Effect of theta-modulated input on LFP gamma amplitude.

<p>(A) The distribution of a composite theta phase/gamma amplitude signal in the complex plane. Color code represents the number of observations; angle corresponds to theta phase (divided into equally-sized bins); radius corresponds to gamma amplitude (divided into equally-sized bins). (B) Histograms of gamma amplitudes occurring in wide phase bins centered at the peak of the theta rhythm (; black) and at the trough (; red). Dashed lines correspond to the observed data histograms; solid lines represent the best-fit gamma distribution for this data. When FS cells receive theta-modulated input, the best-fit distribution for the theta trough is shifted to the right, compared to the distribution for the theta peak (parameter differences are significant, ). (C) Mean gamma amplitude as a function of theta phase. For the two rightmost plots, the best-fit sine functions are shown by a dashed red line. Gamma amplitudes are higher at the trough than at the peak of the theta rhythm, and the lowest and highest gamma amplitudes (indicated by dotted vertical lines) occur somewhat after the theta peak and trough, respectively.</p

A patch of neocortex modelled by a network of interneurons coupled with a network of pyramidal cells.

<p>(A) The macroarchitecture of the model. Shown are the fast-spiking inhibitory interneuron network (circle, left), the pyramidal cell network (triangle, right), the cortical long-range afferent spike trains (top), and the theta-modulated subcortical afferent spike trains (bottom). (B) The ring-like structure of the interneuron model. Shown are some of the inhibitory synaptic connections (solid circles) and gap junctions (‘conduits’ between adjacent cells) for cell 1. (C) The two-dimensional structure of the pyramidal cell network. Shown are some of the excitatory synaptic projections from cell to its neighbours. Note the projections to and are possible because the effective distance from to those cells equals (see Methods for details).</p

Frequency/input curves for the two model subnetworks: the fast-spiking cells (top) and the pyramidal cells (bottom).

<p>The dotted lines perpendicular to the x-axis represent the total range of spike train input experienced by the subnetworks due to the theta-modulated input fibres. Dotted lines perpendicular to the y-axis represent the resulting subnetwork spike activity. While the theta-modulation of input spikes is stronger for the FS cells than for the P cells, the resulting difference in subnetwork spike activity is greater for the P cells, as can be observed from the intersection of the horizontal lines with the y-axis.</p

Shunting inhibition increases robustness in a network of fast-spiking inhibitory interneurons.

<p>(A–B) Rasterplots (top) and spike histograms (bottom) for simulations GABA -synaptic reversal potentials of (A) and (B). For these plots, mean drive , drive variation . Synapses were activated at ; plots are truncated at . (C) Amplitude spectra for spike histograms. Spectral analyses were performed on complete histograms, ending at . (D) Two measures of network synchronization, network coherence (top row) and average spike volley peak height (bottom row), as a function of drive variation over cells (x-axis), synaptic reversal potential (y-axis), and mean drive (separate columns). Shunting values of result in stronger synchronization with increasing drive heterogeneity.</p

Model connectivity values.

<p>Shown is the number of synapses of different types, presented as ratios of the total number of synapses. Model values were either chosen to reflect connectivity known from anatomy (reported anatomical values are from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0045688#pone.0045688-Liley1" target="_blank">[65]</a>), or, in the case of the FS FS connectivity, based on previous modelling work <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0045688#pone.0045688-Vida1" target="_blank">[28]</a>.</p

Pyramidal cells show gamma-synchronized activity when cells receive shunting inhibition.

<p>(A) Spike histograms and simulated LFP traces for the unconnected ( FS to P synapses per P -cell) and connected ( FS to P synapses per P -cell) conditions. Other input to the P -cells consisted of constant-rate Poisson spike trains. (B) Amplitude spectra for the simulated LFP in the connected (red) and unconnected (blue) conditions. The LFP spectrum for the connected condition shows a clear increase in power in the gamma band (30–80 Hz). (C) Relative gamma band power (top) and pyramidal cell network synchronization (bottom) as a function of the average number of GABA -ergic projections from the FS cells to a single P -cell. Relative gamma power increases steadily with the number of synapses, reaching a maximum at synapses per P -cell. Network synchronization starts to occur at synapses per P -cell. Shown are the mean values for simulation runs; error bars represent confidence interval.</p

Effect of theta-modulated input on LFP gamma frequency.

<p>(A) Time-frequency representations of one second of simulated LFP activity. The four panels correspond to theta-modulated input fibres projecting to different parts of the model network. (B) The frequency within the gamma band with the highest power, for the same data segments shown in A. Theta phase/gamma frequency coupling is observed if and only if the FS cells receive theta-modulated input.</p