Target Odor Research Articles

Blockade of NMDA Receptors in Prelimbic Cortex Induces an Enduring Amnesia for Odor–Reward Associative Learning

The competitive antagonist 2-amino-5-phosphonoeptanoic acid (APV) was injected intracerebroventricularly to determine the involvement of NMDA receptors in different stages of memory consolidation. Subsequent experiments used local injections to determine possible sites of drug action. Rats were trained in a rapidly learned olfactory task to find palatable food in a hole in a sponge impregnated with the target odor in the presence of two other sponges with nonrewarded odors. APV injections were made intracerebroventricularly 5 min or 2 hr after the end of the training, and a retention test was given 48 hr later. The results showed that blockade of NMDA receptors immediately after training induces a profound and enduring amnesia with no effect when the treatment is delayed at 2 hr after training. To address the question of the effective sites of action of the intracerebroventricular treatment, APV injections into the hippocampus and into the prelimblic region of the frontal cortex (PLC) were made. Blockade of NMDA receptors into the PLC but not into the hippocampus impaired memory formation of the odor-reward association. The amnesia is not transient, because the retention tests were made 48 hr after training. These results underlie the role of NMDA receptors in the early stage of consolidation of a simple odor-reward associative memory and confirm the role of the PLC in the consolidation of long-term memory.

Olfactory short-term memory and related amygdala recordings in patients with temporal lobe epilepsy.

Olfactory short-term recognition memory was assessed with a delayed odour-matching task in 38 patients with unilateral temporal lobe epilepsy (TLE) and stereotactic electroencephalography (SEEG) recordings taken prior to surgical treatment. The amygdala SEEG activity associated with odorant stimulation was examined in 18 patients. Because the invasive SEEG procedure is only performed in a clinical framework, electrophysiological data obtained from these patients could not be analysed in comparison with data obtained from control subjects. Behavioural results (hits, false alarms, discrimination, bias scores) showed global impairment of odour recognition memory in patients when compared with controls. We also found lower discrimination and higher false alarm scores in left than in right TLE patients, and higher false alarm scores in male than in female patients. The hemisphere effect is discussed in terms of psychosocial trait differences between patients. Electrophysiological recordings collected from the amygdala demonstrated that odorant stimulation was associated with chemosensory evoked potentials (CSEPs). Analysis revealed that CSEPs obtained for target odorants had lower peak amplitudes and latencies than those obtained in response to sample odorants. The reduced peak amplitudes suggest a mechanism of repetition suppression--a process assumed to reflect neural activity related to high-level cognitive processes such as attention, memory and decision making. Latency modulations appear rather to be linked to early stages of information processing and may therefore reflect a facilitation process due to selective attention.

Real-time reference method in odor recorder under environmental change

This paper presents the electronic record of dynamically changing odors under environmental disturbance using a new recording method for the odor recorder called ‘real-time reference method’. The target odor is recorded as the recipe of several odor components. Once the recipe to represent the target odor is determined, it can be reproduced anytime and anywhere. In the real-time reference method, the target and blended odors are alternately exposed to the sensor array every sampling interval to determine the recipe for reproducing the target odor. Since the two odors are measured in the almost same environmental condition, the influence of dynamically changing environmental disturbance (temperature and humidity disturbances) can be reduced. Moreover, the dynamically changing target odor can be recorded because of the real-time monitoring of the target odors. In this paper, the dynamically changing apple flavors composed of four components were successfully quantified under the temperature and humidity disturbances.

Study of recording apple flavor using odor recorder with five components

The odor recorder has been developed using the odor sensing system based on the active sensing method to electronically record odors and reproduce them anytime and anywhere. The recorder developed in this paper has capability of recording the target odor, the mixture of five odor components, using the odor sensor array composed of quartz crystal microbalance sensors. The difference between the sensor response patterns of the recipe and target odors was minimized so that the recipe of the five components for the target odor was determined. In this paper, the method of selecting the most appropriate sensors to record odors was investigated based on the condition number of the sensor array sensitivity matrix. Moreover, the method of determining the parameters of the odor-recording algorithm was studied. As a result, several apple flavors composed of the five components were successfully recorded. Furthermore, the typical apple flavor composed of nine components was approximated using the mixture of the five components. The approximation result by the sensing system was successfully verified by the human sensory test.

A Training Program for Filter-Search Mine Detection Dogs

REST (Remote Explosives Scent Tracing) is an odor detection concept in which air from suspect locations is vacuumed though a polyvinyl chloride (PVC) netting filter. The filters are transferred to dogs trained to signal specific target odors such as drugs or explosives. Application for the detection of landmines involves vacuuming an area of land suspected to contain mines, and requires that the dogs achieve detection skills for very low concentrations of the target odor. Here, we describe the principles behind and results of a training program designed to produce REST dogs with detection skills similar to those obtained on filters from minefields. The entire training process for four dogs took under 6 months, and involved two trainers working for 1-5 days/week for about 5 h/day (dogs were trained most days, but both trainers were not always present). Principles underlying the training program were: (1) minimise dependency on handler, (2) encourage independent search, (3) build extended search by progressively reducing the frequency of occurrence of positive filters (using variable interval reinforcement), and (4) progressively generalise discrimination to lower concentrations of TNT. Reward-based “clicker” training was used exclusively. After 15 weeks, the dogs achieved 95% detection reliability. Properly documented training programs such as this one are essential if the industry is to further develop the REST concept for operational implementation on a broad scale.

Computational capacity of an odorant discriminator: the linear separability of curves.

We introduce and study an artificial neural network inspired by the probabilistic receptor affinity distribution model of olfaction. Our system consists of N sensory neurons whose outputs converge on a single processing linear threshold element. The system's aim is to model discrimination of a single target odorant from a large number p of background odorants within a range of odorant concentrations. We show that this is possible provided p does not exceed a critical value p(c) and calculate the critical capacity alpha(c) = p(c)/N. The critical capacity depends on the range of concentrations in which the discrimination is to be accomplished. If the olfactory bulb may be thought of as a collection of such processing elements, each responsible for the discrimination of a single odorant, our study provides a quantitative analysis of the potential computational properties of the olfactory bulb. The mathematical formulation of the problem we consider is one of determining the capacity for linear separability of continuous curves, embedded in a large-dimensional space. This is accomplished here by a numerical study, using a method that signals whether the discrimination task is realizable, together with a finite-size scaling analysis.

Identification of odors using a sensor array with kinetic working temperature and Fourier spectrum analysis

A method for the identification of odors using a dynamically driven sensor array has been developed, in which transient responses of the sensor array were used to recognize target odors. Fourier transformation was used to transform the transient response curves of the sensor array into Fourier spectra, and patterns composed of some of the magnitudes in the spectra were used in the pattern recognition to identify the odors. Identification of odors was performed using this method with three kinds of 10% ethanol solution of tea extract and three kinds of Japanese soy sauce. In consequence, the sample odors could be correctly recognized without any pretreatment device for separation of minor components from the main component.

実時間参照方式による匂い記録·再生システムの環境変化に対するロバスト性向上

The new type of odor recorder called real-time reference system is proposed to improve robustness against environmental changes, especially humidity and temperature changes. Since an odor sensor depends on humidity and temperature, these conditions have to be precisely controlled in a general odor sensing system. However, the odor recorder we developed in this paper does not need those requirements because of the real-time relative measurement based on the active sensing method, where a target odor and the reproduced odor were alternately exposed to the sensor array to reduce the influence of the dynamic environmental changes. We describe the design of the feedback controller for the real-time reference system and the experimental results of recording odors using the system. The recipes of apple flavors made up of four components were successfully recorded under the varying environments of humidity and temperature. Once the recipe for the target odor is recorded electronically by the odor recorder, it can be reproduced anytime and anywhere using an odor blender.

Odor recorder using active odor sensing system

There have been many works for odor identification and quantification using a sensor array and a pattern recognition technique. Since the odor sensing system should be extended to new area, we propose an odor recorder, by which previously sniffed smell can be reproduced any time. We focused on apple flavor with its features controllable by the recipe of just several components. The recipe determines the impressions of the apple such as softly green note, sour sweet, fruity and the smell of grass. The recipe of the four component vapors were successfully determined using the active odor sensing system with the capability of internally reproducing the target odor. Finally, the human-panel impressions of odors with the determined recipes agreed with those of the target odors.

Recording of Oder Recipe Using Active Odor Sensing System.

Odor recorder, where an odor with its recipe electronically recorded is reproduced by an odor blender, was developed. The odor recipe can be determined within a minute by the active odor sensing system with a QCM gas sensor array and an internal blender. The odor recipe can be obtained after minimizing the difference between the sensor-array output pattern of the target odor and that of the internally blended one using multiple-input multiple-output feedback control. The recipe of an apple flavor made up of four component odors with the impressions such as softly green note, sour sweet, fruity and the smell of grass was successfully determined by the system. Furthermore, it was confirmed that the odor the same as the target odor was reproduced using the internal odor blender. The principle and the fundamental experiments on odor recording are presented here.

Response time based output of metal oxide gas sensors applied to evaluation of meat freshness with neural signal analysis

The resistance response to a steep change of the composition in air is investigated for gas sensors based on metal oxide thin films after the target odour was injected from the chicken meat into the atmosphere of clean air. The change of the response is described using an exponential decrease with few time constants for the slope. The time constants are considered as an output data of the gas sensors. The output data are collected for chicken meat from an array of the sensors. Meat freshness is evaluated basing on the smell when the output data of the gas sensors are processed with a neural network. If the time constants are used for the output, the target smell is recognised even with a single sensor.

Odor-sensing system using preconcentrator with variable temperature

A preconcentrator conventionally used for increasing sensor sensitivity is also effective in an odor-sensing system to enhance the discrimination capability if its temperature suitable for target vapors is set since the desorption temperature depends upon the kind of the vapor. Thus, an autonomous system to adjust its temperature profile according to target odors was successfully developed using a numerical optimization algorithm. The system is a kind of active sensing system with high capability of adaptation compared with the conventional system.

Changes in Odor Sweetness Resulting from Implicit Learning of a Simultaneous Odor-Sweetness Association: An Example of Learned Synesthesia

In two experiments the smelled sweetness of odors was increased by using them as flavorants of sucrose solution. Experiment 1 used blind experimenters to compare a target odor mixed with sucrose with a control odor mixed with water during masked training trials. The increased sweetness of the target odor was unaffected by whether or not subjects revealed some explicit knowledge of the contingencies in a post-conditioning recognition test. Experiment 2 found that such a conditioned increase in odor sweetness occurred whether training solutions were sipped from a cup or sucked through a straw. Using a frequency test designed to provide a sensitive assay of contingency awareness, there was still no indication that this affected conditioning. It was concluded that such modification of the taste-properties of odors results from implicit simultaneous associative learning and provides an example of learned synesthesia.

Role of verbal encoding in short- and long-term odor recognition.

The role of verbal encoding in odor recognition memory was investigated using odors of low familiarity to subjects before the experiment began. The experimental procedure included two phases--odor learning (first phase) and odor memory testing (second phase)--separated by a delay of 7 days. Five experimental conditions were established: three conditions of odor learning with names (labeling conditions), one condition of odor learning without names (sensory familiarization), and one condition of no learning prior to testing (control conditions). The labeling conditions differed from each other regarding label characteristics. The names were those of odor sources (veridical names), those personally generated by subjects (generated names), or those derived from the chemical names of the odorants (chemical names). Subjects were required to learn 20 fixed associations between odors (targets or distractors) and 20 names during two daily sessions. The learning sessions included two identification tests and ended by a verbal memory test in which subjects recalled odor names. The odor memory test was split into two parts separated by a retention interval of either 20 min (short-term memory) or 24 h (long-term memory). Data showed that olfactory recognition memory was enhanced in subjects who associated veridical or generated names to odors during the learning session. Chemical names were not appropriate to facilitate odor recognition. Similarly, the level of odor identification was higher for veridical and generated names than for chemical names, though the level of verbal memory for chemical names was substantial. Recognition response latencies were systematically longer for a target odor implying a positive response than for a distractor odor implying a negative response. Together, these data suggest that odor recognition and identification are sensitive to the semantic content of labels associated with odors. Odor memory was adversively influenced by time, but this influence was less pronounced when the names were endowed with a rich semantic content.

Human memory for odour following monorhinal presentation with and without verbal elaboration.

With 14 target odours, 7 via each nostril, 20 subjects' correct recognition was lower for the right nostril than for the left with verbal elaboration, but nonsignificant without verbal elaboration.

Primacy and Recency in Recognition of Odours and Recall of Odour Names

This study examined the serial position curve for recognition of odours and recall of odour names, both with and without instructions for verbal elaboration. Participants were allocated to one of two experimental conditions, either with instructions to rehearse verbally the stimuli or with no elaboration instructions. After presentation of 17 odours, either recognition or free recall of the odours was tested immediately after presentation of the last target odour. Recognition showed evidence of primacy for the verbal elaboration condition and recency for both instruction conditions. Recall of odour names showed evidence of primacy for the verbal elaboration conditions and recency for both conditions. Instructions to verbalize did not significantly affect over-all performance for either test condition.

Interference with olfactory memory by visual and verbal tasks.

It has been claimed that olfactory memory is distinct from memory in other modalities. This study investigated the effectiveness of visual and verbal tasks in interfering with olfactory memory and included methodological changes from other recent studies. Subjects were allocated to one of four experimental conditions involving interference tasks [no interference task; visual task; verbal task; visual-plus-verbal task] and presented 15 target odours. Either recognition of the odours or free recall of the odour names was tested on one occasion, either within 15 minutes of presentation or one week later. Recognition and recall performance both showed effects of interference of visual and verbal tasks but there was no effect for time of testing. While the results may be accommodated within a dual coding framework, further work is indicated to resolve theoretical issues relating to task complexity.

Scopolamine injection into the olfactory bulb impairs short-term olfactory memory in rats.

A previous experiment showed that systemic administration of the muscarinic antagonist scopolamine altered delayed matching in an olfactory task in rats. The present experiment tested whether the impairment could result from blockade of the cholinergic transmission in the first relay structure of the olfactory system, the olfactory bulb. Drug was infused directly into both olfactory bulbs before test sessions. Results showed that the intrabulbar infusion reproduced the effect of the systemic administration. With a 4-s delay between target odor and choice test, performances of treated rats remained unchanged; but with a 30-s delay, rats performed randomly. Results from a complementary electrophysiological experiment in anesthetized rats support the idea that scopolamine injected into the olfactory bulb was unlikely to have reached more central structures. Further evidence for the involvement of pure sensory areas in short-term memory is concluded.

Recognition and recall of odours: The effects of suppressing visual and verbal encoding processes

This study examines the effects on olfactory recognition and recall of the suppression of visual and verbal encoding processes. Subjects were allocated to one of four experimental conditions (no suppression, visual suppression, verbal suppression, and visual-plus-verbal suppression), presented with 15 target odours, and then tested for free recall or recognition of these odours, both within 10 minutes of presentation and one week later. Recall and recognition performance both showed a significant overall effect for level of suppression, with the 'no-suppression' group performing best in each case. Recognition performance also showed a significant overall effect for time of testing. Methodological problems, and strategies for overcoming them, are discussed.

Age-related differences in short-term retention of separable elements of an odor aversion.

The rate of forgetting over short intervals was tested in preweanling rats, 8, 12, or 18 days postnatal, using procedures that may have analytical advantages over other tests of short-term retention. Separate tests of retention were conducted for the simple occurrence of an odor and for the occurrence of an odor paired with a mild footshock. Forgetting of odors with either of two histories, incidental or target, was more rapid the younger the preweanling, over intervals of less than an hour. There was some indication of more rapid forgetting for incidental than target odors. Finally, although exposure to a CS- (an odor not paired with footshock) was necessary for conditioning of the CS+ (an odor paired with footshock) in rats 8 or 12 days of age, exposure to a CS- had no influence on conditioning of the CS+ in preweanlings 18 days of age. The age-related differences in forgetting over intervals less than an hour long suggest that substantial age-related differences in forgetting can occur that, it is likely, are not accounted for by differential growth.