Hellmuth Petsche

Approaches to verbal, visual and musical creativity by EEG coherence analysis.

Our approach to coherence analysis of the on-going EEG yields data on the cooperation between all possible electrode sites of the 10/20 system. This procedure compares epochs during mental activity with epochs of EEG at rest and takes into account only significant differences which are represented as lines between the respective electrodes on maps of the brain surface. The patterns thus obtained reflect the temporal average of the changes of the overall coherence pattern caused by any mental task. They are interpreted as reflecting differential attention required for the achievement of the mental task in question. Acts of creative thinking, be it verbally, visually or musically, are characterized by more coherence increases between occipital and frontopolar electrode sites than any other mental tasks. The results are interpreted by a stronger involvement of long cortico-cortical fibre systems in creative tasks.

Drawing on mind's canvas: Differences in cortical integration patterns between artists and non-artists†

Our primary question was to learn whether mentally composing drawings of their own choice produce different brain electric features in artists and laymen. To this purpose, we studied multichannel electroencephalograph (EEG) signals from two broad groups (all participants were females): artists (professionally trained in visual arts) and non‐artists (without any training in art). To assess the underlying synchronization, which is assumed to be the platform for general cognitive integration between different cortical regions, three measures inspired by nonlinear dynamical system theory were applied as follows: (1) index based on generalized synchronization; (2) index based on mean phase coherence; and (3) index of phase synchrony based on entropy. Results consistent over all three measures were as follows: comparing the tasks to rest, the artists showed significantly stronger short‐ and long‐range delta band synchronization, whereas the non‐artists showed enhancement in short‐range beta and gamma band synchronization primarily in frontal regions; comparing the two groups during the tasks, the artists showed significantly stronger delta band synchronization and alpha band desynchronization than did the non‐artists. Strong right hemispheric dominance in terms of synchronization was found in the artists. In artists, the higher synchrony in the low‐frequency band is possibly due to the involvement of a more advanced long‐term visual art memory and to extensive top‐down processing. The results demonstrate that in artists, patterns of functional cooperation between cortical regions during mental creation of drawings were significantly different from those in non‐artists. Hum. Brain Mapping, 2005.

Current source density analysis: Methods and application to simultaneously recorded field potentials of the rabbit's visual cortex

This paper deals with the application of current source density (CSD) analysis to simultaneously recorded intracortical field potentials of the rabbits visual cortex. Recordings were made with multielectrodes with either 8 contacts at distances of 300 μm, or 16 contacts at distances of 150 μm on one carrier needle. For synchronized activities, a spatial resolution of 150 μm turned out to be sufficient to record all depth-varying details of the field potentials; for seizure potentials even a spacing of 300 μm was adequate in most cases.For practical application, an appropriate spacing of the measuring points has to be chosen for a satisfactory estimation of the first and second derivatives of the field potentials. For this reason an interpolation procedure is applied to reduce the spacing from 300 μm or 150 μm electrode contact distances, respectively, and to obtain intermediate values at 75 μm distances. With this spacing satisfactory estimations of the second derivative are obtained.Theoretically, CSD analysis has to be made three-dimensionally, but under certain conditions which are discussed, a one-dimensional analysis can be applied. An unknown quantity is σz, the vertical conductivity. It turned out that average values obtained from different experiments are not representative and that the vertical conductivity has to be measured in every experiment. This is caused by the great individual differences of the cortices even if the same stereotactic coordinates are chosen. Therefore, in every experiment relative conductivity measurements are performed. The influence of different conductivity values within the various layers and the influence of a conductivity gradient is discussed and demonstrated by examples.

Shadows of artistry: cortical synchrony during perception and imagery of visual art

Functional and topographical differences between two groups, artists and non-artists, during the performances of visual perception and imagery of paintings were presented by means of EEG phase synchrony analysis. In artists as compared with non-artists, significantly higher phase synchrony was found in the high frequency beta and gamma bands during the perception of the paintings; in the low frequency bands (primarily delta), phase synchrony was mostly enhanced during imagery. Strong decreases in phase synchrony of alpha were found primarily in artists for both tasks. The right hemisphere was found to present higher synchrony than the left in artists, whereas hemispheric asymmetry was less significant in non-artists. In the artists, enhanced synchrony in the high frequency band is most likely due to their enhanced binding capabilities of numerous visual attributes, and enhanced synchrony in the low frequency band seems to be due to the higher involvement of long-term visual memory mostly in imagery. Thus, the analysis of phase synchrony from EEG signals yields new information about the dynamical co-operation between neuronal assemblies during the cognition of visual art.

Phase synchrony analysis of EEG during music perception reveals changes in functional connectivity due to musical expertise

Differences in functional and topographical connectivity patterns between two groups, musicians and non-musicians, during attentively listening to three different pieces of music and to a text of neutral content, were presented by means of EEG phase synchrony analysis in five standard frequency bands: delta ( 30Hz). The degree of phase synchrony or phase coherence between EEG signals was measured by a recently developed index, which is more suitable than classical indices, like correlation or coherence, when dealing with nonlinear and nonstationary signals like EEG. Comparing the music listening task to rest or control condition, musicians showed increase in phase synchrony over distributed cortical areas, both near and distant, in delta, and most conspicuously in gamma frequency band, whereas non-musicians showed enhancement only in delta band. Further, the degree of phase synchrony in musicians was reduced during listening to text as compared to listening to music. Comparing the two groups during the listening tasks, the clear-cut difference was found in gamma band phase synchrony, which was significantly stronger in musicians while listening to every chosen piece of music, yet no large difference between these two groups was found while listening to the chosen text. Musicians also showed stronger higher order inter-frequency phase synchrony between delta band oscillations in anterior regions and gamma band oscillations in posterior regions. In addition, consistent left hemispheric dominance, in terms of the strength of phase synchrony, was observed in musicians while listening to music, whereas right hemispheric dominance was observed in non-musicians. These results suggest that professional training in music is able to elicit context-sensitive functional connectivity between multiple cortical regions resulting in different listening strategies to music.

EEG gamma-band phase synchronization between posterior and frontal cortex during mental rotation in humans

The main purpose of the present paper was: (1) to study the phase synchronization pattern in the gamma-band while performing the classical Shepard-Metzler task of mental rotation; (2) to investigate the role of musical training; and (3) to study hemispheric differences in the degree of synchronization during mental rotation. Multivariate electroencephalograph signals from 20 male subjects (ten musicians and ten non-musicians) were recorded while performing the mental rotation task and also at resting condition. Phase synchronization was measured by a recent index, mean phase coherence. It was found that synchronization between frontal cortex and right parietal cortex was significantly increased during mental rotation with respect to rest, whereby musicians showed significantly higher degrees of synchronization than non-musicians. Left hemispheric dominance in the degree of phase synchronization, stronger in the posterior right parietal and occipital regions, was observed in musicians. Right hemispheric dominance was generally observed in non-musicians.

Universality in the brain while listening to music

The human brain, which is one of the most complex organic systems, involves billions of interacting physiological and chemical processes that give rise to experimentally observed neuroelectrical activity, which is called an electroencephalogram (EEG). The presence of non-stationarity and intermittency render standard available methods unsuitable for detecting hidden dynamical patterns in the EEG. In this paper, a method that is suitable for non-stationary signals and preserving the phase characteristics and that combines wavelet and Hilbert transforms was applied to multivariate EEG signals from human subjects at rest as well as in different cognitive states: listening to music, listening to text and performing spatial imagination. It was found that, if suitably rescaled, the gamma band EEG over distributed brain areas while listening to music can be described by a universal and homogeneous scaling, whereas this homogeneity in scale is reduced at resting conditions and also during listening to text and performing spatial imagination. The degree of universality is characterized by a Kullback - Leibler divergence measure. By statistical surrogate analysis, nonlinear phase interaction was found to play an important role in exhibiting universality among multiple cortical regions.

Thinking with images or thinking with language : a pilot EEG probability mapping study

This pilot EEG mapping study was designed to explore thinking processes using complex mental imagery and thought processes. EEG was recorded with 19 electrodes (10/20 system against averaged ear lobe signals) while volunteers (n = 42) performed two separate tasks: visualization of an abstract concept and interpretation of a painting. Average spectral parameters such as amplitude, local and interhemispheric coherences were computed for five frequency bands (theta, alpha, beta 1, 2 and 3). Results indicate that the frontal regions are strongly involved during these tasks as evidenced by coherence changes. Changes are also present in temporal, parietal and occipital regions and are discussed in relation to information processing with the frontal regions considering the different cognitive functions required by the tasks.

The EEG: An Adequate Method to Concretize Brain Processes Elicited by Music

Whether or not processing of music by the brain can be reflected in an ongoing EEG was studied in a group of 75 healthy students. The parameters considered were location, power, frequency, and coherence. By means of the Fisher permutation test, significant changes of these parameters with respect to control EEG periods were computed and represented as probability maps of brain electrical activity. In spite of the great individual differences in musical ability, education, and interest of the subjects, a number of specific group differences of the EEG parameters could be elucidated for different musical tasks. Significant differences were also seen between the groups of musically trained and untrained subjects, both during listening and even in their EEGs at rest. In addition, considerable sex differences were observed. Part of these differences, particularly those of the parameter power, are most likely caused by the different degrees of attention elicited by these tasks. The greater part of the observed changes, however, concerns coherence and thus conceivably reflects different degrees of the functional cooperation of two adjacent brain regions or the two hemispheres in several musical perception tasks.

Penicillin-induced epileptic phenomena in the rabbit's neocortex I. The development of interictal spikes after epicortical application of penicillin

In an attempt to elucidate the generation mechanisms underlying interictal spikes in the neocortex, the temporal development of spikes after the epicortical penicillin (PNC) application was studied. Field potentials (FP) were recorded simultaneously within the 6 neocortical layers with a multielectrode consisting of 16 contacts (10 X 10 micron 2) in a row at spacings of 150 micron. A one-dimensional current-source-density (CSD) analysis yielded the positions of current, sink and source densities, so that the different electrical events during a spike could be more accurately located within the different neocortical layers. After the epicortical application of PNC a typical succession of events, which underly the development of spikes, was observed. These events are similar in the visual and the motor cortex: immediately after the epicortical PNC application negative transients occur in the two uppermost cortical layers as well as within layers V to III. Due to the diffusion of the drug a characteristic succession of different processes takes place. Fully developed spikes show a typical configuration of sources and sinks, a moderate sink in layer V initiates a massive, double-peaked sink within layers II, III. This configuration of sinks suggests that some sort of triggering mechanism takes place. Since similar events are observed during interictal spikes in the visual and the motor cortex, neuronal structures common to both cortical areas are supposed to be responsible for the generation of PNC spikes.