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Biomedical subjects

Noam Sobel

Publications and source records attributed to Noam Sobel.

12 recordsLinked to original sources
PubMed2006

A comparison of methods for sniff measurement concurrent with olfactory tasks in humans.

There is a growing appreciation for the role of sniffing in the formation of the olfactory percept. With this in mind, monitoring and measurement of sniffing is an important aspect of olfactory experiments. There are several methods for measuring human sniffs concurrent with odor delivery in olfactory experiments. Here, we set out to compare the temporal sensitivity and power of these different methods by applying them all simultaneously with an olfactory task. We discuss the advantages and disadvantages of each method and conclude in recommending the use of a nasal cannula linked to a pressure sensor whenever possible.

Adolescent↗
PubMed2005

The sniff is part of the olfactory percept.

In this review, we use data obtained primarily from humans to argue that sniffs are not merely a stimulus carrier but are rather a central component of the olfactory percept. We argue that sniffs 1) are necessary for the olfactory percept, 2) affect odorant intensity perception and identity perception, 3) drive activity in olfactory cortex, 4) are rapidly modulated in an odorant-dependent fashion by a dedicated olfactomotor system, and 5) are sufficient to generate an olfactory percept of some sort even in the absence of odor.

Humans↗
PubMed2005

Humans as an animal model for systems-level organization of olfaction.

The past 15 years have seen significant advances in the study of olfaction, with particular emphasis on elucidating the molecular building blocks of the sensory process. However, much of the systems-level organization of olfaction remains unexplored. Here, we provide an overview at this level, highlighting results obtained from studying humans, whom we think provide an underutilized, yet critical, animal model for olfaction.

Animals↗
PubMed2005

Brain mechanisms for extracting spatial information from smell.

Forty years ago, von Békésy demonstrated that the spatial source of an odorant is determined by comparing input across nostrils, but it is unknown how this comparison is effected in the brain. To address this, we delivered odorants to the left or right of the nose, and contrasted olfactory left versus right localization with olfactory identification during brain imaging. We found nostril-specific responses in primary olfactory cortex that were predictive of the accuracy of left versus right localization, thus providing a neural substrate for the behavior described by von Békésy. Additionally, left versus right localization preferentially engaged a portion of the superior temporal gyrus previously implicated in visual and auditory localization, suggesting that localization information extracted from smell was then processed in a convergent brain system for spatial representation of multisensory inputs.

Adult↗
PubMed2005

Olfactory impairments in patients with unilateral cerebellar lesions are selective to inputs from the contralesional nostril.

Functional imaging studies of olfaction have consistently reported odorant-induced activation of the cerebellum. However, the cerebellar role in olfaction remains unknown. We examined the olfactory and olfactomotor abilities of patients with unilateral cerebellar lesions, comparing performance within subjects across nostrils, as well as between subjects with age-matched and young controls. Regarding olfactory performance, initial testing revealed that patients had a contralesional impairment in olfactory identification but not olfactory detection threshold. However, when tested under conditions that prevented compensatory sniffing strategies, the patients also exhibited a contralesional olfactory detection impairment. Regarding olfactomotor function, a healthy olfactomotor system generates sniffs that are (1) sufficiently vigorous and (2) inversely proportional to odorant concentration in sniff mean airflow velocity, maximum airflow velocity, volume, and duration. Patients' sniffs were lower in overall airflow velocity and volume in comparison with control participants. Furthermore, reduced sniff velocity predicted poorer detection thresholds in patients. Finally, whereas young controls used concentration-dependent sniffs, there was a trend in that direction only for age-matched controls. Patients used sniffs that were concentration invariant. In conclusion, cerebellar lesions impacted olfactory and olfactomotor performance. These findings strongly implicate an olfactocerebellar pathway prominent in odor identification and detection that functionally connects each nostril primarily to the contralateral cerebellum.

Acoustic Stimulation↗
PubMed2004

Attentional modulation in human primary olfactory cortex.

Central to the concept of attention is the fact that identical stimuli can be processed in different ways. In olfaction, attention may designate the identical flow of air through the nose as either respiration or olfactory exploration. Here we have used functional magnetic resonance imaging (fMRI) to probe this attentional mechanism in primary olfactory cortex (POC). We report a dissociation in POC that revealed attention-dependent and attention-independent subregions. Whereas a temporal subregion comprising temporal piriform cortex (PirT) responded equally across conditions, a frontal subregion comprising frontal piriform cortex (PirF) and the olfactory tubercle responded preferentially to attended sniffs as opposed to unattended sniffs. In addition, a task-specific anticipatory response occurred in the attention-dependent region only. This dissociation was consistent across two experimental designs: one focusing on sniffs of clean air, the other focusing on odor-laden sniffs. Our findings highlight the role of attention at the earliest cortical levels of olfactory processing.

Adult↗
PubMed2004

Neural processing at the speed of smell.

Olfaction is typically described as behaviorally slow, suggesting neural processes on the order of hundreds of milliseconds to seconds as candidate mechanisms in the creation of olfactory percepts. Whereas a recent study challenged this view in suggesting that a single sniff was sufficient for optimal olfactory discrimination, a study by Abraham et al. in this issue of Neuron sets out to negate the challenge by demonstrating increased processing time for discrimination of similar versus dissimilar stimuli. Here we reconcile both studies, which in our view together support the notion of a speed-accuracy tradeoff in olfactory discriminations that are made within about 200 ms. These findings are discussed in light of the challenges related to defining olfactory perceptual similarity in nonhuman animals.

Animals↗
PubMed2003

Olfactomotor activity during imagery mimics that during perception.

Neural representations created in the absence of external sensory stimuli are referred to as imagery, and such representations may be augmented by reenactment of sensorimotor processes. We measured nasal airflow in human subjects while they imagined sights, sounds and smells, and only during olfactory imagery did subjects spontaneously enact the motor component of olfaction--that is, they sniffed. Moreover, as in perception, imagery of pleasant odors involved larger sniffs than imagery of unpleasant odors, suggesting that the act of sniffing has a functional role in creating of olfactory percepts.

Auditory Perception↗
PubMed2003

Dissociating intensity from valence as sensory inputs to emotion.

In this issue of Neuron, Small and colleagues used fMRI to find evidence for a neural segregation of two dimensions underlying human gustatory experience: intensity and valence. These results join several recent reports that challenge long-held notions regarding amygdaloid representation of negatively valenced events.

Amygdala↗
PubMed2003

Rapid olfactory processing implicates subcortical control of an olfactomotor system.

Sniffs are modulated in response to odor content. Higher concentrations of odor induce lesser-volume sniffs. This phenomenon implicates a neural feedback mechanism that measures sensory input (odor concentration) and modulates motor output (sniffing) accordingly. Here we used air-dilution olfactometry to probe the time course of this olfactomotor mechanism. A stainless-steel computer-controlled olfactometer, equipped with mass flow controllers, temperature and humidity control, and on-line photo-ionization detection, was coupled to a highly sensitive pneumatotachograph that measured nasal flow. The olfactometer was used to generate four ascending concentrations of the odorants propionic acid and phenethyl alcohol. Sniff volume was inversely related to odor concentration (P > 0.0001). Sniffs were uniform and concentration independent for the initial 150 ms but acquired a concentration-dependent flowrate as early as 160 ms following sniff onset for propionic acid (P > 0.05) and 260 ms for phenethyl alcohol (P > 0.05). Considering that odorant transduction takes around 150 ms and odorant-induced cortical evoked potentials have latencies of around 300 ms, the rapid motor adjustments measured here suggest that olfactomotor sniff feedback control is subcortical and may rely on neural mechanisms similar to those that modulate eye movements to accommodate vision and ear movements to accommodate audition.

Adult↗
PubMed2003

The prevalence of androstenone anosmia.

It has been estimated that approximately 30% of the population is unable to detect the odor of androstenone. These estimates, however, were made using tests and criteria optimized for identifying detection. Such criteria favor Type II over Type I errors--that is, they are excellent at identifying true detectors at the cost of erroneously labeling some detectors as non-detectors. Because these criteria were used to identify non-detectors, it is possible that the rate of non-detection may have been overestimated. To test this we screened 55 subjects for non-detection employing previously used methods. This screen yielded nine putative non-detectors, a 16.3% putative non-detection rate. We then retested these putative non-detectors using a forced choice (yes-no) paradigm to obtain a precise measure of their sensitivity. We found that this group of putative non-detectors was significantly above chance at detecting androstenone (P < 0.001), despite very low self-confidence in their performance. Based on the results of the signal detection analysis in this sample, we estimate the rate of actual androstenone non-detection in young healthy adults is between 1.8 and 5.96%, which is significantly lower than previously estimated. This finding is significant considering the implications of specific anosmias on the understanding of odor discrimination.

Adolescent↗