerebral level. The trigeminal response differed from the olfactory response up to 300ms after stimulus onset. In this time range, source analysis pointed out that the olfactory stimulation involved olfactory related areas, while trigeminal stimulation involved noxious/somatosensory specific brain areas. Moreover, from 300ms on our data showed a similarity between the two processes. Statistical parametrical mapping of the differences between conditions suggested greater activation in a specific motor/sniffing network for the CO2 stimulation (probably related to a regulation of the potential noxious stimulus) and a greater activation of the ipsilateral primary olfactory cortex for H2S.

Olfactory LOVER: behavioral and neural correlates of autobiographical odor memory

Autobiographical memories (AMs) are personally experienced events that may be localized in time and space. In the present work we present an overview targeting memories evoked by the sense of smell. Overall, research indicates that autobiographical odor memory is different than memories evoked by our primary sensory systems; sight, and hearing. Here, observed differences from a behavioral and neuroanatomical perspective are presented. The key features of an olfactory evoked AM may be referred to the LOVER acronym-Limbic, Old, Vivid, Emotional, and Rare.

Same same but different: the case of olfactory imagery.

In the present work we present an overview of experimental findings corroborating olfactory imagery observations with the visual and auditory modalities. Overall, the results indicate that imagery of olfactory information share many features with those observed in the primary senses although some major differences are evident. One such difference pertains to the considerable individual differences observed, with the majority being unable to reproduce olfactory information in their mind. Here, we highlight factors that are positively related to an olfactory imagery capacity, such as semantic knowledge, perceptual experience, and olfactory interest that may serve as potential moderators of the large individual variation.

Olfactory awareness is positively associated to odour memory

We investigated the relationship between olfactory awareness and olfactory proficiency as determined by a set of standardised olfactory tasks. Olfactory awareness was indexed by scores in questionnaires focusing on odour interest, imagery ability, and prevalence of olfactory dreams. Nineteen subjects with high and 20 subjects with low odour awareness were presented with a set of standardised olfactory tasks: odour threshold, episodic odour recognition, and odour identification. The results showed that individuals with high odour awareness excelled in odour memory and identified more odours as compared with the low awareness group. Interestingly, odour naming ability exerted no influence on odour memory. Furthermore, high odour awareness was not related to a more sensitive olfactory sensory system as determined by olfactory threshold measurements.

Self-grounding visual, auditory and olfactory autobiographical memories

Given that autobiographical memory provides a cognitive foundation for the self, we investigated the relative importance of visual, auditory and olfactory autobiographical memories for the self. Thirty subjects, with a mean age of 35.4years, participated in a study involving a three×three within-subject design containing nine different types of autobiographical memory cues: pictures, sounds and odors presented with neutral, positive and negative valences. It was shown that visual compared to auditory and olfactory autobiographical memories involved higher cognitive and emotional constituents for the self. Furthermore, there was a trend showing positive autobiographical memories to increase their proportion to both cognitive and emotional components of the self, from olfactory to auditory to visually cued autobiographical memories; but, yielding a reverse trend for negative autobiographical memories. Finally, and independently of modality, positive affective states were shown to be more involved in autobiographical memory than negative ones.

The fate of the inner nose: Odor imagery in patients with olfactory loss

Cerebral activations during olfactory mental imagery are fairly well investigated in healthy participants but little attention has been given to olfactory imagery in patients with olfactory loss. To explore whether olfactory loss leads to deficits in olfactory imagery, neural responses using functional magnetic resonance imaging (fMRI) and self-report measures were investigated in 16 participants with acquired olfactory loss and 19 control participants. Participants imagined both pleasant and unpleasant odors and their visual representations. Patients reported less vivid olfactory but not visual images than controls. Results from neuroimaging revealed that activation patterns differed between patients and controls. While the control group showed stronger activation in olfactory brain regions for unpleasant compared to pleasant odors, the patient group did not. Also, activation in critical areas for olfactory imagery was correlated with the duration of olfactory dysfunction, indicating that the longer the duration of dysfunction, the more the attentional resources were employed. This indicates that participants with olfactory loss have difficulties to perform olfactory imagery in the conventional way. Regular exposure to olfactory information may be necessary to maintain an olfactory imagery capacity.