In the past years, a few methods have been developed to translate human EEG to music. In 2009, PloS One 4 e5915, we developed a method to generate scale-free brainwave music where the amplitude of EEG was translated to music pitch according to the power law followed by both of them, the period of an EEG waveform is translated directly to the duration of a note, and the logarithm of the average power change of EEG is translated to music intensity according to the Fechner's law. In this work, we proposed to adopt simultaneously-recorded fMRI signal to control the intensity of the EEG music, thus an EEG-fMRI music is generated by combining two different and simultaneous brain signals. And most importantly, this approach further realized power law for music intensity as fMRI signal follows it. Thus the EEG-fMRI music makes a step ahead in reflecting the physiological process of the scale-free brain.

Funding: The authors acknowledge the following funding supports: the 863 projects 2012AA011601, 2012BAI16B02, the Natural Science Foundations of China No. 90820301, 60835005, 81201159, 60736029 and the ‘111’ project (B12027). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Copyright: © 2012 Lu et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Introduction

Music and language define us as human [1]. Emotional expression and communication, through language or non-linguistic artistic expression, are recognized as being strongly linked to health and sense of well-being [2]. Therefore, as an artistic expression, music may represent human mind or mood.

In 1934, Adrian and Matthews attempted to listen to the brainwave signals via an amplified speaker [3]. During the past decades, scientists and artists found many methods to make an electroencephalogram(EEG) sonification, although it is difficult for composition to balance music principles and EEG features [4]. Meanwhile, in order to learn more about ourselves, researchers also used the deoxyribonucleic acid(DNA) [5], proteins [6], electromyograms (EMGs) [7] to compose music in the last century.

From the 1990s, various new EEG music generating rules were created [8]. One of them was to translate some parameters of EEG to the parameters of music [9], and another one was to utilize some characteristics such as the epileptic discharges to trigger specific music [10], or to link brain states to various music pieces through Brain Computer Interface [4].

In 2009, we proposed a method to translate EEG to music. The translation rules included the direct mapping from the period of an EEG waveform to the duration of a note, the logarithmic mapping of the average power (AP) change of EEG to music intensity according to the Fechner's law [11], and a scale-free based mapping from the amplitude of EEG to music pitch according to the power law [12]. However, in this method, the pitch and intensity were not independent enough under the translation rules as both pitch and intensity are related to EEG amplitude, so that the music was not strictly in accordance with the composition regulation in which pitch and intensity are usually not mutually related. Meanwhile, the intensity of music usually follows power law [13], however, the intensity of our previous brainwave music was obtained from the AP change of EEG within a time window, it didn't obey the power law (Shown in the following Figure 9). In this work, in order to imitate the general music composition better, we selected another brain information to represent the intensity instead of the EEG amplitude. As the intrinsic metabolic functional activities based functional magnetic resonance imaging(fMRI) is widely used to study the operational organization of the human brain [14], and fortunately, the fMRI blood oxygenation level dependent(BOLD) signal does follow the power law [15], thus the currently widely adopted fMRI may provide us a potential information for intensity of brainwave music. In fact, the fMRI BOLD signal is indirectly related to the electrical activities of a group of neurons by neuro-vascular coupling relation, thus it may reflect the brain mental state.