Synchronization between the anterior and posterior cortex determines consciousness level in patients with traumatic brain injury (TBI).

Survivors of traumatic brain injury (TBI) often suffer disorders of consciousness as a result of a breakdown in cortical connectivity. However, little is known about the neural discharges and cortical areas working in synchrony to generate consciousness in these patients. In this study, we analyzed cortical connectivity in patients with severe neurocognitive disorder (SND) and in the minimally conscious state (MCS).

Laterality of temporoparietal causal connectivity during the prestimulus period correlates with phonological decoding task performance in dyslexic and typical readers.

We examined how effective connectivity into and out of the left and right temporoparietal areas (TPAs) to/from other key cortical areas affected phonological decoding in 7 dyslexic readers (DRs) and 10 typical readers (TRs) who were young adults. Granger causality was used to compute the effective connectivity of the preparatory network 500 ms prior to presentation of nonwords that required phonological decoding. Neuromagnetic activity was analyzed within the low, medium, and high beta and gamma subbands.

A comparison of multivariate causality based measures of effective connectivity.

During the past several years a variety of methods have been developed to estimate the effective connectivity of neural networks from measurements of brain activity in an attempt to study causal interactions among distinct brain areas. Understanding the relative strengths and weaknesses of these methods, the assumptions they rely on, the accuracy they provide, and the computation time they require is of paramount importance in selecting the optimal method for a particular experimental task and for interpreting the results obtained. In this paper, the accuracy of the six most commonly used techniques for calculating effective connectivity are compared, namely directed transfer function, partial directed coherence, squared partial directed coherence, full frequency directed transfer function, direct directed transfer function, and Granger causality.

Multichannel least-squares linear regression provides a fast, accurate, unbiased and robust estimation of Granger causality for neurophysiological data.

The most common method for calculating Granger causality requires the fitting of a system of autoregressive equations to multiple interrelated signals. Historically, the Levinson, Wiggins, Robinson (LWR) algorithm and the least-squares linear regression (LSLR) approach are the most widely used methods for fitting these autoregressive equations. In this manuscript we compare these algorithms head-to-head.

Greater Pre-Stimulus Effective Connectivity from the Left Inferior Frontal Area to other Areas is Associated with Better Phonological Decoding in Dyslexic Readers.

Functional neuroimaging studies suggest that neural networks that subserve reading are organized differently in dyslexic readers (DRs) and typical readers (TRs), yet the hierarchical structure of these networks has not been well studied. We used Granger causality to examine the effective connectivity of the preparatory network that occurs prior to viewing a non-word stimulus that requires phonological decoding in 7 DRs and 10 TRs who were young adults. The neuromagnetic activity that occurred 500 ms prior to each rhyme trial was analyzed from sensors overlying the left and right inferior frontal areas (IFA), temporoparietal areas, and ventral occipital-temporal areas within the low, medium, and high beta and gamma sub-bands.

Information communication networks in severe traumatic brain injury.

In this study we explored the use of coherence and Granger causality (GC) to separate patients in minimally conscious state (MCS) from patients with severe neurocognitive disorders (SND) that show signs of awareness. We studied 16 patients, 7 MCS and 9 SND with age between 18 and 49 years. Three minutes of ongoing electroencephalographic (EEG) activity was obtained at rest from 19 standard scalp locations, while subjects were alert but kept their eyes closed.