Biomedical subjects

Sang-Gui Lee

Publications and source records attributed to Sang-Gui Lee.

4 recordsLinked to original sources

PubMed2006

Phase-model analysis of coupled neuronal oscillators with multiple connections.

Synchronization of the coupled neuronal oscillators with multiple connections of different coupling nature is analyzed using the phase-model reduction method. Each coupling connection contributes to the dynamic behavior of the system in a complex nonlinear fashion. In the phase-model scheme, the contribution of the individual connections can be separated in terms of the effective coupling functions associated with each connection and a linear superposition of them provides the total effective coupling of the coupled system. The case of multiple connections with various conduction time delays is also examined, which is shown to be capable of promoting synchronization over an ensemble of spatially distributed neuronal oscillators in an efficient way.

Hippocampus↗

PubMed2006

Bifurcation analysis of mode-locking structure in a Hodgkin-Huxley neuron under sinusoidal current.

Nervous systems under periodic stimuli display rich dynamical states including mode-locking and chaotic responses, which have been a subject of intense studies in neurodynamics. The bifurcation structure of the Hodgkin-Huxley neuron under sinusoidal stimulus is studied in detail. The mechanisms of the firing onset and rich firing dynamics are studied with the help of the codimension-2 bifurcations, which play the role of the organizing center for myriads of saddle-node, period-doubling, and inverse-flip bifurcations forming the boundaries of the complex mode-locking structure. This study provides a useful insight into the organization of similar bifurcation structures in excitable systems such as neurons under periodic forcing.

Action Potentials↗

PubMed2005

Bona fide stochastic resonance and multimodality in the stochastic Hodgkin-Huxley neuron.

The phenomena of stochastic resonance (SR) has attracted much attention in the studies of the excitable systems, in particular, the nervous systems under noise. Recently, an alternative SR condition, called the bona fide SR, was proposed for the bistable system under noise, based on the notion of the residence time distribution. As the forcing frequency increases, there exists an optimal resonant frequency. We study the SR in a stochastic Hodgkin-Huxley neuron, which has an inherent natural frequency in addition to the stochastic time scale. We have observed two resonant conditions; one between periodic forcing and natural frequencies, and the other between the periodic forcing and the stochastic frequencies. These resonance conditions show the bona fide stochastic resonance with multimodality. For comparison, we have studied the bona fide SR in the stochastic FitzHugh-Nagumo neuron, where, the multimodality is not observed. The differences in the resonance structure of two neuron models are understood in terms of differences in the phase portraits.

Action Potentials↗

PubMed2004

Orientation tuning and synchronization in the hypercolumn model.

The orientation selectivity in the firing rate of neurons is one of the most well-known properties of neurons in the primary visual cortex. To understand the dynamical mechanism of the orientation tuning, we introduce a biologically plausible network for a hypercolumn and investigate dynamical responses of its columnar activities. Numerical simulations show that the spike activities between excitatory cells in the same column exhibit strong synchronization and sharp orientation selectivity. The tuning curves for the synchronized activities also show orientation selectivity similar to those for the firing rate. The comparison between the two tuning curves for the firing rate and the synchronized activities suggests that the orientation selectivity is strongly correlated with the synchronized activities. We find from the analysis of columnar activities that the orientation selectivity depends strongly upon the inhibitory coupling strength and the synchronization upon the excitatory coupling strength. In particular, we find that at appropriate coupling parameters both sharp orientation selectivity and maximal synchronization can be achieved. This suggests the importance of the balance between the excitatory coupling and the inhibitory coupling in the primary visual cortex for visual information processing.

Action Potentials↗