In this paper, we study the modulation of low frequency closed-loop electric stimulation on spontaneous activity in cultured hippocampal neuronal networks. First, we plated monolayer cultures of hippocampal neurons from rat embryos (E18) on multi-electrode arrays and the experiments were performed in the networks from the second week to the sixth week continuously. During the experiments, we detected the spontaneous spikes of the networks firstly, and then stimulated the networks at low frequency (0.2 Hz or 1 Hz) stimulation respectively until a desired response was observed 20-80msec after a stimulus. The protocol was closed-loop. After that, we detected the spontaneous spikes of the networks. It is observed that the spontaneous activity in the developing networks is developing, which is oscillatory and periodic. Low frequency (0.2 Hz or 1 Hz) stimulation enhanced the spontaneous synchronous burst activity of the developing networks. These results implicated that activity-dependent mechanism in the modulation of plasticity of synaptic transmission in the cultured neuronal networks. Closed-loop stimulation will give a better view on the functional significance of networks activities. Besides, close-loop stimulation could set up the stimulus-reward system in the neuronal networks, which is of great benefit to the plasticity of synaptic transmission in the cultured neuronal networks.
Burst as a unit of information coding is widely investigated in the developing central nervous system. However the
mechanism underling the bursts generate and disappear is unclear at present. Neurons cultured on the multi-electrode
arrays, are spontaneously active, and show complex pattern with random spikes and bursts firing. With long-term
recording, the course of bursts generation and disappearance was detected. The results showed that the firing pattern
could transform from random spikes to bursts firing. In the beginning, the random spikes rate decreased, accompanied
with bursts occurred once in a while. It appeared both single spikes and bursts at the same time. After that, the random
spikes disappeared. Spontaneous activity displayed a regular occurrence of bursts with shorter interspike interval. During
such bursts the firing rate at the active sites was increased dramatically. After several seconds, firing rate decreased,
interburst interval extended, accompanied with the occurrence of random spikes, opposite to the beginning. At last,
bursts disappeared and the networks just fired in random spikes. The observation showed that the complex
electrophysiological activities of the cultured neuronal networks could implicate the spontaneous generation of burst
firing. Understanding how bursts generate and disappear might be significant for deeply investigating the function and
mechanism of bursts information coding.