Wavelet Coherence and Its Application in Analyzing Auditory and Motor Task Event-Related Potentials

WU Jie，ZHANG Ning，YANG Zhuo，ZHANG Tao, Wavelet coherence and its application in analyzing auditory and motor task event-related potentials.

This paper has been accepted by ACTA BIOPYSICA SINICA，here is its abstract.

Related links:Tips about Wavelet , Wavelet Coherence Method,A Vivid Example to Show How Wavelet Coherence Works, Some Concepts about ERP signals ,Wavelet and EEG Signals. These links can help to gain further information about this paper.

Abstract:
Wavelet coherence method is applied in analyzing single trial of ERP (event-related potential). There are three groups of experiments: auditory single task, motor single task 1 and motor single task 2. Data from 12 participants is analyzed around 40 Hz by wavelet coherence method and the coherence values between prefrontal area and other areas in the brain are calculated. It is found that the coherence values in motor tasks are larger than those in auditory task and there are significantly differences. Furthermore, in different tasks, the distributions of the coherence values are obviously different, and the values are changing in particularly ways according the varying of the time. This analysis indicates that wavelet coherence method has its advantages in investigating short time EEG signals.

Brief descriptions:


The coherence values, around 40Hz between prefrontal area and other areas in the cerebral cortex, were measured. It was found that the coherence values in the MST (Motor Single Task) are larger than that in the AST (Auditory Single Task) with significant differences.Brain dealing with complicated tasks can have more information to process, and there should be more information communication between different areas of the brain. This can be denoted by coherence values.


Wavelet Coherence Values along the time axis. The colors in the images indicate the coherence values between prefrontal area and other areas in the cerebral cortex around 40Hz(the relationship between the color and the value is shown in the color-bar).large coherence values exactly locate in Auditory Cortex at temporal lobe in AST conditions, whilst in MST conditions, the big values are in motor cortex which is in parietal area.

The data show that the wavelet methods calculations of non-stationary signals, compared to the Fourier methods, can characterize the time-frequency features of neural mechanisms underlying cognitive control. Furthermore, wavelet approach can provide higher resolution in both temporal and spatial scales and can be applied in analyzing other physiological signals.

Main reference:
Lachaux, J.-P., et al., Estimating the time-course of coherence between single-trial brain signals: an introduction to wavelet coherence. Neurophysiol Clin., 2002. 32: p. 157-174.

Wavelet Analysis of ERP Recordings for Dual Tasks in Man

WU J, YANG Z, ZHANG T, Wavelet analysis of ERP recordings for dual tasks in man.

This paper has been accepted by ICCN'07 & SICPB'07 which will be held in Shanghai, China during November 17-21, 2007. The abstract is shown as below.

Click Wavelet Packet Transform, Relative Wavelet Energy, ERP for more relevant information.

Abstract:
The study was to examine the application of wavelet packet method to electrophysiological responses recorded during single and dual task performance. Relative energies of both EEG alpha and beta frequency bands were significantly higher in the single task conditions compared with that of the dual task condition (P is less than 0.05). The data demonstrated that relative energy measurements based on wavelet transform could be a useful alternative approach to analyzing short duration EEG signals on a time scale of seconds.

It is impossible and unnecessary to show the details of this paper in a single short article, so only the abstract is shown here.

The most important point is that, compared to the Fourier methods, wavelet method can be an alternative and much better method to deal with short time EEG signals. Accordingly, wavelet method can be used in analyzing other data in our lab, those data include EEG, ERP and RSNA signals. They are all complicated signals and represent nonlinear dynamic systems with high dimensionality.

There will be other artcles in this blog to illustrate the advantages of Wavelet method compared to regular frequency analysis methods.

Some Concepts about ERP signals

Enterprise Resource Planning is usually recognized as ERP for common people, but the "ERP" here means Event related Potential. For brain scientists, it is a common way to investigate the brain. Event-related potential is the measurement of the brain's electrical activity in response to different types of events, such as attention, words, thinking or sounds. By measuring the brain's response to such events we can learn how different types of information are processed.

In an Event related Potential experiment, signals together with the events are recorded. The events (for example, auditory stimulus, vibrative stimulus, human actions) are designed according to the purpose. Thus, ERP experiments provide a possibility to learn how the events are processed in the brain.


Normally, dozens of individual raw ERP experiment signals are averaged together to gain the ERP, this method allow us to cancels out the noise and make the responses clearly. There are three measurable aspects of the ERP waveform, i.e., amplitude, latency, and scalp distribution. Component amplitude provides index of neural activation extent (how the component responds functionally to experimental variables); component latency (the point in time at which the peak occurs) reveals the timing of this activation; and a component’s scalp distribution (the pattern of voltage gradient over the scalp at any point in time) provides information on the overall pattern of activated brain areas.

Note: some contents above comes from Wikipedia


A sample from http://www.city.ac.uk/psychology/research/CNRU/eegintro.html,This is an averaged ERP signal, in which you can see the responses (positive and negative components).Basic research are based on the measurements of this type of components.

In the 20th International CODATA Conference

The 20th International CODATA Conference: Scientific Data and Knowledge within the Information Society, was held during October 23-25th 2006 in Peking. We had two posters there. Some photos and our posters are shown as below.


Welcome Reception


Palace Convention Hall


Wonderful presentations


Our posters and me


Our poster

Our poster

Cocktails

ERPDB: a Database of ERP Data for Neuroinformatics Research

Event-related potential (ERP) is the measurement of the brain's electrical activity in response to different types of events. These signals are useful for learning how information is processed in the human brain. Being a neuroinformatics laboratory, we deal with lots of ERP signals, which come from various research programs. Different programs have different experiment designs, different parameters settings, and different data formats. These could be big problems for our study. For this reason, arranging the data and constructing a database to store them is quite necessary.

ERPDB contains the information of the participants and the rearranged signals.The data have been transformed into more organized data, which are more convenient for further computation and analysis. Also, new data can be easily added into the database according to our standard. This database is available on the web.



Publications:
Qinghong Yan, Ning Zhang, Jie Wu. The Constitution of ERP Database Based on SQL Server2000. The 20th International CODATA Conference (CODATA2006 ABSTRACT，China，Beijing):2006, 308
QingHong Yan, Ning Zhang, Jie Wu, Tao Zhang. ERPDB: an integrated database of ERP datafor neuroinformatics research, Data science journal, 2007