Juvenile and adult mice show similar global brain states under urethane anesthesia.

<p>Relative power spectra corresponding to cortical (<b>A</b>) and hippocampal EEG (<b>B</b>), in juvenile and adult mice, in slow wave and desynchronized states. The data are the relative power encompassed between the 95% confidence intervals of the mean. Juveniles and adults show similar frequency composition of cortical and hippocampal EEG, but hippocampal theta shows a slightly higher frequency in adults (4.33±0.07 vs. 4.67±0.08 Hz; p<0.01, t-test).</p

Recording of mPFC activity under different global brain states.

<p><b>A.</b> Positioning of a multichannel recording “silicon probe” in the medial PFC (left) and of bipolar electrodes in the frontal cortex (cortical EEG) and hippocampus (hippocampal EEG, right). <b>B.</b> Representative example showing the cortical and hippocampal EEG patterns seen in mice under urethane anesthesia, the mirror changes in relative power taking place in a low frequency band recorded from the frontal cortex (purple trace) and the theta band recorded from the hippocampus (light blue), and the epochs selected automatically by the algorithm used to classify the global brain states (green and grey). <b>C.</b> Representative recording during a transition from the slow wave state (box) to the desynchronized state. Note at right the lower amplitude and higher frequency of the cortical EEG accompanied with theta activity in the hippocampus, which are characteristic of the desynchronized state. The two lower traces show activity in one channel of the silicon probe after being bandpass filtered to separate multiunit activity (MUA) and the local field potential (LFP).</p

Neurons synchronize preferentially to gamma activity in the mPFC.

<p><b>A.</b> Representative traces showing the raw multiunit activity (MUA) and local field potential (LFP) recorded through one contact of a silicon probe located in the mPFC of an adolescent mouse. The traces shown below show signals resulting from band-pass digital filtering the LFP for alpha and high gamma bands. The green and red dots mark the occurrence of spikes from a pyramidal neuron sorted from MUA. Note the preferential occurrence of spikes in the troughs of the gamma oscillation. <b>B.</b> Spike-phase plots (bin size 10°) showing a uniform distribution of spikes across phases for the alpha band and a markedly non-uniform distribution for the same spikes across phases for the gamma band (statistically evaluated by the Rayleigh test). The plots correspond to the neuron shown in A. The resultant vector of the distribution has an angle (locking phase) and a length or module (locking strength). The numbers at the upper right quadrant of the plots refer to the radial axes of frequency distribution and vector length.</p

Selective reduction of gamma entrainment of mPFC neurons during adolescence.

<p>The strength of synchronization between spikes and LFP in the mPFC was assessed by computing the resultant vector of circular distributions as shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0062978#pone-0062978-g003" target="_blank">Figure 3</a>. Entrainment magnitude refers to the average vector length ± SEM across units. In <b>A</b>, all spikes in each mPFC recording site (95 sites in juveniles, 98 sites in adults) were used to compute the circular distributions (multiunit activity). <b>B</b> shows the average vector length for all well sorted pyramidal neurons (32 in juvenile and 35 in adult mice), and <b>C</b> shows average vector length for all well isolated interneurons (25 in juvenile and 38 in adult mice). Statistical analysis showed significant interaction between age and oscillatory band in all cases, repeated measures ANOVA interaction: MUA F_4,764 = 21.0 p<0.0001, pyramidal cells F_4,260 = 4.37 p<0.005, interneurons F_4,244 = 2.47 p<0.05; *p<0.05; ***p<0.001 juvenile vs. adult Newman-Keuls post hoc test.</p

Reduced span of interneuron entrainment to gamma oscillations in adults.

<p><b>A.</b> Schematic representation showing the localization of recording sites in the mPFC. A coronal section of a representative animal was photographed under transmitted light and epifluorescence to show the location of fluorescent material left by the labeled silicon probe in the mPFC. To estimate the span of neuronal synchronization to gamma oscillations, we took the spikes of a given recording site and computed their spike-phase circular distribution for the LFP in the recording site from which they were recorded and for LFPs at other recording sites along the electrode. In this example, three circular distributions are depicted for one unit, representing the entrainment with the local LFP (cero distance) and LFPs obtained 100 and 400 µm apart. <b>B</b> and <b>C.</b> Entrainment strength to high-gamma oscillations as function of distance along the mPFC, for pyramidal neurons (<b>B</b>) and interneurons (<b>C</b>). In adults, interneuron entrainment to high gamma is more spatially restricted than in juveniles. * p<0.05 Newman-Keuls post hoc test after a two way ANOVA for repeated measures with significant interaction. Note that pyramidal neurons show a very local entrainment to gamma, whereas interneurons are coupled to gamma recorded 200 µm apart. Entrainment magnitude refers to the average vector length ± SEM at each LFP recording site along the mPFC.</p