Responses to conflicting stimuli in a simple stimulus-response pathway.

The "local bend response" of the medicinal leech (Hirudo verbana) is a stimulus-response pathway that enables the animal to bend away from a pressure stimulus applied anywhere along its body. The neuronal circuitry that supports this behavior has been well described, and its responses to individual stimuli are understood in quantitative detail. We probed the local bend system with pairs of electrical stimuli to sensory neurons that could not logically be interpreted as a single touch to the body wall and used multiple suction electrodes to record simultaneously the responses in large numbers of motor neurons. In all cases, responses lasted much longer than the stimuli that triggered them, implying the presence of some form of positive feedback loop to sustain the response. When stimuli were delivered simultaneously, the resulting motor neuron output could be described as an evenly weighted linear combination of the responses to the constituent stimuli. However, when stimuli were delivered sequentially, the second stimulus had greater impact on the motor neuron output, implying that the positive feedback in the system is not strong enough to render it immune to further input.

Investigating neuronal activity by SPYCODE multi-channel data analyzer.

Multi-channel acquisition from neuronal networks, either in vivo or in vitro, is becoming a standard in modern neuroscience in order to infer how cell assemblies communicate. In spite of the large diffusion of micro-electrode-array-based systems, researchers usually find it difficult to manage the huge quantity of data routinely recorded during the experimental sessions. In fact, many of the available open-source toolboxes still lack two fundamental requirements for treating multi-channel recordings: (i) a rich repertoire of algorithms for extracting information both at a single channel and at the whole network level; (ii) the capability of autonomously repeating the same set of computational operations to 'multiple' recording streams (also from different experiments) and without a manual intervention. The software package we are proposing, named SPYCODE, was mainly developed to respond to the above constraints and generally to offer the scientific community a 'smart' tool for multi-channel data processing.

Interaction of electrically evoked responses in networks of dissociated cortical neurons.

In this work we describe the interaction of the responses of neuronal networks to pairs of electrical stimuli. For this we use networks of dissociated cortical neurons cultured on planar microelectrode arrays. We compare the response to pairs of stimuli with the response to a stimulus in isolation. To evaluate the influence of both stimuli we introduce a normalization of the root-mean square of the response. Furthermore we consider the response to a pair of stimuli as the linear superposition of the two constituents. The two methods combined show that the neuronal network strongly suppresses the second stimulus. At the same time we find a possible window of integration in which two stimuli from separate locations in the network can interact to form a new response.

Activity modulation elicited by electrical stimulation in networks of dissociated cortical neurons.

Recent results indicate that cultures of cortical neurons exhibit large amounts of spontaneous modulation. It has even been suggested that results obtained earlier could be explained by spontaneous development, rather than to be due to the external manipulation. This stresses the importance of having detailed knowledge of how a culture responds to stimulation, in order to discern activity modulation from structural plasticity. In this paper we apply several promising techniques of electrical stimulation to describe global network modulation occurring in these preparations. The results allow to anticipate on integration of this work in goal-directed stimulus-induced plasticity.