Habituation of the infant arousal response.

STUDY OBJECTIVES: Arousal is considered to be an important protective response in a sleeping infant and its depression could leave an infant vulnerable to a life threatening stimulus. We found previously that arousal to a non-respiratory (tactile) stimulus occurs in a sequence of events that begins with spinal, followed by brainstem responses, and then a cortical electroencephalographic (EEG) arousal response. We hypothesized that repeated stimuli would depress the arousal responses by habituation and that spinal and brainstem responses would be more resistant to habituation than cortical responses. PARTICIPANTS: We studied 22 normal infants. INTERVENTIONS: The infants underwent polysomnographic monitoring during a daytime nap. Tactile stimuli was applied to the infants foot at 5-second intervals. MEASUREMENTS AND RESULTS: We found that spinal, brainstem, and cortical responses occurred on the first trial of each test. Repeated trials during non-rapid eye movement (NREM) and rapid eye movement (REM) sleep resulted in a decrease in the incidence of each individual response and eventually elimination of the arousal responses. Cortical responses were eliminated first, followed by brainstem responses and finally spinal responses. The elimination of each of the responses occurred more rapidly during REM sleep that during NREM sleep. CONCLUSIONS: Habituation of the infant arousal sequence occurs with repeated tactile stimulation. There is a serial habituation of responses from the cortical to the spinal level, which occurs more rapidly during REM sleep. Rapid habituation to innocuous stimuli is probably beneficial in avoiding detrimental sleep disruptions. However, in situations requiring the protective functions of arousal, such habituation could be detrimental to an infant.     

Manipulating attentional asymmetry affects self-reported arousal

This investigation examined whether manipulating participants' attention toward the left or right visual field would have consequences for mood state. Based on the premise that right parietal activity is related to the arousal dimension of emotion, it was predicted that activating the right parietal region asymmetrically would differentially affect aspects of mood related to arousal. Half of the participants in the experiment completed a leftward-biased attentional orienting task, and half completed a mirror-image rightward-biased task. Consistent with predictions, participants in the left-biased group showed greater changes in self-reported arousal. Results support the notion of bidirectional causal relations between mood and perceptual asymmetries.     

Induction of sexual arousal in the castrated male rat by intracranial stimulation

Intracranial electrical stimulation in the medial preoptic area in two male rats caused a drastic increase in sexual activity. Stimulation of the castrated rat induced vigorous mounting behavior and even a few intromissions, but no ejaculations.     

The roots of sexual arousal and sexual orientation

Unlike members of other species that are genetically wired to be attracted to their sexual partners, humans learn the cues that guide them in choosing their sexual partners and that trigger sexual arousal. Genetically wired mechanisms must be directing the acquisition of those cues and organizing them in information structures that underlie human sexual behavior. Individual sexuality is a combination of the genetic mechanisms and information learned through personal experiences. This article focuses on the roots of human sexuality - on genetically embedded mechanisms, common to all humans, around which the wide variety of sexual behaviors is built. It proposes a model that defines the basic mechanisms and their role in developing individual sexuality. It is suggested that three brain areas host the roots of human sexuality: the auditory area, which provides stimuli that serve as cues for the identification of a mate; an emotional area, which provides cues for emotional arousal; and a corporal area, which controls the physiological expressions of arousal. The amygdala is a main candidate for the emotional area, and the hypothalamus for the corporal area, but other areas may also provide those inputs. Experimental observations that support this model are discussed, and an outline of additional experiments for validating the model is proposed. If validated, the model would provide knowledge that fills a gap in the understanding of human sexuality - knowledge that would benefit individuals, the medical profession, and society as a whole.     

Activation of POMC neurons during general arousal but not sexual behavior in male rats

Exogenous opioids influence male rat sexual behavior, suggesting that endogenous opioid peptides are released during mating. Supporting this hypothesis, the authors recently showed that mating induced activation of mu opioid receptors. However, it is unknown which ligand(s) is acting on these receptors during mating. The current set of experiments tested the hypothesis that beta-endorphin-producing neurons, that is, proopiomelanocortin (POMC) neurons, are activated during sexual behavior. Mating-induced activation of POMC neurons was investigated during either the dark phase or the light phase, following different components of male rat sexual behavior or following control manipulations that resulted in general arousal. Results show activation of POMC neurons in the mediobasal hypothalamus following general arousal but not specifically related to sexual behavior per se. In addition, mating did not activate the subpopulation of POMC neurons that project to the medial preoptic nucleus. These results suggest that it is unlikely that POMC neurons contribute to the action of endogenous opioids in the brain area during sexual behavior but instead may contribute to the change in arousal state essential for the expression of sexual behavior.     

Yohimbine and naloxone: effects on male rat sexual behavior.

We evaluated the effects of yohimbine (2 mg/kg) and naloxone (5 mg/kg), separately and in combination, on copulatory behavior in male rats. In Experiment 1, yohimbine evinced decrements in intromission frequency, ejaculation latency, and copulatory efficiency, whereas naloxone administration was followed by an increased ejaculation latency, and the combination of yohimbine plus naloxone was without effect. In Experiment 2, yohimbine evinced decreases in intromission frequency, ejaculation latency, copulatory efficiency in the first, but not subsequent, copulatory series, as well as a decreased latency to sexual exhaustion. Further, treatment with yohimbine alone, naloxone alone, or yohimbine plus naloxone was followed by a reduction in the number of ejaculation prior to sexual exhaustion. Thus, at the doses tested, no synergistic effects were observed for the combination of yohimbine plus naloxone.     

Endomorphin-1, effects on male sexual behavior

We examined the effect of endomorphin-1 (EM-1), an endogenous opioid peptide that binds selectively to the μ receptor, on male copulatory behavior in sexually vigorous Wistar rats. In the first experiment, four doses of EM-1 (1, 10, 50, and 100 μM) injected intracerebroventricularly produced a marked increase in ejaculation latency and interintromission interval and reduced the number of ejaculations during the test. In experiment 2 the effects of EM-1 were completely blocked by pretreatment with naloxone (5 mg/kg) 30 min prior to intracerebroventricular injection of EM-1 (100 μM). Collectively these results indicate that the activation of μ receptors by EM-1 modifies parameters associated with ejaculation (increases ejaculation latency and reduces the number of ejaculations) confirming that opioids are released during sexual behavior.     

Effects of androstenol on human sexual arousal

The hypothesis that 5-alpha-androst-16-en-3 alpha-ol increases the sexual arousal of the human female was examined. This substance is produced by the male and has been suggested to be a possible human pheromone. Groups of female subjects were asked to read either a neutral or a sexually-arousing passage in the presence of either androstenol or a placebo. Although sexual arousal was clearly manipulated by the experimental conditions, there was no evidence that androstenol influenced sexual feelings.     

Optimal attentional focus during exposure in specific phobia: A meta-analysis

Over the last 30 years, researchers have disagreed over the consequences of diverting attention from threat for exposure efficacy, which is an important theoretical and clinical debate. Therefore, the present meta-analysis assessed the efficacy of attentionally focused exposure against distracted and attentionally uninstructed exposure regarding distress, behavioral, and physiological outcomes. We included 15 randomized studies with specific phobia, totaling 444 participants and targeting outcomes at post-exposure and follow-up. Results indicated no difference between the efficacy of distracted exposure as opposed to focused or uninstructed exposure for distress and physiology. For behavior, at post-exposure, results were marginally significant in favor of distracted as opposed to focused exposure, while at follow-up results significantly favored distraction. However, concerning behavior, uninstructed exposure was superior to distraction. Moderation analyses revealed that, regarding distress reduction and approach behavior, distracted exposure significantly outperformed focused exposure when the distracter was interactive (g = 1.010/g = 1.128) and exposure was spread over the course of multiple sessions (g = 1.527/g = 1.606). No moderation analysis was significant for physiological measures. These findings suggest that distraction during exposure could be less counterproductive than previously considered and even beneficial under certain circumstances. Theoretical implications and future directions for research are discussed.     

Influence of daylength on male hamster sexual behavior: masking effects of testosterone

Exposure of male hamsters to short photoperiods for 6-8 weeks cause deficits in sexual behavior with receptive females. The present experiment tested the hypothesis that short photoperiodic effects on behavior could be masked in the presence of chronic and stable levels of testosterone. Males were castrated and administered Silastic capsules of testosterone while housed in long (16L:8D) or short (8L:16D) photoperiodic conditions for 7 weeks. Sexual behavior tests at this time indicated that the short photoperiod males copulated less well, but group differences were not robust. Testosterone capsules were then removed and half the animals in both 16L:8D and 8L:16D were transferred to the opposite photoperiod. Sexual behavior was tested 18 days later as the effects of this functional castration developed. These tests indicate that photoperiodic effects were much more obvious in the absence of testosterone than they were during week 7 tests when testosterone was still present. The behavior of the males that were transferred from one photoperiod to the other demonstrated that exposure to the short photoperiod for only 18 days was not sufficient to generate short photoperiod-like sexual behavior deficits. In contrast, exposure to the long photoperiod for 18 days was sufficient to reverse short photoperiodic effects that had already developed.     

Assessment of female sexual arousal: Response specificity and construct validity

Specificity of vaginal pulse amplitude and vaginal blood volume in reaction to visual sexual stimuli was investigated by comparing responses to sexual, anxiety-inducing, sexually threatening, and neutral film excerpts. Subjective sexual arousal, body sensations, emotional experience, skin conductance, and heart rate were monitored along with the genital measures. Self-report data confirmed the generation of affective states as intended. Results demonstrated response specificity of vaginal vasocongestion to sexual stimuli. In terms of both convergent and divergent validity, vaginal pulse amplitude was the superior genital measure. Skin conductance discriminated among stimuli only to a small degree, whereas heart rate failed to discriminate among stimuli altogether.     

Olfactory bulb removal: effects on sexual behavior and partner-preference in male rats

Control and bilaterally bulbectomized male rats were tested in an arena where the male could choose to spend time with (and mate with) a sexually receptive female, a nonreceptive female, or be in a neutral compartment. Control males mated with, and showed a strong preference for, sexually receptive females. Bulbectomy virtually eliminated mating. In addition, bulbectomized males showed no preference for a receptive female over a nonreceptive female, and spent their time equally between the receptive female, the nonreceptive female, and the neutral compartment. Effects of bulbectomy on preference and copulation could be consequences of a severely impaired ability to smell--the perception of odors may be essential for sexual arousal, or the absence of preference and copulation after bulbectomy might reflect a deficit in the male's ability to make odor-dependent classification of conspecifics as appropriate sexual partners. Or the behavioral effects of bulbectomy might reflect a disruption of tonic input to the forebrain that has little or nothing to do with the sensory impairment that follows bulb removal. But whatever the reason, in partner-preference tests bulbectomized males show a striking indifference to the sexual status of females, and it seems likely that the failure to mate is causally linked to this effect of surgery.     

Determinants of subjective experience of sexual arousal in women: Feedback from genital arousal and erotic stimulus content

Sixty-two women participated in a study designed to explore the association between gential and subjective sexual arousal. Four stimulus conditions were created, designed to evoke differential patterns of genital arousal over time. Subjects were instructed to report sensations in their genitalia while being exposed to the same erotic stimulus on repeated trials or to a series of varying erotic stimuli. Detection of genital arousal was facilitated by the occurrence of changes in genital arousal over trials. That is, genital and subjective sexual arousal were linearly related in conditions that resulted in large differences in genital arousal over trails, whereas such a relation was absent in conditions in which genital arousal levels remained relatively constant. In women, peripheral feedback from consciously detected genital arousal seems to be a relatively unimportant determinant of subjective sexual arousal.     

Hyperprolactinemia and male sexual behavior: effects of steroid replacement with estrogen plus dihydrotestosterone

To determine if alterations in the availability of the active metabolites of testosterone (T) are involved in the inhibition of sexual activity in hyperprolactinemic animals, the effects of four ectopic pituitary grafts on copulatory behavior were examined in castrated male rats given subcutaneous implants of T or estradiol-17 beta (E2) plus 5 alpha-dihydrotestosterone (DHT). Two weeks after implantation of the steroid-filled capsules, half the animals of each group were given pituitary grafts and the remainder were sham-operated. Tests of copulatory behavior were performed prior to, and one, two, and three months following pituitary transplantation. Pituitary grafting caused significant inhibition of copulatory behavior in both T and E2 + DHT treated animals. PRL levels were significantly higher in E2 + DHT treated grafted males than in T treated grafted animals (2000 +/- 140 vs. 395 +/- 26 ng/ml), but did not differ between the corresponding control groups (61 +/- 8 vs. 73 +/- 6 ng/ml). The results of these experiments preclude the possible involvement of alterations in steroid secretion by the testes or modifications of the conversion of T to its active metabolites in the effects of hyperprolactinemia on copulatory behavior.