Daniel B. Kurtz

Odorant Receptor Expression Patterns Are Restored in Lesion-Recovered Rat Olfactory Epithelium

Lesions of the olfactory periphery provide a means for examining the reconstitution of a diverse and highly regulated population of sensory neurons and the growth, en masse, of nascent axons to the bulb. The olfactory epithelium and its projection onto the bulb are reconstituted after ablation by methyl bromide gas, and some measure of olfactory function is restored. The extent to which the system regenerates the full repertoire of odorant receptor-expressing neurons, particularly their spatially restricted distribution across the epithelial sheet, is unknown, however, and altered odorant receptor expression might contribute to the persistent distortion of odorant quality that is observed in the lesioned-recovered animals. To address the question of receptor expression in the recovered epithelium, we performed in situ hybridization with digoxigenin-labeled riboprobes for eight odorant receptors on the olfactory epithelium from unilaterally methyl bromide-lesioned and control rats. The data demonstrate that the distribution of sensory neuron types, as identified and defined by odorant receptor expression, is restored to normal or nearly so by 3 months after lesion. Likewise, the numbers of probe-labeled neurons in the lesioned-recovered epithelium are nearly equivalent to the unlesioned side at this time. Finally, our evidence suggests that odorant receptors are distributed in multiple overlapping bands in the normal, unlesioned, and lesioned-recovered epithelium rather than in the conventionally accepted three or four zones. Thus, the primary sensory elements required for functional recovery of the olfactory system after damage are restored, and altered function implies the persistence of a more central failure in regeneration.

Odorant confusion matrix : The influence of patient history on patterns of odorant identification and misidentification in hyposmia

The odorant confusion matrix (OCM) is an odorant identification test in which the number of correct odorant identifications quantifies the level of olfactory function. As with other confusion matrices, the OCM reflects distortions of sensory perception as errors in identification. Previous work with the OCM suggests that, within an individual, hyposmia is associated with a stable shift in odorant perception. The current study examined whether consistent shifts in odorant perception are also characteristic of the various pathologies that lead to an olfactory loss. In a retrospective study, OCM response patterns for 135 hyposmic patients were fit into a five-dimensional space in which the distances between subjects reflected the dissimilarities between their OCM response patterns. Multivariate regression was performed relating position in the five-dimensional space to each of 11 factors representing 33 demographic and medical history variables. One factor, named congestion (gathering the variables of past polyposis, current polyposis, and current nasal obstruction due to swelling), was significantly indicative of patterns of responses on the OCM, independent of the level of hyposmia. These data suggest that conductive olfactory loss may be associated with alterations in odorant perception, which are reflected in consistent odorant confusions. Such alterations in perception may eventually serve as a basis for a clinical test to provide differential diagnoses as to the sources of olfactory losses.

Phonological and perceptual components of short-term memory for odors.

Just as a written word can be encoded and retained in memory verbally or visually, an odor might be retained as a verbal description or perceptual (olfactory) code. However, one view holds that olfactory memory in the short term does not exist as a separate perceptual code. This was examined in an experiment in which memory errors could be seen as deriving from the substitution of similar verbal or olfactory codes. The odorants presented for recall were divided into three groups: base odorants (which might be replaced in memory by similar verbal or olfactory representations), verbal foils (stimuli dissimilar to the base stimuli in odor but similar in name), and odor foils (the reverse). The substitution errors made in attempting to recall test odorants were classified as verbal or olfactory. A substantial proportion of the errors were olfactory, but verbal errors also occurred. These results support the presence of short-term perceptual olfactory memory rather than simply verbal encoding of olfactory perceptions.

Odorant quality perception: a metric individual differences approach.

Perceptual spaces, in which similar stimuli are located close to each other and dissimilar stimuli are located far apart, have aided in the understanding of the physiological and psychological bases for sensory quality coding. Differences in perception between individuals should be reflected by differences in the spatial relationships between stimuli. If the dimensionality of the perceptual space is small (e.g., color space), individual differences that reflect specific pathologies are readily apparent from visual inspection. On the other hand, if the dimensionality of the perceptual space is large (as is proposed for odor space), visual inspection alone may not reveal individual differences in quality perception. The present work presents an information-theory-based method for quantifying individual differences in quality perception from perceptual confusion matrices. The ability of this method to quantify individual differences in quality perception is shown in a hypothetical example of specific anosmia. Finally, the method is applied to the examination of intrasubject consistency of odorant quality perception.

The labeled dissimilarity scale: A metric of perceptual dissimilarity

Fundamental to the concept ofpsychological distance is the idea that confusability allows discovery of the perceptual relationships between objects, which provides understanding of the underlying principles that govern the functioning of a system. Thus, judgments of dissimilarity (conceptually proportional to the inverse of confusability) may provide insight into the elusive underlying quality-coding mechanisms in that sensory system. In the present experiments, a labeled dissimilarity scale (LDS) that reflects the magnitude of odorant dissimilarity was developed in a fashion similar to that reported by Green (Green, Shaffer, & Gilmore, 1993). This scale was produced by rating the perceptual intensity implied by adverbs describing different levels of dissimilarity, and then attaching those descriptors to appropriate locations on a numerical scale. The usefulness of the scale was demonstrated by its ability to produce visual color space with ratings of dissimilarity of Munsell color chips. The stability and reliability of the LDS was evaluated by comparing it with the traditional scaling technique of magnitude estimation (ME). It was found that the scales produced similar ratings of odorant dissimilarity and showed a similar susceptibility to the effects of contrast convergence. However, the coefficients of variation of dissimilarities rated with ME were much higher than those produced with the LDS. The subjects also dealt with the LDS without the anxiety that usually accompanies first-time users of ME. The LDS provided stable ratings of odorant dissimilarity and preserved the inferred ratio scale properties of ME.

Anosmic Patients Can Separate Trigeminal and Nontrigeminal Stimulants

Anosmia is the inability of the first cranial nerve pathway to detect airborne odorant molecules. In humans, however, information about airborne odorant molecules comes from a variety of sensory systems in addition to the first cranial nerve. As a first step in determining the degree of involvement of other sensory systems in the smell deficits of anosmic patients, a retrospective study was undertaken to determine if these patients could separate trigeminal and nontrigeminal odorants.