Theta-Rhythmic Oscillation of Working Memory Performance

Representations held in working memory are crucial in guiding human attention in a goal-directed fashion. Currently, it is debated whether only a single representation or several of these representations can be active and bias behavior at any given moment. In the present study, 25 university students performed a behavioral dense-sampling experiment to produce an estimate of the temporal-activation patterns of two simultaneously held visual templates. We report two key novel results. First, performance related to both representations was not continuous but fluctuated rhythmically at 6 Hz. This corresponds to neural oscillations in the theta band, the functional importance of which in working memory is well established. Second, our findings suggest that two concurrently held representations may be prioritized in alternation, not simultaneously. Our data extend recent research on rhythmic sampling of external information by demonstrating an analogous mechanism in the cyclic activation of internal working memory representations.

Unravelling the enigma of cortical tremor and other forms of cortical myoclonus

Cortical tremor is a fine rhythmic oscillation involving distal upper limbs, linked to increased sensorimotor cortex excitability, as seen in cortical myoclonus. Cortical tremor is the hallmark feature of autosomal dominant familial cortical myoclonic tremor and epilepsy (FCMTE), a syndrome not yet officially recognized and characterized by clinical and genetic heterogeneity. Non-coding repeat expansions in different genes have been recently recognized to play an essential role in its pathogenesis. Cortical tremor is considered a rhythmic variant of cortical myoclonus and is part of the ‘spectrum of cortical myoclonus’, i.e. a wide range of clinical motor phenomena, from reflex myoclonus to myoclonic epilepsy, caused by abnormal sensorimotor cortical discharges. The aim of this update is to provide a detailed analysis of the mechanisms defining cortical tremor, as seen in FCMTE. After reviewing the clinical and genetic features of FCMTE, we discuss the possible mechanisms generating the distinct elements of the cortical myoclonus spectrum, and how cortical tremor fits into it. We propose that the spectrum is due to the evolution from a spatially limited focus of excitability to recruitment of more complex mechanisms capable of sustaining repetitive activity, overcoming inhibitory mechanisms that restrict excitatory bursts, and engaging wide areas of cortex. Finally, we provide evidence for a possible common denominator of the elements of the spectrum, i.e. the cerebellum, and discuss its role in FCMTE, according to recent genetic findings.

Overcoming Oscillation Quenching via Mean-Field Feedback

Observational studies have shown that many natural systems need to remain in rhythmic oscillation activity. Yet, the appearance of oscillation quenching phenomena lead to the breakdown of intrinsic behavior of practical systems, often causing unpredictable results. To address the important problem about how to avoid or revive the paralyzed system, in this work, we use the mean-field function of the entire system as an external feedback acts on every unit. Taking the classical limit cycle of Stuart–Landau model as example, we find that oscillation quenching state can be eliminated effectively and thus revoke the deprived oscillation. Through extensive theoretical analyses and numerical simulations, the results show for various death scenarios that the oscillation quenching regions shrink drastically in the parameter space with increasing feedback strength. Our method can be regarded as a general framework to maintain or retrieve the continued oscillation for coupled nonlinear systems in diverse applications.

Taxonomy of neural oscillation events in primate auditory cortex

Electrophysiological oscillations in neocortex have been shown to occur as multi-cycle events, with onset and offset dependent on behavioral and cognitive state. To provide a baseline for state-related and task-related events, we quantified oscillation features in resting-state recordings. We used two invasively-recorded electrophysiology datasets: one from human, and one from non-human primate auditory system. After removing event related potentials, we used a wavelet transform based method to quantify oscillation features. We identified about 2 million oscillation events, classified within traditional frequency bands: delta, theta, alpha, beta, gamma, high gamma. Oscillation events of 1-44 cycles were present in at least one frequency band in 90% of the recordings, consistent across human and non-human primate. Individual oscillation events were characterized by non-constant frequency and amplitude. This result naturally contrasts with prior studies which assumed such constancy, but is consistent with evidence from event-associated oscillations. We measured oscillation event duration, frequency span, and waveform shape. Oscillations tended to exhibit multiple cycles per event, verifiable by comparing filtered to unfiltered waveforms. In addition to the clear intra-event rhythmicity, there was also evidence of inter-event rhythmicity within bands, demonstrated by finding that coefficient of variation of interval distributions and Fano Factor measures differed significantly from a Poisson distribution assumption. Overall, our study demonstrates that rhythmic oscillation events dominate auditory cortical dynamics.

Sympatho–Vagal Dysfunction in Patients with End-Stage Lung Disease Awaiting Lung Transplantation

Although the literature demonstrates that cardiac autonomic control (CAC) might be impaired in patients with chronic pulmonary diseases, the interplay between CAC and disease severity in end-stage lung disease has not been studied yet. We investigated the effects of end-stage lung disease on CAC through the analysis of heart rate variability (HRV) among patients awaiting lung transplantation. Forty-nine patients on the waiting list for lung transplantation (LTx; 19 men, age 38 ± 15 years) and 49 healthy non-smoking controls (HC; 22 men, age 40 ± 16 years) were enrolled in a case–control study at Policlinico Hospital in Milan, Italy. LTx patients were divided into two groups, according to disease severity evaluated by the Lung Allocation Score (LAS). To assess CAC, electrocardiogram (ECG) and respiration were recorded at rest for 10 min in supine position and for 10 min during active standing. Spectral analysis identified low and high frequencies (LF, sympathetic, and HF, vagal). Symbolic analysis identified three patterns, i.e., 0V% (sympathetic) and 2UV% and 2LV% (vagal). Compared to HCs, LTx patients showed higher markers of sympathetic modulation and lower markers of vagal modulation. However, more severely affected LTx patients, compared to less severely affected ones, showed an autonomic profile characterized by loss of sympathetic modulation and predominant vagal modulation. This pattern can be due to a loss of sympathetic rhythmic oscillation and a subsequent prevalent respiratory modulation of heart rate in severely affected patients.

Standardisation of electrocardiographic examination in corn snakes (Pantherophis guttatus)

IntroductionCorn snakes are a very common pet reptile species, yet there is an absence of evidence-based literature standardising collection of ECG or detailing ECG deflection morphology in the normal animal. The authors describe a well-tolerated, reproducible technique and detail the cardiac cycle in terms of lead 2 equivalent waveforms and intervals.Animals29 adult corn snakes.Materials and methodsThis prospective study evaluated, under species-appropriate, standardised conditions, a technique for producing standard six-lead ECG tracings. Lead 2 equivalent cardiac cycles were described in detail and statistically analysed for sex, weight, length, heart rate and mean electrical axis.ResultsHigh-quality tracings demonstrated common ECG characteristics for this species, including no Q, S or SV waves, prolonged PR and RT intervals, rhythmic oscillation of the baseline, short TP segments, and a right displaced mean electrical axis. An influence of sex, weight or length on heart rate and mean electrical axis was not identified.ConclusionsTo the authors’ knowledge, this is the first study to describe a standardised technique for recording ECG in significant numbers of normal corn snakes. Ranges have been provided that may be of diagnostic value or form the basis for future development of reference intervals for this species.

Dynamic compensation mechanism gives rise to period and duty-cycle level sets in oscillatory neuronal models

Rhythmic oscillation in neurons can be characterized by various attributes, such as the oscillation period and duty cycle. The values of these features depend on the amplitudes of the participating ionic currents, which can be characterized by their maximum conductance values. Recent experimental and theoretical work has shown that the values of these attributes can be maintained constant for different combinations of two or more ionic currents of varying conductances, defining what is known as level sets in conductance space. In two-dimensional conductance spaces, a level set is a curve, often a line, along which a particular oscillation attribute value is conserved. In this work, we use modeling, dynamical systems tools (phase-space analysis), and numerical simulations to investigate the possible dynamic mechanisms responsible for the generation of period and duty-cycle levels sets in simplified (linearized and FitzHugh-Nagumo) and conductance-based (Morris-Lecar) models of neuronal oscillations. A simplistic hypothesis would be that the tonic balance between ionic currents with the same or opposite effective signs is sufficient to create level sets. According to this hypothesis, the dynamics of each ionic current during a given cycle are well captured by some constant quantity (e.g., maximal conductances), and the phase-plane diagrams are identical or are almost identical (e.g., cubic-like nullclines with the same maxima and minima) for different combinations of these maximal conductances. In contrast, we show that these mechanisms are dynamic and involve the complex interaction between the nonlinear voltage dependencies and the effective time scales at which the ionic current's dynamical variables operate.

Rhythmic modulation of visual contrast discrimination triggered by action

Recent evidence suggests that ongoing brain oscillations may be instrumental in binding and integrating multisensory signals. In this experiment, we investigated the temporal dynamics of visual–motor integration processes. We show that action modulates sensitivity to visual contrast discrimination in a rhythmic fashion at frequencies of about 5 Hz (in the theta range), for up to 1 s after execution of action. To understand the origin of the oscillations, we measured oscillations in contrast sensitivity at different levels of luminance, which is known to affect the endogenous brain rhythms, boosting the power of alpha-frequencies. We found that the frequency of oscillation in sensitivity increased at low luminance, probably reflecting the shift in mean endogenous brain rhythm towards higher frequencies. Importantly, both at high and at low luminance, contrast discrimination showed a rhythmic motor-induced suppression effect, with the suppression occurring earlier at low luminance. We suggest that oscillations play a key role in sensory–motor integration, and that the motor-induced suppression may reflect the first manifestation of a rhythmic oscillation.

Prominent Russian pharmacologist N.P.Kravkov and his contribution to the world pharmacology (in memoriam to 150 years from the birth)

In every field of science there are the proper prominent scientists. In Russia, there was Nikolai Pavlovich Kravkov (1865-1924), a founder of the Russian pharmacology. In the paper, the life and scientific achievements of Professor N.P. Kravkov, headed the Department of Pharmacology, Military Medical Academy, St. Petersburg, were described. N. P. Kravkov carried out significant investigations in pharmacology of gas metabolism, drug toxicology, aged and evolutionary pharmacology, clinical pharmacology (discovery of intravenous and combined narcosis). The main achievement of N. P. Kravkov became the cycle of investigations on isolated organs (ear, heart, lung, spleen, pancreatic gland, thyroid gland, adrenal gland, uterus of the mammalians, head and gills of pike, human fingers, heart and spleen). In these investigations, the rhythmic oscillation of the vascular tonus was proved, the theory of phasic action of pharmacological drugs on tissues, presentations on sensitiveness limits of living protoplasma, possibilities of animation of mummified tissues were postulated. N. P. Kravkov created a large scientific school (S. V. Anichkov, M. I. Gramenitskii, G. L. Shkavera, M. N. Nikolaev, A. I. Kuznetsov, B. S. Sentyurin, V. V. Zakusov, V. A. Valdman).