Olfactory Neural Responses Research Articles

Electrophysiological correlates of top-down attentional modulation in olfaction

The capacity to pay attention is important for the cognitive ability, for example, evaluating an object for its qualities. Attention can selectively prioritize the neural processes that are relevant to a given task. Neuroimaging investigations on human attention are primarily focused on vision to the exclusion of other sensory systems, particularly olfaction. Neural underpinnings of human olfactory attention are still not clearly understood. Here, we combined electroencephalographic measurements of olfactory event related potential with electrical neuroimaging to investigate how the neural responses after inhaling the same odor differ between conditions with varying levels of attention, and, in which brain areas. We examined the neural responses when participants attended to a rose-like odor of phenylethyl alcohol for evaluating its pleasantness versus its passive inhalation. Our results gathered significant evidence for attentional modulation of the olfactory neural response. The most prominent effect was found for the late positive component, P3, of olfactory event related potential within a second from the odor onset. The source reconstruction of this data revealed activations in a distributed network of brain regions predominantly in inferior frontal cortex, insula, and inferior temporal gyrus. These results suggest that the neuronal modulations from attention to olfactory pleasantness may be subserved by this network.

The effect of verbal context on olfactory neural responses

Odor names refer usually to "source" object categories. For example, the smell of rose is often described with its source category (flower). However, linguistic studies suggest that odors can also be named with labels referring to categories of "practices". This is the case when rose odor is described with a verbal label referring to its use in fragrance practices ("body lotion," cosmetic for example). It remains unknown whether naming an odor by its practice category influences olfactory neural responses differently than that observed when named with its source category. The aim of this study was to investigate this question. To this end, functional MRI was used in a within-subjects design comparing brain responses to four different odors (peach, chocolate, linden blossom, and rose) under two conditions whereby smells were described either (1) with their source category label (food and flower) or (2) with a practice category label (body lotion). Both types of labels induced activations in secondary olfactory areas (orbitofrontal cortex), whereas only the source label condition induced activation in the cingulate cortex and the insula. In summary, our findings offer a new look at olfactory perception by indicating differential brain responses depending on whether odors are named according to their source or practice category.

The Sniff as a Unit of Olfactory Processing

Sniffing is a rhythmic motor process essential for the acquisition of olfactory information. Recent behavioral experiments show that using a single sniff rats can accurately discriminate between very similar odors and fail to improve their accuracy by taking multiple sniffs. This implies that each sniff has the potential to provide a complete snapshot of the local olfactory environment. The discrete and intermittent nature of sniffing has implications beyond the physical process of odor capture as it strongly shapes the flow of information into the olfactory system. We review electrophysiological studies-primarily from anesthetized rodents-demonstrating that olfactory neural responses are coupled to respiration. Hence, the "sniff cycle" might play a role in odor coding, by allowing the timing of spikes with respect to the phase of the respiration cycle to encode information about odor identity or concentration. We also discuss behavioral and physiological results indicating that sniffing can be dynamically coordinated with other rhythmic behaviors, such as whisking, as well as with rhythmic neural activity, such as hippocampal theta oscillations. Thus, the sniff cycle might also facilitate the coordination of the olfactory system with other brain areas. These converging lines of empirical data support the notion that each sniff is a unit of olfactory processing relevant for both neural coding and inter-areal coordination. Further electrophysiological recordings in behaving animals will be necessary to assess these proposals.

Analysis of Olfactory Neural Responses by a Method of Spike Train Matching

Analysis of Olfactory Neural Responses by a Method of Spike Train Matching

The spatial distribution of ciliated and microvillous olfactory receptor neurons in the channel catfish is not matched by a differential specificity to amino acid and bile salt stimuli

The distribution of two receptor cell types, stellate microvillous and ciliated, was quantitatively examined in the sensory regions of the olfactory lamellae of the channel catfish, Ictalurus punctatus . Using scanning electron microscopy (SEM), these two cell types were seen to exhibit an incomplete segregation across the sensory epithelium. The density of stellate microvillous cells was greatest in the dorso-medial portion of the sensory region of the lamella and markedly decreased ventrally and laterally. The ciliated cells were more numerous in the ventro-lateral portion of the sensory region and decreased in number dorso-medially. Multi-unit olfactory neural responses to amino acids and bile salts were recorded from the dorso-medial and ventro-lateral portions of the sensory region. In both portions of the sensory region, L-cysteine, L-alanine and L-norleucine were highly stimulatory, while the sodium salts of cholic acid, taurocholic acid and taurolithocholic acid (i.e., bile salts) were the least stimulatory compounds tested. With the exception of L-norleucine, no significant differences were found in the responses from the dorso-medial and ventro-lateral portions of the sensory region for the compounds tested. These results indicate that in I. punctatus the response specificities of the microvillous and ciliated olfactory receptor cells are similar for amino acids and bile salts.

Dissociation of Olfactory Neural Response and Mucosal Potential

The olfactory mucosal slow potential decreased remarkably or disappeared when part of the mucus on the olfactory epithelium was removed with absorbent paper. In contrast, the neural response was not changed much, while unitary spikes in response to odor also appeared in the epithelium. The paper reduced the thicknèss of the mucus by about half, but olfactory cilia were still present. This evidence suggests that the slow potential is not the generator potential.