Manipulating the features of stimulation waveforms changes the effects of rhythmic electrical stimulation.

Features of oscillatory waveform shape have been related to physiological processes and behaviors.

New methods have been developed to quantify the nonsinusoidal features of oscillations and account for these features when using traditional spectral analysis.

Electrical recordings from many brain regions, at multiple spatial scales, exhibit neural oscillations that are nonsinusoidal.

The properties of neural oscillations are commonly correlated to disease or behavior states. These measures are mostly derived using traditional spectral analysis techniques that assume a sinusoidal basis.

Oscillations are a prevalent feature of brain recordings. They are believed to play key roles in neural communication and computation. Current analysis methods for studying neural oscillations often implicitly assume that the oscillations are sinusoidal. While these approaches have proven fruitful, we show here that there are numerous instances in which neural oscillations are nonsinusoidal. We highlight approaches to characterize nonsinusoidal features and account for them in traditional spectral analysis. Instead of being a nuisance, we discuss how these nonsinusoidal features may provide crucial and so far overlooked physiological information related to neural communication, computation, and cognition.

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Phase synchronization between alpha and beta oscillations in the human electroencephalogram.

Lack of evidence for cross-frequency phase–phase coupling between theta and gamma oscillations in the hippocampus.

Cross-frequency phase coupling of brain rhythms during the orienting response.

Phase synchrony among neuronal oscillations in the human cortex.

Electrocorticography reveals beta desynchronization in the basal ganglia–cortical loop during rest tremor in Parkinson's disease.

Regulation of motor representation by phase-amplitude coupling in the sensorimotor cortex.

Oscillatory multiplexing of population codes for selective communication in the mammalian brain.

Movement-related dynamics of cortical oscillations in Parkinson's disease and essential tremor.

Detection of epileptic seizures using phase–amplitude coupling in intracranial electroencephalography.

Theta–gamma coupling increases during the learning of item–context associations.

Robust oscillation detection index and characterization of oscillating signals for valve stiction detection.

The temporal structures and functional significance of scale-free brain activity.

Non-zero mean and asymmetry of neuronal oscillations have different implications for evoked responses.

A new series of anticonvulsant drugs tested by experiments on animals.

A novel mechanism for evoked responses in the human brain.

Modulations in oscillatory activity with amplitude asymmetry can produce cognitively relevant event-related responses.

Rapid fragmentation of neuronal networks at the onset of propofol-induced unconsciousness.

Neural mechanisms of transient neocortical beta rhythms: converging evidence from humans, computational modeling, monkeys, and mice.

Comparison between spontaneous and kainate-induced gamma oscillations in the mouse hippocampus in vitro.

Muscarinic blockade weakens interaction of gamma with theta rhythms in mouse hippocampus.

Carbachol-induced EEG ‘theta’ in hippocampal formation slices: evidence for a third generator of theta in CA3c area.

Behavior-dependent coordination of multiple theta dipoles in the hippocampus.

Laminar distribution of hippocampal rhythmic slow activity (RSA) in the behaving rat: current-source density analysis, effects of urethane and atropine.

7 to 12 Hz activity in rat gustatory cortex reflects disengagement from a fluid self-administration task.

On the activity of the corticostriatal networks during spike-and-wave discharges in a genetic model of absence epilepsy.

Genetic animal models for absence epilepsy: a review of the WAG/Rij strain of rats.

Association of seizures with cortical spreading depression and peri-infarct depolarisations in the acutely injured brain.

The EEG, eye-movement and dreams of the blind.

Dynamics of the human alpha rhythm: evidence for non-linearity?.

The functional significance of mu rhythms: translating ‘seeing’ and ‘hearing’ into ‘doing’.

Cortical networks produce three distinct 7-12 Hz rhythms during single sensory responses in the awake rat.

The interpretation of potential waves in the cortex.

The use of stationarity and nonstationarity in the detection and analysis of neural oscillations.

Comparison of matching pursuit algorithm with other signal processing techniques for computation of the time-frequency power spectrum of brain signals.

Are the electroencephalograms mainly rhythmic? Assessment of periodicity in wide-band time series.

Phase–amplitude coupling is elevated in deep sleep and in the onset zone of focal epileptic seizures.

Dual origins of measured phase-amplitude coupling reveal distinct neural mechanisms underlying episodic memory in the human cortex.

Non-sinusoidal activity can produce cross-frequency coupling in cortical signals in the absence of functional interaction between neural source.

Different origins of gamma rhythm and high-gamma activity in macaque visual cortex.

When brain rhythms aren’t ‘rhythmic’: implication for their mechanisms and meaning.

Phase-clustering bias in phase–amplitude cross-frequency coupling and its removal.

Distinguishing mechanisms of gamma frequency oscillations in human current source signals using a computational model of a laminar neocortical network.

Quantifying neural oscillatory synchronization: a comparison between spectral coherence and phase-locking value approaches.

Behavioral detection of tactile stimuli during 7-12 Hz cortical oscillations in awake rats.

Distinct alpha and beta band rhythms over rat somatosensory cortex with similar properties as in humans.

Hippocampal network patterns of activity in the mouse.

Abnormal UP/DOWN membrane potential dynamics coupled with the neocortical slow oscillation in dentate granule cells during the latent phase of temporal lobe epilepsy.

Rhythm sequence through the olfactory bulb layers during the time window of a respiratory cycle.

A respiration-coupled rhythm in the rat hippocampus independent of theta and slow oscillations.

Recognition memory and theta–gamma interactions in the hippocampus.

Toward a proper estimation of phase-amplitude coupling in neural oscillations.

Cross-frequency phase–phase coupling between theta and gamma oscillations in the hippocampus.

Temporal coupling of parahippocampal ripples, sleep spindles and slow oscillations in humans.

Grouping of spindle activity during slow oscillations in human non-rapid eye movement sleep.

EEG slow (∼1 Hz) waves are associated with nonstationarity of thalamo-cortical sensory processing in the sleeping human.

A novel slow (<1 Hz) oscillation of neocortical neurons in vivo: depolarizing and hyperpolarizing components.

Neuronal and glial membrane potentials during sleep and paroxysmal oscillations in the neocortex.

Nonsinusoidal oscillations underlie pathological phase–amplitude coupling in the motor cortex in Parkinson's disease.

Mu rhythm modulation during observation of an object-directed grasp.

On the existence of different types of central beta rhythms below 30 Hz.

Mu rhythm (de)synchronization and EEG single-trial classification of different motor imagery tasks.

Functional significance of the mu rhythm of human cortex: an electrophysiologic study with subdural electrodes.

Glossary

the magnitude of an oscillation in a signal, measured in volts.

a periodic waveform in which one extremum is consistently sharper than the opposite.

a biophysical interaction between two oscillators with different fundamental frequencies.

multiple streams of information encoded in a single signal.

an oscillatory waveform shape that deviates from a sine wave.

a periodic component of a time series, such that the phase at one timepoint can be predicted by the phase at a past timepoint. In electrical recordings, the voltage fluctuates between two extremes, with some variability in frequency and amplitude.

a point in a periodic cycle, such as the peak, trough, or zero-crossing.

a subtype of CFC defined by a statistical correlation between the phase of one oscillation and the amplitude of a second oscillation. Oscillations can be from the same recording (’within-channel’) or from separate simultaneously recorded channels (’cross-channel’)

a periodic waveform that fluctuates between two extrema with a fast rise (or decay) and a slow, linear decay (or rise).

a description of the shape of oscillatory extrema. Extrema are relatively sharp if the rate of voltage change around the extrema is relatively high.

the imaginary component of the trajectory at a constant angular frequency along a circle in the complex plane. The sinusoid is a smoothly varying periodic signal that has special mathematical properties, allowing it to be used as the basis for the Fourier transform. A sinusoid is defined by its frequency, amplitude, and phase.

a family of techniques used to quantify the phase and amplitude of a neural oscillation by focusing on a small frequency range of interest.

a stereotyped waveform that is commonly observed in epileptic tissue. The waveform consists of a brief, sharp spike and a slower wave.

a high-magnitude deflection in a time series that lasts a short period of time.