Abstract
Optogenetically evoked local field potential (LFP) recorded from the medial prefrontal cortex (mPFC) of mice during basal conditions and following a systemic cocaine administration were analyzed. Blue light stimuli were delivered to mPFC through a fiber optic every 2 s and each trial was repeated 100 times. As in the previous study, we used a surrogate data method to check that nonlinearity was present in the experimental LFPs and only used the last 1.5 s of steady activity to measure the LFPs phase resetting induced by the brief 10 ms light stimulus. We found that the steady dynamics of the mPFC in response to light stimuli could be reconstructed in a three-dimensional phase space with topologically similar “8”-shaped attractors across different animals. Therefore, cocaine did not change the complexity of the recorded nonlinear data compared to the control case. The phase space of the reconstructed attractor is determined by the LFP time series and its temporally shifted versions by a multiple of some lag time. We also compared the change in the attractor shape between cocaine-injected and control using (1) dendrogram clustering and (2) Frechet distance. We found about 20% overlap between control and cocaine trials when classified using dendrogram method, which suggest that it may be possible to describe mathematically both data sets with the same model and slightly different model parameters. We also found that the lag times are about three times shorter for cocaine trials compared to control. As a result, although the phase space trajectories for control and cocaine may look similar, their dynamics is significantly different.
Highlights
Pyramidal cells together with spiny stellates constitute more than 70% of the excitatory neural population of the cortex (Feldman, 1984; Bannister, 2005)
In this paper series, we investigated the local field potential (LFP) using delay-embedding method of nonlinear dynamics to estimate the number of degrees of freedom of the steady activity of medial prefrontal cortex (mPFC) neural network
The activity of the medial prefrontal cortex in six mice systemically injected with cocaine (20 mg/ kg ip) was optogenetically perturbed with brief laser pulses
Summary
Pyramidal cells together with spiny stellates constitute more than 70% of the excitatory neural population of the cortex (Feldman, 1984; Bannister, 2005). Pyramidal cells form wide interconnected network spanning layers 2–6 (Bannister, 2005). They serve, among other functions, maintaining prefrontal cortex activity during working memory (Sanchez-Vives and McCormick, 2000) and generate the UP states of persistent network activity (Luczak et al, 2007; Compte et al, 2008). PV+ interneurons present a significant heterogeneity of projections to pyramidal cells processes that allow them a fine-tuned functional control of pyramidal cells (DeFelipe and Farinas, 1992). It has been established that projections of PV+ neurons to pyramidal cells soma and proximal dendrites are very effective in modulating their firing rate (Halasy et al, 1996; Booker et al, 2013), whereas synapses on the axons of pyramidal cells can block action potentials (Melchitzky and Lewis, 2003; Henry et al, 2004; Micheva et al, 2016)
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