Laminar Distribution of Phase-Amplitude Coupling of Spontaneous Current Sources and Sinks.

Amir Shmuel,Shmuel Naaman,Aleksandra Bortel,Pascal Kropf,Victor M Mocanu,Roberto C Sotero,Martin Villeneuve

doi:10.3389/fnins.2015.00454

Amir Shmuel, Shmuel Naaman + Show 5 more

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https://doi.org/10.3389/fnins.2015.00454

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Abstract

Although resting-state functional connectivity is a commonly used neuroimaging paradigm, the underlying mechanisms remain unknown. Thalamo-cortical and cortico-cortical circuits generate oscillations at different frequencies during spontaneous activity. However, it remains unclear how the various rhythms interact and whether their interactions are lamina-specific. Here we investigated intra- and inter-laminar spontaneous phase-amplitude coupling (PAC). We recorded local-field potentials using laminar probes inserted in the forelimb representation of rat area S1. We then computed time-series of frequency-band- and lamina-specific current source density (CSD), and PACs of CSD for all possible pairs of the classical frequency bands in the range of 1–150 Hz. We observed both intra- and inter-laminar spontaneous PAC. Of 18 possible combinations, 12 showed PAC, with the highest measures of interaction obtained for the pairs of the theta/gamma and delta/gamma bands. Intra- and inter-laminar PACs involving layers 2/3–5a were higher than those involving layer 6. Current sinks (sources) in the delta band were associated with increased (decreased) amplitudes of high-frequency signals in the beta to fast gamma bands throughout layers 2/3–6. Spontaneous sinks (sources) of the theta and alpha bands in layers 2/3–4 were on average linked to dipoles completed by sources (sinks) in layer 6, associated with high (low) amplitudes of the beta to fast-gamma bands in the entire cortical column. Our findings show that during spontaneous activity, delta, theta, and alpha oscillations are associated with periodic excitability, which for the theta and alpha bands is lamina-dependent. They further emphasize the differences between the function of layer 6 and that of the superficial layers, and the role of layer 6 in controlling activity in those layers. Our study links theories on the involvement of PAC in resting-state functional connectivity with previous work that revealed lamina-specific anatomical thalamo-cortico-cortical connections.

Highlights

Cross-frequency coupling describes statistical dependencies between the phases and/or amplitudes of different frequency bands of one or more signals
The amplitudes of the sources and sinks were higher for smaller diameters, the spatiotemporal patterns were similar for the standard current source density (CSD) and inverse CSD (iCSD) methods and across the assumed diameters for the sources and sinks
(2) Statistically, significant phase-amplitude coupling (PAC) exists for all combinations of phases of the delta, theta and alpha bands and amplitudes of the higher rhythms, from beta to fast gamma; the highest PAC values were obtained for the combinations of phases of the theta and delta bands and the amplitudes of the middle- and fast-gamma bands

Summary

Introduction

Cross-frequency coupling describes statistical dependencies between the phases and/or amplitudes of different frequency bands of one or more signals. Three main modalities of cross-frequency coupling have been observed in local field potentials (LFP): phase-phase coupling (PPC), amplitudeamplitude coupling (AAC), and phase-amplitude coupling (PAC). PAC takes place when the phase of a low-frequency signal modulates the amplitude of a higher frequency one. Bragin et al (1995) demonstrated a classic example of PAC in the CA1 region of the hippocampus, where the phase of the theta band modulates the power of the gamma band. PAC has been detected in pairs of other frequency bands, including the delta, alpha, and beta rhythms in the cortex (Lakatos et al, 2005; Spaak et al, 2012; Wang et al, 2012; de Hemptinnea et al, 2013)

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