Neural encoding in orbitofrontal cortex and basolateral amygdala during olfactory discrimination learning.
Orbitofrontal cortex (OFC) is part of a network of structures involved in adaptive behavior and decision making. Interconnections between OFC and basolateral amygdala (ABL) may be critical for encoding the motivational significance of stimuli used to guide behavior. Indeed, much research indicates that neurons in OFC and ABL fire selectively to cues based on their associative significance. In the current study recordings were made in each region within a behavioral paradigm that allowed comparison of the development of associative encoding over the course of learning. In each recording session, rats were presented with novel odors that were informative about the outcome of making a response and had to learn to withhold a response after sampling an odor that signaled a negative outcome. In some cases, reversal training was performed in the same session as the initial learning. Ninety-six of the 328 neurons recorded in OFC and 60 of the 229 neurons recorded in ABL exhibited selective activity during evaluation of the odor cues after learning had occurred. A substantial proportion of those neurons in ABL developed selective activity very early in training, and many reversed selectivity rapidly after reversal. In contrast, those neurons in OFC rarely exhibited selective activity during odor evaluation before the rats reached the criterion for learning, and far fewer reversed selectivity after reversal. The findings support a model in which ABL encodes the motivational significance of cues and OFC uses this information in the selection and execution of an appropriate behavioral strategy. (+info)
Quantitative structure-activity relationships for nasal pungency thresholds of volatile organic compounds.
A model was developed for describing the triggering of nasal pungency in humans, based on the partition of volatile organic compounds (VOCs) between the air phase and the biophase. Two partition parameters are used in the model: the water-air partition coefficient and the octanol-water partition coefficient. The model was validated using data from the literature, principally on alcohols, acetates and ketones. The model suggests that all test compounds, regardless of their chemical functional groups, bind to a common receptor site within the hydrophobic interior of the bilayer membrane of the trigeminal nerve endings. There is probably only a slight, non-specific interaction between the VOC molecule and the receptor molecule, whereas this type of non-specific interaction for the detection of odor is much stronger. In practical terms, the suggestion that all VOCs share a common irritation receptor site implies that nasal-pungency thresholds of individual VOCs may be additive. Quantitative structure-activity relationships (QSARs) for nasal-pungency thresholds were also developed from the model, which can be used to predict nasal-pungency thresholds of common VOCs. Although the present model does not offer additional precision over that of M.H. Abraham et al., 1996, Fundam. Appl. Toxicol. 31, 71-76, it requires fewer descriptors and offers a physiological basis to the QSAR. Another advantage of the present model is that it also provides a basis for comparison between the olfactory process and nasal pungency. (+info)
A technique for assessing the effects of olfaction on feed preference in lactating Holstein cows.
Our objective was to develop a method for assessing the effects of olfaction on feed preference. Two multiparous lactating Holstein cows were offered a totally mixed ration consisting of corn silage, alfalfa haylage, and a ground corn and soybean meal-based concentrate mixture (25:25:50 on a DM basis) for their ad libitum consumption in four consecutive 2.5-h periods daily for 5 d. An apparatus was developed that allowed odorants to be distributed at a set rate over two feeding containers with limited possibility of odor carryover. Four odorants and a control (no odorant) were compared against each other. All possible comparisons were conducted on the left and right feeding sides to avoid potential lateral-preference effects. Rank values of 0 or .5 were assigned to each odorant based on the percentage of total feed consumed in a period. A test of overall equality based on the sums of squares of ranks was used to determine whether odors affected preference. The limited results indicated that inhalation of odorants did not affect preference. Rank values were doubled for several odorants when compared with others, which suggested that the sample size limited experimental sensitivity. To attain reasonable power, we estimated that at least six cows were needed per study. Large effects of odorants on feed preference would have been required to reach statistical significance in this trial; however, the method provides a practical technique for testing the effects of olfaction on feed preference in cattle when the suggested number of cows is used. (+info)
Blind smell: brain activation induced by an undetected air-borne chemical.
EEG and behavioural evidence suggests that air-borne chemicals can affect the nervous system without being consciously detected. EEG and behaviour, however, do not specify which brain structures are involved in chemical sensing that occurs below a threshold of conscious detection. Here we used functional MRI to localize brain activation induced by high and low concentrations of the air-borne compound oestra-1,3,5(10),16-tetraen-3yl acetate. Following presentations of both concentrations, eight of eight subjects reported verbally that they could not detect any odour (P = 0.004). Forced choice detection performed during the presentations revealed above-chance detection of the high concentration, but no better than chance detection of the low concentration compound. Both concentrations induced significant brain activation, primarily in the anterior medial thalamus and inferior frontal gyrus. Activation in the inferior frontal gyrus during the high concentration condition was significantly greater in the right than in the left hemisphere (P = 0.03). A trend towards greater thalamic activation was observed for the high concentration than the low concentration compound (P = 0.08). These findings localize human brain activation that was induced by an undetectable air-borne chemical (the low concentration compound). (+info)
The effect of age on odor-stimulated functional MR imaging.
BACKGROUND AND PURPOSE: The effects of age, sex, and handedness on olfaction have not been adequately addressed with odor-stimulated functional MR imaging studies. We sought to determine the effect of age on functional MR imaging experiments performed with odor stimulation. METHODS: Five right-handed subjects with a mean age of 73 years and five right-handed subjects with a mean age of 24 years underwent gradient-echo echo-planar functional MR imaging using binasal olfactory stimulation. Imaging parameters included 3000/30 (TR/TE) and a 5-mm section thickness in a 6-minute sequence with 30 seconds of pulsed odorants alternating with 30 seconds of room air. The data were normalized to a standard atlas, and individual and group statistical parametric maps (SPMs) were generated for each task. The SPMs were thresholded for a P < .01, and the volumes of activation and distribution of cluster maxima were compared for the two groups. RESULTS: Analysis of the group SPMs revealed activated voxels in the frontal lobes, perisylvian regions, and cingulate gyri, with greater volume in the younger group than in the older group. The right inferior frontal, right perisylvian, and right and left cingulum had the largest number of voxels activated. The most common sites of activation on individual maps in both groups were the right inferior frontal regions and the right and left superior frontal and perisylvian zones. CONCLUSION: Given similar olfactory task paradigms, younger subjects showed a greater number of activated voxels than did older subjects. One must be cognizant of this effect when designing studies of odor-stimulated functional MR imaging. (+info)
The effect of odour priming on long latency visual evoked potentials of matching and mismatching objects.
This study reports a cross-modal, olfactory/visual event related potential (ERP) using odours as olfactory primes. The results show a difference in the ERP waveform for the N400 waveform when a visual image does not match the priming odour. An N400 peak was produced for both the matched and mismatched conditions but the peaks were significantly more negative for the mismatched condition. By the use of non-food odours this study extends an earlier finding by Grigor, who, using the same ERP paradigm, obtained similar results for food odours and photographs of food. (+info)
Visual event related potentials modulated by contextually relevant and irrelevant olfactory primes.
Visual evoked potentials were recorded from 16 scalp locations on 10 young subjects during presentation of a series of high-quality photographs on a computer screen. The photographs consisted of equal numbers of pictures of fruit (citrus and non-citrus fruits), flowers (roses and other flowers) and objects (e.g. buildings, vehicles, animals etc.). Every picture was different in order to avoid repetition effects. The pictures were presented under four odour conditions: no odour, rose odour, jasmine odour and citrus odour. In order to keep the subjects alert they were asked to make categorizing decisions for the visual stimuli (e.g. flower or fruit). No decision was required concerning the relationship between the visual stimulus and the odour. As expected, the N400 peak was more negative when the picture stimulus did not match the odour. It is hypothesized that the N400 peak can be used as a measure of relatedness of a sensory stimulus to a previous or on-going prime, irrespective of the mode of the stimuli. (+info)
Sensory perception is related to the rate of change of volatile concentration in-nose during eating of model gels.
The relationship between perceived aroma and the volatile concentration measured in-nose was investigated during eating of a model food. Sensory ranking and time-intensity analysis (TI) were used to measure perceived aroma, while in-nose volatile concentration was monitored by atmospheric pressure ionization mass spectrometry, which produced time release data. A gelatine-sucrose gel with a range of gelatine concentrations (2-8% w/w) and flavoured with furfuryl acetate was used as the model food. Sensory scaling showed decreased flavour intensities and TI showed a decrease in the flavour perceived over time, as the gelatine concentration increased. Studies in model systems and in people demonstrated that the different rates of release observed for different gelatine concentrations were not due to binding of volatile to protein in the gel, nor to mucous membranes, but were due to different rates of gel breakdown in-mouth. There were no significant differences in the maximum in-nose volatile concentrations for the different gelatine concentrations, so the amount of volatile present did not correlate well with the sensory analysis. However, the rates of volatile release were different for the different gels and showed a good correlation with sensory data. (+info)