Marzena Ciszak

Spatiotemporal dynamics of the electrical network activity in the root apex

The study of electrical network systems, integrated with chemical signaling networks, is becoming a common trend in contemporary biology. Classical techniques are limited to the assessment of signals from doublets or triplets of cells at a fixed temporal bin width. At present, full characteristics of the electrical network distribution and dynamics in plant cells and tissues has not been established. Here, a 60-channels multielectrode array (MEA) is applied to study spatiotemporal characteristics of the electrical network activity of the root apex. Both intense spontaneous electrical activities and stimulation-elicited bursts of locally propagating electrical signals have been observed. Propagation of the spikes indicates the existence of excitable traveling waves in plants, similar to those observed in non-nerve electrogenic tissues of animals. Obtained data reveal synchronous electric activities of root cells emerging in a specific root apex region. The dynamic electrochemical activity of root apex cells is proposed to continuously integrate internal and external signaling for developmental adaptations in a changing environment.

Characterization of the anticipated synchronization regime in the coupled FitzHugh–Nagumo model for neurons

We characterize numerically the regime of anticipated synchronization in the coupled FitzHugh–Nagumo model for neurons. We consider two neurons, coupled unidirectionally (in a master–slave configuration), subject to the same random external forcing and with a recurrent inhibitory delayed connection in the slave neuron. We show that the scheme leads to anticipated synchronization, a regime in which the slave neuron fires the same train of pulses as the master neuron, but earlier in time. We characterize the synchronization in the parameter space (coupling strength, anticipation time) and introduce several quantities to measure the degree of synchronization.

Swarming Behavior in Plant Roots

Interactions between individuals that are guided by simple rules can generate swarming behavior. Swarming behavior has been observed in many groups of organisms, including humans, and recent research has revealed that plants also demonstrate social behavior based on mutual interaction with other individuals. However, this behavior has not previously been analyzed in the context of swarming. Here, we show that roots can be influenced by their neighbors to induce a tendency to align the directions of their growth. In the apparently noisy patterns formed by growing roots, episodic alignments are observed as the roots grow close to each other. These events are incompatible with the statistics of purely random growth. We present experimental results and a theoretical model that describes the growth of maize roots in terms of swarming.

Dynamical mechanism of anticipating synchronization in excitable systems

We analyze the phenomenon of anticipating synchronization of two excitable systems with unidirectional delayed coupling which are subject to the same external forcing. We demonstrate for different paradigms of excitable system that, due to the coupling, the excitability threshold for the slave system is always lower than that for the master. As a consequence the two systems respond to a common external forcing with different response times. This allows us to explain in a simple way the mechanism behind the phenomenon of anticipating synchronization in excitable systems.

Chaotic spiking and incomplete homoclinic scenarios in semiconductor lasers with optoelectronic feedback

We demonstrate experimentally and theoretically the existence of slow chaotic spiking sequences in the dynamics of a semiconductor laser with ac-coupled optoelectronic feedback. The timescale of these dynamics is fully determined by the high-pass filter in the feedback loop and their erratic, though deterministic, nature is evidenced by means of the interspike interval (ISI) probability distribution. We eventually show that this regime is the result of an incomplete homoclinic scenario to a saddle-focus, where an exact homoclinic connection does not occur.

The Electrical Network of Maize Root Apex is Gravity Dependent

Investigations carried out on maize roots under microgravity and hypergravity revealed that gravity conditions have strong effects on the network of plant electrical activity. Both the duration of action potentials (APs) and their propagation velocities were significantly affected by gravity. Similarly to what was reported for animals, increased gravity forces speed-up APs and enhance synchronized electrical events also in plants. The root apex transition zone emerges as the most active, as well as the most sensitive, root region in this respect.

Electrical spiking in bacterial biofilms

In nature, biofilms are the most common form of bacterial growth. In biofilms, bacteria display coordinated behaviour to perform specific functions. Here, we investigated electrical signalling as a possible driver in biofilm sociobiology. Using a multi-electrode array system that enables high spatio-temporal resolution, we studied the electrical activity in two biofilm-forming strains and one non-biofilm-forming strain. The action potential rates monitored during biofilm-forming bacterial growth exhibited a one-peak maximum with a long tail, corresponding to the highest biofilm development. This peak was not observed for the non-biofilm-forming strain, demonstrating that the intensity of the electrical activity was not linearly related to the bacterial density, but was instead correlated with biofilm formation. Results obtained indicate that the analysis of the spatio-temporal electrical activity of bacteria during biofilm formation can open a new frontier in the study of the emergence of collective microbial behaviour.

Control of transient synchronization with external stimuli.

A network of coupled chaotic oscillators can switch spontaneously to a state of collective synchronization at some critical coupling strength. We show that for a locally coupled network of units with coexisting quiescence and chaotic spiking states, set slightly below the critical coupling value, the collective excitable or bistable states of synchronization arise in response to a stimulus applied to a single node. We provide an explanation of this behavior and show that it is due to a combination of the dynamical properties of a single node and the coupling topology. By the use of entropy as a collective indicator, we present a new method for controlling the transient synchronization.

COUPLING AND FEEDBACK EFFECTS IN EXCITABLE SYSTEMS: ANTICIPATED SYNCHRONIZATION

This paper reviews our recent work on the synchronization of excitable systems in a master–slave configuration and when the slave system includes a delayed self-coupling term. Particularly, we address the existence of the so-called anticipated synchronization, i.e. a dynamical regime in which the slave system is able to reproduce in advance the evolution of the master. This is most remarkable since the anticipated synchronization appears even when the excitable spikes are induced by random terms, such as white noise. After providing a short review of the general theory of synchronization as well as the main features of excitable systems, we present numerical and experimental results in coupled excitable systems of the FitzHugh–Nagumo type driven by different types of noise. The experiments have been done in electronic implementations of the model equations. We present the conditions (values of the coupling intensity and delay time) for which the anticipated synchronization regime is a stable one and show that it is possible to increase the anticipation time by using a cascade of several coupled systems. We use a particular limit of the FitzHugh–Nagumo system, as well as a simple excitable model, to give evidence that the physical reason for the existence of anticipated synchronization is the lowering of the excitability threshold of the slave due to the coupling. Finally, we propose a hypothesis for a possible explanation of the zero-lag synchronization observed in some real neuron systems.

Plant shoots exhibit synchronized oscillatory motions.

ABSTRACT In animals, the ability to move has evolved as an important means of protection from predators and for enhancing nutrient uptake. In the animal kingdom, an individuals movements may become coordinated with those of other individuals that belong to the same group, which leads, for example, to the beautiful collective patterns that are observed in flocks of birds and schools of fish or in animal migration. Land plants, however, are fixed to the ground, which limits their movement and, apparently, their interactions and collective behaviors. We show that emergent maize plants grown in a group exhibit synchronized oscillatory motions that may be in-phase or anti-phase. These oscillations occur in short bursts and appear when the leaves rupture from the coleoptile tip. The appearance of these oscillations indicates an abrupt increase in the plant growth rate, which may be associated with a sudden change in the energy uptake for photosynthesis. Our results suggest that plant shoots behave as a complex network of biological oscillators, interacting through biophysical links, e.g. chemical substances or electric signals.