LORETA EEG phase reset of the default mode network.

Robert W Thatcher,Carl J Biver,Duane M North

doi:10.3389/fnhum.2014.00529

Abstract

Objectives: The purpose of this study was to explore phase reset of 3-dimensional current sources in Brodmann areas located in the human default mode network (DMN) using Low Resolution Electromagnetic Tomography (LORETA) of the human electroencephalogram (EEG).Methods: The EEG was recorded from 19 scalp locations from 70 healthy normal subjects ranging in age from 13 to 20 years. A time point by time point computation of LORETA current sources were computed for 14 Brodmann areas comprising the DMN in the delta frequency band. The Hilbert transform of the LORETA time series was used to compute the instantaneous phase differences between all pairs of Brodmann areas. Phase shift and lock durations were calculated based on the 1st and 2nd derivatives of the time series of phase differences.Results: Phase shift duration exhibited three discrete modes at approximately: (1) 25 ms, (2) 50 ms, and (3) 65 ms. Phase lock duration present primarily at: (1) 300–350 ms and (2) 350–450 ms. Phase shift and lock durations were inversely related and exhibited an exponential change with distance between Brodmann areas.Conclusions: The results are explained by local neural packing density of network hubs and an exponential decrease in connections with distance from a hub. The results are consistent with a discrete temporal model of brain function where anatomical hubs behave like a “shutter” that opens and closes at specific durations as nodes of a network giving rise to temporarily phase locked clusters of neurons for specific durations.

Highlights

IntroductionWhen one is at rest and not engaged in a task and absorbed in a ruminating self-narrative about the past and future it is during these reflective moments that the default mode network (DMN) is activated and the attention network is anti-correlated or reciprocally deactivated (Raichle et al, 2001; Raichle, 2010)
The results are consistent with a discrete temporal model of brain function where anatomical hubs behave like a “shutter” that opens and closes at specific durations as nodes of a network giving rise to temporarily phase locked clusters of neurons for specific durations
When one is at rest and not engaged in a task and absorbed in a ruminating self-narrative about the past and future it is during these reflective moments that the default mode network (DMN) is activated and the attention network is anti-correlated or reciprocally deactivated (Raichle et al, 2001; Raichle, 2010)

Summary

Introduction

When one is at rest and not engaged in a task and absorbed in a ruminating self-narrative about the past and future it is during these reflective moments that the default mode network (DMN) is activated and the attention network is anti-correlated or reciprocally deactivated (Raichle et al, 2001; Raichle, 2010). The reciprocal relationship between the DMN related to an ongoing internal self-narrative and the attention network focused on the external world is an important dynamic, fMRI has a limited temporal resolution and is unable to resolve millisecond periods of phase lock and phase shift of neurons located in network nodes and functional connections that comprise the DMN. Activation of the DMN significantly increases demand on blood glucose and oxygen as well as changes in the synchrony of synaptic potentials on the dendrites and cell bodies of cortical pyramidal neurons as measured in the human EEG using 3-dimensional electrical neuroimaging methods (Pascual-Marqui et al, 1994; Pascual-Marqui, 1999; Michel et al, 2009) referred to as EEG Tomography (tEEG) (Cannon et al, 2009; Thatcher, 2011; Thatcher et al, 2011) or Brain Electromagnetic Tomography (BET) (Valdés-Sosa et al, 1992; Bosch-Bayard et al, 2001; Hernandez-Gonzalez et al, 2011)

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Conclusion