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ABSTRACT: The theta-gamma cross-frequency coupling (CFC) in hippocampus was reported to reflect memory process. In this study, we measured the CFC of hippocampal local field potentials (LFPs) in a two-vessel occlusion (2VO) rat model, combined with both amplitude and phase properties and associated with short and long-term plasticity indicating the memory function. Male Wistar rats were used and a 2VO model was established. STP and LTP were recorded in hippocampal CA3-CA1 pathway after LFPs were collected in both CA3 and CA1. Based on the data of relative power spectra and phase synchronization, it suggested that both the amplitude and phase coupling of either theta or gamma rhythm were involved in modulating the neural network in 2VO rats. In order to determine whether the CFC was also implicated in neural impairment in 2VO rats, the coupling of CA3 theta-CA1 gamma was measured by both phase-phase coupling (n:m phase synchronization) and phase-amplitude coupling. The attenuated CFC strength in 2VO rats implied the impaired neural communication in the coordination of theta-gamma entraining process. Moreover, compared with modulation index (MI) a novel algorithm named cross frequency conditional mutual information (CF-CMI), was developed to focus on the coupling between theta phase and the phase of gamma amplitude. The results suggest that the reduced CFC strength probably attributed to the disruption of the phase of CA1 gamma envelop. In conclusion, it implied that the phase coupling and CFC of hippocampal theta and gamma played an important role in supporting functions of neural network. Furthermore, synaptic plasticity on CA3-CA1 pathway was reduced in line with the decreased CFC strength from CA3 to CA1. It partly supported our hypothesis that directional CFC indicator might probably be used as a measure of synaptic plasticity.
Frontiers in Computational Neuroscience 01/2013; 7:27. · 2.15 Impact Factor
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ABSTRACT: Alterations in oscillatory brain activity are strongly correlated with cognitive performance in various physiological rhythms. The present study investigated whether the directionality of neural information flow (NIF) could be used to characterize the synaptic plasticity in thalamocortical (TC) pathway, and examined which frequency field oscillations were mostly related to the cognitive deficiency in depression. Two novel algorithms were employed to determine the coupling interaction between the LD thalamus and medial prefrontal cortex (mPFC) in five frequency bands, using the phase signals of local field potentials (LFP) in these two regions. The results showed that the power of neural activity in mPFC was increased in delta, theta and beta frequency bands in depression. However, the nonlinear characteristics of LFP activity were weakened in depression by means of sample entropy measurements. In the analysis of phase dynamics, the phase synchronization values were reduced in theta rhythm in stressed rats. Importantly, the coupling direction index d and the unidirectional influence from LD thalamus to mPFC were significantly reduced at the theta rhythm in rats in depression, and increased after memantine treatment, which were associated with the LTP alterations and cognitive impairment in our previous report. Moreover, the fact that the reduced entropy value was only found in mPFC might implicate postsynaptic effect involved in synaptic plasticity alteration in the depression model. The results suggest that the effects of depression on cognitive deficits are mediated via profound alterations in information flow in the TC pathway, and the directional index at theta rhythm could be used as a measurement of synaptic plasticity.
Journal of Computational Neuroscience 05/2012; · 2.51 Impact Factor
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ABSTRACT: To examine whether the directionality index of neural information flow (NIF) over specific oscillatory bands is useful in measuring synaptic plasticity, we employed the IM approach to determine the direction of NIF between the cortex and thalamus in normal and stressed animals. The experiment was performed by inducing long-term potentiation (LTP) of the thalamocortical pathway after recording local field potential (LFP). Additionally, comparison of IM measurement between broad- and narrowbands was performed, while a numerical study was also carried out for assessing the number of data points. The results show that the instantaneous phases extracted from narrowband vary monotonically, while these phases are jagged in broadband. Our data show that there is a predominant driving effect (coupling directional index d >0) from the thalamus to the frontal cortex in normal animals; however, the value of d is significantly reduced in the chronic stressed group in both the delta and theta bands. Furthermore, the field LTP data show that chronic stress decreases medial prefrontal cortex synaptic plasticity, which is certainly in line with the LFP findings. Together, these data suggest that using an IM algorithm, the directionality index of NIF in specific oscillatory frequency bands will probably be used as a measure of synaptic plasticity.
Neurosignals 08/2011; 19(4):189-97. · 2.11 Impact Factor
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ABSTRACT: Growing evidence suggests the involvement of stress in the pathophysiology of depression. This study was designed to test behavioral and electrophysiological changes in a stressed model of depression. Rats were randomly divided into control and stressed groups. Chronic unpredictable stress combined with isolation rearing was applied in rats of stressed group for three weeks. Weight and sucrose consumption were measured during the model establishing period. Behavior was measured by Morris water maze. Electroencephalography (EEG) of thalamus and prefrontal cortex was recorded after behavioral tests, followed by recording long-term potentiation (LTP) of the same thalamocortical pathway. Results showed that rats' weight and sucrose intake were significantly lower in stressed group than those in control group. In stressed group, escape latency of reversal training stage in water maze test was significantly prolonged, and platform crossings of reversal probe trials were significantly decreased. EEG test showed that the extent of thalamus driving prefrontal cortex was decreased in stressed group. LTP test showed lower postsynaptic potential amplitude in stressed group as compared to that in control group. In conclusion, chronic stress could cause certain behavioral changes in rats, with possible mechanism of impairing EEG of certain thalamocortical pathway and prefrontal cortical synaptic plasticity.
Brain research bulletin 03/2011; 85(3-4):109-16. · 2.18 Impact Factor
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ABSTRACT: This investigation examined whether the directionality of neural information flow could be used to index the measurement of synaptic plasticity in the chronic unpredictable stress (CUS) animals. Evolution map approach (EMA) was employed to determine the direction of information flow between the cortex and thalamus, while the experiment was performed by inducing long-term potentiation of the thalamocortical pathway after recording intracranial EEG at the same two positions in Wistar rats of both normal and stressed groups. The results showed that the coupling direction index was significantly diverted in stressed state compared to that in normal state, while the strength of thalamus driving frontal cortex was considerably reduced in the rats of CUS model. Moreover, the data obtained from LTP experiment exhibited that chronic stress decreased medial prefrontal cortex (mPFC) synaptic plasticity, which was certainly in accordance with the EEG findings. These results demonstrated that using EMA measurement, directionality index of neural information flow may be as a measure of synaptic plasticity.
Neuroscience Letters 02/2011; 490(1):52-6. · 2.11 Impact Factor
