Modulation Of Oscillations Research Articles

Regulating synchronous oscillations of cerebellar granule cells by different types of inhibition.

Synchronous oscillations in neural populations are considered being controlled by inhibitory neurons. In the granular layer of the cerebellum, two major types of cells are excitatory granular cells (GCs) and inhibitory Golgi cells (GoCs). GC spatiotemporal dynamics, as the output of the granular layer, is highly regulated by GoCs. However, there are various types of inhibition implemented by GoCs. With inputs from mossy fibers, GCs and GoCs are reciprocally connected to exhibit different network motifs of synaptic connections. From the view of GCs, feedforward inhibition is expressed as the direct input from GoCs excited by mossy fibers, whereas feedback inhibition is from GoCs via GCs themselves. In addition, there are abundant gap junctions between GoCs showing another form of inhibition. It remains unclear how these diverse copies of inhibition regulate neural population oscillation changes. Leveraging a computational model of the granular layer network, we addressed this question to examine the emergence and modulation of network oscillation using different types of inhibition. We show that at the network level, feedback inhibition is crucial to generate neural oscillation. When short-term plasticity was equipped on GoC-GC synapses, oscillations were largely diminished. Robust oscillations can only appear with additional gap junctions. Moreover, there was a substantial level of cross-frequency coupling in oscillation dynamics. Such a coupling was adjusted and strengthened by GoCs through feedback inhibition. Taken together, our results suggest that the cooperation of distinct types of GoC inhibition plays an essential role in regulating synchronous oscillations of the GC population. With GCs as the sole output of the granular network, their oscillation dynamics could potentially enhance the computational capability of downstream neurons.

Intensity distribution, evolution, and dispersion of discrete spin wave modes in nanoscale spin-torque oscillator

Spin wave dynamics form the foundation of spin-torque oscillator (STO) modulation. In addition to the uniform spin wave mode with wave vector k = 0, multiple spin wave modes with different wave vectors and frequencies coexist in the nanoscale STO. To characterize these spin wave modes and the interactions between them, the distribution and evolution of spin wave intensity in k space need to be investigated together with spin wave dispersion of the individual mode, stressing energy degeneracy. To this end, using micromagnetic simulation, we studied the dynamics of the discrete spin wave modes in a nanoscale STO with structure enhancing spin wave propagation. Simulation using the object oriented micromagnetic framework demonstrated that although they were generated with different spin currents, spin wave modes evolved similarly in k space, according to the wave vector. Furthermore, magnetization pinning at the corners of yttrium iron garnet led to two-magnon scattering. This interaction affects spin wave dynamics in two ways: multivalued dispersion occurs with two-magnon scattering and the uniform mode can become weaker than the near-uniform modes (spin wave modes with wave vector close to zero) in the strong excitation region. The latter phenomenon is supported by the results of studies on the spin wave dispersion of the individual mode, which demonstrate the energy degeneracy between the uniform mode and the near-uniform modes.

Cholinergic-Induced Specific Oscillations in the Medial Prefrontal Cortex to Reverse Propofol Anesthesia.

General anesthesia is a drug-induced reversible state comprised of altered states of consciousness, amnesia, analgesia, and immobility. The medial frontal cortex (mPFC) has been discovered to modulate the level of consciousness through cholinergic and glutamatergic pathways. The optogenetic tools combined with in vivo electrophysiological recording were used to study the neural oscillatory modulation mechanisms in mPFC underlying the loss of consciousness (LOC) and emergence. We found that optogenetic activation of both cholinergic and glutamatergic neurons in the basal forebrain (BF) reversed the hypnotic effect of propofol and accelerated the emergence from propofol-induced unconsciousness. The cholinergic light-activation during propofol anesthesia increased the power in the β (12–20 Hz) and low γ (20–30 Hz) bands. Conversely, glutamatergic activation increased the power at less specific broad (1–150 Hz) bands. The cholinergic-induced alteration to specific power bands after LOC had opposite effects to that of propofol. These results suggested that the cholinergic system might act on more specific cortical neural circuits related to propofol anesthesia.

Transcranial alternating current stimulation entrains alpha oscillations by preferential phase synchronization of fast-spiking cortical neurons to stimulation waveform

Computational modeling and human studies suggest that transcranial alternating current stimulation (tACS) modulates alpha oscillations by entrainment. Yet, a direct examination of how tACS interacts with neuronal spiking activity that gives rise to the alpha oscillation in the thalamo-cortical system has been lacking. Here, we demonstrate how tACS entrains endogenous alpha oscillations in head-fixed awake ferrets. We first show that endogenous alpha oscillations in the posterior parietal cortex drive the primary visual cortex and the higher-order visual thalamus. Spike-field coherence is largest for the alpha frequency band, and presumed fast-spiking inhibitory interneurons exhibit strongest coupling to this oscillation. We then apply alpha-tACS that results in a field strength comparable to what is commonly used in humans (<0.5 mV/mm). Both in these ferret experiments and in a computational model of the thalamo-cortical system, tACS entrains alpha oscillations by following the theoretically predicted Arnold tongue. Intriguingly, the fast-spiking inhibitory interneurons exhibit a stronger entrainment response to tACS in both the ferret experiments and the computational model, likely due to their stronger endogenous coupling to the alpha oscillation. Our findings demonstrate the in vivo mechanism of action for the modulation of the alpha oscillation by tACS.

Changes in theta and alpha oscillatory signatures of attentional control in older and middle age.

Recent behavioural research has reported age-related changes in the costs of refocusing attention from a temporal (rapid serial visual presentation) to a spatial (visual search) task. Using magnetoencephalography, we have now compared the neural signatures of attention refocusing between three age groups (19-30, 40-49 and 60+ years) and found differences in task-related modulation and cortical localisation of alpha and theta oscillations. Efficient, faster refocusing in the youngest group compared to both middle age and older groups was reflected in parietal theta effects that were significantly reduced in the older groups. Residual parietal theta activity in older individuals was beneficial to attentional refocusing and could reflect preserved attention mechanisms. Slowed refocusing of attention, especially when a target required consolidation, in the older and middle-aged adults was accompanied by a posterior theta deficit and increased recruitment of frontal (middle-aged and older groups) and temporal (older group only) areas, demonstrating a posterior to anterior processing shift. Theta but not alpha modulation correlated with task performance, suggesting that older adults' stronger and more widely distributed alpha power modulation could reflect decreased neural precision or dedifferentiation but requires further investigation. Our results demonstrate that older adults present with different alpha and theta oscillatory signatures during attentional control, reflecting cognitive decline and, potentially, also different cognitive strategies in an attempt to compensate for decline.

Dynamics of interacting Airy beams in the fractional Schrödinger equation with a linear potential

We investigate analytically and numerically the dynamics of interacting Airy beams in the fractional Schrödinger equation with a linear potential. It is shown that, for interaction of two Airy beams without the potential, the two components continue to diffract after collision when the Lévy index α=2, while symmetric splitting discrete diffraction-free beams are formed in the limiting case α=1. With increasing the beams interval, the two main peaks split into four stronger diffraction-free beams, and there exist diffraction-free beams with weaker intensity between the two adjacent stronger diffraction-free beams for initial negative interval. If the external linear potential is considered, the interacting Airy beams exhibit a periodical modulated oscillation with a zigzag trajectory during propagation. The period is proportional to the absolute value of the potential depth coefficient. The propagation trajectory of the beams changes gradually from linear to parabolic when the Lévy index increases. The propagation features of three interacting Airy beams are the same as that of two interacting Airy beams, but the propagation modes are different.

Differential Contributions of Inhibitory Subnetwork to Visual Cortical Modulations Identified via Computational Model of Working Memory.

Extrastriate visual neurons show no firing rate change during a working memory (WM) task in the absence of sensory input, but both αβ oscillations and spike phase locking are enhanced, as is the gain of sensory responses. This lack of change in firing rate is at odds with many models of WM, or attentional modulation of sensory networks. In this article we devised a computational model in which this constellation of results can be accounted for via selective activation of inhibitory subnetworks by a top-down working memory signal. We confirmed the model prediction of selective inhibitory activation by segmenting cells in the experimental neural data into putative excitatory and inhibitory cells. We further found that this inhibitory activation plays a dual role in influencing excitatory cells: it both modulates the inhibitory tone of the network, which underlies the enhanced sensory gain, and also produces strong spike-phase entrainment to emergent network oscillations. Using a phase oscillator model we were able to show that inhibitory tone is principally modulated through inhibitory network gain saturation, while the phase-dependent efficacy of inhibitory currents drives the phase locking modulation. The dual contributions of the inhibitory subnetwork to oscillatory and non-oscillatory modulations of neural activity provides two distinct ways for WM to recruit sensory areas, and has relevance to theories of cortical communication.

Modulation of sensorimotor cortical oscillations in athletes with yips

The yips, an involuntary movement impediment that affects performance in skilled athletes, is commonly described as a form of task-specific focal dystonia or as a disorder lying on a continuum with focal dystonia at one end (neurological) and chocking under pressure at the other (psychological). However, its etiology has been remained to be elucidated. In order to understand sensorimotor cortical activity associated with this movement disorder, we examined electroencephalographic oscillations over the bilateral sensorimotor areas during a precision force task in athletes with yips, and compared them with age-, sex-, and years of experience-matched controls. Alpha-band event-related desynchronization (ERD), that occurs during movement execution, was greater in athlete with yips as compared to controls when increasing force output to match a target but not when adjusting the force at around the target. Event-related synchronization that occurs after movement termination was also greater in athletes with yips. There was no significant difference in task performance between groups. The enhanced ERD is suggested to be attributed to dysfunction of inhibitory system or increased allocation of attention to the body part used during the task. Our findings indicate that sensorimotor cortical oscillatory response is increased during movement initiation in athletes with yips.

Delta oscillation underlies the interictal spike changes after repeated transcranial direct current stimulation in a rat model of chronic seizures

BackgroundTranscranial direct current stimulation (tDCS) provides a noninvasive polarity-specific constant current to treat epilepsy, through a mechanism possibly involving excitability modulation and neural oscillation. ObjectiveTo determine whether EEG oscillations underlie the interictal spike changes after tDCS in rats with chronic spontaneous seizures. MethodsRats with kainic acid-induced spontaneous seizures were subjected to cathodal tDCS or sham stimulation for 5 consecutive days. Video-EEG recordings were collected immediately pre- and post-stimulation and for the subsequent 2 weeks following stimulation. The acute pre-post stimulation and subacute follow-up changes of interictal spikes and EEG oscillations in tDCS-treated rats were compared with sham. Ictal EEG with seizure behaviors, hippocampal brain-derived neurotrophic factor (BDNF) protein expression, and mossy fiber sprouting were compared between tDCS and sham rats. ResultsInterictal spike counts were reduced immediately following tDCS with augmented delta and diminished beta and gamma oscillations compared with sham. Cathodal tDCS also enhanced delta oscillations in normal rats. However, increased numbers of interictal spikes with a decrease of delta and theta oscillations were observed in tDCS-treated rats compared with sham during the following 2 weeks after stimulation. Resuming tDCS suppressed the increase of interictal spike activity. In tDCS rats, hippocampal BDNF protein expression was decreased while mossy fiber sprouting did not change compared with sham. ConclusionsThe inverse relationship between the changes of delta oscillation and interictal spikes during tDCS on and off stimulation periods indicates that an enhanced endogenous delta oscillation underlies the tDCS inhibitory effect on epileptic excitability.

New methods for oscillation analyses push new theories of discrete cognition.

Classical ways of analyzing neural time series data has led to static views on cognition, in which the cognitive processes are linked to sustained neural activity and interpreted as stationary states. The core analytical focus was on slow power modulations of neural oscillations averaged across many experimental trials. Whereas this custom analytical approach reduces the complexity and increases the signal-to-noise ratio, it may disregard or even remove important aspects of the underlying neural dynamics. Novel analysis methods investigate the instantaneous frequency and phase of neural oscillations and relate them to the precisely controlled timing of brief successive sensory stimuli. This enables to capture how cognitive processes unfold in discrete windows within and across oscillatory cycles. Moreover, several recent studies analyze the oscillatory power modulations on single experimental trials. They suggest that the power modulations are packed into discrete bursts of activity, which occur at different rates and times, and with different durations from trial-to-trial. Here, we review the current work that made use of these methodological advances for neural oscillations. These novel analysis perspectives emphasize that cognitive processes occur in discrete time windows, instead of sustained, stationary states. Evidence for discretization was observed for the entire range of cognitive functions from perception and attention to working memory, goal-directed thought and motor actions, as well as throughout the entire cortical hierarchy and in subcortical regions. These empirical observations create demand for new psychological theories and computational models of cognition in the brain, which integrate its discrete temporal dynamics.

Studies of a modulated Hall thruster

A typical Hall thruster is powered from a DC power supply and operates with a constant discharge voltage. In operation, the discharge current is subject to strong low frequency oscillations (so-called breathing oscillations). Recent studies have shown that not only can these breathing oscillations be correlated with improved performance, but these oscillations can be induced and controlled by modulating the anode voltage. In this work, a systematic experimental study of the plasma flow in a modulated cylindrical Hall thruster was performed to characterize the effect of natural and modulated breathing oscillations on thruster performance. Measurements suggest that modulating the anode voltage in resonance with the natural breathing frequency does increase the thrust, but a corresponding phase alignment of discharge current and discharge voltage causes the efficiency gains to be insignificant. In addition, the outward shift of the acceleration region causes the plasma plume divergence to increase at the resonance condition and thereby, limit the thrust increase. Mechanisms underlying the relative phase between discharge current, ion current, and discharge voltage are investigated experimentally and corroborated with one-dimensional hybrid simulations of the thruster discharge.

Complexity-Dependent Modulations of Beta Oscillations for Verbal and Nonverbal Movements

Purpose The planning and execution of motor behaviors require coordination of neurons that are established through synchronization of neural activity. Movements are typically preceded by event-related desynchronization (ERD) in the beta range (15-30 Hz) primarily localized in the motor cortex, while movement onset is associated with event-related synchronization (ERS). It is hypothesized that ERD is important for movement preparation and execution, and ERS serves to inhibit movement and update the motor plan. The primary objective of this study was to determine to what extent movement-related oscillatory brain patterns (ERD and ERS) during verbal and nonverbal tasks may be affected differentially by variations in task complexity. Method Seventeen right-handed adult participants (nine women, eight men; M age = 25.8 years, SD = 5.13) completed a sequential button press and verbal task. The final analyses included data for 15 participants for the nonverbal task and 13 for the verbal task. Both tasks consisted of two complexity levels: simple and complex sequences. Magnetoencephalography was used to record modulations in beta band brain oscillations during task performance. Results Both the verbal and button press tasks were characterized by significant premovement ERD and postmovement ERS. However, only simple sequences showed a distinct transient synchronization during the premovement phase of the task. Differences between the two tasks were reflected in both latency and peak amplitude of ERD and ERS, as well as in lateralization of oscillations. Conclusions Both verbal and nonverbal movements showed a significant desynchronization of beta oscillations during the movement preparation and holding phase and a resynchronization upon movement termination. Importantly, the premovement phase for simple but not complex tasks was characterized by a transient partial synchronization. In addition, the data revealed significant differences between the two tasks in terms of lateralization of oscillatory modulations. Our findings suggest that, while data from the general motor control research can inform our understanding of speech motor control, significant differences exist between the two motor systems that caution against overgeneralization of underlying neural control processes.

Modulation of Peak Alpha Frequency Oscillations During Working Memory Is Greater in Females Than Males.

Peak alpha frequency is known to vary not just between individuals, but also within an individual over time. While variance in this metric between individuals has been tied to working memory performance, less understood are how short timescale modulations of peak alpha frequency during task performance may facilitate behavior. This gap in understanding may be bridged by consideration of a key difference between individuals: sex. Inconsistent findings in the literature regarding the relationship between peak alpha frequency and cognitive performance, as well as known sex-related-differences in peak alpha frequency and its modulation motivated our hypothesis that cognitive and neural processes underlying working memory—modulation of peak alpha frequency in particular—may differ based upon sex. Targeting sex as a predictive factor, we analyzed the EEG data of participants recorded while they performed four versions of a visual spatial working memory task. A significant difference between groups was present: females modulated peak alpha frequency more than males. Task performance did not differ by sex, yet a relationship between accuracy and peak alpha frequency was present in males, but not in females. These findings highlight the importance of considering sex as a factor in the study of oscillatory activity, particularly to further understanding of the neural mechanisms that underlie working memory.

An emerging impact of Eurasian spring snow cover on summer rainfall in Eastern China

Eurasian spring snow cover is widely considered as an important predictor of Asian summer monsoon rainfall, but its possible role in the formation of the north–south dipole structure of rainfall anomalies (NSDR)—a major mode of the eastern China summer rainfall variability—remains elusive. Here, we show that, there is a close connection between the western Eurasian spring snow cover (WESS) and NSDR during our research period 1967–2018, with less WESS tends to be accompanied by a wetter south-drier north pattern over eastern China, and vice versa. However, this relationship was not significant before the late 1990s, but has since become significant. Further analyses demonstrate that the shift in the WESS–NSDR relationship could be attributed to the modulation of summer North Atlantic Oscillation (SNAO). After the late 1990s, the WESS-related anomalous atmospheric circulations during summer are largely reinforced by the constructive superposition of those with same signs induced by SNAO, which in turn would intensify the impact of WESS and hence lead to a strong WESS–NSDR connection. In contrast, the influences of WESS are counteracted by those with opposite signs associated with SNAO before the late 1990s and thereby result in a weak snow–rainfall relationship. Our findings, along with the decline in Eurasian spring snow cover, provide a potential explanation for the recent ‘South Flood–North Drought’ pattern observed over eastern China.

Extracting statistically significant eddy signals from large Lagrangian datasets using wavelet ridge analysis, with application to the Gulf of Mexico

Abstract. A method for objectively extracting the displacement signals associated with coherent eddies from Lagrangian trajectories is presented, refined, and applied to a large dataset of 3770 surface drifters from the Gulf of Mexico. The method, wavelet ridge analysis, is a general method for the analysis of modulated oscillations, here modified to be more suitable to the eddy-detection problem. A means for formally assessing statistical significance is introduced, addressing the issue of false positives arising by chance from an unstructured turbulent background and opening the door to confident application of the method to very large datasets. Significance is measured through a frequency-dependent comparison with a stochastic dataset having statistical and spectral properties that match the original, but lacking organized oscillations due to eddies or waves. The application to the Gulf of Mexico reveals major asymmetries between cyclones and anticyclones, with anticyclones dominating at radii larger than about 50 km, but an unexpectedly rich population of highly nonlinear cyclones dominating at smaller radii. Both the method and the Gulf of Mexico eddy dataset are made freely available to the community for noncommercial use in future research.

Disrupted Modulation of Alpha and Low Beta Oscillations Mediates Temporal Sequence Memory Deficits in People With Schizophrenia

BackgroundPeople with schizophrenia (SZ) exhibit impaired episodic memory when relating objects to each other in time and space. Empirical studies and computational models suggest that low-frequency neural oscillations may be a mechanism by which the brain keeps track of temporal relationships during encoding and retrieval, with modulation of oscillatory power as sequences are learned. It is unclear whether sequence memory deficits in SZ are associated with altered neural oscillations. MethodsUsing electroencephalography, this study examined neural oscillations in 51 healthy control subjects and 37 people with SZ during a temporal sequence learning task. Multiple 5-object picture sequences were presented across 4 study-test blocks in either fixed or random order. Participants answered semantic questions for each object (e.g., living/nonliving), and sequence memory was operationalized as faster responses for fixed versus random sequences. Differences in oscillatory power between fixed versus random sequences provided a neural index of temporal sequence memory. ResultsAlthough both groups showed reaction time differences in late blocks (blocks 3 and 4), this evidence of sequence memory was reduced in people with SZ relative to healthy control subjects. Decreases in globally distributed prestimulus alpha (8–12 Hz) and beta 1 (13–20 Hz) power for fixed versus random sequences in late blocks were also attenuated in people with SZ relative to healthy control subjects. Moreover, changes in oscillatory power predicted individual reaction time differences and fully mediated the relationship between group and sequence memory. ConclusionsDisrupted modulation of alpha and beta 1 electroencephalography oscillations is a candidate mechanism of temporal sequence memory deficits in people with SZ.

Modulation of winter precipitation associated with tropical cyclone of the western North Pacific by the stratospheric Quasi-Biennial oscillation

Tropical cyclone precipitation (TCP) has increasing impacts on many coastal regions under global warming. Causes of TCP variation have been principally explored in the troposphere. This study identifies the significant modulation of the stratosphere Quasi-Biennial oscillation (QBO) on the winter TCP in the coastal regions of the western North Pacific (WNP). In the westerly QBO winter, the zonal wind vertical shear anomalies in the stratosphere strengthen (weaken) convective activities around the East China Sea (the Philippines) and cause middle-level easterly (westerly) anomalies of the middle (low) latitudes in the troposphere, leading to more (less) TC activities around the East China Sea (the Philippines). Consequently, a TCP dipole pattern can be observed. The TCP increases in East China, Korean peninsula, Japan and Russian Far East, but decreases in Indo–China Peninsula, South China and the Philippines. These results not only improve the knowledge of QBO-TCP relationship but also provide a potential indicator for the seasonal prediction of the TCP in the coastal regions of the WNP due to the high predictability of the QBO.

High-Frequency Oscillations in the Pallidum: A Pathophysiological Biomarker in Parkinson's Disease?

Abnormal oscillatory neural activity in the beta-frequency band (13-35 Hz) is thought to play a role in Parkinson's disease (PD); however, increasing evidence points to alterations in high-frequency ranges (>100 Hz) also having pathophysiological relevance. Studies have found that power in subthalamic nucleus (STN) high-frequency oscillations is increased with dopaminergic medication and during voluntary movements, implicating these brain rhythms in normal basal ganglia function. The objective of this study was to investigate whether similar signaling occurs in the internal globus pallidus (GPi), a nucleus increasingly used as a target for deep brain stimulation (DBS) for PD. Spontaneous and movement-related GPi field potentials were recorded from DBS leads in 5 externalized PD patients on and off dopaminergic medication, as well as from 3 rhesus monkeys before and after the induction of parkinsonism with the neurotoxin 1-methyl-4-phenyl-1,2,3,6 tetrahydropyridine. In the parkinsonian condition, we identified a prominent oscillatory peak centered at 200-300 Hz that increased during movement. In patients the magnitude of high-frequency oscillation modulation was negatively correlated with bradykinesia. In monkeys, high-frequency oscillations were mostly absent in the naive condition but emerged after the neurotoxin 1-methyl-4-phenyl-1,2,3,6 tetrahydropyridine. In patients, spontaneous high-frequency oscillations were significantly attenuated on-medication. Our findings provide evidence in support of the hypothesis that exaggerated, movement-modulated high-frequency oscillations in the GPi are pathophysiological features of PD. These findings suggest that the functional role(s) of high-frequency oscillations may differ between the STN and GPi and motivate additional investigations into their relationship to motor control in normal and diseased states.

The intervention of mechanical tactile stimulation modulates somatosensory evoked magnetic fields and cortical oscillations

The different cortical activity evoked by a mechanical tactile stimulus depends on tactile stimulus patterns, which demonstrates that simple stimuli (i.e., global synchronous stimulation the stimulus area) activate the primary somatosensory cortex alone, whereas complex stimuli (i.e., stimulation while moving in the stimulus area) activate not only the primary somatosensory cortex but also the primary motor area. Here, we investigated whether the effects of a repetitive mechanical tactile stimulation (MS) on somatosensory evoked magnetic fields (SEFs) and cortical oscillations depend on MS patterns. This single-blinded study included 15 healthy participants. Two types interventions of MS lasting 20min were used: a repetitive global tactile stimulation (RGS) was used to stimulate the finger by using 24 pins installed on a finger pad, whereas a sequential stepwise displacement tactile stimulation (SSDS) was used to stimulate the finger by moving a row of six pins between the left and right sides on the finger pad. Each parameter was measured pre- and post-intervention. The P50m amplitude of the SEF was increased by RGS and decreased by SSDS. The modulation of P50m was correlated with its amplitude before RGS and with the modulation of beta band oscillation at the resting state after SSDS. This study showed that the effects of a 20-min MS on SEFs and cortical oscillations depend on mechanical tactile stimulus patterns. Moreover, our results offer potential for the modulation of tactile functions and selection of stimulation patterns according to cortical states.

Experimental analysis of two-period quasi-periodic oscillations in a turbulent hydrogen combustor

The thermo-acoustic instability behavior of non-premixed hydrogen combustion is analyzed in the present work with the inlet Reynolds number, Re as the control parameter. It is observed that the dominant frequency (mode) shifts from the fundamental duct-acoustic mode to the first harmonic, as Re is varied. Continuous wavelet transform of the pressure oscillations reveals that at different Re, the dynamical nature of oscillations is topologically different, although they have identical spectral content. An interesting dynamical behavior identified as two-period quasi-periodic oscillations is observed, which has not been reported in prior literature. The state is seen to be unstable to incremental changes in Re and transitioning to limit cycle oscillations subsequently. Further diagnosis employing time-resolved OH* chemiluminescence and particle image velocimetry reveals the amplitude modulation of the quasi-periodic oscillation as a result of staggered vorticity distribution across the bluff body which results in asymmetric heat release rate distribution. A general framework for such oscillations is then applied, leading to identifying specific conditions that need to be satisfied to enable the existence of these oscillations. This study leads to novel observations on the asymmetric nature of shear layers, which can result in hitherto observed dynamical states.