The effects of social defeat and other stressors on the expression of circadian rhythms

Most biological functions display a 24 h rhythm that, in mammals, is under the control of an endogenous circadian oscillator located in the suprachiasmatic nuclei (SCN) of the hypothalamus. The circadian system provides an optimal temporal organization for physiological processes and behavior in relation to a cyclic environment imposed upon organisms by the regular alternation of day and night. In line with its function as a clock that serves to maintain a stable phase-relationship between endogenous rhythms and the light-dark cycle, the circadian oscillator appears to be well protected against unpredictable stressful stimuli. Available data do not provide convincing evidence that stress is capable of perturbing the central circadian oscillator in the SCN. However, the shape and amplitude of a rhythm is not determined exclusively by the SCN and certain stressors can strongly affect the output of the clock and the expression of the rhythms. In particular, social stress in rodents has been found to cause severe disruptions of the body temperature, heart rate and locomotor activity rhythms, especially in animals that are subject to uncontrollable stress associated with defeat and subordination. Such rhythm disturbances may be due to effects of stress on sub-oscillators that are known to exist in many tissues, which are normally under the control of the SCN, or due to other effects of stress that mask the output of the circadian system. These disturbances of peripheral rhythms represent an imbalance between normally precisely orchestrated physiological and behavioral processes that may have severe consequence for the health and well being of the organism.     

Age-specific problems in rhythmic timing

The authors investigated performance in 2 rhythm tasks in young (M = 23.8 years) and older (M = 71.4 years) amateur pianists to test whether slowing of a central clock can explain age-related changes in timing variability. Successive keystrokes in the rhythm tasks were separated by either identical (isochronous) time intervals or varying (anisochronous) intervals. Variability was comparable for young and older adults in the isochronous task; pronounced age effects were found for the anisochronous rhythm. Analyses of covariances between intervals rule out slowing of a central clock as an explanation of the findings, which instead support the distinction between target specification, timekeeper execution, and motor implementation proposed by the rhythm program hypothesis (D. Vorberg & A. M. Wing, 1996). Age stability was found at the level of motor implementation, but there were age-related deficits for processes related to target-duration specification.     

Diurnal mood variation in major depressive disorder

Depression disturbs mood, but a clear picture of diurnal mood rhythms in depression has yet to emerge. This study examined variations in positive affect (PA) and negative affect (NA), two dimensions of mood that generate diurnal patterns among healthy individuals. Repeated measurements of NA and PA in daily life were obtained over 6 days from 47 depressed outpatients and 39 healthy individuals using the Experience Sampling Method. Relative to healthy individuals, depressed individuals exhibited increasing PA levels during the day with a later acrophase. In contrast, depressed persons' NA exhibited a more pronounced diurnal rhythm and was more variable from moment to moment than healthy individuals'. Ambulatory mood measurements in depression suggest distinct diurnal disturbances of positive and negative affect.     

Diurnal cortisol rhythm and cognitive functioning in toddlers: The Generation R Study

Little is known about the relationship between diurnal cortisol secretion patterns and cognitive function early in life. This population-based study examined whether diurnal cortisol rhythms and cognitive functioning in toddlers are related. Within the Generation R Study, parents of 364 infants (median age: 14.2 months) collected saliva samples at five moments during one day. We assessed the diurnal cortisol rhythm by calculating the area under the curve (AUC), the cortisol awakening response (CAR), and the diurnal slope. Verbal cognitive functioning and fine motor development was determined at age 18 months. Nonverbal cognitive functioning was assessed at age 30 months. A more positive CAR was associated with a lower risk of delay in language comprehension (OR per 1-SD CAR: 0.62, 95%CI: 0.40–0.98, p = .04), a lower risk of nonoptimal fine motor development (OR per 1-SD slope: 0.74, 95%CI: 0.57–0.96, p = .03), and a lower risk of delay in nonverbal cognitive development (OR per 1-SD CAR: 0.58, 95%CI: 0.38–0.90, p = .02). Also, children with flatter slopes had a lower risk of delay in nonverbal cognitive development (OR per 1-SD slope: 0.51, 95%CI: 0.34–0.76, p = .001). Higher AUC levels were associated with a higher risk of delay in language production. These results show that variations in diurnal cortisol rhythms are already associated with variations in cognitive functioning at a young age. Infants with a diurnal cortisol pattern indicative of less stress and more cortisol reactivity, that is, lower AUC levels and a more positive CAR, show a lower risk of delay in cognitive functioning as toddlers.     

The role of neuropeptide Y in the amygdala on corticotropin-releasing factor receptor-mediated behavioral stress responses in the rat

Neuropeptide Y (NPY) is one of the most abundant peptides in the brain and has been shown to be a critical regulator of emotionality, most notably for its effect in decreasing anxiety-like behaviors. The stress response in both humans and animals has been shown to involve a cascade of biological events initiated by corticotropin releasing factor (CRF), another centrally acting peptide. Interestingly, NPY and CRF are present in similar brain regions mediating stress responses and may act in an opposing fashion. The basolateral nucleus of the amygdala (BLA) is a distinct division of the amygdala and contains CRF receptors and the highest concentration of NPY neurons. The current study investigates the behavioral effects in rodents when NPY is injected directly into the BLA prior to the pharmacological stressor, urocortin I (Ucn; a CRF receptor agonist) or the emotional stressor, restraint. The animals that underwent restraint were evaluated in the social interaction (SI) test, while those injected with Ucn into the BLA were assessed in the two floor choice test, a modified version of the conditioned-place avoidance paradigm. The results showed that injections of NPY into the BLA prior to Ucn significantly blocked the development of the avoidance behavior in the two floor choice test and the decrease in SI time that is usually seen following restraint stress. These results provide further support that an interaction between NPY and CRF within the BLA may be critical for maintaining a normal homeostatic emotional state.     

The fast and the slow of skilled bimanual rhythm production: parallel versus integrated timing

Professional pianists performed 2 bimanual rhythms at a wide range of different tempos. The polyrhythmic task required the combination of 2 isochronous sequences (3 against 4) between the hands; in the syncopated rhythm task successive keystrokes formed intervals of identical (isochronous) durations. At slower tempos, pianists relied on integrated timing control merging successive intervals between the hands into a common reference frame. A timer-motor model is proposed based on the concepts of rate fluctuation and the distinction between target specification and timekeeper execution processes as a quantitative account of performance at slow tempos. At rapid rates expert pianists used hand-independent, parallel timing control. In alternative to a model based on a single central clock, findings support a model of flexible control structures with multiple timekeepers that can work in parallel to accommodate specific task constraints.     

The effect of tempo and tone duration on rhythm discrimination

Rhythm constancy was investigated in two experiments. In Experiment 1, the first rhythm was presented at one tempo, the second rhythm was presented at a different tempo, and subjects judged whether the relative timing structures were identical (i.e., was the first rhythm merely sped up or slowed down to generate the second rhythm?). For the nonmetric rhythms used here, subjects perceived the rhythm in terms of the figural grouping of the tones, and rhythm constancy broke down between slower and faster tempos. In Experiment 2, the first rhythm was presented in tones of one duration; the second rhythm was presented in tones of a different duration; and subjects judged whether the timing structures of the tone onsets were identical (the two rhythms were presented at the same tempo). These results indicated a high degree of constancy; subjects found it easy to discriminate the timing structures. These results confirm that the onset timing is critical to rhythm perception and suggest that rhythm perception at slower rates (2 elements/sec) differs from rhythm perception at faster rates (3–4 elements/sec).     

Movement synchrony and perceived entitativity

Movement synchrony has been theoretically linked to the emergence of a social unit. To empirically investigate whether similar movement rhythms are an antecedent of perceived entitativity, movement rhythms were experimentally manipulated in four studies. Using this novel approach, stick figures waving in synchrony were found to be rated higher on entitativity than stick figures waving in different rhythms (Study 1), and this effect was extended to interactional synchrony, where different movements are performed in the same rhythm (Study 2). Objective differences in movement rhythms are linearly related to ratings of perceived entitativity, and this relationship is partially mediated by the subjectively perceived similarity of movement rhythms (Study 3). These results also held for entitativity judgments for videotaped individuals waving rhythmically (Study 4). These results support the hypothesis that movement rhythms are an important source of information which observers use to infer the extent to which individuals are a social unit.     

Audiovisual beat induction in complex auditory rhythms: Point-light figure movement as an effective visual beat

This study investigated whether explicit beat induction in the auditory, visual, and audiovisual (bimodal) modalities aided the perception of weakly metrical auditory rhythms, and whether it reinforced attentional entrainment to the beat of these rhythms. The visual beat-inducer was a periodically bouncing point-light figure, which aimed to examine whether an observed rhythmic human movement could induce a beat that would influence auditory rhythm perception. In two tasks, participants listened to three repetitions of an auditory rhythm that were preceded and accompanied by (1) an auditory beat, (2) a bouncing point-light figure, (3) a combination of (1) and (2) synchronously, or (4) a combination of (1) and (2), with the figure moving in anti-phase to the auditory beat. Participants reproduced the auditory rhythm subsequently (Experiment 1), or detected a possible temporal change in the third repetition (Experiment 2). While an explicit beat did not improve rhythm reproduction, possibly due to the syncopated rhythms when a beat was imposed, bimodal beat induction yielded greater sensitivity to a temporal deviant in on-beat than in off-beat positions. Moreover, the beat phase of the figure movement determined where on-beat accents were perceived during bimodal induction. Results are discussed with regard to constrained beat induction in complex auditory rhythms, visual modulation of auditory beat perception, and possible mechanisms underlying the preferred visual beat consisting of rhythmic human motions.     

Some influences of accent structure on melody recognition

Two experiments were carried out to investigate the roles of joint accent structure and familiarity in delayed recognition of relatively long tonal melodies. Melodic themes of target melodies were defined by correlating contour-related pitch accents with temporal accents (accent coupling) during an initial familiarization phase. Later, subjects gave recognition responses to key-transposed versions of the target melodies as well as to decoys with same and different contour accent patterns. In Experiment 1, all to-be-recognized melodies occurred both in an original rhythm, which preserved accent coupling, and in a new rhythm, which did not. Listeners were best at distinguishing targets from different decoys, especially in the original rhythm. In Experiment 2, the familiarity of target tunes and the rhythmic similarity in recognition were varied. Similar rhythms preserved accent coupling, whereas dissimilar rhythms did not. Listeners were most adept in distinguishing familiar targets from different decoys (Experiment 2A), particularly when they appeared in novel but similar rhythms. However, in similar rhythm conditions, listeners also frequently mistook same decoys for targets. With less familiar targets (Experiment 2B), these effects were attenuated, and performance showed general effects of pitch contour.     

A psychological pulse train: how young children use this cognitive framework to structure simple rhythms

Summary This paper examines the reproduction of both regular rhythms and irregular sequences by 5- and 7-year-old children, concentrating on the important role played by their organization around a pulse train. It is shown that: (a) the closer rhythms are to a regular beat the easier they are to reproduce and the greater are the improvements with age; (b) memory capacity is limited by the number of pulses around which the rhythm is organized rather than by the number of elements it contains; (c) all the children's productions contain two interval lengths that are in a ratio close to 1:2 and arranged in preferential sequences which we have called stereotypes; (d) arrhythmic sequences can only be reproduced if the intervals undergo a systematic distortion towards regularity. These results are interpreted in relation to a pulse-train hypothesis which states that on hearing a rhythm an internal clock or time base is evoked around which the rhythm is structured.     

Apparent motion enhances visual rhythm discrimination in infancy

Many studies have demonstrated that infants exhibit robust auditory rhythm discrimination, but research on infants' perception of visual rhythm is limited. In particular, the role of motion in infants' perception of visual rhythm remains unknown, despite the prevalence of motion cues in naturally occurring visual rhythms. In the present study, we examined the role of motion in 7-month-old infants' discrimination of visual rhythms by comparing experimental conditions with apparent motion in the stimuli versus stationary rhythmic stimuli. Infants succeeded at discriminating visual rhythms only when the visual rhythm occurred with an apparent motion component. These results support the view that motion plays a role in infants' perception of visual temporal information, consistent with the manner in which natural rhythms appear in the visual world.     

Effects of metric and harmonic rhythm on the detection of pitch alterations in melodic sequences

Tested response time to alterations. Metric rhythm and harmonic rhythm of 13-note tonal sequences were either matched or mismatched. Metric rhythm (3/4 or 4/4 meter) was induced by dynamic accents. Harmonic rhythm was induced by implied chord progressions initiated on the first note and on either every third or every fourth note. Responses were not always faster for matched rhythms or for alterations occurring on the dynamic accent. Responses were consistently faster for sequences presented in 4/4 meter. Musically untrained Ss performed similarly to trained Ss, but were slower and more variable. Accuracy of recall on a music dictation task also favored 4/4 meter rather than matched rhythms. Coding of pitch content may have been facilitated by the structural framework of 4/4 meter rather than by expectancies arising from the match of temporal and pitch organization.     

节律在听觉言语理解中的作用

言语理解是听者接受外部语音输入并且获得意义的心理过程。日常交流中, 听觉言语理解受多尺度节律信息的影响, 常见有韵律结构节律、语境节律、和说话者身体语言节律三方面外部节律。它们改变听者在言语理解中的音素判别、词汇感知以及言语可懂度等过程。内部节律表现为大脑内神经振荡, 其能够表征外部言语输入在不同时间尺度下的层级特征。外部节律性刺激与内部神经活动的神经夹带能够优化大脑对言语刺激的处理, 并受到听者自上而下的认知过程的调节进一步增强目标言语的内在表征。我们认为它可能是实现内外节律相互联系并共同影响言语理解的关键机制。对内外节律及其联系机制的揭示能够为理解言语这种在多层级时间尺度上具有结构规律的复杂序列提供了一个研究窗口。     

Perception–production relationships and phase correction in synchronization with two-interval rhythms

Two experiments investigated the effects of interval duration ratio on perception of local timing perturbations, accuracy of rhythm production, and phase correction in musicians listening to or tapping in synchrony with cyclically repeated auditory two-interval rhythms. Ratios ranged from simple (1:2) to complex (7:11, 5:13), and from small (5:13 = 0.38) to large (6:7 = 0.86). Rhythm production and perception exhibited similar ratio-dependent biases: rhythms with small ratios were produced with increased ratios, and timing perturbations in these rhythms tended to be harder to detect when they locally increased the ratio than when they reduced it. The opposite held for rhythms with large ratios. This demonstrates a close relation between rhythm perception and production. Unexpectedly, however, the neutral “attractor” was not the simplest ratio (1:2 = 0.50) but a complex ratio near 4:7 (= 0.57). Phase correction in response to perturbations was generally rapid and did not show the ratio-dependent biases observed in rhythm perception and production. Thus, phase correction operates efficiently and autonomously even in synchronization with rhythms exhibiting complex interval ratios.     

A population approach to the study of emotion: diurnal rhythms of a working day examined with the Day Reconstruction Method

To date, diurnal rhythms of emotions have been studied with real-time data collection methods mostly in relatively small samples. The Day Reconstruction Method (DRM), a new survey instrument that reconstructs the emotions of a day, is examined as a method for enabling large-scale investigations of rhythms. Diurnal cycles were observed for 12 emotion adjectives in 909 women over a working day. Bimodal patterns with peaks at noon and evenings were detected for positive emotions; peaks in negative emotions were found at mid-morning and mid-afternoon. A V-shaped pattern was found for tired and an inverted U-shaped pattern for competent. Several diurnal patterns from prior studies were replicated. The DRM appears to be a useful tool for the study of emotions.     

Lateralization of auditory rhythm length in temporal lobe lesions

In the visual modality, short rhythmic stimuli have been proven to be better processed (sequentially) by the left hemisphere, while longer rhythms appear to be better (holistically) processed by the right hemisphere. This study was set up to see if the same holds in the auditory modality. The rhythm task as originally designed by Seashore was computerized and is part of the Fepsy Neuropsychological battery. This task was performed by 85 patients with intractable temporal lobe epilepsy (left TLE = 32; right TLE = 53) enrolled in the Dutch Collaborative Epilepsy Surgery Program. They performed the task before and 6 months after surgery. The task consists of 30 pairs of rhythmic patterns in 3 series of 10 items. The series contains patterns of 5, 6, or 7 notes. The purpose is to indicate whether the two patterns are the same or different. Reaction times are also measured. If the hypothesis is true, the short-item sequence will be better processed by patients with right temporal lobe epilepsy (nonimpaired left temporal lobe), the longer sequence will be better processed by the left temporal epilepsy group (nonimpaired right temporal lobe). No overall laterality effect on rhythm perception could be found and no difference was found between both test moments. IQ did not correlate with rhythm performance. However, there was an interaction effect of laterality and rhythm length on performance and reaction time. This effect can be explained by the increase after the operation of the score of the left focus group and a decrease in the right focus group on the longer rhythms. This effect was somewhat less strong in the reaction times: a clear tendency for faster reaction times after surgery in the left and longer reaction times in the right focus group. The effect could not be explained for by the difference in extent of resection in either temporal lobe. This study showed that memory for and discrimination of auditory rhythm is dependent on which hemisphere is used in processing. The effect could be demonstrated for the right hemisphere, which uses a holistic processing of stimuli, which outperforms the left in rhythms consisting of a long sequence. In left temporal resections an improvement occurs on the longer rhythms and in right temporal resections the performance on the longest rhythms decreases.     

Use of rhythm in acquisition of a computer-generated tracking task.

This research assessed whether rhythm aids acquisition of motor skills by providing cues for the timing of those skills. Rhythms were presented to participants visually or visually with auditory cues. It was hypothesized that the auditory cues would facilitate recognition and learning of the rhythms. The three timing principles of rhythms were also explored. It was hypothesized that rhythms that satisfied all three timing principles would be more beneficial in learning a skill than rhythms that did not satisfy the principles. Three groups learned three different rhythms by practicing a tracking task. After training, participants attempted to reproduce the tracks from memory. Results suggest that rhythms do help in learning motor skills but different sets of timing principles explain perception of rhythm in different modalities.     

Hypothalamic expression of NPY mRNA, vasopressin mRNA and CRF mRNA in response to food restriction and central administration of the orexigenic peptide GHRP-6

In this study, we examined the effects of restricted feeding and of central administration of an orexigenic ghrelin agonist GHRP-6 on peptide mRNA expression in the hypothalamus. We compared rats fed ad libitum with rats that were allowed food for only 2?h every day, and treated with a continuous chronic i.c.v. infusion of GHRP-6 or vehicle. Ad libitum fed rats exposed to GHRP-6 increased their food intake and body weight over 6 days, but, at the end of this period, neuropeptide Y mRNA expression in the arcuate nucleus was not different to that in control rats. By contrast, expression of neuropeptide Y mRNA in the arcuate nucleus was elevated in food-restricted rats, consistent with the interpretation that increased expression reflects increased hunger. However, neuropeptide Y mRNA expression was no greater in food-restricted rats infused with GHRP-6 than in food-restricted rats infused with vehicle; thus if the drive to eat was stronger in rats infused with GHRP-6, this was not reflected by higher levels of neuropeptide Y mRNA expression. Expression of vasopressin mRNA and corticotrophin releasing factor (CRF) mRNA in the paraventricular nucleus (PVN) was not changed by food restriction. GHRP-6 infusion increased CRF mRNA expression in ad libitum rats only.