Yawning Frequency Research Articles

Driver fatigue detection based on deeply-learned facial expression representation

Driver fatigue detection is a significant application in smart cars. In order to improve the accuracy and timeliness of driver fatigue detection, a fatigue detection algorithm based on deeply-learned facial expression analysis is proposed. Specifically, the face key point detection model is first trained by multi block local binary patterns (MB-LBP) and Adaboost classifier. Subsequently, the eyes and mouth state are detected by using the trained model to detect the 24 facial features. Afterwards, we calculate the number of two parameters that can describe the driver's fatigue state and the proportion of the closed eye time within the unit time (PERCLOS) and yawning frequency. Finally, the fuzzy inference system is utilized to deduce the driver's fatigue state (normal, slight fatigue, severe fatigue). Experimental results show that the proposed algorithm can detect driver fatigue degree quickly and accurately.

Manipulating neck temperature alters contagious yawning in humans

The existence of yawning across a diverse array of species has led many researchers to postulate its neurological significance. One hypothesis, which has garnered recent support, posits that yawns function to cool the brain by flushing hyperthermic blood away from the skull while simultaneously introducing a cooler arterial supply. The current study tested this hypothesis by examining how manipulations aimed at modifying carotid artery temperature, which in turn directly alters cranial temperature, influences contagious yawning in humans. Participants held either a warm (46 °C), cold (4 °C) or room temperature (22 °C) pack firmly to their neck, just over their carotid arteries, for a period of five minutes prior to watching a contagious yawning stimulus. Thermographic imaging verified that these manipulations produced predicted changes in temperature at the superomedial orbital area, a region previously used as a noninvasive measure of brain temperature (i.e., the brain temperature tunnel). As predicted by past research, both the urge to yawn and overall yawn frequency significantly diminished in the cooling condition (p < .05). Less than half (48.5%) of the participants in the cooling condition reported the urge to yawn, while this urge was expressed by the vast majority of participants in the warming condition (84.8%). Moreover, there was a threefold difference in the mean number of yawns per participant between the cooling and warming conditions (0.364 compared to 1.121). These findings are consistent with previous research indicating that yawns function as a compensatory brain cooling mechanism.

Real-Time Driver-Drowsiness Detection System Using Facial Features

The face, an important part of the body, conveys a lot of information. When a driver is in a state of fatigue, the facial expressions, e.g., the frequency of blinking and yawning, are different from those in the normal state. In this paper, we propose a system called DriCare, which detects the drivers’ fatigue status, such as yawning, blinking, and duration of eye closure, using video images, without equipping their bodies with devices. Owing to the shortcomings of previous algorithms, we introduce a new face-tracking algorithm to improve the tracking accuracy. Further, we designed a new detection method for facial regions based on 68 key points. Then we use these facial regions to evaluate the drivers’ state. By combining the features of the eyes and mouth, DriCare can alert the driver using a fatigue warning. The experimental results showed that DriCare achieved around 92% accuracy.

Rats selectively bred for showing divergent behavioral traits in response to stress or novelty or spontaneous yawning with a divergent frequency show similar changes in sexual behavior: the role of dopamine.

Sexual behavior plays a fundamental role for reproduction in mammals and other animal species. It is characterized by an anticipatory and a consummatory phase, and several copulatory parameters have been identified in each phase, mainly in rats. Sexual behavior varies significantly across rats even when they are of the same strain and reared under identical conditions. This review shows that rats of the same strain selectively bred for showing a divergent behavioral trait when exposed to stress or novelty (i.e. Roman high and low avoidance rats, bred for their different avoidance response to the shuttle box, and high and low novelty exploration responders rats, bred for their different exploratory response to a novel environment) or a spontaneous behavior with divergent frequency (i.e. low and high yawning frequency rats, bred for their divergent yawning frequency) show similar differences in sexual behavior, mainly in copulatory pattern, but also in sexual motivation. As shown by behavioral pharmacology and intracerebral microdialysis experiments carried out mainly in Roman rats, these sexual differences may be due to a more robust dopaminergic tone present in the mesocorticolimbic dopaminergic system of one of the two sub-lines (e.g. high avoidance, high novelty exploration, and low yawning rat sub-lines). Thus, differences in genotype and/or in prenatal/postnatal environment lead not only to individual differences in temperament and environmental/emotional reactivity but also in sexual behavior. Because of the highly conserved mechanisms controlling reproduction in mammals, this may occur not only in rats but also in humans.

Thermal imaging reveals sizable shifts in facial temperature surrounding yawning in budgerigars (Melopsittacus undulatus)

ABSTRACTAccumulating comparative and interdisciplinary research supports a brain cooling function to yawning. In particular, previous research has shown significant decreases in both brain and skull temperature following yawning in mammals. In a recent study using a thermal imaging camera, significant reductions in both the cornea and concha temperature were observed following yawns in the high-yawning subline of Sprague-Dawley rats. Here, we performed a similar experiment to investigate shifts in facial temperature surrounding yawning in an avian species with more typical yawning patterns: budgerigars (Melopsittacus undulatus). In particular, we took maximal surface temperature recordings from the face (cere or eye) from 13 birds over a one-hour period to track changes before and after yawns. Similar to previous findings in high-yawning rats, we identified significant cooling (−0.36°C) of the face 10–20 seconds following yawning in budgerigars. Consistent with the hypothesis that yawns serve a thermoregulatory function, facial temperatures were slightly elevated just prior to yawning and then decreased significantly below baseline levels immediately thereafter. Similarly, birds that yawned during the trials had consistently higher facial temperatures compared to those that did not yawn. Moreover, yawn latency and overall yawn frequency were strongly correlated with the highest facial temperature recorded from each bird across trials. These results provide convergent evidence in support of a brain cooling function to yawning, and further validate the use of thermal imaging to monitor changes in skull temperature surrounding yawning events.

Yawning, a thermoregulatory mechanism during fever? A study of yawning frequency and its predictors during experimentally induced sickness

Yawning has been proposed to serve both physiological and social functions, the latter likely to have developed later in its evolution. A central hypothesis is that yawning cools the brain but whether yawning is a thermoregulatory mechanism that is activated during hyperthermia (i.e., thermoregulatory failure) or is activated in any instance of brain temperature increase (e.g., also during fever) is unclear and experimental assessments of yawning during fever are lacking. In this study, we determined the effect of experimentally induced fever on yawning frequency. We also explored alternative predictors of yawning during sickness (sleepiness, autonomic nervous system indexes and sickness symptoms). Twenty-two healthy human subjects participated in a randomized, placebo-controlled, cross-over study, where the subjects received an injection of the bacterial endotoxin lipopolysaccharide (LPS) at a dose of 2ng/kg body weight in one condition and placebo in the other. Yawning was scored from video recordings from 30min before to 4h after the injection. Body temperature was measured frequently, alongside with heart rate, blood pressure, nausea and overall sickness symptoms. Yawning frequency was found to significantly increase over time during experimentally induced sickness, but not in the placebo condition. In particular, yawning frequency was increased during the rising phase of body temperature induced by LPS administration, although no significant correlation was found between body temperature increase and yawning frequency. In addition, exploratory analyses showed that a higher yawning frequency was associated with less increase in sickness symptoms and nausea intensity. While the current study adds to previous research showing significant increase in yawning frequency during hyperthermia, further studies are needed if we are to properly characterize the brain cooling role of yawning in humans. The investigation of other functions, such as being a vasovagal inhibitory, may shed stronger light on the functions of yawning.

There is no difference in contagious yawning between men and women.

Norscia et al. [1] recently reported the first evidence for a sex bias in contagious yawning among humans. Based on previous research showing an indirect connection between contagious yawning and empathy (e.g. [2–4], but see [5,6]) and that levels of empathy appear to be higher in women compared with men (e.g. [7–9]), the authors investigated whether there is also a sex difference in the expression of contagious yawning through an observational study on humans. By examining 92 dyads already showing evidence of contagious yawning, which was a subset of a much larger sample of individuals, Norscia et al. report that both social bond and sex were significant predictors of this response. In particular, contagious yawning was more common if the dyad was strongly bonded and when the individual catching the yawn was female. Here, we call into question these conclusions about a sex difference in contagious yawning. First, we draw attention to more than a dozen previous publications on contagious yawning in humans, many of which were not cited by Norscia et al. showing no difference in susceptibility to yawn contagiously and/or contagious yawning frequency between men and women. Similarly, we do the same for nearly a dozen unacknowledged publications in the comparative literature. Lastly, we challenge the validity of the reported sex difference within the Norscia et al. study itself, based on their analysis of only a restricted subset of documented contagious yawners. A close examination of the empirical literature clearly shows that the sex difference reported by Norscia et al. stands in stark contrast to previous findings on contagious yawning in humans. While Norscia et al. only reference a single publication that did not find a difference in the frequency of contagious …

Real-time physiological and facial monitoring for safe driving.

This work is to develop an intelligent driver-assistance system which can perceive the physiological state of a driver to avoid fatigue driving. The proposed system includes a camera, a wireless ElectroCardioGram (ECG) sensor patch, and a computation platform. The camera in front of a driver is to catch a face image which is processed to obtain features of a mouth for identifying a yawn. The sensor patch records ECG signals which are computed to yield six Heart Rate Variability (HRV) parameters. Seven healthy subjects of 6 males and 1 female had individually driven a car, which was embedded with our system, for 3 hours at a well-known route, mostly in a freeway road. Based on the captured video and measured ECG signals, the correlations between the yawning frequency and six HRV parameters are investigated by using the regression method to discover that the ratio (LF/HF) of Low-Frequency (LF) spectrum power over High-Frequency (HF) spectrum power yields the relatively highest correlation. In order to effectively identity driver's fatigue, the variations of differential LF/HF are further characterized to attain two thresholds which are accompanied with yawning frequencies to build a fair detection mechanism. The practical road tests demonstrate that the proposed system is very feasible and easily adapted to different drivers.

Social Presence Diminishes Contagious Yawning in the Laboratory.

Contagious yawning may be a useful measure of social psychological functioning, and thus it is important to evaluate the variables influencing its expression in laboratory settings. Previous research has documented that humans yawn less frequently in crowded environments and when under direct observation, but the impact of social presence on contagious yawning remains unknown. Here we present the first study to systematically alter the degree of social presence experienced by participants in the laboratory to determine its effect on contagious yawning frequency. Our results demonstrate that both implied and actual social presence significantly diminish yawn contagion in comparison to a control condition, indicating a key social component to contagious yawning. These findings provide a framework for pursuing additional research investigating the social factors influencing contagious yawning, while also offering applications for measuring this response in laboratory settings.

ID 318 – Pre-ictal forceful yawning in a patient with temporal lobe epilepsy

Objective Yawning has been described in various medical conditions. The occurrence of yawning as a part of peri-ictal semiology in focal epilepsy has been described, mostly in case reports. In our case report we study pre-ictal yawning and temporal lobe epilepsy. Methods Clinical case report. Results A 48-year old women, left handed with no neurological antecedents. Began haven epileptic attacks at age 20. The seizure semiology comprised psychic aura (anxiety) and generalized tonic–clonic seizures GTCS. Since the age of 20 years Phenobarbital PB at 100 mg/day was used in monotherapy. Brain CT and MR imaging were normal. Video-EEG recording showed yawning in the pre-ictal period followed by slow waves over left temporal regions. He had repetitive, irresistible and forceful yawning starting from one to 12 s. Yawning started with a deep inspiration through her wide-open mouth. She received carbamazepine CBZ 600 mg/day (start dose of 100 mg). We noted decrease in the frequency of yawning. Conclusions Video-EEG recording is useful in diagnosis of temporal epilepsy in patients with repetitive, irresistible and forceful yawning.

Differential organization of male copulatory patterns in high- and low-yawning-frequency sublines versus outbred Sprague–Dawley rats

The temporal organization of masculine sexual behavior in rats is highly stereotyped; involving a sequence of mounts, intromissions and ejaculations. Sexual behavior has been described in exogamic and genetically manipulated rodent species. In this work, we compare the male sexual behavior of outbred Sprague–Dawley (SD) to those of rats inbred for high (HY)- and low (LY)- spontaneous yawning frequency. In the first experiment, the percentage of inexperienced rats' ejaculatory behavior is significantly lower in the HY and LY respect to Sprague–Dawley rats. The latency to ejaculate for inexperienced HY was shorter than the LY and SD rats. In the second experiment, we examined the differences between inbred sublines and Sprague–Dawley rats once the subjects had become sexually experienced after four copulatory sessions. HY rats still have slower proportion of ejaculators respect to LY and SD rats. Additionally, postejaculatory latencies were longer for HY rats, with longer intercopulatory intervals and higher number of copulatory bouts that delayed ejaculation. Both sublines show lower copulatory efficiency respect to SD rats. In conclusion, both sublines show alterations in the temporal organization of sexual motor pattern that are due at least partially to strong inbreeding process to select them

Contagious yawning and psychopathy

Psychopathy is characterized by a general antisocial lifestyle with behaviors including being selfish, manipulative, impulsive, fearless, callous, possibly domineering, and particularly lacking in empathy. Contagious yawning in our species has been strongly linked to empathy. We exposed 135 students, male and female, who completed the Psychopathic Personality Inventory-Revised (PPI-R), to a yawning paradigm intended to induce a reactionary yawn. Further, we exposed males to an emotion-related startle paradigm meant to assess peripheral amygdalar reactivity. We found that scores on the PPI-R subscale Coldheartedness significantly predicted a reduced chance of yawning. Further, we found that emotion-related startle amplitudes were predictive of frequency of contagious yawning. These data suggest that psychopathic traits may be related to the empathic nature of contagious yawning in our species.

Experimental evidence of contagious yawning in budgerigars (Melopsittacus undulatus).

Experimental evidence of contagious yawning has only been documented in four mammalian species. Here, we report the results from two separate experimental studies designed to investigate the presence of contagious yawning in a social parrot, the budgerigar (Melopsittacus undulatus). In Study 1, birds were paired in adjacent cages with and without visual barriers, and the temporal association of yawning was assessed between visual conditions. In Study 2, the same birds were exposed to video stimuli of both conspecific yawns and control behavior, and yawning frequency was compared between conditions. Results from both studies demonstrate that yawning is contagious. To date, this is the first experimental evidence of contagious yawning in a non-mammalian species. We propose that future research could use budgerigars to explore questions related to basic forms of empathic processing.

Temperature-Dependent Variation in Self-Reported Contagious Yawning

The thermoregulatory theory posits that yawns function to cool the brain in part due to counter-current heat exchange with the deep inhalation of ambient air. In support of this theory, previous cross-cultural research on humans has shown that self-reported contagious yawning frequency varies between seasons with distinct ambient temperature ranges. However, it remains possible that differences in yawning across seasons are a result of physiological circadian changes across the year rather than variation in ambient temperature. In an attempt to address this question, here we discuss the results of a study investigating the variation in the frequency of self-reported contagious yawning within a restricted range of a single season in one geographic location. A total of 142 pedestrians were recruited outdoors during an 18-day period over the summer in an equatorial monsoon climate in southern Florida, USA. Consistent with the thermoregulatory theory of yawning, results showed that self-reported contagious yawning frequency varied predictably across temperature gradients. This was true after statistically controlling for relative humidity, time of day, time spent outside, testing day, age of participant, and amount of sleep the night before. These findings provide further evidence suggesting a brain cooling function to yawning.

Yawning, acute stressors, and arousal reduction in Nazca booby adults and nestlings

Yawning is a familiar and phylogenetically widespread phenomenon, but no consensus exists regarding its functional significance. We tested the hypothesis that yawning communicates to others a transition from a state of physiological and/or psychological arousal (for example, due to action of a stressor) to a more relaxed state. This arousal reduction hypothesis predicts little yawning during arousal and more yawning (above baseline) during and after down-regulation of arousal. Experimental capture-restraint tests with wild adult Nazca boobies (Sula granti), a seabird, increased yawning frequency after release from restraint, but yawning was almost absent during tests. Natural maltreatment by non-parental adults also increased yawning by nestlings, but only after the maltreatment ended and the adult left. CORT (corticosterone) was a logical a priori element of the stress response affecting the stressor–yawning relationship under the arousal reduction hypothesis, and cannot be excluded as such for adults in capture-restraint tests but is apparently unimportant for nestlings being maltreated by adults. The arousal reduction hypothesis unites formerly disparate results on yawning: its socially contagious nature in some taxa, its clear pharmacological connection to the stress response, and its temporal linkage to transitions in arousal between consciousness and sleep.

Importance of yawning in the evaluation of excessive daytime sleepiness: a prospective clinical study.

As a dark and not fully understood side of human nature, yawning is believed to be a signs of various physiological or pathological behaviors of human. In this study, we aimed to investigate the importance of yawning in the evaluation of sleepiness. One hundred and twenty-nine snorers who were suspected to have obstructive sleep apnea syndrome underwent polysomnography and were asked to fill the Epworth sleepiness scale. The number of yawnings of patients was counted during the day following polysomnography. Patients were stratified into two groups: those have apnea hypopnea index <5 (n = 43, group 1) and those have apnea hypopnea index >30 (n = 86, group 2). Mean duration of sleep phases, oxygen saturations, sleep efficacies, yawning frequencies and Epworth scores of the groups were compared. Correlations of yawning frequency with Epworth scores, duration of sleep phases and mean oxygen saturations were investigated. Sleep efficacies were similar between the groups (p > 0.05). Yawning frequencies in group 1 and group 2 were 43.48 and 75.76 (mean rank), respectively (p < 0.01). Mean N1, N2, N3 phase durations and oxygen saturations were significantly lower in group 2 (p < 0.01). While there was a negative correlation between yawning frequency and duration of the non-REM phases and mean oxygen saturation (r = -0.53 and r = -0.31, respectively, p < 0.05), yawning frequency was positively correlated with Epworth scores (r = 0.46, p < 0.05). In addition to the shortened phases of sleep, increased Epworth score and decreased oxygen saturation, increased yawning frequency may indicate sleep deprivation.

Occurrences of yawn and swallow are temporally related.

Yawning is a stereotyped motor behavior characterized by deep inhalation and associated dilation of the respiratory tract, pronounced jaw opening, and facial grimacing. The frequency of spontaneous yawning varies over the diurnal cycle, peaking after waking and before sleep. Yawning can also be elicited by seeing or hearing another yawn, or by thinking about yawning, a phenomenon known as "contagious yawning". Yawning is mediated by a distributed network of brainstem and supratentorial brain regions, the components of which are shared with other airway behaviors including respiration, swallowing, and mastication. Nevertheless, the possibility of behavioral coordination between yawning and other brainstem-mediated functions has not been examined. Here we show, with a double-blind methodology, a greater-than-fivefold increase in rest (saliva) swallowing rate during the 10-s period immediately following contagious yawning elicited in 14 adult humans through the viewing of videotaped yawn stimuli. Sixty-five percent of yawns were followed by a swallow within 10s and swallows accounted for 26% of all behaviors produced during this post-yawn period. This novel finding of a tight temporal coupling between yawning and swallowing provides preliminary evidence that yawning and swallowing are physiologically related, thus extending current models of upper airway physiology and neurophysiology. Moreover, our finding suggests the possibility that yawning plays a role in eliciting rest swallowing, a view not considered in previous theories of yawning. As such, the present demonstration of a temporal association between yawning and swallowing motivates a re-examination of the longstanding question, "Why do we yawn?".

Abnormal yawning in stroke patients: the role of brain thermoregulation.

Krestel et al. (2013) recently investigated the potential contributing factors associated with abnormal yawning (defined as ≥3 yawns/15 min) in 10 patients with acute anterior circulation stroke. Though frequent yawning had previously been observed in stroke patients (Cattaneo et al., 2006; Singer et al., 2007), this study attempted to assess the influence of specific physiologic and lesion topographic variables contributing to this association. All patient parameters were taken within 1 h after admission and emergency nurses recorded a single axillary body temperature with a digital thermometer (Krestel, personal communication). Using MRI lesion maps, and reportedly finding no associations between various physiologic measures, including blood oxygen saturation, glucose, body temperature, blood pressure, and heart rate, the authors concluded that ischemic lesions in the posterior insula and caudate nucleus might facilitate high frequency yawning in stroke patients. While this report improves our neurological understanding regarding the association between frequent yawning in stroke patients, limitations in the analysis and interplay of temperature need to be addressed. Yawning is characterized by a powerful gaping of the jaw with inspiration, a brief period of peak muscle contraction, and a passive closure of the jaw with shorter expiration (Barbizet, 1958). The localized circulatory changes resulting from this action pattern have led researchers to hypothesize that yawns may function to cool the brain (Gallup and Gallup, 2007). For example, yawns produce increases in blood flow to the skull and enhanced venous return (Bhangoo, 1974), while the deep inhalation during yawning can modify the temperature of venous blood draining from the nasal and oral orifices into the cavernous sinus, which surrounds the internal carotid artery (Zenker and Kubik, 1996). Together, these processes act like a radiator removing hyperthermic blood from brain while introducing cooler arterial blood to the brain. Moreover, the flexing of the musculature during yawning may encourage the evaporation of the sinus mucosa (see Gallup and Hack, 2011). Research supporting the brain cooling hypothesis has accumulated over the past 5 years, including evidence for predicted brain and body temperature fluctuations surrounding yawning events, indirect manipulations of brain temperature causing a reduction in yawn frequency, and an altered expression of yawning which appears to be driven by ambient temperature manipulation/variation (reviewed by Gallup and Eldakar, 2013). For example, by directly monitoring continuous changes in prelimbic cortex temperature of rats it was shown that yawning is preceded by intermittent and rapid increases in brain temperature (i.e., ~0.1°C/min), and that following the completion of a yawn the slope of the temperature change reverses and quickly returns to baseline (Shoup-Knox et al., 2010). While the breadth of physiologic measures taken by Krestel et al. (2013) is laudable, a single measure of axillary temperature taken long after the onset of the yawning episode is inadequate for assessing this relationship. Since distinct brain temperature changes in rats occur before and after single yawns on a rather short temporal scale; i.e., 60–90 s (Shoup-Knox et al., 2010), and isolated bouts of excessive yawning in humans have been shown to reduce skull temperature by as much as 0.4°C (Gallup and Gallup, 2010), it remains possible that the pathological yawning experienced by these patients was accompanied by recurrent changes in temperature that were never recorded. Furthermore, temperature measures taken from the skull (e.g., oral, tympanic, forehead) would be more informative since the motor pattern of yawning and the associated circulatory changes are localized to this area. That said, even these measurements could miss important temperature fluctuations confined to particular brain regions. The use of MRI lesion maps to establish a relationship between ischemic lesions in the posterior insula and caudate nucleus and the duration of abnormal yawning is certainly of great importance (Krestel et al., 2013). At this point, however, it is premature to declare that there was “no evidence of other potential causes” related to abnormal yawning in these patients. To the contrary, frequent or abnormal yawning in stroke patients may be a consequence of thermoregulatory dysfunction associated with the brain injury (Gallup and Gallup, 2008). Given the close temporal association between yawning and changes in brain/skull temperature, future research monitoring patients with abnormal or excessive yawning bouts should take continuous temperature measures from areas proximate to the cranium in order to properly assess this relationship.

Social modulation of contagious yawning in wolves.

On the basis of observational and experimental evidence, several authors have proposed that contagious yawn is linked to our capacity for empathy, thus presenting a powerful tool to explore the root of empathy in animal evolution. The evidence for the occurrence of contagious yawning and its link to empathy, however, is meagre outside primates and only recently domestic dogs have demonstrated this ability when exposed to human yawns. Since dogs are unusually skilful at reading human communicative behaviors, it is unclear whether this phenomenon is deeply rooted in the evolutionary history of mammals or evolved de novo in dogs as a result of domestication. Here we show that wolves are capable of yawn contagion, suggesting that such ability is a common ancestral trait shared by other mammalian taxa. Furthermore, the strength of the social bond between the model and the subject positively affected the frequency of contagious yawning, suggesting that in wolves the susceptibility of yawn contagion correlates with the level of emotional proximity. Moreover, female wolves showed a shorter reaction time than males when observing yawns of close associates, suggesting that females are more responsive to their social stimuli. These results are consistent with the claim that the mechanism underlying contagious yawning relates to the capacity for empathy and suggests that basic building blocks of empathy might be present in a wide range of species.

Eating high fat chow and the behavioral effects of direct-acting and indirect-acting dopamine receptor agonists in female rats.

Eating high fat chow increases the sensitivity of male rats to some behavioral effects of the direct-acting dopamine receptor agonist quinpirole; it is not known whether sensitivity to quinpirole is similarly enhanced in female rats eating high fat chow. Female Sprague-Dawley rats had free access to standard chow (5.7% fat) or either free or restricted access (i.e. body weight matched to rats eating standard chow) to high fat (34.3% fat) chow. Quinpirole (0.0032-0.32 mg/kg) produced hypothermia and a low frequency of yawning. Eating high fat chow produced insulin resistance without affecting quinpirole-induced yawning or hypothermia. Pretreatment with the dopamine D2 receptor antagonist L-741,626 failed to increase quinpirole-induced yawning, indicating that the low frequency of yawning was not due to enhanced D2 receptor sensitivity. Compared with younger (postnatal day 75), drug-naive female rats in a previous study, rats in the present study (postnatal day 275) were more sensitive to cocaine-elicited (1-17.8 mg/kg) locomotion and the development of sensitization across 5 weeks; however, eating high fat chow did not further enhance these effects. These results suggest that drug history and age might modulate the effects of diet on sensitivity to drugs acting on dopamine systems.