Spatial‐temporal structures of human alpha rhythms: Theory, microcurrent sources, multiscale measurements, and global binding of local networks

Abstract

A theoretical framework supporting experimental measures of dynamic properties of human EEG is proposed with emphasis on distinct alpha rhythms. Robust relationships between measured dynamics and cognitive or behavioral conditions are reviewed, and proposed physiological bases for EEG at cellular levels are considered. Classical EEG data are interpreted in the context of a conceptual framework that distinguishes between locally and globally dominated dynamic processes, as estimated with coherence or other measures of phase synchronization. Macroscopic (scalp) potentials generated by cortical current sources are described at three spatial scales, taking advantage of the columnar structure of neocortex. New EEG data demonstrate that both globally coherent and locally dominated behavior can occur within the alpha band, depending on narrow band frequency, spatial measurement scale, and brain state. Quasi-stable alpha phase structures consistent with global standing waves are observed. At the same time, alpha and theta phase locking between cortical regions during mental calculations is demonstrated, consistent with neural network formation. The brain-binding problem is considered in the context of EEG dynamic behavior that generally exhibits both of these local and global aspects. But specific experimental designs and data analysis methods may severely bias physiological interpretations in either local or global directions.

Individual analysis of EEG frequency and band power in mild Alzheimer's disease

“…The present results confirm previous evidence (Leuchter et al, 1993;Besthorn et al, 1997;Rodriguez et al, 1999) that the cholinergic and intracortical deficits of AD mainly impair synchronization mechanisms at the basis of the resting alpha power, which is modulated by cortico-cortical and cortico-thalamo-cortical interactions (Steriade and Llinas, 1988;Pfurtscheller and Lopes da Silva, 1999;Nunez et al, 2001). Based on the determination of individual EEG sub-bands, the power reduction in AD was noted to occur at the low (about 8 -10 Hz) and high alpha bands (about 10 -12 Hz).…”

“…Such impairment could slow the conduction time of the action potentials throughout the cortico-thalamo-cortical pathways (Tomasch, 1954;Steriade and Llinas, 1988;Pfurtscheller and Lopes da Silva, 1999), interfering with the inhibitory control of the reciprocal cortico-thalamo-cortical modulations (Sarter and Bruno, 1997;Destexhe et al, 1998;Doiron et al, 2003). Computational models have previously shown that the EEG frequency relies on axonal delay and synaptic time of the cortico-thalamo-cortical interactions as well as on the activity of inhibitory reticulo-thalamic neurons (Lopes da Silva et al, 1976;Nunez et al, 2001;Doiron et al, 2003). Additionally, the prevalence of the white matter damage could not exclude an impairment of the gray matter, even though less evident than in AD patients.…”

“…Scalp alpha rhythms result from sequences of inhibitory and excitatory post-synaptic potentials at the dendrites of cortical pyramidal neurons. These potentials depend mainly on the influence of near and distant cortical modules (Nunez et al, 2001), as well as on the interactions of excitatory cortico-thalamo-cortical relay fibers and inhibitory thalamic reticular fibers (Lopes da Silva et al, 1980;Suffczynski et al, 2001). An emerging feature of these integrated cortico-cortical and cortico-thalamocortical systems is that, in a resting condition, the higher the number of synchronously active neurons, the higher the amplitude of the alpha rhythm, and the slower the frequency of the alpha power peak (Elul, 1972;Lopes da Silva et al, 1976;Singer, 1993;Pfurtscheller and Lopes da Silva, 1999).…”

Evaluation of spectral ratio measures from spontaneous MEG recordings in patients with Alzheimer's disease

“…An important advantage of MEG over EEG arises from the practical insensitivity of magnetic fields to tissue conductivities differences. In this sense, scalp EEG can be viewed as the result of a spatial filtering of the electrical cortical recordings by the volume conductor [10]. The effect of this process is to filter out high frequency components between the cortex and the scalp and, therefore, modify the spectral content of the cortical electric field [10].…”

“…In this sense, scalp EEG can be viewed as the result of a spatial filtering of the electrical cortical recordings by the volume conductor [10]. The effect of this process is to filter out high frequency components between the cortex and the scalp and, therefore, modify the spectral content of the cortical electric field [10]. This fact makes MEG recordings to be less distorted than EEG signals on the scalp [9].…”