The functions of taste and olfaction

Principles of odor coding in vertebrates and artificial chemosensory systems

The biological olfactory system is the sensory system responsible for the detection of the chemical composition of the environment. Several attempts to mimic biological olfactory systems have led to various artificial olfactory systems using different technical approaches. Here we provide a parallel description of biological olfactory systems and their technical counterparts. We start with a presentation of the input to the systems, the stimuli, and treat the interface between the external world and the environment where receptor neurons or artificial chemosensors reside. We then delineate the functions of receptor neurons and chemosensors as well as their overall I-O relationships. Up to this point, our account of the systems goes along similar lines. The next processing steps differ considerably: while in biology the processing step following the receptor neurons is the "integration" and "processing" of receptor neuron outputs in the olfactory bulb, this step has various realizations in electronic noses. For a long period of time, the signal processing stages beyond the olfactory bulb, i.e., the higher olfactory centers were little studied. Only recently there has been a marked growth of studies tackling the information processing in these centers. In electronic noses, a third stage of processing has virtually never been considered. In this review, we provide an up-to-date overview of the current knowledge of both fields and, for the first time, attempt to tie them together. We hope it will be a breeding ground for better information, communication, and data exchange between very related but so far little connected fields.

Potential New Approaches for Diagnosis of Alzheimer's Disease and Related Dementias

Dementia is an umbrella term-caused by a large number of specific diagnoses, including several neurodegenerative disorders. Alzheimer's disease (AD) is now the most common cause of dementia in advanced countries, while dementia due to neurosyphilis was the leading cause a century ago. Many challenges remain for diagnosing dementia definitively. Some of these include variability of early symptoms and overlap with similar disorders, as well as the possibility of combined, or mixed, etiologies in some cases. Newer technologies, including the incorporation of PET neuroimaging and other biomarkers (genomics and proteomics), are being incorporated into revised diagnostic criteria. However, the application of novel diagnostic methods at clinical sites is plagued by many caveats including availability and access. This review surveys new diagnostic methods as well as remaining challenges-for clinical care and clinical research.

On the Communicative Function of Body Odors

Humans use multiple senses to navigate the social world, and the sense of smell is arguably the most underestimated one. An intriguing aspect of the sense of smell is its social communicative function. Research has shown that human odors convey information about a range of states (e.g., emotions, sickness) and traits (e.g., individuality, gender). Yet, what underlies the communicability of these states and traits via smell? We fill this explanatory gap with a framework that highlights the dynamic and flexible aspects of human olfactory communication. In particular, we explain how chemical profiles, associative learning (i.e., the systematic co-occurrence of chemical profiles with state- or trait-related information), and top-down contextual influences could interact to shape human odor perception. Our model not only helps to integrate past research on human olfactory communication but it also opens new avenues for future research on this fascinating, yet to date poorly understood, field.

Connectional networks within the orbital and medial prefrontal cortex of macaque monkeys

The intrinsic cortico-cortical connections within the orbital and medial prefrontal cortex (OMPFC) were demonstrated with retrograde and anterograde tracers injected into each of the architectonic areas that constitute this region. Although many of the connections linked neighboring areas, others selectively connected relatively distant areas. Most, but not all, of the connections were reciprocal. Altogether, the connections formed at least two distinct networks within the OMPFC. The "orbital" prefrontal network linked most of the areas within the orbital cortex, with very few connections to medial prefrontal areas. Areas Iam, Iapm, Ial, 12l, 12m, and 12r in the caudal and lateral parts of the orbital cortex (which received inputs from several sensory modalities) had convergent connections with areas 13l, 13m, and 13b in the central orbital cortex, with further connections to the rostral orbital area 11l. For the connections between areas Iapm, Iam, Ial, 13m, 13l, and 11l, rostrally directed fibers arose mainly in layer V, whereas caudally directed fibers originated mainly in layer III. The "medial" prefrontal network selectively involved medial areas 14r, 14c, 24, 25, 32, and 10m, rostral orbital areas 10o and 11m, and agranular insular area Iai in the posterior orbital cortex. Two orbital areas, 13a and 12o, had substantial connections to both networks and may serve as points of interaction between them; otherwise there were relatively few interconnections. The two networks also had distinct connections with other cortical regions, with limbic structures, and with the mediodorsal thalamic nucleus. Their role in guidance of affective behaviour is discussed.

Sensory and premotor connections of the orbital and medial prefrontal cortex of macaque monkeys

Sensory and premotor inputs to the orbital and medial prefrontal cortex (OMPFC) were studied with retrograde axonal tracers. Restricted areas of the lateral and posterior orbital cortex had specific connections with visual-, somatosensory-, olfactory-, gustatory-, and visceral-related structures. More medial areas received few direct sensory inputs. Within the lateral and posterior orbital cortex, area 12l received a substantial projection from visual areas in the inferior temporal cortex (TE). Area 12m received somatosensory input from face, digit, or forelimb regions in the opercular part of area 1-2, in area 7b, in the second somatosensory area (SII), and in the anterior infraparietal area (AIP). Areas 13m and 13l also received a projection from the opercular part of areas 1-2 and 3b. The posteromedial and lateral agranular insular areas (Iapm and Ial, respectively) received fibers from the ventral part of the parvicellular division of the ventroposterior medial nucleus of the thalamus (VPMpc) that may represent a visceral afferent system. The dorsal part of VPMpc projected to the adjacent gustatory cortex. These restricted inputs from several sensory modalities and the convergent corticocortical connections to orbital areas 13l and 13m suggest a network related to feeding. The OMPFC was also connected to premotor cortex in ventral area 6 (areas 6va and 6vb), in cingulate area 24c, and probably in the supplementary eye field. Area 6va projected to area 12m, whereas a region of area 6vb projected to area 13l. The region of the supplementary eye field projected to areas 12l, 12o, and 12r. Area Ial received fibers from area 24c. Lighter and more diffuse projections also reached wider areas of the OMPFC. For example, injections in several orbital areas labeled a few cells scattered through the anterior part of area TE and the superior temporal gyrus. There was also a projection to the intermediate agranular insular area (Iai) and to areas 13a and 12o from the apparently multimodal areas in the superior temporal sulcus and gyrus.

Rat preference for food-related odors

Preferences for food-related odors and the effects of fasting on those preferences were investigated during rat bar pressing for brief odor presentation. A rat was housed in an equilateral octagonal cage and had free access to food and water, except during fasting. Among 8 food-related odor substances (black pepper, cheese, coffee, milk, nut, peppermint, plum and orange), black pepper, milk and coffee were most preferred, and cheese was least preferred, but even the bar pressing rate for cheese was above the operant level. This data indicates that all 8 odors were preferred by rats, although there were different degrees of preference in individual animals. Fasting substantially increased the rate of bar pressing for odors and changed the odors preferences. This result was probably due to increased search for food and water. Since bar pressing was reinforced by nothing other than odor presentation, the results reveal inherent odor preferences of rats.

Effects of antibodies to dynorphin A and beta-endorphin on lateral hypothalamic self-stimulation in ad libitum fed and food-deprived rats

Many laboratories have reported that systemically administered naloxone has little or no effect on lateral hypothalamic self-stimulation (LH ICSS). In the present study, lateral ventricular infusion of beta-endorphin antiserum and a high dose of naloxone (100 micrograms) produced small but significant increases in stimulation frequency threshold for LH ICSS. beta-Endorphin activity, mediated by a non-mu (e.g. delta or epsilon) receptor, may therefore be involved in the reinforcement of self-stimulation behavior. When rats are deprived of food for 24 h, LH ICSS thresholds decline. Under this condition, systemic naloxone elevates the LH ICSS threshold, often returning it to the pre-deprivation level. In the present study, lateral ventricular infusion of dynorphin A(1-13) antiserum similarly reversed the threshold-lowering effect of food deprivation. The effects of systemic naloxone and intraventricular dynorphin A antiserum on LH ICSS, which are specific to food-deprived animals, may be related to previous findings that these two treatments elevate LH stimulation threshold for eliciting feeding behavior. Results of the ICSS and stimulation-induced feeding studies suggest a model for the mediation of incentive stimuli by dynorphin A activity that is afferent to LH 'reward' neurons and positively gated by 'hunger'. An hypothesized role for 'hunger'-gated dynorphin A release in potentiating the hedonic response to alimentary stimuli and drugs of abuse is discussed.