Inherent Rhythm Research Articles

Systemic neurophysiological entrainment to behaviorally relevant rhythmic stimuli.

Physiological oscillations, such as those involved in brain activity, heartbeat, and respiration, display inherent rhythmicity across various timescales. However, adaptive behavior arises from the interaction between these intrinsic rhythms and external environmental cues. In this study, we used multimodal neurophysiological recordings, simultaneously capturing signals from the central and autonomic nervous systems (CNS and ANS), to explore the dynamics of brain and body rhythms in response to rhythmic auditory stimulation across three conditions: baseline (no auditory stimulation), passive auditory processing, and active auditory processing (discrimination task). Our findings demonstrate that active engagement with auditory stimulation synchronizes both CNS and ANS rhythms with the external rhythm, unlike passive and baseline conditions, as evidenced by power spectral density (PSD) and coherence analyses. Importantly, phase angle analysis revealed a consistent alignment across participants between their physiological oscillatory phases at stimulus or response onsets. This alignment was associated with reaction times, suggesting that certain phases of physiological oscillations are spontaneously prioritized across individuals due to their adaptive role in sensorimotor behavior. These results highlight the intricate interplay between CNS and ANS rhythms in optimizing sensorimotor responses to environmental demands, suggesting a potential mechanism of embodied predictive processing.

The Aesthetics and Mechanics of African Dance, Costumes and Rattles in Yibo Koko’s Seki Dance Drama

With its distinctive form and content, African dance stands apart, carving out a unique identity that sets it apart from other continents. Its inherent rhythm possesses a magnetic quality capable of compelling people to move, transcending language barriers—an attribute that has propelled African musicians, particularly those from Nigeria, to a dominating position on the global music stage. This paper delves into traditional African dance, explicitly focusing on the rhythmic opulence found in the dance of rattles, costumes, and water pots within Seki. This captivating dance drama pays homage to the vibrant culture of the Niger Delta in Nigeria, Africa. Authored by Yibo Koko, the Seki dance drama undergoes a transformative journey, skilfully repackaging the traditional village square theatre into a digitalized theatrical experience accessible both as a live performance and in the dynamic space of new media. The paper employs a robust methodology and theoretical framework, drawing on dance theories, historical surveys, and analytical reviews of Seki performances to unravel the nuanced layers of this artistic expression. In scrutinizing Seki, this paper not only sheds light on the captivating exploration of rhythmic elements, including rattles, costumes, and water pots, but also underscores the broader impact of Seki's performance. The dance drama is a compelling canvas that radiates colours and a flawless rhythm, capturing global attention and playing a pivotal role in restoring the splendour of African ancestry. Through this repackaged theatre experience, Seki becomes a vehicle for exporting African culture, offering a renewed perspective that transcends borders and celebrates the rich heritage embedded in the dance's vibrant tapestry.

Identification and Extraction of Features from Malayalam Poems for Analyzing Syllable Duration Patterns

Text-to-speech (TTS) synthesis is an active area of research to generate synthetic speech from the underlying text. Compared to English and many European languages, TTS is yet to mature in Malayalam, the principal language of the South Indian state of Kerala. A syllable has to be uttered with proper durational and prosodic characteristics to emulate natural speech. When it comes to poems in Malayalam, many of them have an inherent rhythm attached to them. In Malayalam, this property is characterized by the Vruta [ 28 ] in which the poem is written. Vruta decides the meter of narration of the poem. Therefore, it is only consequential that Vruta can give away vital cues about the durational and prosodic characteristics of the poem verses recited. This study intends to identify the features that determine the durational characteristics of a poem written in a particular Vruta and develop an algorithm to extract those features required to build a dataset to model the duration of syllable utterances for tuneful TTS in Malayalam. Poems written in three Vrutas, namely Kakali, Manjari, and Keka, are considered in this study. Nineteen extractible features from the orthographic representation of a poem are identified for this purpose. A standard dataset is built using these extracted features. Later, support vector machine and feed forward neural network based estimators are proposed to model the duration of Malayalam poem syllables for tuneful speech synthesis. The hyperparameters are optimized using the GridsearchCV algorithm from the Scikit-learn machine learning library [ 15 ].

Beta rhythmicity in human motor cortex reflects neural population coupling that modulates subsequent finger coordination stability

Human behavior is not performed completely as desired, but is influenced by the inherent rhythmicity of the brain. Here we show that anti-phase bimanual coordination stability is regulated by the dynamics of pre-movement neural oscillations in bi-hemispheric primary motor cortices (M1) and supplementary motor area (SMA). In experiment 1, pre-movement bi-hemispheric M1 phase synchrony in beta-band (M1-M1 phase synchrony) was online estimated from 129-channel scalp electroencephalograms. Anti-phase bimanual tapping preceded by lower M1-M1 phase synchrony exhibited significantly longer duration than tapping preceded by higher M1-M1 phase synchrony. Further, the inter-individual variability of duration was explained by the interaction of pre-movement activities within the motor network; lower M1-M1 phase synchrony and spectral power at SMA were associated with longer duration. The necessity of cortical interaction for anti-phase maintenance was revealed by sham-controlled repetitive transcranial magnetic stimulation over SMA in another experiment. Our results demonstrate that pre-movement cortical oscillatory coupling within the motor network unknowingly influences bimanual coordination performance in humans after consolidation, suggesting the feasibility of augmenting human motor ability by covertly monitoring preparatory neural dynamics.

The art of facilitation: a delicate hormonal balance!

The art of facilitation: a delicate hormonal balance!

Entrainment of superoxide rhythm by menadione in HCT116 colon cancer cells

Reactive oxygen species (ROS) are primary effectors of cytotoxicity induced by many anti-cancer drugs. Rhythms in the pseudo-steady-state (PSS) levels of particular intracellular ROS in cancer cells and their relevance to drug effectiveness are unknown thus far. We report that the PSS levels of intracellular superoxide (SOX), an important ROS, exhibit an inherent rhythm in HCT116 colon cancer cells, which is entrained (reset) by the SOX inducer, menadione (MD). This reset was dependent on the expression of p53, and it doubled the sensitivity of the cells to MD. The period of oscillation was found to have a linear correlation with MD concentration, given by the equation, T, in h = 23.52 − 1.05 [MD concentration in µM]. Further, we developed a mathematical model to better understand the molecular mechanisms involved in rhythm reset. Biologically meaningful parameters were obtained through parameter estimation techniques; the model can predict experimental profiles of SOX, establish qualitative relations between interacting species in the system and serves as an important tool to understand the profiles of various species. The model was also able to successfully predict the rhythm reset in MD treated hepatoma cell line, HepG2.

Rhythms of wet and dry: Temporalising the land-water nexus

This article argues for conceptualising the land-water nexus not primarily in spatial terms, but above all as a set of spatiotemporal rhythms of increasing and decreasing wetness and fluidity. By investigating human engagement with water and land as rhythms, the corresponding and conflicting dynamics of particular places becoming – for longer or shorter periods – land, water or a mixture of both can be traced as an evolving web of relationships between human imaginations and practices, and the materialities of water, mud, sediment, dams, floodgates, etc.The article illustrates this approach with two brief ethnographic examples from northern Europe: In the depopulated Estonian Soomaa wetlands, some of the few remaining inhabitants are in the process of redefining unruly fluctuating water as a tourism destination. In doing so, however, these tourism operators are finding themselves and their “products” caught up in volatile and complicated spatiotemporal dynamics, including the difficulty to predict flooding and to coordinate high water with their potential customers’ spare time, which is bound to working/school weeks and public holidays. On the Kemi River in Finnish Lapland, water flows are not only conditioned by precipitation and seasons, but also – through an intricate hydropower infrastructure – by the electricity market, triggering continued disputes about appropriate spatiotemporal rhythms in the land-water nexus.Seasonality and hydroelectricity generation point to the inherent rhythmicity of the land-water nexus, which is significant not only because it reflects the experience of people inhabiting and engaging with their in-between environments. A rhythms approach can also de-centre the (often illusive) quest for what the water-land nexus is, and instead focus on how this nexus continually comes into being and is negotiated by both its inhabitants and other people. This argument builds on anthropological thinking about temporality and materiality, and indicates how the two must be combined for better understanding how human life relates to the land-water nexus.

P 120 A machine learning approach to detecting sleep and sleep disorders in acceleration sensor data

The major diagnostic sleep laboratory tool for assessing excessive daytime sleepiness (EDS), the multiple sleep latency test (MSLT), is increasingly criticized for poor precision in the differentiation of idiopathic hypersomnia (IH) and narcolepsy ( Trotti et al., 2013 , Johns, 2000 ). Recent evidence suggests that actigraphy can supplement the diagnostic process by providing information about the sleep-wake rhythm ( Kretzschmar et al., 2016 , Filardi et al., 2015 , Bruck et al., 2005 ). An actigraphy analysis tool is introduced that processes actigraphy recordings with machine learning methods. It is preliminarily validated for recordings of hypersomnolent patients. Sleep is detected using a support vector machine (SVM) with 61 features describing the actigraphy signal. Testing the prediction against polysomnographically validated labels on nocturnal recordings of hypersomnolent patients showed an accuracy of 87%, a sensitivity of 93% and a specificity of 51%. Post-processing the prediction with morphological operations increases the specificity to 73%, with only minor declines in accuracy and sensitivity (85% and 88%, respectively). Individually training an SVM per patient revealed the most promising results with 95% accuracy, 73% specificity and 99% sensitivity. Each detected sleep phase is automatically verified in order to not be confused with episodes of unattached actigraphy device. Moreover, an SVM is trained to identify the main sleep episode of each day, based on features describing a sleep phase’s probability of being a nap. Testing with manually generated labels of 14-day actigraphies of EDS patients showed that 90% of the sleep phases receive the correct label (diurnal or nocturnal sleep), with a specificity of 96% and a sensitivity of 86%. Finally, the classifiers’ annotations are used to calculate 217 sleep-wake rhythm and motor activity parameters. Comparing the automatically derived sleep-wake parameters of 15 long-term actigraphies from IH patients to previously published results ( Filardi et al., 2015 ) showed good accordance. Altogether, the developed tool and the methods used appear a promising pathway for future investigations in the search for disorder inherent sleep-wake rhythm and motor activity patterns in big patient cohorts.

Control of annual gonadal cycles in Indian songbirds

Reproduction is a part of life cycle with great environmental dependence. In contrast to temperate avian species, which mostly breed during summer, the Indian songbirds have more flexible breeding programs and exhibit a spectrum of reproductive strategies with the breeding season scattered all over the year. Control of breeding cycles in the Indian songbirds, therefore, are broadly viewed in light of two strategies (i) birds showing strong photoperiodic component in regulation of reproductive and post-reproductive events (ii) birds that do not exhibit typical photoperiodic regulation indicating the involvement of an inherent rhythm of reproduction. Both circadian and circannual rhythms have been demonstrated to regulate annual gonadal cycles of Indian songbirds. While photoperiod continues to be a predominant proximate factor for timing of breeding in majority of Indian songbirds investigated so far, some studies reveal the role of non photoperiodic cues such as the food availability, temperature, rainfall, etc. in timing/modulating the timing of breeding. The conversion or non-conversion of thyroxine to triiodothyronine may act as a long or short photoperiod signal and may up or downregulate the synthesis and release of GnRH-I in hypothalamus, FSH and LH in anterior pituitary and gonadal steroids in gonads causing gonadal growth or regression, respectively.

The GnRH Pulse Generator

The pulsatile secretion of hormones is an efficient way of coding a large variety of chemical messages. The GnRH pulse pattern determines which gonadotropin is released when and at what concentration, prescribing a detailed set of instructions to the gonads that produce changes in the steroid hormone milieu. Although GnRH neurons possess some inherent rhythmicity, they are diffusely situated within the hypothalamus and in isolation are only capable of generating physiologically irrelevant messages, hence a synchronization module exists upstream. The identity of the neural unit comprising the GnRH pulse generator is now generally thought to include KNDy neurons in the arcuate nucleus. These neurons coexpress the neuropeptides kisspeptin, neurokinin B and dynorphin A, as well as other transmitters, and are in intimate contact with the GnRH network. The GnRH pulse generator’s function is the precise control of GnRH neuron excitability, coordinated activation, stimulation of neurosecretory events, modulation of gene transcription and the mediation of the negative feedback effect of gonadal steroids. Additionally, the GnRH pulse generator is an ideal venue for the integration of various sensory and homeostatic cues that regulate reproductive functions. In this chapter we provide a historical perspective of the elegant science that sparked interest in the central mechanisms underlying the functions of the reproductive system, explain how hypotheses surrounding GnRH pulse generation have evolved and describe the current state of knowledge within the dynamic field of GnRH pulse generator research.

Ex vivo motility in the base of the rabbit caecum and its associated structures: an electrophysiological and spatiotemporal analysis.

We examined the coordination between contractile events at different sites in the basal portion of the rabbit caecum and its associated structures that were identified by electrophysiological recordings with simultaneous one-dimensional, and a novel two-dimensional, spatiotemporal mapping technique. The findings of this work provide evidence that the caecum and proximal colon/ampulla coli act reflexly to augment colonic outflow when the caecum is distended and mass peristalsis instituted, the action of the latter overriding the inherent rhythm and direction of haustral propagation in the adjacent portion of the proximal colon but not in the terminal ileum. Further, the findings suggest that the action of the sacculus rotundus may result from its distension with chyme by ileal peristalsis and that the subsequent propagation of contraction along the basal wall of the caecum towards the colon may be augmented by this local distension.

Respiratory, metabolic and cardiac functions are altered by disinhibition of subregions of the medial prefrontal cortex

The prefrontal cortex (PFC) is referred to as the visceral motor cortex; however, little is known about whether this region influences respiratory or metabolic outflows. The aim of this study was to describe simultaneous changes in respiratory, metabolic and cardiovascular functions evoked by disinhibition of the medial PFC (mPFC) and adjacent lateral septal nucleus (LSN). In urethane-anaesthetized rats, bicuculline methiodide was microinjected (2 mm; GABA-A receptor antagonist) into 90 sites in the mPFC at 0.72-4.00 mm from bregma. Phrenic nerve amplitude and frequency, arterial pressure, heart rate, splanchnic and lumbar sympathetic nerve activities (SNA), expired CO2, and core and brown adipose tissue temperatures were measured. Novel findings included disturbances to respiratory rhythm evoked from all subregions of the mPFC. Injections into the cingulate cortex evoked reductions in central respiratory function exclusively, whereas in ventral sites, particularly the infralimbic region, increases in respiratory drive and frequency, and metabolic and cardiac outflows were evoked. Disinhibition of sites in surrounding regions revealed that the LSN could evoke cardiovascular changes accompanied by distinct oscillations in SNA, as well as increases in respiratory amplitude. We show that activation of neurons within the mPFC and LSN influence respiratory, metabolic and cardiac outflows in a site-dependent manner. This study has implications with respect to the altered PFC neuronal activity seen in stress-related and mental health disorders, and suggests how basic physiological systems may be affected.

Cardiac Arrhythmias During Pregnancy

This article reviews the appropriate evaluation and management of cardiac arrhythmias in the pregnant patient. Any treatment strategy in this patient population has the inherent potential to adversely affect the health of the unborn child. As such, there is no room for empiric therapy in these patients. Adequate arrhythmia documentation is paramount, preferably by noninvasive means. The decision to treat should be based on symptom severity and the risk to both mother and fetus posed by potentially recurring arrhythmia episodes throughout the pregnancy. Minimal symptoms in the setting of a structurally normal heart call for a conservative approach. Less is better. If pharmacologic therapy is justified, drugs with historically demonstrated safety profiles in pregnancy should be tried first. The safety profiles of virtually all drugs used to treat cardiac arrhythmias during human pregnancy are based solely on an accumulation of past clinical experience. Newer antiarrhythmics therefore carry a largely unknown risk. Most inherent rhythm disorders manifest long before a woman reaches childbearing age. Women with previously diagnosed arrhythmias frequently experience a recurrence or worsening of their arrhythmia during the pregnancy. Counseling of these individuals and perhaps preemptive treatment by means such as arrhythmia ablation prior to a planned pregnancy would seem optimal.

On a standing wave Central Pattern Generator and the coherence problem

An electrophysiological phenomenon running up and down the spine, elicited by light pressure contact at very precise points and thereafter taking the external appearance of an undulatory motion of the spine, is analyzed from its standing wave, coherence, and synchronization-at-a-distance properties. This standing spinal wave can be elicited in both normal and quadriplegic subjects, which demonstrates that the neuronal circuitry is embedded in the spine. The latter, along with the inherent rhythmicity of the motion, its wave properties, and the absence of external sensory input once the phenomenon is elicited reveal a Central Pattern Generator (CPG). The major investigative tool is surface electromyographic (sEMG) wavelet signal analysis at various points along the paraspinal muscles. Statistical correlation among the various points is used to establish the standing wave phenomenon on a specific subband of the Daubechies wavelet decomposition of the sEMG signals. More precisely, ∼ 10 Hz coherent bursts reveal synchronization between sensory-motor loops at a distance larger, and a frequency slower, than those already reported. As a potential therapeutic application, it is shown that partial recovery from spinal cord injury can be assessed by the correlation between the sEMG signals on both sides of the injury.

The impact of altered climatic conditions and altitude on circadian physiology

Knowing the output of the “body clock” is fundamental to the science of chronobiology. As the clock resides within the suprachiasmatic nuclei, direct measurement is not feasible and therefore, characteristics of the clock are often inferred from the measurement of marker rhythms, one of which is core temperature. Core temperature is often the marker rhythm of choice due to ease of measurement, particularly in field conditions. However, if the output of the “body clock” is to be inferred from measurement of this variable, it is important to establish whether environmental conditions change or moderate the circadian rhythm of core temperature. Although the majority of circadian patterns do demonstrate independence from such exogenous influences, there does appear to be seasonal variation to their period. Given that humans can easily travel to environments of altered temperature and altitude, there is a need to ascertain the exact effect of such change on the rhythm of core temperature. This review will therefore outline the evidence that the circadian rhythm of core temperature is affected by ambient temperature and by hypoxia. Furthermore, the review will discuss whether these environmental factors act as zeitgebers (affecting the endogenous rhythm) or as masking influences of the inherent rhythm.

Heartbeat reversal after sectioning the dorsal vessel and removal of the brain of diapausing pupae of Manduca sexta (Lepidoptera: Sphingidae)

Reversal of heartbeat was monitored in vivo by noninvasive, multisensor, thermo-cardiographic and pulse-light, opto-cardiographic techniques. The dorsal vessel was sectioned at the beginning, in the middle and near the end of the abdomen. Changes in the heartbeat were simultaneously monitored in both the disconnected anterior and posterior sections of the heart. The results revealed the existence of a caudal regulatory cardiac centre located in the fused A7-A10 abdominal segments. Posterior sections, containing this terminal ampulla of the heart always exhibited a more or less normal heartbeat reversal, including both anterograde and retrograde pulsations. This shows that the forward-oriented as well as the reciprocal, backward-oriented peristaltic waves of the heart are both regulated from the posterior regulatory center, without involvement of the cephalic region. The cardiac pulsations in the anterior sections of the heart were paralysed and seriously impaired by the lesions. During the acute phase after the lesions, anterior sections showed only some convulsion-like, unidirectional, backward-oriented peristaltic pulsations of low frequency. Within one or two days after the lesions, isolated anterior sections of the heart developed a subsidiary heartbeat regulation associated with the oscillating, bi-directional peristaltic waves running alternatively, forward and backward in opposite directions. After a few days, the previously paralysed anterior sections of the heart were able to develop perfectly coordinated patterns of heartbeat reversal. At this time, the two asynchronous heartbeat patterns ran separately in each of the divided sections of the heart. One or two weeks later, reversal of the heartbeat occasionally occurred synchronously along the entire length of the dorsal vessel. Sectioning of the ventral nerve cord, removal of the cephalic nervous system (brain, frontal ganglion, suboesophageal ganglion and the associated nerves) or removal of the fused terminal abdominal ganglionic mass and adjacent caudal nerves, had no effect on the pattern of heartbeat reversal. These facts indicate that the pupal heart of M. sexta operates purely myogenically, like the human heart. The myogenic pacemakers of the caudal regulatory cardiac centre (analogous to the atrio-ventricular nodes of the human heart) are autonomous, generating inherent rhythmicity without intervention from the nervous system. Development of subsidiary pacemakers regulating rhythmicity in the lesioned myocardium and restitution of the synchronized contracting integrity between the two disconnected sections of the heart are new cardiological features, which merit further investigation.

Chronobiology of Alcohol: From Chronokinetics to Alcohol-related Alterations of the Circadian System

The development of concepts in chronobiology is intimately linked to studies on alcohol, as a number of these are based on chronobiological variations observed in the metabolism of ethanol. This concerns circadian differences in its metabolism (chronokinetics) and effects (chronoefficacy and chronotoxicity) and also inherent circadian rhythmicity in the sensitivity of target organs to its effects (chronesthesy). Chronobiologic discoveries are also fertile grounds for understanding the biological and psychotropic effects of alcohol. Confusing effects, which are difficult to explain by conventional homeostatic theory, are easy to understand when considered in the context of the concepts of chronopharmacology, and thereby uncovering new pathways of investigation. Beyond the studies that have elucidated the rhythm-dependent variation in ethanol, chronobiology is opening new explanatory pathways concerning the attributes of the alcohol withdrawal syndrome and effects of alcohol on the development of the central nervous system, particularly the development of the internal clock, and on the alcohol-dependency syndrome. The concepts of chronopharmacology and chronotoxicology are of equal importance to the fields of occupational medicine and industry medicine.

Mechanical aspects of heartbeat reversal in pupae of Manduca sexta

Pulsations of the dorsal vessel were investigated with new optocardiographic techniques based on the transmission and reflection of pulse-light through optic fibers. This noninvasive technique enabled simultaneous, in vivo multisensor recordings of the heartbeat without touching the pupal integument. There was a very regular heartbeat reversal with 3 distinctive phases: (a) a backward-oriented (retrograde) cardiac pulsation; (b) a forward-oriented (anterograde) pulsation with faster frequency; and (c) shorter or longer periods of temporary cardiac standstill that usually occurred after the termination of the anterograde phase. Occasionally, there were localized series of systolic cardiac contractions during the retrograde phase. Simultaneous recordings from the base and the tail of the abdomen revealed a reciprocal, “mirror image-like”, quantitative relationship. The most intensive anterograde hemolymph flow occurred at the base while the most intensive retrograde flow occurred at the tail of the abdomen. The bi-directional switchovers of heartbeat (reversal) were occasionally associated with modifications during each of the unidirectional cardiac phases. Anterograde peristalsis showed a 2-fold higher frequency of pulsation in the thoracic aorta in comparison with the posterior parts of the heart. Thus, in addition to the “odd” peristaltic waves originating at the tail, there were intercallated “even” peristaltic waves originating in the middle of the abdomen. Both of them propagated hemolymph through the thoracic aorta into the head; the first waves took the hemolymph in from the distal end, while the second sucked it from the middle of the abdomen. The use of multiple optocardiographic sensors also enabled detection of cardiac pulsations on the opposite, ventral side of the body, within the ventral perineural sinus. The ventral side of the head showed only the presence of an anterograde pulse, whereas the ventral side of the tail exhibited a strong reciprocal retrograde phase and a very weak anterograde phase. These results explain why the existence of a periodic heartbeat reversal should be essential for circulatory functions at both extremities of the cylindrical insect body. In diapausing pupae, regular cycles of heartbeat reversal were substituted by prolonged periods of anterograde pulsation during the entire duration of bursts of CO 2 release (average duration of the burst was 18–20 min, periodicity 5 to 18 h). The physiological nature of such feed-back correlation between heartbeat and metabolic CO 2 production is not yet clear, because the anterograde heartbeat could be also induced by a number of nonspecific factors unrelated to CO 2 (mechanical irritation, injury, injections, elevated temperature). During the postdiapause, developing pharate–adult stage, the correlation between CO 2 and anterograde heartbeat completely disappeared. It has been concluded that regulation of insect heartbeat represents a highly coordinated, myogenic stereotype with inherent rhythmicity, which can be modified by a number of external and internal factors.

The functional logic of cortico-pulvinar connections.

The pulvinar is an 'associative' thalamic nucleus, meaning that most of its input and output relationships are formed with the cerebral cortex. The function of this circuitry is little understood and its anatomy, though much investigated, is notably recondite. This is because pulvinar connection patterns disrespect the architectural subunits (anterior, medial, lateral and inferior pulvinar nuclei) that have been the traditional reference system. This article presents a simplified, global model of the organization of cortico-pulvinar connections so as to pursue their structure-function relationships. Connections between the cortex and pulvinar are topographically organized, and as a result the pulvinar contains a 'map' of the cortical sheet. However, the topography is very blurred. Hence the pulvinar connection zones of nearby cortical areas overlap, allowing indirect transcortical communication via the pulvinar. A general observation is that indirect cortico-pulvino-cortical circuits tend to mimic direct cortico-cortical pathways: this is termed 'the replication principle'. It is equally apt for certain pairs (or groups) of nearby cortical areas that happen not to connect with each other. The 'replication' of this non-connection is achieved by discontinuities and dislocations of the cortical topography within the pulvinar, such that the associated pair of connection zones do not overlap. Certain of these deformations can be used to divide the global cortical topography into specific sub-domains, which form the natural units of a connectional subdivision of the pulvinar. A substantial part of the pulvinar also expresses visual topography, reflecting visual maps in occipital cortex. There are just two well-ordered visual maps in the pulvinar, that both receive projections from area V1, and several other occipital areas; the resulting duplication of cortical topography means that each visual map also acts as a separate connection domain. In summary, the model identifies four topographically ordered connection domains, and reconciles the coexistence of visual and cortical maps in two of them. The replication principle operates at and below the level of domain structure. It is argued that cortico-pulvinar circuitry replicates the pattern of cortical circuitry but not its function, playing a more regulatory role instead. Thalamic neurons differ from cortical neurons in their inherent rhythmicity, and the pattern of cortico-thalamic connections must govern the formation of specific resonant circuits. The broad implication is that the pulvinar acts to coordinate cortical information processing by facilitating and sustaining the formation of synchronized trans-areal assemblies; a more pointed suggestion is that, owing to the considerable blurring of cortical topography in the pulvinar, rival cortical assemblies may be in competition to recruit thalamic elements in order to outlast each other in activity.

Physiology of the menstrual cycle.

The normal female life cycle is associated with a number of hormonal milestones: menarche, pregnancy, contraceptive use, menopause, and the use of replacement sex hormones. All these events and interventions alter the levels and cycling of sex hormones and may cause a change in the prevalence or intensity of headache. The menstrual cycle is the result of a carefully orchestrated sequence of interactions among the hypothalamus, pituitary, ovary, and endometrium, with the sex hormones acting as modulators and effectors at each level. Oestrogen and progestins have potent effects on central serotonergic and opioid neurons, modulating both neuronal activity and receptor density. The primary trigger of menstrual migraine appears to be the withdrawal of oestrogen rather than the maintenance of sustained high or low oestrogen levels. However, changes in the sustained oestrogen levels with pregnancy (increased) and menopause (decreased) appear to affect headaches. Headaches that occur with premenstrual syndrome appear to be centrally generated, involving the inherent rhythm of CNS neurons, including perhaps the serotonergic pain-modulating systems.