Theresa L. White

The effect of NMDA-NR2B receptor subunit over-expression on olfactory memory task performance in the mouse

The N-methyl-D-aspartate (NMDA) receptor in the forebrain is thought to modulate some forms of memory formation, with the NR2B subunit being particularly relevant to this process. Relative to wild-type mice, transgenic animals in which the NR2B subunit was over-expressed demonstrate superior memory in a number of behavioral tasks, including object recognition [Nature 401 (1999) 63]. The purpose of the present study was to explore the generality of such phenomena, interpreted as the effect of increasing NR2B expression on the retention of other types of sensory-related information. To accomplish this, we focused our evaluation on the highly salient sensory modality of olfaction. In the first experiment, mice performed both a novel-object-recognition task identical to that performed by Tang et al. [Nature 401 (1999) 63] and a novel-odor-recognition task analogously constructed. Although the results of the object recognition task were consistent with the previous literature, there was no evidence of an effect of NR2B over-expression on the retention of odor recognition memory in the specific task performed. As it was possible that, unlike object recognition memory, novel odor recognition is not NMDA-receptor-dependent, a second task was designed using the social transmission of food preference paradigm. In contrast to the foregoing olfactory task, there is evidence that the latter procedure is, indeed, NMDA-dependent. The results of the second study demonstrated that transgenic mice with NR2B over-expression had a clear memory advantage in this alternative odor memory paradigm. Taken together, these results suggest the NR2B subunit is an important component in some but not all forms of olfactory memory organization. Moreover, for those functions that are NMDA-receptor-dependent, these data support the growing literature demonstrating the importance of the NR2B subunit.

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.

A second look at the structure of human olfactory memory.

How do we remember olfactory information? Is the architecture of human olfactory memory unique compared with that of memory for other types of stimuli? Ten years ago, a review article evaluated these questions, as well as the distinction between long‐ and short‐term olfactory memory, with three lines of evidence: capacity differences, coding differences, and neuropsychological evidence, though serial position effects were also considered. From the data available at the time, the article preliminarily suggested that olfactory memory was a two‐component system that was not qualitatively different from memory systems for other types of stimuli. The decade that has elapsed since then has ushered in considerable changes in theories of memory structure and provided huge advances in neuroscience capabilities. Not only have many studies exploring various aspects of olfactory memory been published, but a model of olfactory perception that includes an integral unitary memory system also has been presented. Consequently, the structure of olfactory memory is reevaluated in the light of further information currently available with the same theoretical lines of evidence previously considered. This evaluation finds that the preponderance of evidence suggests that, as in memory for other types of sensory stimuli, the short‐term–long‐term distinction remains a valuable dissociation for conceptualizing olfactory memory, though perhaps not as architecturally separate systems.

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.

Metacognitive knowledge of olfactory dysfunction in Parkinson's disease.

It is well known that patients with Parkinsons Disease (PD) suffer from olfactory impairments, but it is not clear whether patients are aware of their level of deficit in olfactory functioning. Since PD is a neurodegenerative disorder and its progression may be correlated with olfactory loss (Ansari & Johnson, 1975; but see also Doty, Deems, & Stellar, 1988), it is possible that these patients would be subject to metacognitive errors of over-estimation of olfactory ability (White & Kurtz, 2003). Nineteen non-demented PD patients and 19 age-matched controls were each given an objective measure of olfactory identification (the UPSIT, Doty, Shaman, Kimmelman, & Dann, 1984) and a subjective measure involving a questionnaire that asked them to self-rate both their olfactory function generally and their ability to smell each of 20 odors, 12 of which were assessed on the UPSIT. All of the PD patients showed impaired olfactory ability, as did 7 of the controls, according to the UPSIT norms. Self-rated and performance-based olfactory ability scores were significantly correlated in controls (r=.49, p=.03) but not in patients with PD (r=.20, p=.39). When the 12 odors common to both the self-rated questionnaire and UPSIT were compared, PD patients were less accurate than controls (t(36)=-4.96, p<.01) at estimating their own ability and the number of over-estimation errors was significantly higher (tone-tailed(29)=1.80, p=.04) in PD patients than in the control group, showing less metacognitive awareness of their ability than controls. These results support the idea that olfactory metacognition is often impaired in PD, as well as in controls recruited for normosmic ability (Wehling, Nordin, Espeseth, Reinvang, & Lundervold, 2011), and indicate that people with PD generally exhibit over-estimation of their olfactory ability at a rate that is higher than controls. These findings imply that PD patients, unaware of their olfactory deficit, are at greater risk of harm normally detected through olfaction, such as smoke or spoiled foods.

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.

Adding Cocoa to Sucrose: The Effect on Cold Pain Tolerance

The sweet taste of sucrose acts as an analgesic, whereas the taste of a bitter substance decreases pain tolerance. The present experiment explores the analgesic effect of a complex taste and asks how adding cocoa, a substance often associated with sweet foods but that has a bitter taste, to a sucrose solution affects cold pain tolerance. The 24 male participants were exposed to Cold Pressor Tests (CPTs) while holding 1 of 3 tastants in their mouths: water, sucrose, or sucrose with cocoa added. After each CPT, participants rated pain intensity and tastant qualities. Intraoral sucrose increased the amount of time that men were able to leave their hands in cold water, whereas the cocoa solution did not. Solutions did not differ in pleasantness or sweetness, but the cocoa solution was rated as more bitter. Bitterness ratings of cocoa exceeded the ratings of sucrose (corrected for water) by an average of 16.9% (P = 0.02), which, in turn, produced a 30% reduction in the duration of pain tolerance (P = 0.002). These results suggest that the addition of a bitter substance reduces cues to the nutritive value of sucrose that may drive its analgesic effect.

Sexual Preference and the Self-Reported Role of Olfaction in Mate Selection

IntroductionOlfactory cues are important in mating in many species, including humans. These odorants may be relevant because of their value as a cue to the reproductive fitness of a potential mate (Trivers 1972), but they could also be important as a signal of mate appropriateness in terms of sexual preference (Lübke and Pause 2015). One way to discriminate between these ideas is to examine whether the importance of olfaction in determining a mate is decreased in homosexual individuals, for whom selecting a mate is dissociated from the selection of a reproductive partner. The present research question asked whether the value of olfactory cues for attraction varies between homosexual and heterosexual groups.MethodThe present study examined odor importance in mating by presenting the Romantic Interest Survey (Herz and Inzlich 2002) to 453 individuals: 142 heterosexual women, 161 heterosexual men, and 150 gay men.ResultsRegression analysis indicated that heterosexual men valued the sense of smell when selecting a mate more than gay men did. In contrast, gay men valued the sound of a partner’s voice more than did heterosexual men. Heterosexual men and women did not differ by sex in terms of the value of olfaction; both men and women value olfactory aspects of a potential mate highly.ConclusionsThe higher value of olfactory cues to heterosexual individuals supports the idea that olfaction in mate selection may act as a cue to reproductive fitness, and indicates that olfactory information is not as valuable to gay men in mate selection.ImplicationsThese findings suggest that many people seem to be looking for similar attributes when searching for a potential romantic partner, and that olfaction is an important aspect of the process.

Olfactory Awareness and the Self-Reported Importance of Olfactory Information in Romantic Interest

IntroductionMany people seem to be looking for similar attributes when searching for a potential romantic partner. Olfactory social cues can be important parts of the process, though there are individual differences as to their value. Gay men, for example, value scent less in selecting a romantic partner than do heterosexual men (White and Cunningham, Chemosens Percept 10:31–41, 2017). Is it possible that the relative importance of olfaction in mate selection is simply a natural consequence of being generally aware of odorants?MethodThe present study examined the relationship between odor awareness and odor importance in mating in two studies. Participants in each of the studies completed both the Romantic Interests Survey (Herz and Inzlich, Evol Hum Behav 23:359–364, 2002) and the Odor Awareness Survey (Smeets et al., Chem Senses 33:725–734, 2008). In the first study, 455 college-aged heterosexual individuals were surveyed, while in the second study, 453 individuals varying in sexual preference (142 heterosexual women, 161 heterosexual men, and 150 gay men) completed the questionnaires.ResultsPrinciple components analyses from both studies revealed two different components underlying scores on the RIS; one component best accounted for OAS scores. Regression analysis for both studies indicated that OAS scores predicted the first RIS principle component, but not the second one.ConclusionsThe value of odorants in selecting a romantic partner seems to reflect two different underlying attitudes. The first attitude values all aspects of the smell of a lover, while the second only finds it important that the lover does not smell badly. Odor awareness is related only to the first of these attitudes.ImplicationsThese findings suggest that odor awareness accounts for some of the attitudes concerning the value of odors in mate selection, but not all of them. Other factors, such as the need to avoid aversive stimuli, may also contribute to the relative importance of olfaction in selecting a partner.