Working memory (WM) plays a crucial role in human brain functions. The application of brain connectivity analysis helps to understand the brain network properties in WM. Combination of functional and effective connectivity can provide new insights for exploring network attributes. Nevertheless, few studies have combined these two modes in WM. Near-infrared spectroscopy was used to investigate the connectivity properties in the prefrontal cortex (PFC) during n-back (0-back and 2-back) tasks by combining functional and effective connectivity analysis. Our results demonstrated that the PFC network showed small-world properties in both WM tasks. The characteristic path length was significantly longer in the 2-back task than in the 0-back task, while there was no obvious difference in the clustering coefficient between two tasks. Regarding the effective connectivity, the Granger causality (GC) was higher for right PFC→left PFC than for left PFC→right PFC in the 2-back task. Compared with the 0-back task, GC of right PFC→left PFC was higher in the 2-back task. Our findings show that, along with memory load increase, long range connections in PFC are enhanced and this enhancement might be associated with the stronger information flow from right PFC to left PFC.
Deciphering the fine morphology and precise location of neurons and neural circuits are crucial to enhance our understanding of brain function and diseases. Traditionally, we have to map brain images to coarse axial-sampling planar reference atlases to orient neural structures. However, this means might fail to orient neural projections at single-cell resolution due to position errors resulting from individual differences at the cellular level. Here, we present a high-throughput imaging method that can automatically obtain the fine morphologies and precise locations of both neurons and circuits, employing wide-field large-volume tomography to acquire three-dimensional images of thick tissue and implementing real-time soma counterstaining to obtain cytoarchitectonic landmarks during the imaging process. The reconstruction and orientation of brain-wide neural circuits at single-neuron resolution can be accomplished for the same mouse brain without additional counterstains or image registration. Using our method, mouse brain imaging datasets of multiple type-specific neurons and circuits were successfully acquired, demonstrating the versatility. The results show that the simultaneous acquisition of labeled neural structures and cytoarchitecture reference at single-neuron resolution in the same brain greatly facilitates precise tracing of long-range projections and accurate locating of nuclei. Our method provides a novel and effective tool for application in studies on genetic dissection, brain function and the pathology of the nervous system.
The spontaneous synchronous activity is a common behavior in a developing brain and plays a critical role in
establishing appropriate connections and certain clinical diseases. Therefore, the investigation of the synchronous firing
is important for understanding the formation of functional circuits and their implications in the network plasticity. In a
limited period of time during development, the neuronal networks show synchronous activities, which occur
simultaneously on a large amount of cells and varies wildly among different preparations. In this study, the spontaneous
synchronous bursts are observed during the development of cultured neuron networks on multi-electrode array. The
initiating site of a round of spontaneous synchronous burst, estimated from the relative delays of onsets of activities
between electrodes, distributed randomly from each burst, while our statistical results confirmed that the positions of
such initiating sites are stable. By calculating the
cross-correlation function of the spike trains recorded from different
electrodes simultaneously, the spreading mode and the spreading topography of the synchronized bursting activity were
described. To access the changes in firing patterns in disinhibited cultured networks, the spontaneous activities were
compared with the firings when the network exposed to bicuculline, the blocker of GABAA receptor. The results showed
that the generation of synchronous bursts in cultured neuron networks is governed by the level of spontaneous activities
and by the balance between excitation and inhibition circuits.
Both neuroscience and nonlinear science have focused attention on the dynamics of the neural network. However, litter
is known concerning the electrical activity of the cultured neuronal network because of the high complexity and moment
change. Instead of traditional methods, we use chaotic time series analysis and temporal coding to analyze the
spontaneous firing spike train recorded from hippocampal neuronal network cultured on multi-electrode array. When
analyzing interspike interval series of different firing patterns, we found when single spike and burst alternate, the largest
Lyapunov exponent of interspike interval (ISI) series is positive. It suggests that chaos should exist. Furthermore, a
nonlinear phenomenon of bifurcation is found in the ISI vs. number histogram. It determined that this complex firing
pattern of neuron and the irregular ISI series were resulted from deterministic factors and chaos should exist in cultured
term.These results suggest that chaotic time series analysis and temporal coding provide us effective methods to
investigate the role played by deterministic and stochastic component in neuron information coding, but further research
should be carried out because of the high complexity and remarkable noise of the electric activity.
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.
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.
Transient and substantial elevation of postsynaptic calcium was important for hippocampal long-term potentiation (LTP), so detection of calcium changes in spine was necessary to understand the mechanisms underlying synaptic plasticity. Unfortunately most recent calcium fluorescence indicators severely perturbed calcium transients, and traditional cameleons’ poor dynamic ranges prevented detection of changes of calcium. We presented a new method to monitor quantificationally free calcium concentration in dendritic spines with a new yellow cameleon (YC3.60) basing on culture of hippocampal neurons and calcium phosphate transfection technique and confocal microscopy with 458nm laser. In transiently transfected hippocampal neurons, the ratio of YFP to CFP was detected as FRET level. In our study, we got the parameters of YC3.60 excited with 458nm laser. Under control conditions, FRET levels in different dendritic spines of cultured hippocampal neurons were diverse but showed robust increases upon treatment with potassium chloride. FRET levels in different parts of hippocampal neurons were also different, the calcium concentration decreased with the distance from soma. These results suggested that the FRET methodology with YC3.60 could monitor calcium concentration in spines and it might be useful in analyzing mechanisms underlying synaptic plasticity.
The technology of micro-electrode arrays is getting more and more important in the research of brain neural networks and its dynamics because of the ability to stimulate and record more neurons’ activities simultaneously. When the signals of many neurons with several noises in a local region are picked up with a microelectrode, a neurophysiologist may wish to sort these signals by assigning particular spikes to putative neurons with some degree of reliability. Spike sorting is a key step in whole data process and is a general problem in neural electrophysiology. Many algorithms for spike sorting have been brought forward based on the features of the spike waveforms from different neurons. In this article, I have accomplished spike sorting through analyzing the amplitude, shape and principal components of the spikes.
As a ubiquitous intracellular signal, calcium is responsible for controlling numerous cellular processes, such as neuronal signal transmission. In this paper we show that calcium imaging of cultured neuronal network from hippocampus of newborn rats, revealed synchronized calcium wave in intracellular Ca2+ concentration and induced calcium oscillation by stimulating embedded-microelectrode on glass substrate.
Learning is crucial for brain functioning, especially for hippocampus. To understand the basis of physiological information processing of hippocampus, we developed the networks of purified-cultured rat hippocampus neurons on a planar 60-microelectrode array MEA. We describe how these networks are prepared, their structure, and the forms of spontaneous activity they exhibit. We stimulate the network at a low frequency until a desired predefined response is observed 50- 10 msec after a stimulus, at which point the stimulus is stopped for 5 min. Repeated cycles of this procedure ultimately lead to the desired response being directly elicited by the stimulus. These results demonstrate that there is learning in networks composed of purified-cultured hippocampus neurons.
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