A Gail | PubMed Health

PubMed2006

Complex dynamics of a single neuron model.

We study a mathematical model of a single neuron with self-coupling. The model is based on the FitzHugh-Nagumo oscillator and an equation describing synaptic properties of the neuron. The analysis of the model is focused on its dynamics, depending on parameters characterizing synaptic time constants and external signals that affect the neuron. Applying Lyapunov exponents and bifurcation analysis, we point out the occurrence of parameter regions with different behavior such as bursting (chaotic or periodic), spiking, and multistable phenomena. Moreover, we can describe the dynamics of the model using an analytical approximation of the one-dimensional Poincaré map extracted from the numerical simulations.

Action Potentials↗

PubMed2000

Contour decouples gamma activity across texture representation in monkey striate cortex.

Previous work on figure-ground coding in monkey V1 revealed enhanced spike rates within an object's surface representation, synchronization of gamma oscillations (gamma = 35-90 Hz) in object and background regions, but no decrease in signal correlation across the representation of a contour. The latter observation seems to contradict previous statements on the role of gamma-synchronization for scene segmentation. We re-examine these findings by analyzing different coupling measures and frequency ranges of population activities potentially contributing to figure-ground segregation. Multiple unit activity (MUA) and local field potentials (LFPs) were recorded by parallel mu-electrodes in monkey V1 during stimulation by a grating in which an object was defined by a shifted rectangle. In contradiction to the conclusions in previous work, we find strong decoupling of population activity between figure and ground representations compared to the situation in which the object is absent. In particular, coherence of late gamma-LFPs is strongly reduced, while reduction is absent during the early epochs of high-amplitude transients for LFP- and MUA-coherence at all frequencies, and at low frequencies also in the subsequent epochs. Our results of decoupling in late LFP gamma-components among figure and ground representations suggest that these signals may support figure-ground segregation.

Animals↗