Sex differences in the adolescent brain

Adolescence is a time of increased divergence between males and females in physical characteristics, behavior, and risk for psychopathology. Here we will review data regarding sex differences in brain structure and function during this period of the lifespan. The most consistent sex difference in brain morphometry is the 9–12% larger brain size that has been reported in males. Individual brain regions that have most consistently been reported as different in males and females include the basal ganglia, hippocampus, and amygdala. Diffusion tensor imaging and magnetization transfer imaging studies have also shown sex differences in white matter development during adolescence. Functional imaging studies have shown different patterns of activation without differences in performance, suggesting male and female brains may use slightly different strategies for achieving similar cognitive abilities. Longitudinal studies have shown sex differences in the trajectory of brain development, with females reaching peak values of brain volumes earlier than males. Although compelling, these sex differences are present as group averages and should not be taken as indicative of relative capacities of males or females.     

Sex differences in behavioral reactions to provocation of anger

The purpose of this study was to examine sex differences in behavioral reactions to provocation of anger. In a field study, 72 subjects recorded all anger-arousing incidents for a 2-wk. period. Physical and Verbal Antagonism were found in more reports by men while Passive Consent was noted in more reports by women. For a laboratory study, 101 subjects responded to self-report scales of behavioral responses after exposure to an insulting letter. No sex differences were noted in subjects' self-reports of behavioral reactions. Variations in design are brought to bear in interpreting the findings.     

Determination of discount functions in rats with an adjusting-amount procedure.

An adjusting-amount procedure was used to measure discounting of reinforcer value by delay. Eight rats chose between a varying amount of immediate water and a fixed amount of water given after a delay. The amount of immediate water was systematically adjusted as a function of the rats' previous choices. This procedure was used to determine the indifference point at which each rat chose the immediate amount and the delayed amount with equal frequency. The amount of immediate water at this indifference point was used to estimate the value of the delayed amount of water. In Experiment 1, the effects of daily changes in the delay to the fixed reinforcer (100 microliters of water delivered after 0, 2, 4, 8, or 16 s) were tested. Under these conditions, the rats reached indifference points within the first 30 trials of each 60-trial session. In Experiment 2, the effects of water deprivation level on discounting of value by delay were assessed. Altering water deprivation level affected the speed of responding but did not affect delay discounting. In Experiment 3, the effects of varying the magnitude of the delayed water (100, 150, and 200 microliters) were tested. There was some tendency for the discounting function to be steeper for larger than for smaller reinforcers, although this difference did not reach statistical significance. In all three experiments, the obtained discount functions were well described by a hyperbolic function. These experiments demonstrate that the adjusting-amount procedure provides a useful tool for measuring the discounting of reinforcer value by delay.     

Sex differences in the effects of disinhibition,perceived peer drinking,and delay discounting on drinking among Japanese college students

Disinhibition, perceived peer drinking, and delay discounting are considered significant predictors of drinking in young adults. This study examined whether perceived peer drinking and delay discounting mediate the association between disinhibition and drinking for young men and women. In this study, 258 Japanese college students (109 men and 149 women, mean age 19.17 (SD = 1.20) years old) completed a self-administered questionnaire that included four measures—the disinhibition subscale of the Sensation Seeking Scale for Japanese Adolescents, the proportion of friends who drink as an index of perceived peer drinking behaviors, the Monetary Choice Questionnaire, and participants’ own drinking behavior. In the multiple mediator models analyzed using structural equation modeling, for both sexes, perceived peer drinking had the largest direct effect on participants’ drinking, followed by disinhibition and delay discounting. However, the results of mediation analyses indicated that perceived peer drinking mediated the association between disinhibition and drinking for only women. The results of this study imply that it is important to consider sex differences in the association between personality traits and peer influence to develop programs aiming to reduce drinking among young adults in Japan.     

Sex differences in behavioral consequences of defeat in the rat are not organized by testosterone during early development

Male and female rats react differently to losing an aggressive encounter, the presence of testosterone (at the time of confrontation) being a critical factor in the manifestation of this sex difference. Female rats were androgenized by 250 μg testosterone propionate sc on days 1 and 5 after birth. When adult they received a sc testosterone proprionate (TP) implant and were subjected to repeated defeats by being placed in the cage of an aggressive resident female. In contrast to males, which freeze and become permanently submissive, androgenized females showed no freezing or other signs of submission. The sex difference in response to defeat is therefore not dependent on the presence of testosterone during the period of post-natal sexual differentiation.     

Sexual reinforcement in the female rat.

Sexual reinforcement in the female rat was studied in a preparation that allowed continuous operant responding for access to a male rat leading to intromission. Experiment 1 used a high operant level nose-poke response to test the possible reinforcing effects of some components of access to a male. A simple tone stimulus used as a conditioned reinforcer and two odor stimuli, target male bedding and emulsified preputial gland, were tested. None of these contingent events altered responding above or below operant level. Access to the male, which was always accompanied by intromission, immediately increased response rate when it was made contingent upon the nose-poke response. Performance on fixed-ratio schedules was erratic, and response rate was low in comparison to typical food-reinforced responding. An interresponse-time analysis indicated, however, that some effect of the ratio contingency may have been present. In Experiment 2, several modifications of the procedure were tested with the objective of creating a more tractable preparation for behavior analysis. Response type and the hormone delivery method were changed, and 2 target males were used instead of 1. The latter tripled the average number of reinforcers earned in a single session. Differences between sexual and other reinforcers are discussed in terms of procedural, quantitative, and motivational aspects of the sexual reinforcement procedure.     

Sex differences in maternal behaviors of immature rats: The role of emotionality

Immature rats are able to give maternal care to pups and may increase their inclusive fitness by helping newborn siblings. Immature males are generally reported to be more maternal than females. In this research we studied sex differences and the extent to which they may be due to a different emotional response to novelty. We studied maternal response in two groups of immature rats of both sexes: in the naive group, juveniles aged from 18 to 30 days were given one test and showed clear-cut sex differences. The experience group was submitted to repeated tests from 18 to 30 days of age, thus eliminating the effects of novelty: as a result, all differences between sexes disappeared. A second experiment was designed in 24-day-old females to differentiate the effects of repeated handling and exposure to the test situation from that of repeated exposure to pups; moreover, the effects of an anxiety-reducing drug (diazepam) were studied. Exposure to pups is particularly efficient in facilitating maternal response. Diazepam injection was also effective, but its control showed that the injection per se was responsible for the effect. In conclusion, our results stress the importance of response to novelty and suggest that sex differences in maternal behavior of immature rats may be modulated by different emotional responses by males and females. In fact, emotionality competes with, and may exert an inhibitory effect on, the expression of a vast array of behaviors. © 1994 Wiley-Liss, Inc.     

Cognitive antecedents to adolescent health risk: Discriminating between behavioral intention and behavioral willingness

Abstract

A model of adolescent health risk behavior that is both cognitive and social-psychological in orientation is described, and an aspect of the model is tested empirically. The model suggests that health risk behaviors (e.g., smoking or drunk driving), especially among adolescents, are not always intended or premeditated, but instead are often reactions to risk-conducive circumstances. Because they are not entirely premeditated, such behaviors are not accurately predicted by “traditional” behavioral intention measures, but are predicted by a central construct in the model labeled behavioral willingness. Results of two studies indicate that both intention (expectation) and willingness measures predict future risk behaviors, and do so independent of one another. Additional analyses provide further evidence of discriminant validity between the two constructs by indicating that they relate differently to perceptions of personal vulnerability to the health risks associated with these behaviors.     

Concurrent-chains schedules as a method to study choice between alcohol-associated conditioned reinforcers

An extensive body of research using concurrent-chains schedules of reinforcement has shown that choice for one of two differentially valued food-associated stimuli is dependent upon the overall temporal context in which those stimuli are embedded. The present experiments examined whether the concurrent chains procedure was useful for the study of behavior maintained by alcohol and alcohol-associated stimuli. In Experiment 1, rats responded on concurrent-chains schedules with equal variable-interval (VI) 10-s schedules in the initial links. Across conditions, fixed-interval schedules in the terminal links were varied to yield 1∶1, 9∶1, and 1∶9 ratios of alcohol delivery. Initial-link response rates reflected changes in terminal-link schedules, with greater relative responding in the rich terminal link. In Experiment 2, terminal-link schedules remained constant with a 9∶1 ratio of alcohol delivery rates while the length of two equal duration initial-link schedules was varied. Preference for the rich terminal link was less extreme when initial links were longer (i.e., the initial-link effect), as has been previously reported with food reinforcers. This result suggests that the conditioned reinforcing value of an alcohol-associated stimulus depends on the temporal context in which it is embedded. The concurrent-chains procedure and quantitative models of concurrent chains performance may provide a useful framework within which to study how contextual variables modulate preference for drug-associated conditioned reinforcers.     

Individual differences in impulsive choice and timing in rats

Individual differences in impulsive choice behavior have been linked to a variety of behavioral problems including substance abuse, smoking, gambling, and poor financial decision-making. Given the potential importance of individual differences in impulsive choice as a predictor of behavioral problems, the present study sought to measure the extent of individual differences in a normal sample of hooded Lister rats. Three experiments utilized variations of a delay discounting task to measure the degree of variation in impulsive choice behavior across individual rats. The individual differences accounted for 22-55% of the variance in choice behavior across the three experiments. In Experiments 2 and 3, the individual differences were still apparent when behavior was measured across multiple choice points. Large individual differences in the rate of responding, and modest individual differences in timing of responding were also observed during occasional peak trials. The individual differences in timing and rate, however, did not correlate consistently with individual differences in choice behavior. This suggests that a variety of factors may affect choice behavior, response rate, and response timing.     

The effect of ethanol treatment on social behavior in male rats

The effect of 0.50 g/kg of EtOH in male rats interacting with a stimulus male juvenile in a newly developed test of social interaction was examined. The adult male rats were treated with EtOH (8.0 to 12.0 g/kg/day) or equicaloric dextrin maltose for 2 weeks (studies 1 and 2) or 8 weeks (study 3) and social interaction was assessed both before and after chronic drug treatment was ended in study 1 and after chronic drug treatment was ended in studies 2 and 3. It was found that prior to chronic drug treatment, in study 1, 0.50 g/kg of EtOH increased both aggressive behavior and time spent interacting with the stimulus juvenile male from the first presentation of the juvenile to the second presentation (20 min apart) while saline injection decreased it. After chronic drug treatment was ended, in study 1 animals treated chronically with EtOH were more aggressive when they were not intoxicated than when they had been treated with 0.50 g/kg of EtOH. In studies 2 and 3, after chronic drug treatment was ended, aggressive behavior and time spent interacting with the juvenile were greater in the animals treated chronically with EtOH, regardless of whether they were injected with saline or 0.50 g/kg of EtOH. The results of these studies showed that chronic EtOH treatment can produce long-lasting changes in social behavior after drug treatment is over and can alter the animal's normal response to EtOH in a social setting.     

Sex differences in the behavioral responses of dogs exposed to human chemosignals of fear and happiness

Animal Cognition - This research focuses on sex differences in the behavioral patterns of dogs when they are exposed to human chemosignals (sweat) produced in happy and fear contexts. No age, breed...     

Individual differences in trait urgency moderate the role of the affect heuristic in adolescent binge drinking

This study investigated the roles of the affect heuristic and outcome beliefs in explaining the relationship between negative urgency and adolescent binge drinking behaviour. The sample consisted of 391 Australian high school students, who were selected to be low or high on urgency. We hypothesised that highly urgent adolescents would be more likely than adolescents low in urgency to utilise the affect heuristic (i.e., to rely upon affective input) when making alcohol-related decisions. Multiple-group path analysis supported this prediction. Adolescents high in urgency exhibited greater use of the affect heuristic by displaying a direct path from affective associations to binge drinking; whereas adolescents low in urgency exhibited greater reliance upon rational processing by displaying an indirect path via outcome beliefs.     

Sex differences in responding to rectal cancer symptoms

Many people who develop cancer symptoms wait inordinate amounts of time before seeking medical attention. Studies have found that symptom appraisal time–the time that passes before the individual concludes that their symptoms could be serious–accounts for most of the total delay time across subjects. It is thus important to understand the individual characteristics associated with slow recognition of dangerous symptoms. In this study, 62 patients (38 males) recently diagnosed with rectal cancer answered questions regarding the development of symptoms as well as their decisions and behaviors prior to seeking help. One subgroup of patients–males with the lowest scores on a measure of trait anxiety–took significantly longer to recognize the seriousness of their symptoms as compared to all other patients. This finding is discussed in the context of recent studies where the interaction of sex and negative affect is related to symptom reporting and other health-related behaviors.     

Sex differences and estropausal phase effects on water maze performance in aged rats

An age-related decline in memory has been reported in male rats; however, there are few studies that have addressed these changes in aged female rats. In young female rats, hormonal cycles influence behavior. By the age of 22 months most female rats have not had regular hormonal cycles for at least 9 months. In the current study we examined how the hormonal status (persistent estrus and pseudo-pregnant) of the aged (22-24 months) female rat (Long Evans) influenced performance on a spatial version of the Morris water maze and compared this to aged male rats. Aged females in persistent estrus showed better performance on the water maze than both aged females that were pseudopregnant and aged males. Thus, postestropausal hormonal status may influence the course of aging in females.     

Sex differences in attention to disgust facial expressions

Research demonstrates that women experience disgust more readily and with more intensity than men. The experience of disgust is associated with increased attention to disgust-related stimuli, but no prior study has examined sex differences in attention to disgust facial expressions. We hypothesised that women, compared to men, would demonstrate increased attention to disgust facial expressions. Participants (n?=?172) completed an eye tracking task to measure visual attention to emotional facial expressions. Results indicated that women spent more time attending to disgust facial expressions compared to men. Unexpectedly, we found that men spent significantly more time attending to neutral faces compared to women. The findings indicate that women’s increased experience of emotional disgust also extends to attention to disgust facial stimuli. These findings may help to explain sex differences in the experience of disgust and in diagnoses of anxiety disorders in which disgust plays an important role.     

Sex differences in behavioral and hormonal response to social threat: commentary on Taylor et al. (2000)

Taylor and colleagues proposed that women uniquely respond to stressors by tending to children and befriending other women rather than by fighting or fleeing (S. E. Taylor et al., 2000). In this article, the authors expand Taylor et al.'s evolutionary frame and incorporate several unique aspects of human social dynamics. First, humans are characterized by extensive paternal investment, and thus men's tending is predicted and observed in some stressful contexts. Second, the dynamics of women's befriending suggest an evolutionary elaboration of the mechanisms that support reciprocal altruism. Third, coalitional male-male competition indicates that men's befriending is a predicted component of their fight-or-flight response. Finally, men's tending should result in the evolution of female-female competition over this form of parental investment.     

Effects of negative incentive shifts in food reward on rats' consumption of concurrent ethanol solutions

Frustration stress, typically operationalized as the unexpected loss of reinforcement, has been shown to engender substance use. Abrupt reductions in reinforcer magnitude likely also function as frustration stressors. These negative incentive shifts were previously shown to produce tap‐ and sweetened‐water drinking in rats. The purpose of this study was to investigate whether these shifts in food reward would occasion oral ethanol self‐administration. Nine male Long‐Evans rats operated on a two‐component multiple fixed‐ratio schedule with signaled components producing either a large (4 pellets) or small (1pellet) reinforcer. Components were pseudorandomly arranged to present 4 transitions between past and upcoming reinforcer magnitudes: small‐to‐large, small‐to‐small, large‐to‐large, and large‐to‐small (negative incentive shift). Experiment 1 investigated the effects of negative incentive shifts on consumption of concurrent, freely available 10% sucrose, 10% sucrose plus 10% ethanol, and following sucrose fading, 10% ethanol. Experiment 2 entailed continuation of schedule contingencies with a dose manipulation of 4 ethanol concentrations (0, 5, 10, and 20%) to assess dose‐dependent differences in transition‐type control and consumption. A lever‐press extinction condition was then conducted with 10% ethanol availability. In this novel model of frustration stress, negative incentive shifts prompted ethanol self‐administration at each dose investigated, whereas the other transitions did not.