Biomedical subjects

Paul L Nunez

Publications and source records attributed to Paul L Nunez.

5 recordsLinked to original sources

PubMed2006

A theoretical basis for standing and traveling brain waves measured with human EEG with implications for an integrated consciousness.

OBJECTIVE: We propose a theoretical framework for EEG and evoked potential studies based on the single postulate that these data are composed of a combination of waves (as this term is used in the physical sciences) and thalamocortical network activity. METHODS: Using known properties of traveling and standing waves, independent of any neocortical dynamic theory, our simple postulate leads to experimental predictions, several of which have now been verified. A mathematical-physiological theory of "brain waves" based on known (but highly idealized) properties of cortical synaptic action and corticocortical fibers is used to support the framework. RESULTS: Brain waves are predicted with links between temporal frequencies and the spatial distributions of synaptic activity. Such dispersion relations, which essentially define more general phenomena as waves, are shown to restrict the spatial-temporal dynamics of synaptic action with many experimental EEG consequences. CONCLUSIONS: The proposed framework accounts for several salient features of spontaneous EEG and evoked potentials. SIGNIFICANCE: We conjecture that wave-like behavior of synaptic action may facilitate interactions between remote cell assemblies, providing an important mechanism for the functional integration underlying conscious experience.

Algorithms↗

PubMed2006

Steady-state visual evoked potentials: distributed local sources and wave-like dynamics are sensitive to flicker frequency.

Steady-state visual evoked potentials (SSVEPs) are used in cognitive and clinical studies of brain function because of excellent signal-to-noise ratios and relative immunity to artifacts. SSVEPs also provide a means to characterize preferred frequencies of neocortical dynamic processes. In this study, SSVEPs were recorded with 110 electrodes while subjects viewed random dot patterns flickered between 3 and 30 Hz. Peaks in SSVEP power were observed at delta (3 Hz), lower alpha (7 and 8 Hz), and upper alpha band (12 and 13 Hz) frequencies; the spatial distribution of SSVEP power is also strongly dependent on the input frequency suggesting cortical resonances. We characterized the cortical sources that generate SSVEPs at different input frequencies by applying surface Laplacians and spatial spectral analysis. Laplacian SSVEPs recorded are sensitive to small changes (1-2 Hz) in the input frequency at occipital and parietal electrodes indicating distinct local sources. At 10 Hz, local source activity occurs in multiple cortical regions; Laplacian SSVEPs are also observed in lateral frontal electrodes. Laplacian SSVEPs are negligible at many frontal electrodes that elicit strong potential SSVEPs at delta, lower alpha, and upper alpha bands. One-dimensional (anterior-posterior) spatial spectra indicate that distinct large-scale source distributions contribute SSVEP power in these frequency bands. In the upper alpha band, spatial spectra indicate the presence of long-wavelength (> 15 cm) traveling waves propagating from occipital to prefrontal electrodes. In the delta and lower alpha band, spatial spectra indicate that long-wavelength source distributions over posterior and anterior regions form standing-wave patterns. These results suggest that the SSVEP is generated by both (relatively stationary) localized sources and distributed sources that exhibit characteristics of wave phenomena.

Adult↗

PubMed2006

Source analysis of EEG oscillations using high-resolution EEG and MEG.

We investigated spatial properties of the source distributions that generate scalp electroencephalographic (EEG) oscillations. The inherent complexity of the spatio-temporal dynamics of EEG oscillations indicates that conceptual models that view source activity as consisting only of a few "equivalent dipoles" are inadequate. We present an approach that uses volume conduction models to characterize the distinct spatial filtering of cortical source activity by average reference EEG, high-resolution EEG, and magnetoencephalography (MEG). By comparing these three measures, we can make inferences about the sources of EEG oscillations without having to make prior assumptions about the sources. We apply this approach to spontaneous EEG oscillations observed with eyes closed at rest. Both EEG and MEG recordings show robust alpha rhythms over posterior regions of the cortex; however, the dominant frequency of these rhythms varies between EEG and MEG recordings. Frontal alpha and theta rhythms are generated almost exclusively by superficial radial dipole layers that generate robust EEG signals but very little MEG signals; these sources are presumably mainly in the gyral crowns of frontal cortex. MEG and high-resolution EEG estimates of alpha rhythms provide evidence of local tangential and radial sources in the posterior cortex, lying mainly on sulcal and gyral surfaces. Despite the detailed information about local radial and tangential sources potentially afforded by high-resolution EEG and MEG, it is also evident that the alpha and theta rhythms receive contributions from non-local source activity, for instance large dipole layers distributed over lobeal or (potentially) even larger spatial scales.

Animals↗

PubMed2004

Dynamic sculpting of brain functional connectivity is correlated with performance.

In this study, we examined the relationship between cortical coupling, reflected in event related partial coherence (ERPC) and cognitive processing speed while subjects performed a set of Raven's Progressive Matrices (RPM), a task used to measure IQ. Fifty-five participants (29 males) performed a computerized version of the RPM where they were required to identify the shape (probe) that is consistent with a matrix of displayed shapes. Participants indicated a match or non-match by pressing a micro-switch with either the right or left hand. The steady state visually evoked potential (SSVEP) was elicited by a 13 Hz uniform visual flicker superimposed over the visual fields and the SSVEP event-related coherence (SSVEP-ERPC) calculated for all 2016 unique electrode pairs. The linear correlation between SSVEP-ERPC and processing speed (the inverse of reaction time) was calculated for all electrode pairs for all time points during the 3 sec interval that the probes were on the screen. Using correlation coeffident thresholds corresponding to p=0.001 we identified those electrode pairs where SSVEP-ERPC or neural synchronization was significantly correlated with processing speed. At a point 0.8 sec before the appearance of the probe we observed that the synchronization between specific prefrontal, frontal and central sites was correlated with processing speed. We suggest that this relationship may reflect the efficiency of working memory processes and speed of information processing.

Adolescent↗

PubMed2003

Fronto-parietal evoked potential synchronization is increased during mental rotation.

We used steady state visually evoked potential event related partial coherence (SSVEP-ERPC) to examine the SSVEP synchronization between brain regions while 22 males undertook a sequential version of the Shepard and Metzler mental rotation task. Compared to the 60 degrees rotation, the 180 degrees rotation was associated with increased synchronization between bilateral prefrontal and parieto-occipital sites, between left frontal and right parietal sites and between bilateral parietal and occipital sites. We suggest that the increased synchronization between prefrontal and parieto-occipital regions may be associated with the working memory components of the task, while the left frontal to right parietal synchronization may represent the increased interaction between these regions thought to occur in a variety of visuo-motor tasks.

Adult↗