Dynamics of on-off neural firing patterns and stochastic effects near a sub-critical Hopf bifurcation.

On-off firing patterns, in which repetition of clusters of spikes are interspersed with epochs of subthreshold oscillations or quiescent states, have been observed in various nervous systems, but the dynamics of this event remain unclear. Here, we report that on-off firing patterns observed in three experimental models (rat sciatic nerve subject to chronic constrictive injury, rat CA1 pyramidal neuron, and rabbit blood pressure baroreceptor) appeared as an alternation between quiescent state and burst containing multiple period-1 spikes over time. Burst and quiescent state had various durations. The interspike interval (ISI) series of on-off firing pattern was suggested as stochastic using nonlinear prediction and autocorrelation function. The resting state was changed to a period-1 firing pattern via on-off firing pattern as the potassium concentration, static pressure, or depolarization current was changed. During the changing process, the burst duration of on-off firing pattern increased and the duration of the quiescent state decreased. Bistability of a limit cycle corresponding to period-1 firing and a focus corresponding to resting state was simulated near a sub-critical Hopf bifurcation point in the deterministic Morris-Lecar (ML) model. In the stochastic ML model, noise-induced transitions between the coexisting regimes formed an on-off firing pattern, which closely matched that observed in the experiment. In addition, noise-induced exponential change in the escape rate from the focus, and noise-induced coherence resonance were identified. The distinctions between the on-off firing pattern and stochastic firing patterns generated near three other types of bifurcations of equilibrium points, as well as other viewpoints on the dynamics of on-off firing pattern, are discussed. The results not only identify the on-off firing pattern as noise-induced stochastic firing pattern near a sub-critical Hopf bifurcation point, but also offer practical indicators to discriminate bifurcation types and neural excitability types.

Correlation between memory function of patients of generalized seizures and magnetic resonance spectroscopy of hippocampal in patients with generalized seizures / 中华神经科杂志

Objective To investigate the features of the memory function disturbance in patients of generalized seizures and the correlation between the memory function and proton magnetic resonance spectroscopy(1H-MRS).Methods The clinical memory scale of 45 general seizures and 20 normal age and sex-matched controls wss measured and a1 H-MRs was performed in the bilateral hippoeampal.The levels of NAA.Cho.Cr and the ratios of NAA/Cr+Cho were compared between these two groups.Meanwhile,tHe correlation coefficients was calculated and the results of clinical memory scale scoreB and the level of NAA,Cho.Cr and the ratios of NAA/Cr+Cho in groups were compared.Results As compared with the controls.the scores of pointing memory(17.19±5.86),associational learning(20.00±6.77),image free memory(18.44±6.62),association memory of portrait(13.19±6.62)and memory quotient (MQ,79.07±20.20)excepts insignificant figure recognition wcrc significandy decreased in patients of seizures(t=4.794-10.224,all P<0.01);The scores of scale and MQ of both the group of patients who wok antiepileptic drugs(AEDs)and the group of patients whose frequency exceeded 3 per month were significantly lower than the group who didn't take AEDs and the group whose frequency was lower than 3 per month(t=3.267-6.537,all P<0.01).The volumes of hippocampal formations(2.45 ±0.25 on left and 2.56 ±0.31 on right),the level of NAA(12.93 ±1.73 on left and 11.88 ±1.69 on right),Cho(15.02 ±0.86 on left and 14.94 ±0.96 on right),Cr(11.86 ±0.71 on left and 10.71 ±0.42 on right)and the ratios of NAA/Cr+Cho(0.48 ±0.08 on left and 0.39 ±0.07 on riht)in the group of pailents of generalized seizures were significantly difference than those in the controls(t=4.103-5.768,all P<0.01).Patients with seizures showed significant correlation between tlle scores of all items.MQ in clinical memory scale and NAA,NAA/Cr+Cho ratio(r=0.489-0.727,all P<0.01),and inverse correlation between the scores and MQ and Cho of in the bilateral hippocampal(r=-0.604-0.484,all P<0.01).However,there was no correlation between the scores and MQ and Cr of in the bilateral hippocampal.Condusions The patients of the general seizures do have the problem of the disturbance of short-term memory including acoustic memory and some visual memory.Both the high frequency of seizure and AEDs could affect the short-term memory function.The correlation between the scores of all the items and MQ in clinical memory scale proved that lack of nerve cell and hyperplasia of gliocyte was one of the reasons of the short-term memory disorder in epileptic.