Anterior thalamic nuclei: A critical substrate for non-spatial paired-associate memory

The anterior thalamic nuclei (ATN), a central node in a complex memory system, process spatial and temporal memory. Here, we show that ATN lesions do not affect acquisition of a simple odour discrimination or a simple object discrimination in a runway apparatus. The same procedures were used to test learning of an arbitrary association between non-spatial object-odour pairings (A+X or B+Y were rewarded; but not A+Y or B+X). If ATN lesions recapitulate hippocampal function, specifically CA1 function, then they should disrupt acquisition only when an explicit delay (i.e., a 10-second trace) is inserted between the odour and object. Acquisition was completely abolished by ATN lesions, irrespective of the presence of the temporal trace, and despite extensive training (50x12-trial sessions). Faster acquisition with the 10-second trace was found in the sham-lesion rats. During recall, 5 days after criterion, sham rats but not ATN-lesion rats showed elevated Zif268 expression in hippocampal CA1 for the trace compared to no-trace condition; both sham and lesion rats tested in the trace condition showed increased IEG expression in the superficial layers of the prefrontal cortex and retrosplenial cortex. ATN lesions markedly reduced Zif268 expression in the prefrontal cortex and retrosplenial cortex. This is the first evidence that ATN lesions impair non-spatial paired-associate tasks. The findings suggest that the ATN influence memory beyond time and space, and constitute a critical neural structure for learning arbitrary associations even in the task version that is not disrupted by hippocampal lesions.

Acupuncture is associated with a positive effect on odour discrimination in patients with postinfectious smell loss—a controlled prospective study

Introduction Smell disorders are common in the general population and occur e.g., after infections, trauma or idiopathically Treatment strategies for smell loss range from surgery, medication to olfactory training, depending on the pathology, but they are limited This study examined the effect of acupuncture on olfactory function. Methods Sixty patients with smell loss following infections of the upper respiratory tract were included in this investigation Half of the study group were randomly assigned to verum acupuncture and the other half to sham acupuncture Olfaction was measured by means of the “Sniffin’ Sticks” test battery (odour threshold, discrimination and identification). Results Compared to sham acupuncture, verum was associated with an improvement of smell function as measured by the TDI score (p = 0.039) The improvement was largely determined by improvement in odour discrimination, and was significantly better in patients with a shorter duration of the disorder. Conclusion The present results suggest that acupuncture is an effective supplementary treatment option for patients with olfactory loss.

Very rapid multi-odour discrimination learning in the ant Lasius niger

Insects can be very good learners. For example, they can form associations between a cue and a reward after only one exposure. Discrimination learning, in which multiple cues are associated with different outcomes, is critical for responding correctly complex environments. However, the extent of such discrimination learning is not well explored. Studies concerning discrimination learning within one valence are also rare. Here we ask whether Lasius niger ants can form multiple concurrent associations to different reward levels, and how rapidly such associations can be learned. We allowed individual workers to sequentially feed on up to four different food qualities, each associated with a different odour cue. Using pairwise preference tests, we found that ants can successfully learn at least two, and likely three, odour/quality associations, requiring as little as one exposure to each combination in order for learning to take place. By testing preference between two non-extreme values (i.e. between 0.4 M and 0.8 M having been trained to the qualities 0.2, 0.4, 0.8 and 1.6) we exclude the possibility that ants are only memorising the best and worst values in a set. Such rapid learning of multiple associations, within one valence and one modality, is impressive, and makes Lasius niger a very tractable model for complex training paradigms.

Examination Techniques of the First Cranial Nerve: What Neurosurgical Residents Should Know

Olfactory or smell dysfunction is often overlooked by clinicians despite being prevalent in the population. To date in Malaysia, there is no standard and reliable test to examine the function of olfaction. Tests used at developed countries such as the Sniffin’ Sticks Test (SST), the Connecticut Chemosensory Clinical Research Center (CCCRC) test, the University of Pennsylvania Smell Identification Test (UPSIT) and the Brief Smell Identification Test (B-SIT) are not readily available in this region and may be costly to procure. The first cranial nerve can be tested using commonly available materials to assess: i) the function of odour detection; ii) the odour discrimination; and iii) the odour identification. An abnormal odour detection threshold test generally indicates a peripheral olfactory problem while the odour discrimination and identification test attribute the problem to the cerebral cortex. An olfactory complaint should not be taken lightly and a proper olfactory function examination is important: i) to determine the legitimacy of a patient’s complaint; ii) to monitor the progress of patient’s olfactory function; iii) to establish insurance payout for disability; and iv) to characterise the specific nature of the problem. A video has been produced to demonstrate the examination techniques explained in this article.

Flexible Representations of Odour Categories in the Mouse Olfactory Bulb

SUMMARYThe ability to group sensory stimuli into categories is crucial for efficient interaction with a rich and ever-changing environment. In olfaction, basic features of categorical representation of odours were observed as early as in the olfactory bulb (OB). Categorical representation was described in mitral cells (MCs) as sudden transitions in responses to odours that were morphed along a continuum. However, it remains unclear to what extent such response dynamics actually reflects perceptual categories and decisions therein. Here, we tested the role of learning on category formation in the mouse OB, using in vivo two-photon calcium imaging and behaviour. We imaged MCs responses in naïve mice and in awake behaving mice as they learned two tasks with different classification logic. In one task, a 1-decision boundary task, animals learned to classify odour mixtures based on the dominant compound in the mixtures. As expected, categorical representation of close by odours, which was evident already in naïve animals, further increased following learning. In a second task, a multi-decision boundary task, animals learned to classify odours independent of their chemical similarity. Rather, odour discrimination was based on the meaning ascribed to them (either rewarding or not). Following the second task, odour representations by MCs reorganized according to the odour value in the new category. This functional reorganization was also reflected as a shift from predominantly excitatory odour responses to predominantly inhibitory odour responses. Our data shows that odour representations by MCs is flexible, shaped by task demands, and carry category-related information.

Störungen des Geruchssinns: Psychiatrisch-neurologische Bezüge und Diagnostik

ZusammenfassungUntersuchungen zur olfaktorischen Wahrnehmung bei psychiatrischen und neurodegenerativen Erkrankungen zeigen vielfältige Veränderungen auf psychophysikalischer, neurophysiologischer und anatomischer Ebene. Diese Veränderungen stellen sich zum Teil erkrankungsspezifisch dar. So wird z. B. die dysfunktionale Geruchswahrnehmung bei affektiven Erkrankungen mit anatomisch-funktionellen Überlappungen von geruchs- und emotionsverarbeitenden Arealen in Verbindung gebracht. Auf Basis der aktuellen Datenlange zur veränderten Riechfähigkeit bei Major Depression, Schizophrenie, Alzheimer-Demenz und der Parkinson-Erkrankung wird hier die Erfassung der olfaktorischen Wahrnehmung als zusätzlicher diagnostischer Marker bei neuropsychiatrischen Erkrankungen diskutiert. Dabei besteht die Notwendigkeit einer objektiven Erfassung der Riechfunktion über validierte Testverfahren, verknüpft mit Kenntnissen in der Interpretation der erhaltenen Befunde. Ziel dieser Übersichtsarbeit ist es, die Veränderungen der olfaktorischen Wahrnehmung bei den genannten Erkrankungen darzustellen und ausgewählte, im deutschen Sprachraum verfügbare Verfahren vorzustellen und anwendungsbezogen einzuordnen. Eigene aktuelle Daten zur Validierung eines Geruchsdiskriminationstests (Düsseldorf Odour Discrimination Test) an einer klinischen Stichprobe werden vorgestellt.

Food quality and conspicuousness shape improvements in olfactory discrimination by mice

How animals locate nutritious but camouflaged prey items with increasing accuracy is not well understood. Olfactory foraging is common in vertebrates and the nutritional desirability of food should influence the salience of odour cues. We used signal detection analysis to test the effect of nutritional value relative to the conspicuousness of food patches on rates of foraging improvement of wild house mice Mus musculus searching for buried food (preferred peanuts or non-preferred barley). Olfactory cues were arranged to make food patches conspicuous or difficult to distinguish using a novel form of olfactory camouflage. Regardless of food type or abundance, mice searching for conspicuous food patches performed significantly better than mice searching for camouflaged patches. However, food type influenced how mice responded to different levels of conspicuousness. Mice searching for peanuts improved by similar rates regardless of whether food was easy or hard to find, but mice searching for barley showed significant differences, improving rapidly when food was conspicuous but declining in accuracy when food was camouflaged. Our results demonstrate a fundamental tenet of olfactory foraging that nutritional desirability influences rates of improvement in odour discrimination, enabling nutritious but camouflaged prey to be located with increasing efficiency.

Sensory specificity and speciation: a potential neuronal pathway for host fruit odour discrimination in Rhagoletis pomonella

Behavioural changes in habitat or mate choice can trigger population divergence, leading to speciation. However, little is known about the neurological bases for such changes. Rhagoletis pomonella (Diptera: Tephritidae) is a model for ecological speciation via host plant shifts. Within the past 180 years, Rhagoletis flies infesting hawthorn ( Crataegus spp.) shifted to attack domesticated apple ( Malus pumila ). The two populations differ in their olfactory preferences for apple versus hawthorn fruit. Here, we looked for patterns of sensory organization that may have contributed to this shift by characterizing the morphology, specificity and distribution of olfactory sensory neurons (OSNs) on the antennae of Rhagoletis responding to host fruit and non-host volatiles. Of 28 OSN classes identified, two colocalized OSN pairs were found that specifically responded to the major behavioural attractant and antagonist volatiles for each fly population. A reversal in the response of these OSNs to fruit volatiles, either through a switch in receptor expression between these paired neurons or changes in neuronal projections in the brain, could therefore account for the behavioural difference between apple and hawthorn flies. The finding supports the hypothesis that relatively minor changes in olfactory sensory pathways may contribute to rapid host shifting and divergence in Rhagoletis .