Rhythmic Oscillations Research Articles

Hippocampal network oscillations at the interplay between innate anxiety and learned fear.

The hippocampus plays a central role as a hub for episodic memory and as an integrator of multimodal sensory information in time and space. Thereby, it critically determines contextual setting and specificity of episodic memories. It is also a key site for the control of innate anxiety states and involved in psychiatric diseases with heightened anxiety and generalized fear memory such as post-traumatic stress disorder (PTSD). Expression of both innate "unlearned" anxiety and "learned" fear requires contextual processing and engagement of a brain-wide network including the hippocampus together with the amygdala and medial prefrontal cortex. Strikingly, the hippocampus is also the site of emergence of oscillatory rhythms that coordinate information processing and filtering in this network. Here, we review data on how the hippocampal network oscillations and their coordination with amygdalar and prefrontal oscillations are engaged in innate threat evaluation. We further explore how such innate oscillatory communication might have an impact on contextualization and specificity of "learned" fear. We illustrate the partial overlap of fear and anxiety networks that are built by the hippocampus in conjunction with amygdala and prefrontal cortex. We further propose that (mal)-adaptive interplay via (dis)-balanced oscillatory communication between the anxiety network and the fear network may determine the strength of fear memories and their resistance to extinction.

A detailed anatomical and mathematical model of the hippocampal formation for the generation of sharp-wave ripples and theta-nested gamma oscillations

The mechanisms underlying the broad variety of oscillatory rhythms measured in the hippocampus during the sleep-wake cycle are not yet fully understood. In this article, we propose a computational model of the hippocampal formation based on a realistic topology and synaptic connectivity, and we analyze the effect of different changes on the network, namely the variation of synaptic conductances, the variations of the CAN channel conductance and the variation of inputs. By using a detailed simulation of intracerebral recordings, we show that this is able to reproduce both the theta-nested gamma oscillations that are seen in awake brains and the sharp-wave ripple complexes measured during slow-wave sleep. The results of our simulations support the idea that the functional connectivity of the hippocampus, modulated by the sleep-wake variations in Acetylcholine concentration, is a key factor in controlling its rhythms.

On the resonant hydroelastic behaviour of ice shelves

Rhythmic hydroelastic oscillations of ice shelves are a key mechanism believed to affect several phenomena observed in Polar Regions, such as the disintegration of ice shelves due to ocean wave impact or even the formation of localised distinctive atmospheric waves. The fundamental and lower hydroelastic modes of an ice-shelf/sub-ice-shelf cavity configuration can be studied by coupling shallow water theory and flexure dynamics of a slender, floating, cantilever beam. A crucial aspect of the analysis is the selection of appropriate boundary conditions at the grounding line of the ice shelf and at the freely floating end. The present study aims to determine appropriate and realistic homogeneous boundary conditions for eigenproblems of resonant ice-shelf vibrations. Through the formulation and solution of a wave impact Reflection-Transmission problem, frequencies that maximise specific norms of the ice-shelf response are identified. It is established that homogeneous conditions on the sub-ice-shelf cavity wave potential value, applied at the front of an ice-shelf, produce eigenfrequencies that in general match the norm maximisation frequencies. The methodology is employed for the prediction of characteristic periods of the Ross and Larsen C ice shelves.

Lesion localization algorithm of high-frequency epileptic signal based on Teager energy operator

Abstract High-frequency oscillations reflect the abnormal brain electrical activity in patients with epilepsy. It is significant to research the relationship between high-frequency oscillation and epilepsy originating area for the diagnosis and treatment of epilepsy. In view of the identification of epileptic EEG and the location of epileptic foci, a localization algorithm based on Teager operator is proposed. Firstly, the original epileptic EEG data are preprocessed, the wavelet weighted threshold and the frequency notch method are used to denoise the original epileptic high frequency oscillation signal. Taking into account the frequency characteristics of the high frequency oscillating signal itself, the FIR (Finite Impulse Response) digital filter is used to filter the epileptic high-frequency oscillation signal. Secondly, because the high frequency oscillation rhythm has the characteristics of high frequency, high energy and low amplitude, the Teager energy operator and curve length method are used to extract the characteristics. The PSD (Power Spectral Density) method is applied to qualitative analysis of epileptic lesion location. Finally, the EMD (Empirical Mode Decomposition) algorithm is used to decompose the high-frequency oscillation signal. Combined with Teager energy operator, Teager-huang transform is used to analyze the signal by time-frequency energy analysis. Quantitative analysis of epileptic lesion location is made by using EMD energy entropy method for different lead epileptic signals. The algorithm can effectively locate the location of the focus, independent of individual parameters and high degree of automation. It has good clinical application prospects.

Large-scale structure and individual fingerprints of locally coupled sleep oscillations

Slow oscillations and sleep spindles, the canonical electrophysiological oscillations of nonrapid eye movement sleep, are thought to gate incoming sensory information, underlie processes of sleep-dependent memory consolidation, and are altered in various neuropsychiatric disorders. Accumulating evidence of the predominantly local expression of these individual oscillatory rhythms suggests that their cross-frequency interactions may have a similar local component. However, it is unclear whether locally coordinated sleep oscillations exist across the cortex, and whether and how these dynamics differ between fast and slow spindles, and sleep stages. Moreover, substantial individual variability in the expression of both spindles and slow oscillations raises the possibility that their temporal organization shows similar individual differences. Using two nights of multichannel electroencephalography recordings from 24 healthy individuals, we characterized the topography of slow oscillation-spindle coupling. We found that while slow oscillations are highly restricted in spatial extent, the phase of the local slow oscillation modulates local spindle activity at virtually every cortical site. However, coupling dynamics varied with spindle class, sleep stage, and cortical region. Moreover, the slow oscillation phase at which spindles were maximally expressed differed markedly across individuals while remaining stable across nights. These findings both add an important spatial aspect to our understanding of the temporal coupling of sleep oscillations and demonstrate the heterogeneity of coupling dynamics, which must be taken into account when formulating mechanistic accounts of sleep-related memory processing.

Polarity-dependent modulation of multi-spectral neuronal activity by transcranial direct current stimulation

The ability to preferentially deploy neural resources to the visual space is an important component of normative cognitive function, however, the population-level cortical dynamics that sub-serve this ability are not fully understood. Specifically, rhythmic activity in the occipital cortices (e.g., theta, alpha, and gamma oscillations) has been strongly implicated in this cognitive process, but these neural responses are difficult to non-invasively manipulate in a systematic manner. In this study, transcranial direct-current stimulation (tDCS) was used to modulate brain activity, while high-density magnetoencephalography (MEG) was employed to quantify changes in rhythm-specific neural activity in the occipital cortices of 57 adults performing a visuospatial processing paradigm. All MEG data was analyzed using advanced source reconstruction and oscillatory analysis methods. Our results indicated that basal levels of occipital alpha activity were increased by an occipital-anodal/supraorbital-cathodal tDCS montage, while basal gamma levels in the same cortices were decreased by tDCS using the same montage with its polarity reversed (occipital-cathodal/supraorbital-anodal). In other words, stimulation with the occipital-anodal montage increased local spontaneous alpha (10–16 Hz) activity, while stimulation with the occipital-cathodal montage selectively decreased local gamma (64–90 Hz) activity. Neither polarity affected stimulus-induced oscillations in the alpha or gamma range. Additionally, these modulations strongly predicted the subsequent formation of fronto-visual functional connectivity within distinct oscillatory rhythms, as well as behavior on the visuospatial discrimination task. These findings provide insight into the multifaceted effects of tDCS on cortical activity, as well as the dynamic oscillatory coding of salient information in the human brain.

Anticonvulsant and Neuroprotective Effects of Cannabidiol During the Juvenile Period.

Anticonvulsant effects of cannabidiol (CBD), a nonpsychoactive cannabinoid, have not been investigated in the juvenile brain. We hypothesized that CBD would attenuate epileptiform activity at an age when the brain first becomes vulnerable to neurotoxicity and social/cognitive impairments. To induce seizures, kainic acid (KA) was injected either into the hippocampus (KAih) or systemically (KAip) on postnatal (P) day 20. CBD was coadministered (KA + CBDih, KA + CBDip) or injected 30 minutes postseizure onset (KA/CBDih, KA/CBDip). Hyperactivity, clonic convulsions, and electroencephalogram rhythmic oscillations were attenuated or absent after KA + CBDih and reduced after KA + CBDip. NeuN immunohistochemistry revealed neuroprotection. Augmented reactive glia number and expression were reversed in CA1 but persisted deep within the dentate hilus. Parvalbumin-positive (PV+) interneurons were reduced in both models, whereas immunolabeling was dramatically increased within ipsilateral and contralateral dendritic/neuropilar fields following KA + CBDih. Cannabinoid receptor 1 (CB1) expression was minimally affected after KAih contrasting elevations observed after KAip. Intracranial coadministration data suggest that CBD has higher efficacy in epilepsy with hippocampal focus rather than when extrahippocampal amygdala/cortical structures are triggered by systemic treatments. Inhibition of surviving PV+ and CB1+ interneurons may be facilitated by CBD implying a protective role in regulating hippocampal seizures and neurotoxicity at juvenile ages.

Tremor in motor neuron disease may be central rather than peripheral in origin.

Motor neuron disease (MND) refers to a spectrum of degenerative diseases affecting motor neurons. Recent clinical and post-mortem observations have revealed considerable variability in the phenotype. Rhythmic involuntary oscillations of the hands during action, resembling tremor, can occur in MND, but their pathophysiology has not yet been investigated. A total of 120 consecutive patients with MND were screened for tremor. Twelve patients with action tremor and no other movement disorders were found. Ten took part in the study. Tremor was recorded bilaterally using surface electromyography (EMG) and triaxial accelerometer, with and without a variable weight load. Power spectra of rectified EMG and accelerometric signal were calculated. To investigate a possible cerebellar involvement, eyeblink classic conditioning was performed in five patients. Action tremor was present in about 10% of our population. All patients showed distal postural tremor of low amplitude and constant frequency, bilateral with a small degree of asymmetry. Two also showed simple kinetic tremor. A peak at the EMG and accelerometric recordings ranging from 4 to 12 Hz was found in all patients. Loading did not change peak frequency in either the electromyographic or accelerometric power spectra. Compared with healthy volunteers, patients had a smaller number of conditioned responses during eyeblink classic conditioning. Our data suggest that patients with MND can present with action tremor of a central origin, possibly due to a cerebellar dysfunction. This evidence supports the novel idea of MND as a multisystem neurodegenerative disease and that action tremor can be part of this condition.

Coexistence of scale-invariant and rhythmic behavior in self-organized criticality.

Scale-free behavior as well as oscillations are frequently observed in the activity of many natural systems. One important example is the cortical tissues of mammalian brain where both phenomena are simultaneously observed. Rhythmic oscillations as well as critical (scale-free) dynamics are thought to be important, but theoretically incompatible, features of a healthy brain. Motivated by the above, we study the possibility of the coexistence of scale-free avalanches along with rhythmic behavior within the framework of self-organized criticality. In particular, we add an oscillatory perturbation to local threshold condition of the continuous Zhang model and characterize the subsequent activity of the system. We observe regular oscillations embedded in well-defined avalanches which exhibit scale-free size and duration in line with observed neuronal avalanches. The average amplitude of such oscillations are shown to decrease with increasing frequency consistent with real brain oscillations. Furthermore, it is shown that optimal amplification of oscillations occur at the critical point, further providing evidence for functional advantages of criticality.

Astrocytic modulation of cortical oscillations

Brain waves are rhythmic voltage oscillations emerging from the synchronization of individual neurons into a neuronal network. These oscillations range from slow to fast fluctuations, and are classified by power and frequency band, with different frequency bands being associated with specific behaviours. It has been postulated that at least ten distinct mechanisms are required to cover the frequency range of neural oscillations, however the mechanisms that gear the transition between distinct oscillatory frequencies are unknown. In this study, we have used electrophysiological recordings to explore the involvement of astrocytic K+ clearance processes in modulating neural oscillations at both network and cellular levels. Our results indicate that impairment of astrocytic K+ clearance capabilities, either through blockade of K+ uptake or astrocytic connectivity, enhance network excitability and form high power network oscillations over a wide range of frequencies. At the cellular level, local increases in extracellular K+ results in modulation of the oscillatory behaviour of individual neurons, which underlies the network behaviour. Since astrocytes are central for maintaining K+ homeostasis, our study suggests that modulation of their inherent capabilities to clear K+ from the extracellular milieu is a potential mechanism to optimise neural resonance behaviour and thus tune neural oscillations.

Rhythmic activities of the brain: Quantifying the high complexity of beta and gamma oscillations during visuomotor tasks.

Electroencephalography (EEG) signals depict the electrical activity that takes place at the surface of the brain and provide an important tool for understanding a variety of cognitive processes. The EEG is the product of synchronized activity of the brain, and variations in EEG oscillations patterns reflect the underlying changes in neuronal synchrony. Our aim is to characterize the complexity of the EEG rhythmic oscillations bands when the subjects perform a visuomotor or imagined cognitive tasks (imagined movement), providing a causal mapping of the dynamical rhythmic activities of the brain as a measure of attentional investment. We estimate the intrinsic correlational structure of the signals within the causality entropy-complexity plane H×C, where the enhanced complexity in the gamma 1, gamma 2, and beta 1 bands allows us to distinguish motor-visual memory tasks from control conditions. We identify the dynamics of the gamma 1, gamma 2, and beta 1 rhythmic oscillations within the zone of a chaotic dissipative behavior, whereas in contrast the beta 2 band shows a much higher level of entropy and a significant low level of complexity that correspond to a non-invertible cubic map. Our findings enhance the importance of the gamma band during attention in perceptual feature binding during the visuomotor/imagery tasks.

γ-Aminobutyric Acid Type A Receptor Potentiation Inhibits Learning in a Computational Network Model.

Propofol produces memory impairment at concentrations well below those abolishing consciousness. Episodic memory, mediated by the hippocampus, is most sensitive. Two potentially overlapping scenarios may explain how γ-aminobutyric acid receptor type A (GABAA) potentiation by propofol disrupts episodic memory-the first mediated by shifting the balance from excitation to inhibition while the second involves disruption of rhythmic oscillations. We use a hippocampal network model to explore these scenarios. The basis for these experiments is the proposal that the brain represents memories as groups of anatomically dispersed strongly connected neurons. A neuronal network with connections modified by synaptic plasticity was exposed to patterned stimuli, after which spiking output demonstrated evidence of stimulus-related neuronal group development analogous to memory formation. The effect of GABAA potentiation on this memory model was studied in 100 unique networks. GABAA potentiation consistent with moderate propofol effects reduced neuronal group size formed in response to a patterned stimulus by around 70%. Concurrently, accuracy of a Bayesian classifier in identifying learned patterns in the network output was reduced. Greater potentiation led to near total failure of group formation. Theta rhythm variations had no effect on group size or classifier accuracy. Memory formation is widely thought to depend on changes in neuronal connection strengths during learning that enable neuronal groups to respond with greater facility to familiar stimuli. This experiment suggests the ability to form such groups is sensitive to alteration in the balance between excitation and inhibition such as that resulting from administration of a γ-aminobutyric acid-mediated anesthetic agent.

1/f electrophysiological spectra in resting and drug-induced states can be explained by the dynamics of multiple oscillatory relaxation processes

Neurophysiological recordings are dominated by arhythmical activity whose spectra can be characterised by power-law functions, and on this basis are often referred to as reflecting scale-free brain dynamics (1/fβ). Relatively little is known regarding the neural generators and temporal dynamics of this arhythmical behaviour compared to rhythmical behaviour. Here we used Irregularly Resampled AutoSpectral Analysis (IRASA) to quantify β, in both the high (5–100 Hz, βhf) and low frequency bands (0.1–2.5 Hz, βlf) in MEG/EEG/ECoG recordings and to separate arhythmical from rhythmical modes of activity, such as, alpha rhythms. In MEG/EEG/ECoG data, we demonstrate that oscillatory alpha power dynamically correlates over time with βhf and similarly, participants with higher rhythmical alpha power have higher βhf. In a series of pharmaco-MEG investigations using the GABA reuptake inhibitor tiagabine, the glutamatergic AMPA receptor antagonist perampanel, the NMDA receptor antagonist ketamine and the mixed partial serotonergic agonist LSD, a variety of effects on both βhf and βlf were observed. Additionally, strong modulations of βhf were seen in monkey ECoG data during general anaesthesia using propofol and ketamine. We develop and test a unifying model which can explain, the 1/f nature of electrophysiological spectra, their dynamic interaction with oscillatory rhythms as well as the sensitivity of 1/f activity to drug interventions by considering electrophysiological spectra as being generated by a collection of stochastically perturbed damped oscillators having a distribution of relaxation rates.

Vasomotion as an oscillatory sign of functional impairment in the human internal thoracic artery: A study based on risk factors and vessel reactivity.

What is the central question of this study? Vasomotion has been viewed as a rhythmic oscillation of the vascular tone that is physiologically important for optimal tissue perfusion. Also, it has been studied primarily in the microcirculation. However, the precise underlying mechanisms and the physiological significance remain unknown. What is the main finding and its importance? Vasomotion is not specific to the microcirculation, as shown by our findings. In human arteries from patients undergoing cardiac surgery, an increased incidence was associated with endothelial dysfunction settings. Therefore, this oscillatory behaviour might be a signal of functional impairment and not of integrity. Vasomotion has been defined as the rhythmic oscillation of the vascular tone, involved in the control of the blood flow and subsequent tissue perfusion. Our aims were to study the incidence of vasomotion in the human internal thoracic artery and the correlation of this phenomenon with the clinical profile and parameters of vascular reactivity. In our study, vasomotion was elicited with a single-dose contractile stimulation of noradrenaline (10μm) in internal thoracic artery segments, from patients undergoing coronary artery bypass grafting, mounted in tissue organ bath chambers. The incidence was 29.1%. Vessel samples with vasomotion presented significantly higher contractility in response to both potassium chloride (maximal response or Emax of 7.65±5.81mN versus 4.52±3.73mN in control vessels, P=0.024) and noradrenaline (Emax of 7.60±5.93mN versus 2.96±4.41mN in control vessels, P<0.001). Predictive modelling through multivariable logistic regression analysis showed that female sex (odds ratio=9.82) and increasing maximal response to noradrenaline (odds ratio=1.19, per 1mN increase) were associated with a higher probability of the occurrence of vasomotion, whereas increasing kidney function (expressed as estimated glomerular filtration rate) was associated with a lower probability (odds ratio=0.97, per 1mlmin-1 (1.73m)-2 ]. Our results provide a characterization of the phenomenon of vasomotion in the internal thoracic artery and suggest that vasomotion might be associated with endothelial dysfunction settings, as determined by a multivariable analysis approach. Considering the associations observed in our results, vasomotion might be a signal of functional impairment and not of integrity.

Особенности ритмической активности головного мозга при заболеваниях глаз

Objective. The bioelectric activity of the brain was studied in 80 patients with various diseases of the organ of vision (glaucoma, myopia, age-related macular dystrophy, cataracts). Methods. The study was conducted with electroencephalograph 'Neuron-spectr-1' with the use of specialized package of applications on spectral analysis of human brain rhythmic activity for usage in medicine to early diagnose pathology of internal organs. It was used the technology of recording the global brain rhythmic activity with narrow-band filtering and a long summation time with predominantly long-term current rhythmic oscillations in the frequency spectrum ranging from 0.1 to 30 Hz. Results. In case of a primary open angle glaucoma and macular dystrophy we observed a general pattern of 'pathological' activity predominantly in frequency spectra of autonomic receptors. This is the evidence of the activation of local sympathetic and suppression of parasympathetic tonus. Changes of brain rhythmic activity were detected in patients with low degree myopia; they characterized the state of a-ad re no receptors and M-cho-linergic receptors of the ciliary muscle of the eye. Patients with initial age-related cataracts were dominated by low-frequency processes in the projection segments of the eye. Conclusions. Features of bioelectrical brain activity revealed in glaucoma, macular dystrophy, myopia, and cataracts can be a basis for development of additional criteria of screening diagnostics of early stages of eye diseases.

Light exposure influences the diurnal oscillation of gut microbiota in mice

The gut microbiota exhibit diurnal compositional and functional oscillations that influence the host homeostasis. However, the upstream factors that affect the microbial oscillations remain elusive. Here, we focused on the potential impact of light exposure, the main factor that affects the host circadian oscillation, on the diurnal oscillations of intestinal microflora to explore the upstream factor that governs the fluctuations of the gut microbes. The gut microbiota of the mice that were underwent regular light/dark (LD) cycles exhibited a robust rhythm at both compositional and functional level, in all parts of the intestine. Comparably, constant darkness (Dark-Dark, DD) led to the loss of the rhythmic oscillations in almost all parts of the intestine. Additionally, the abundance of Clostridia in DD conditions was dramatically enhanced in the small intestine. Our data indicated light exposure is the upstream factor that governs the regular diurnal fluctuations of gut microbiota in vivo.

S128. Oscillatory responses evoked by single-pulse electrical stimulation in human cerebral cortex – A Cortico-Cortical Evoked Potential (CCEP) study

Introduction Human brain operates with oscillatory activity in different frequency bands. For example, mu rhythm is well known as an idling rhythm observed in the central area related to motor function. We observed some rhythmic pattern in the averaged waveforms in the CCEP investigation (called “oscillatory response” here), which is originally a method to trace connectivity by single electrical pulse stimulation. We report on the frequency and distribution of the oscillatory responses in CCEP. Methods Subjects are 5 intractable epilepsy patients who underwent chronic implantation of subdural electrodes for presurgical evaluation. Written informed consents were obtained from all subjects. Single-pulse stimuli (0.3 ms, 8–10 mA, alternating polarity, 30 × 2 trials) were applied through two adjacent electrodes (52.8 ± 15.3 stimulus sites per patient). CCEP was recorded from subdural electrodes (105.2 ± 31.8 electrodes per patient) placed on the lateral and medial aspect of the cerebral hemisphere. Lateral fronto-parietal area was covered in all subjects. An oscillatory response in CCEP was detected by visual inspection on the averaged waveform according to the following criteria; (1) it has at least two pairs of peak and trough spaced equally, (2) it can be overlapped with other evoked responses (typical N1/ N2 response). If more than one rhythms with different frequencies were observed in the same electrode, we counted the largest one in amplitude. Results Totally, 2362 oscillatory responses (7.9%) were detected in 29891 observations in 5 subjects, including 443 alpha-band responses (7.5–13.5 Hz), 312 beta-band responses (13.5–30 Hz) and 1505 theta-band responses (3.5–7.5 Hz). Theta rhythm was observed predominantly in the temporal lobe including the basal temporal area (the occurrence rate was 12.45%). Alpha rhythm was observed more often in the parietal lobe including the postcentral gyrus (the occurrence rate was 4.57%), while beta rhythm was often observed around precentral gyrus (the occurrence rate was 1.98%). The frequency of the resting rhythmic activity was equal to that of oscillatory CCEP response in the alpha band in the postcentral gyrus in all subjects. This alpha activity was considered as mu rhythm in all the 3 subjects who performed a hand grasping task. Conclusion Single pulse electrical stimulation evoked oscillatory CCEP responses preferentially in the temporal lobe and the perirolandic area. The correspondence of frequency between the oscillatory response and mu rhythm implies the phase resetting of the physiological oscillation by exogenous input. This unique oscillatory CCEP may help to map these functionally important cortical regions.

Comparative Evaluation of Heart Rate Variability Based on the Data of ECG and Blood Pressure Measurements

The development of new approaches to the assessment of heart rate variability (HRV) is an important problem, since HRV reflects the functioning of cardiovascular control and is affected by various diseases. The purpose of this study was to evaluate the informative value of statistical and spectral HRV parameters calculated from pulse interval (PI) data of blood pressure as compared with those calculated from RR-interval data of electrocardiograms (ECG). We recorded ECG in conscious rats using skin adhesive electrodes simultaneously with blood pressure signal obtained through a catheter in the femoral artery. It has been found that the PI sequence can be used to calculate the statistical HRV indices that describe the HRV at time intervals about 1 min or longer, but statistical indices of the PI and RR intervals may differ in the analysis of beat-tobeat variations. The power spectra of the RR intervals and PI coincide in the low-frequency region, including the band of baroreflex cardiac rhythm oscillation. However, they can differ in the high-frequency region (at respiration frequency and above).

Asymmetric distribution and spatial switching of dynein activity generates ciliary motility.

Motile cilia and flagella are essential, highly conserved organelles, and their motility is driven by the coordinated activities of multiple dynein isoforms. The prevailing "switch-point" hypothesis posits that dyneins are asymmetrically activated to drive flagellar bending. To test this model, we applied cryo-electron tomography to visualize activity states of individual dyneins relative to their locations along beating flagella of sea urchin sperm cells. As predicted, bending was generated by the asymmetric distribution of dynein activity on opposite sides of the flagellum. However, contrary to predictions, most dyneins were in their active state, and the smaller population of conformationally inactive dyneins switched flagellar sides relative to the bending direction. Thus, our data suggest a "switch-inhibition" mechanism in which force imbalance is generated by inhibiting, rather than activating, dyneins on alternating sides of the flagellum.

Switching how to make flagella beat

Cilia and Flagella Motile cilia and flagella are hairlike cellular appendages that power the movement of individual cells or liquid across tissues, as exemplified by the cilia found in airways. The question of how they move in rhythmic oscillations has puzzled scientists for centuries. Lin and Nicastro used cryo–electron tomography (cryo-ET) to visualize the activity states of individual dynein motors with respect to their locations within beating flagella. They observed an asymmetric distribution of dynein activity and the switching of conformations of dyneins and their regulators between opposite sides of active flagella. The results confirm the switching aspect of the prevailing “switch-point” hypothesis but change the view with respect to how dynein activities are coordinated to drive flagellar motility. Science , this issue p. [eaar1968][1] [1]: /lookup/doi/10.1126/science.aar1968