# Sang-Yoon KimInstitute for Computational Neuroscience, S. Korea · Computational Modeling Division

Sang-Yoon Kim

Ph.D

## About

126

Publications

6,861

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1,074

Citations

Citations since 2016

Introduction

Our current works are to mainly investigate the effect of synaptic plasticity on brain functions (learning, memory, and development) and neural diseases (Parkinson's disease and epilepsy).

Additional affiliations

February 2009 - March 2010

January 2002 - March 2003

February 1996 - February 1997

Education

April 1984 - March 1987

## Publications

Publications (126)

We investigate population and individual firing behaviors in sparsely synchronized rhythms (SSRs) in a spiking neural network of the hippocampal dentate gyrus (DG). The main encoding granule cells (GCs) are grouped into lamellar clusters. In each GC cluster, there is one inhibitory (I) basket cell (BC) along with excitatory (E) GCs, and they form t...

We study the disynaptic effect of the hilar cells on pattern separation in a spiking neural network of the hippocampal dentate gyrus (DG). The principal granule cells (GCs) in the DG perform pattern separation, transforming similar input patterns into less-similar output patterns. In our DG network, the hilus consists of excitatory mossy cells (MCs...

We consider a biological network of the hippocampal dentate gyrus (DG). Computational models suggest that the DG would be a preprocessor for pattern separation (i.e., a process transforming a set of similar input patterns into distinct nonoverlapping output patterns) which could facilitate pattern storage and retrieval in the CA3 area of the hippoc...

We consider the Pavlovian eyeblink conditioning (EBC) via repeated presentation of paired conditioned stimulus (tone) and unconditioned stimulus (US; airpuff). In an effective cerebellar ring network, we change the connection probability $p_c$ from Golgi to granule (GR) cells, and make a dynamical classification of various firing patterns of the GR...

We consider a cerebellar ring network for the optokinetic response (OKR), and investigate the effect of diverse recoding of granule (GR) cells on OKR by varying the connection probability $p_c$ from Golgi to GR cells. For an optimal value of $p_c^*~(=0.06)$, individual GR cells exhibit diverse spiking patterns which are in-phase, anti-phase, or com...

We consider a two-population network consisting of both inhibitory (I) interneurons and excitatory (E) pyramidal cells. This I–E neuronal network has adaptive dynamic I to E and E to I interpopulation synaptic strengths, governed by interpopulation spike-timing-dependent plasticity (STDP). In previous works without STDPs, fast sparsely synchronized...

We consider a scale-free network of inhibitory Hindmarsh-Rose (HR) bursting neurons, and make a computational study on coupling-induced cluster burst synchronization by varying the average coupling strength $J_0$. For sufficiently small $J_0$, non-cluster desynchronized states exist. However, when passing a critical point $J^*_c~(\simeq 0.16)$, the...

We are concerned about burst synchronization (BS), related to neural information processes in health and disease, in the Barabási-Albert scale-free network (SFN) composed of inhibitory bursting Hindmarsh-Rose neurons. This inhibitory neuronal population has adaptive dynamic synaptic strengths governed by the inhibitory spike-timing-dependent plasti...

We consider the Watts-Strogatz small-world network (SWN) consisting of inhibitory fast spiking Izhikevich interneurons. This inhibitory neuronal population has adaptive dynamic synaptic strengths governed by the inhibitory spike-timing-dependent plasticity (iSTDP). In previous works without iSTDP, fast sparsely synchronized rhythms, associated with...

We consider an excitatory population of subthreshold Izhikevich neurons which cannot fire spontaneously without noise. As the coupling strength passes a threshold, individual neurons exhibit noise-induced burstings. This neuronal population has adaptive dynamic synaptic strengths governed by the spike-timing-dependent plasticity (STDP). In the abse...

We consider an excitatory population composed of subthreshold neurons which exhibit noise-induced spikings. This neuronal population has adaptive dynamic synaptic strengths governed by the spike-timing-dependent plasticity (STDP). In the absence of STDP, stochastic spike synchronization (SSS) between
noise-induced spikings of subthreshold neurons w...

We consider the Watts-Strogatz small-world network consisting of subthreshold neurons which exhibit noise-induced spikings. This neuronal network has adaptive dynamic synaptic strengths governed by the spike-timing-dependent plasticity (STDP). In previous works without STDP, stochastic spike synchronization (SSS)
between noise-induced spikings of s...

For studying how dynamical responses to external stimuli depend on the synaptic-coupling type, we consider two types of excitatory and inhibitory synchronization (i.e., synchronization via synaptic excitation and inhibition) in complex small-world networks of excitatory regular spiking (RS) pyramidal neurons and inhibitory fast spiking (FS) interne...

By taking into consideration the inhomogeneous population of interneurons in real neural circuits, we consider an inhomogeneous small-world network (SWN) composed of inhibitory short-range (SR) and long-range (LR) interneurons, and investigate the effect of network architecture on emergence of sparsely synchronized rhythms by varying the fraction o...

We investigate the effect of network architecture on burst and spike synchronization in a directed scale-free network (SFN) of bursting neurons, evolved via two independent α- and β-processes. The α-process corresponds to a directed version of the Barabási–Albert SFN model with growth and preferential attachment, while for the β-process only prefer...

We consider a clustered network with small-world sub-networks of inhibitory
fast spiking interneurons, and investigate the effect of inter-modular
connection on emergence of fast sparsely synchronized rhythms by varying both
the inter-modular coupling strength $J_{inter}$ and the average number of
inter-modular links per interneuron $M_{syn}^{(inte...

We are interested in characterization of population synchronization of bursting neurons
which exhibit both the slow bursting and the fast spiking timescales, in contrast to spiking
neurons. Population synchronization may be well visualized in the raster plot of neural
spikes which can be obtained in experiments. The instantaneous population firing...

We are interested in characterization of synchronization transitions of bursting neurons in the frequency domain. Instantaneous population firing rate (IPFR) R(t), which is directly obtained from the raster plot of neural spikes, is often used as a realistic collective quantity describing population activities in both the computational and the expe...

For modeling complex synaptic connectivity, we consider the Watts-Strogatz
small-world network which interpolates between regular lattice and random
network via rewiring, and investigate the effect of small-world connectivity on
emergence of noise-induced population synchronization in an inhibitory
population of subthreshold bursting Hindmarsh-Rose...

We consider a directed Barab\'{a}si-Albert scale-free network model with
symmetric preferential attachment with the same in- and out-degrees, and study
emergence of sparsely synchronized rhythms for a fixed attachment degree in an
inhibitory population of fast spiking Izhikevich interneurons. For a study on
the fast sparsely synchronized rhythms, w...

Fast cortical rhythms with stochastic and intermittent neural discharges have
been observed in electric recordings of brain activity. We study the effect of
network architecture on these fast sparsely synchronized rhythms in an
inhibitory population of suprathreshold fast spiking (FS) Izhikevich
interneurons (which fire spontaneously without noise)...

Synchronized brain rhythms, associated with diverse cognitive functions, have been observed in electrical recordings of brain activity. Neural synchronization may be well described by using the population-averaged global potential VG in computational neuroscience. The time-averaged fluctuation of VG plays the role of a "thermodynamic" order paramet...

We consider an excitatory population of subthreshold Izhikevich neurons which exhibit noise-induced firings. By varying the coupling strength J, we investigate population synchronization between the noise-induced firings which may be used for efficient cognitive processing such as sensory perception, multisensory binding, selective attention, and m...

Sparsely-synchronized cortical rhythms, associated with diverse cognitive functions, have been observed in electric recordings of brain activity. At the population level, cortical rhythms exhibit small-amplitude fast oscillations while at the cellular level, individual neurons show stochastic firings sparsely at a much lower rate than the populatio...

We consider a population of subthreshold Izhikevich neurons that cannot fire spontaneously without noise. As the coupling strength passes a threshold, individual neurons exhibit noise-induced burstings (i.e., discrete groups or bursts of noise-induced spikes). We investigate stochastic bursting synchronization by varying the noise intensity. Throug...

We study inhibitory coherence (i.e. collective coherence by synaptic inhibition) in a population of globally coupled type-I neurons, which can fire at arbitrarily low frequency. No inhibitory coherence is observed in a homogeneous population composed of only subthreshold neurons, which exhibit noise-induced firings. In addition to subthreshold neur...

By varying the noise intensity, we study stochastic spiking coherence (i.e., collective coherence between noise-induced neural spikings) in an inhibitory population of subthreshold neurons (which cannot fire spontaneously without noise). This stochastic spiking coherence may be well visualized in the raster plot of neural spikes. For a coherent cas...

We study the effect of network structure on the stochastic spiking coherence (i.e., collective coherence emerging via cooperation of noise-induced neural spikings) in an inhibitory population of subthreshold neurons (which cannot fire spontaneously without noise). Previously, stochastic spiking coherence was found to occur for the case of global co...

We study the transition from a silent state to a bursting state by varying the dc stimulus in the Hindmarsh-Rose neuron under quasiperiodic stimulation. For this quasiperiodically-forced case, a new type of strange nonchaotic (SN) bursting state is found to occur between the silent state and the chaotic bursting state. This is in contrast to the pe...

We consider a large population of N globally coupled inhibitory subthreshold neurons (which cannot fire spontaneously without noise). In a range of noise intensity, an oscillating ensemble-averaged collective potential with small amplitude emerges via cooperation of the complex potentials of individual neurons. To characterize this "weak" collectiv...

We study the transition from a silent state to a spiking state by varying the dc stimulus in the quasiperiodically-forced Hodgkin-Huxley neuron. or Has quasiperiodically-forced case, a new type of strange nonchaotic (SN) spiking state is found to appear between the silent state, and the chaotic spiking state as intermediate one. Using a rational ap...

We consider two symmetrically-coupled logistic maps, and investigate the effect of symmetry on Hopf bifurcations, giving rise to the birth of the daughter orbits encircling the symmetric anti-phase mother orbit (with a time shift of half a period). When the rotation numbers v of daughter orbits are rational (i.e., v = r/s; r and s: coprimes), anoma...

As a representative model for Poincaré maps of coupled period-doubling oscillators, we consider two symmetrically coupled Hénon maps. Each invertible Hénon map has a constant Jacobian b (0 < b < 1) controlling the "degree" of dissipation. For the singular case of infinite dissipation (b = 0), it reduces to the non-invertible logistic map. Instead o...

We consider a large ensemble of globally coupled subthreshold Morris-Lecar neurons. We numerically investigate collective coherence of noise-induced spikings by varying the coupling strength J. As J passes a lower threshold, a transition to collective spiking coherence, which is described in terms of an order parameter, occurs because the coupling...

We numerically study dynamical behaviors of the quasiperiodically forced
Hodgkin-Huxley neuron and compare the dynamical responses with those for the
case of periodic stimulus. In the periodically forced case, a transition from a
periodic to a chaotic oscillation was found to occur via period doublings in
previous numerical and experimental works....

We consider a large population of globally coupled subthreshold Morris-Lecar neurons. By varying the noise intensity D, we numerically investigate stochastic spiking coherence (i.e., collective coherence between noise-induced neural spikings). As D passes a lower threshold, a transition from an incoherent to a coherent state occurs because of a con...

We study dynamical responses of the self-oscillating Morris-Lecar (ML) neuron under quasiperiodic stimulation. For the case
of periodic stimulation on the self-oscillating ML neuron, a transition from a periodic to a chaotic oscillation occurs through
period doublings. We investigate the effect of the quasiperiodic forcing on this period-doubling r...

We consider an ensemble of globally coupled subthreshold Morris-Lecar neurons. As the coupling strength passes a lower threshold, the coupling stimulates coherence between noise-induced spikings. This coherent transition is well described in terms of an order parameter. However, for sufficiently large J, "stochastic oscillator death" (i.e., quenchi...

We consider a large population of globally coupled subthreshold Morris-Lecar neurons. By varying the noise intensity D, we investigate numerically stochastic spiking coherence (i.e., noise-induced coherence between neural spikings). As D passes a threshold, a transition from an incoherent to a coherent state occurs. This coherent transition is desc...

As a representative model for quasiperiodically forced period-doubling systems, we consider the quasiperiodically forced logistic map, and investigate the dynamical mechanism for the interior crises. For small quasiperiodic forcing ε, a chaotic attractor abruptly widens via a “standard” interior crisis when it collides with a smooth unstable torus....

We study the coupling effect on the occurrence of partial synchronization in four coupled one-dimensional maps by varying a parameter w (0⩽w⩽1) which tunes the “weight” in the next-nearest-neighbor coupling from the local nearest-neighbor coupling (w=0) to the global coupling (w=1). As the coupling parameter ε decreases and passes a threshold value...

We study the scaling behavior in two unidirectionally coupled one-dimensional maps near tricrit-ical points which lie at ends of Feigenbaum critical lines and near edges of the complicated parts of the boundary of chaos. Note that both period-doubling cascades to chaos and multistability (as-sociated with saddle-node bifurcations) occur in any neig...

We investigate the effect of parameter mismatch on partial synchronization in three coupled one-dimensional maps. A completely synchronized attractor on the diagonal loses its transverse stability through a blowout bifurcation, and then partial synchronization may occur on an invariant plane. Due to the existence of positive local transverse Lyapun...

As a representative model for quasiperiodically forced period-doubling systems, we consider the quasiperiodically forced Hénon map and investigate the dynamical mechanism for the band-merging route to intermittent strange nonchaotic attractors (SNAs). Using the rational approximation to quasiperiodic forcing, we show that a band-merging transition...

We study three unidirectionally coupled one-dimensional unimodal maps by changing the order α (1 ≤ α ≤ 2) of the local maximum. A fully synchronized chaotic attractor on the diagonal becomes transversely unstable via a blowout bifurcation; then, partial synchronization or complete desynchronization occurs depending on the value of α. For the quadra...

As a representative model for the Poincar´e map of quasiperiodically forced oscillators, we consider
the quasiperiodically forced H´enon map and investigate the mechanism for boundary crises. Using
rational approximations to quasiperiodic forcing, we show that a new type of boundary crisis occurs
for a nonchaotic attractor (smooth torus or strange...

We investigate the dynamical mechanism for the partial synchronization in three coupled one-dimensional maps. A completely synchronized attractor on the diagonal becomes transversely unstable via a blowout bifurcation, and then a two-cluster state, exhibiting on-off intermittency, appears on an invariant plane. If the newly created two-cluster stat...

As a representative model for quasiperiodically forced period-doubling systems, we consider the quasiperiodically forced logistic map, and investigate the mechanism for the band-merging transition. When the smooth unstable torus loses its accessibility from the interior of the basin of an attractor, it cannot induce the “standard” band-merging tran...

We investigate the mechanism for boundary crises in the quasiperiodically forced logistic map which is a representative model for quasiperiodically forced period-doubling systems. For small quasiperiodic forcing ɛ, a chaotic attractor disappears suddenly via a “standard” boundary crisis when it collides with the smooth unstable torus. However, when...

To examine the universality for the parameter-mismatching effect on weak chaotic synchronization, we study coupled multidimensional invertible systems such as the coupled Hénon maps and coupled pendula. By generalizing the method proposed in coupled one-dimensional (1D) noninvertible maps, we introduce the parameter sensitivity exponent δ to measur...

We investigate the noise effect on weak chaotic synchronization in coupled invertible systems such as coupled Hénon maps and coupled pendula. Weakly stable synchronous chaotic attractors (SCAs) with positive local transverse Lyapunov exponents are sensitive with respect to variations in the noise intensity. To quantitatively characterize such noise...

To examine the universality for the intermittent route to strange nonchaotic attractors (SNAs), we investigate the quasiperiodically forced Hénon map, ring map and Toda oscillator which are high-dimensional invertible systems. In these invertible systems, dynamical transition to an intermittent SNA occurs via a phase-dependent saddle–node bifurcati...

Intermittent strange nonohaotic attractors (SNAs) appear typically in quasiperiodically forced systems. As a basic model, we consider the quasiperiodically forced Hénon map and investigate the mechanism for the intermittent transition to SNAs. Using rational approximations to the quasiperiodic forcing, it is shown that dynamical transition to an in...

We investigate the effect of parameter mismatch on weak synchronization in unidirectionally coupled invertible Hénon maps. Due to the existence of positive local transverse Lyapunov exponents, a weakly stable synchronized attractor (SCA) becomes sensitive with respect to the variation of the mismatching parameter. As in coupled noninvertible one-di...

The critical behavior of the system of two coupled invertible maps with period-doubling was in-vestigated. We obtain that the critical behavior of the FQ-type exists in the invertible systems only when partial systems are coupled in a special way: with dissipative coupling. The coordinates of the critical (FQ) point in the system of dissipatively c...

We investigate the dynamical origin for the occurrence of asynchronous hyperchaos and chaos via blowout bifurcations in coupled chaotic systems. An asynchronous hyperchaotic or chaotic attractor with a positive or negative second Lyapunov exponent appears through a blowout bifurcation. It is found that the sign of the second Lyapunov exponent of th...

We investigate the global effect of transverse bifurcations in symmetrically coupled one-dimensional maps. A transition from strong to weak synchronization occurs via a first transverse bifurcation of a periodic saddle embedded in a synchronous chaotic attractor (SCA). For the case of a supercritical transverse bifurcation, a soft bubbling transiti...

We investigate the consequence of a blow-out bifurcation of a chaotic attractor in an invariant line in a family of piecewise linear planar maps by changing a positive parameter β controlling the reinjection. Through a supercritical blow-out bifurcation, a chaotic or hyperchaotic attractor, exhibiting on-off intermittency, is born, depending on the...

We investigate mechanisms for the hard bubbling transition in symmetrically coupled one-dimensional maps. A transition from strong to weak synchronization occurs via a first period-doubling or pitchfork transverse bifurcation of a periodic saddle embedded in the synchronous chaotic attractor. The consequence of such transverse bifurcations depends...

Intermittent strange nonchaotic attractors (SNAs) appear typically in quasiperiodically forced period-doubling systems. As a representative model, we consider the quasiperiodically forced logistic map and investigate the mechanism for the intermittent route to SNAs using rational approximations to the quasiperiodic forcing. It is found that a smoot...

We consider the existence of robust strange nonchaotic attractors in a simple class of quasiperiodically forced systems. Rigorous results are presented demonstrating that the resulting attractors are strange in the sense that their box-counting dimension D0 is larger than their information dimension D1 by 1 (i.e., D(0)=D(1)+1). We also show how thi...

We investigate the noise effect on weak synchronization in two coupled identical one-dimensional (1D) maps. Due to the existence of positive local transverse Lyapunov exponents, the weakly stable synchronous chaotic attractor (SCA) becomes sensitive with respect to the variation of noise intensity. To quantitatively characterize such noise sensitiv...