LAB MANUAL

OF

ELECTROENCEPHALOGRAPHY (EEG)

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Contents

1) Electroencephalography Background of EEG Recording EEG Components of EEG waveform Required Equipment

2) Power Lab Data Acquisition Software Used

3) Lab Tutor Access to Lab Tutor Perform Experiments Equipment Setup Exercise 1: Recognizing Artifacts Exercise 2: Alpha And Beta Rhythms Exercise 3: Mental Activity Exercise 4: Auditory Stimulation

4) Lab Chart Equipment Setup Exercise 1: Recognizing Artifacts Exercise 2: Alpha Waves in EEG Spectral Analysis

5) Conclusion

1) Electroencephalography

In this experiment, we will examine an electroencephalogram (EEG) and explore the electrical activity of the brain. We will record an electroencephalogram from a volunteer, look at interfering signals, and examine the effects of visual activity on alpha brain waves.

BackgroundThe cerebral cortex contains huge numbers of neurons. Activity of these neurons is to some extent synchronized in regular firing rhythms. These are referred to as brain waves. Electrodes placed in pairs on the scalp can pick up variations in electrical potential that derive from this underlying cortical activity. The recording of the electrical activity is called an electroencephalogram (EEG). EEG signals are affected by the state of arousal of the cerebral cortex and show characteristic changes in different stages of sleep. EEG signals are also affected by stimulation from the external environment and brain waves can become entrained to external stimuli. Electroencephalography is used, among other things, in the diagnosis of epilepsy and the diagnosis of brain death.

Recording the EEGEEG recording is technically difficult, mainly because of the small size of the voltage signals, which are typically 50 µV peak-to-peak. The signals are small because the recording electrodes are separated from the brain's surface by the scalp, the skull, and a layer of cerebrospinal fluid. A specially designed amplifier, such as the Bio Amp built into the Power Lab, is essential to record EEGs. It is also important to use electrodes made of the right material and to connect them properly. Even with these precautions, recordings may be spoiled by a range of unwanted interfering influences, known as artifacts. Here, we will record EEG activity with two electrodes: a frontal electrode on the forehead, and an occipital electrode on the scalp at the back of the head. A third (ground or earth) electrode is also attached, to reduce electrical interference. In clinical EEG, it is usual to record many channels of activity from multiple recording electrodes placed in an array over the head.

Components of the EEG waveformThe EEG waveform contains component waves of different frequencies. These can be extracted and provide information about different brain activities. The types of brain waves are:

alpha (between 8 to 13 Hz; average amplitudes of 30 to 50 µV peak-to-peak) which will be studied in this experiment. Alpha rhythm is seen when the eyes are closed and the volunteer relaxed. It is abolished by eye opening and by mental effort such as doing calculations or concentrating on an idea. It is thus thought to indicate the degree of cortical activation. The greater the activation, the lower the alpha activity. Alpha waves are strongest over the occipital (back of the head) cortex and also over the frontal cortex.

beta (13 to 30 Hz; <20 µV peak-to-peak) which are prominent in alert individuals with their eyes open. The beta rhythm may be absent or reduced in

areas of cortical damage and can be accentuated by sedative-hypnotic drugs such as benzodiazepines and barbiturates.

theta (4 and 8 Hz; <30 µV peak-to-peak) which are seen in awake children but not adults. The theta rhythm is normal during sleep at all ages. However, some researchers separate this frequency band into two components, low theta (4 - 5.45 Hz) activity that they correlate with decreased arousal and increased drowsiness, and high theta (6 - 7.45 Hz) activity that it is claimed is enhanced during tasks involving working memory.

delta (0.5 and 4 Hz; up to 100 - 200 µV peak-to-peak) which is the dominant rhythm in sleep stages three and four but not seen in conscious adults. The delta rhythm tends to have the highest amplitude of any of the component EEG waves. EEG artifacts caused by movements of jaw and neck muscles can produce waves in the same frequency band.

gamma (30 and 50 Hz). Most people recognize gamma rhythm, but its importance is controversial. It may be associated with higher mental activity, including perception and consciousness and it disappears under general anesthesia. One suggestion is that the gamma rhythm reflects the mental activity involved in integrating various aspects of an object (color, shape, movement, etc.) to form a coherent picture.

In general, the more active the brain the higher the frequency and the lower the amplitude of the EEG. Conversely, the more inactive the brain the lower the frequency and the higher the amplitude of the signal.

Required Equipment Lab Chart software Power Lab Data Acquisition Unit 5 Lead Shielded Bio Amp Cable EEG Flat Electrodes Electrode Paste Abrasive Gel or Abrasive Pad Alcohol Swabs Ballpoint pen Medical tape Elastic bandage

2) Power LabPowerLab (before 1998 was referred to as MacLab) is a data acquisition system developed

by AD Instruments comprising hardware and software and designed for use in life science

research and teaching applications. It is commonly used in physiology, pharmacology,

biomedical engineering, sports/exercise studies and psychophysiology laboratories to record and

analyze physiological signals from human or animal subjects or from isolated organs. The

system consists of an input device connected to a Microsoft Windows or Mac OS computer

using a USB cable and LabChart software which is supplied with the PowerLab and provides the

recording, display and analysis functions. The use of PowerLab and supplementary AD

Instruments products have been demonstrated on the Journal of visualized Experiments.

The original MacLab unit was developed in the late 1980s to run with

only Macintosh computers to perform computer-based data acquisition and analysis. The

MacLab product range was renamed "PowerLab" in 1997 to reflect the cross-platform nature of

the system.

The PowerLab system is essentially a peripheral device designed to perform various functions

needed for data acquisition, signal conditioning and pre-processing. Versatile display options and

analysis functions are complemented by the ability to export data to other software (such as

Microsoft Excel).

How is data acquired? External signals detected are converted into analog electrical signal.

Signals are amplified to amplify signals and filtered to remove unwanted

frequencies or noise. Analog signal is multiplexed to an analog to digital converter.

The digitized signal is transmitted to the computer using USB connection.

Software receives, displays, analyses and records data in real time.

Software for Power Lab LabChart

Formerly known as Chart. The software functions like a traditional multi-

channel chart recorder, XY plotter, polygraph and digital voltmeter. It is

compatible with both Windows and Macintosh operating systems. The software

has hardware settings control, performs analysis in real-time and offline without

the loss of raw data, procedure automation via editable macros, and multiple

block samplings for the recording and settings of different signals within one

file. Large specialized add-ons called Modules provide data acquisition and

analysis features for specific applications such as ECG, blood pressure, cardiac

output, HRV and etc. Smaller software plugins provides additional and

specialized functionality to LabChart. Extensions perform functions such as file

translations into other formats (including PVAN and Igor Pro) and specialist

analysis functions (for specific research areas such as spirometery and ventricular

pressure). The last version of LabChart6 (version 6.1.3) was released on January

2009.

In April 2009, LabChart 7 was released and incorporates the features of a multi-

channel digital oscilloscope that allows recording and averaging of up to sixteen

signals in real time. Latest version of LabChart7 is version 7.0.

LabTutorSoftware provides a range of hands-on laboratory background for students that

includes experimental background & protocols, data acquisition & analysis, and

report generation within one interface. The software and accompanying PowerLab

hardware is configured for immediate use with step by step instructions designed

to maximize student productivity by applying independent learning techniques to

a suite of human and animal physiological experiments. Recently, LabAuthor

software was released to provide educators the ability to design or edit existing

LabTutor experiments and tailor the experiments to suit their practical classes

without the need of programming or html skills.

3) Lab Tutor

Acess LabTutorTo access LabTutor one can use the desktop shortcut created during the LabTutor Client installation. The student login page address can also be manually typed into the web browser using the server name or the server IP address:

http://<server IP address>

http://<computer name>There are two modes of operation for LabTutor Client, depending on the licensing model that is purchased:1. Require PowerLabs – Students can log in and perform experiments if the computer on which LabTutor Client is installed has a PowerLab connected.2. LabTutor Online mode – Where LabTutor Online is activated, and a student is licensed as such in Bulk or Student Access Card modes, they may log in and start or continue an experiment on any computer on which LabTutor Client is installed, with or without a PowerLab connected. LabTutor Client can be installed on any number of computers.

Perform Experiments In the web browser, navigate to the LabTutor student login page.

Log in using a student login.

Choose the course and experiment that you want to start.

Select experiment EEG from the Human Physiology course list.

Read the Introduction part of the experiment.

Equipment Setup Plug the Bio-Amp cable into the Bio-Amp socket on the PowerLab. Connect the leads of three EEG flat electrodes to Earth, CH1 NEG and POS, on

the Bio-Amp cable.

Exercise 1: Recognizing Facts

Procedure

Blinking Artifact1. Click Start and ask the volunteer to blink repeatedly.2. Watch the volunteer and push the enter key to enter the comment each

time the volunteer blinks.3. After 5 to 10 seconds, click Stop.

Eye Movements1. Click Start and ask the volunteer to gaze alternately left and then right in a

repeated pattern. The volunteer should keep the head still during these movements.

2. Watch the volunteer and push the enter key to enter the comment each time their eyes moves.

3. After 5 to 10 seconds, click Stop.

Head Movements1. Click Start and ask the volunteer to move head alternately left and then

right in a repeated pattern.2. Watch the volunteer and push the enter key to enter the comment each

time their head moves.3. After 5 to 10 seconds, click Stop.

Analysis

Examine the recordings using scroll bar at the bottom of the LabTutor panel and by adjusting the vertical scale.

True EEG signal rarely exceed +50µV and -50µV. We have to find the large signals outside the ±50µV range that belong to blinking artifacts, eye movements and head movements. These large signals are artifacts.

Exercise 2: alpha and beta rhythmHere we examine the alpha and beta waves in the EEG and the effect of having the eyes shut or open on this rhythm.

Procedure

Ensure that the volunteer is relaxed and is lying quietly with both eyes open. Click Start. Type “shut” in the comments panel. After about 30 seconds, ask the volunteer to

shut both the eyes. Immediately click Add to enter the comment and continue recording.

Type “open” in the comments panel. After about 30 seconds, ask the volunteer to open both the eyes. Immediately click Add to enter the comment.

Record for a few more seconds and then click Stop. Repeat this procedure twice more to give three sets of result.

Analysis

From the first recording, for the period when the volunteer’s eyes were open select a portion relatively free from artifacts.

On making a selection the four value panels will display measurements of amplitude and frequency for both alpha and beta waves for selected period. Drag values to appropriate cell in the table.

Repeat the same for “eyes shut” and for two other recordings. The table will display average amplitude and frequency along with the standard deviation.

Once completed use the navigation buttons below the table to view a graph of these variables.

Exercise 3: Mental ActivityHere we examine the effect of mental arithmetic task on alpha and beta rhythm, while the eyes are closed.

Procedure

Ensure that the volunteer is relaxed and is lying quietly with both eyes closed. Click Start.

Enter the comment “shut” in the comments panel. After about 30 seconds of sustained alpha rhythm give the volunteer some instructions regarding some easy arithmetic calculation. Instruct to merely think the response and not to speak it.

Add the comment “math” when you instruct to start the mental arithmetic. After another 30 seconds instruct the volunteer to stop calculating and to relax. Record for a few more seconds and then click Stop. Repeat the procedure for further sets of recording.

Analysis

From the first recording, for the period when the volunteer’s eyes were shut but they weren’t perform any mental arithmetic.

Drag the calculated measurements of amplitude and frequency from the value panels to appropriate cell in the table.

Repeat the same for “eyes shut” with and without arithmetic for two other recordings. The table will display average amplitude and frequency along with the standard deviation.

Once completed use the navigation buttons below the table to view a graph of these variables.

Exercise 4: Auditory StimulationHere we examine the effect of different types and volumes of music on alpha and beta rhythm, with the eyes closed.

Procedure

We’ll need a set of headphones and a method of playing music to a subject. Cue the following types of music for presentation to the volunteer:

o Soothing (classical) music, volume lowo Soothing (classical) music, volume higho English (Rock) music, volume lowo English (Rock) music, volume high

Ensure that the volunteer is relaxed and is lying quietly with headphones on and the both eyes closed.

Click Start. Enter the comment “shut” in the comments panel. After about 30 seconds of

sustained alpha rhythm present the first type of music and add an appropriate comment.

After another 30 seconds of recording stop the music. Record for a few more seconds and then click Stop. Repeat this procedure for each different type and volume of music.

Analysis

From the first recording, for the period when the volunteer’s eyes were shut with no music playing.

Drag the calculated measurements of amplitude and frequency from the value panels to appropriate cell in the table.

Repeat the same for “eyes shut” with and without the different types of music for two other recordings. The table will display average amplitude and frequency.

Once completed use the navigation buttons below the table to view a graph of these variables.

At the end one can submit the report by giving the answers to various question given. Also one can print the pdf file of the report.

4) Lab Chart

Equipment Setup and Electrode Attachment

1. Make sure the Power Lab is turned off and the USB cable is connected to the computer.

2. Connect the 5 Lead Shielded Bio Amp Cable to the Bio Amp Connector on the front panel of the Power Lab (Figure 1). The hardware needs to be connected before you open the settings file.

3. Attach the leads of the EEG Flat Electrodes to the Earth, CH1 NEG and POS pins closest to the labeled side on the Bio Amp Cable. Channel 1 “positive” will lead to the inion (the bump on the back of the head above the neck) and Channel 1 “negative” will lead to the forehead. Channel 2 will be empty and the Earth will lead to the temple.

4. Remove any jewelry from the volunteer’s face, ears, and neck. Use a ballpoint pen to mark a small cross on the skin on the back of the head, forehead, and temple. Use Figure 1 as a guide.

5. Abrade the skin with Abrasive Gel or Pad. This is important as abrasion helps reduce the skin’s resistance.

6. After abrasion, clean the area with an alcohol swab to remove the dead skin cells. While the skin is drying, scoop Electrode Paste into the EEG Flat Electrodes. When the skin is dry stick the electrodes to the skin (Figure 1). Immediately hold the electrodes and wires in place with the medical tape.

7. Make sure the tape firmly holds the electrodes against the head. Use the elastic bandage to wrap tightly around the head. This will help the electrodes maintain good contact with the skin. The volunteer should lie in a comfortable position on their back, with their head turned so that none of the electrodes are disturbed or compressed.

8. Check that all three electrodes are properly connected to the volunteer and the Bio Amp Cable before proceeding. Turn on the Power Lab.

Figure 1. Equipment Setup for PowerLab 26T

Exercise 1: Recognizing ArtifactsTo examine some of the artifacts that can contaminate an EEG record.

Procedure1. Launch Lab Chart and open the settings file “EEG Settings” from the

Experiments tab in the Welcome Center. It will be located in the folder for this experiment.

2. Select Bio Amp from the EEG Channel Function pop-up menu. It should be the only channel visible. Make sure the settings are as follows: Range 200 µV, High Pass 0.5 Hz, and Low Pass 50 Hz.

Figure 2. Bio Amp Dialog

3. Start recording. Add a comment “blinking,” and have the volunteer blink repeatedly. Stop recording after 10 seconds.

4. Repeat step 3, this time, have the volunteer make eye movements. Add a comment “eye movements.” Have the volunteer gaze up-and-down and left-and-right in a repeated pattern. Make sure the volunteer’s head is still and only the eyes move.

5. Repeat step 3, this time, have the volunteer make head movements. Add a comment “head movements.” Have the volunteer gently move his/her head in a repeated pattern.

6. Save your data, and open a new file with the same settings.

Exercise 2: Alpha Waves in the EEGTo examine alpha waves (alpha rhythm) in the EEG, and the effect of opening the eyes.

Procedure 1. Make sure the volunteer is relaxed and comfortable. Have the volunteer

close his/her eyes and remain quiet. Keep noise to a minimum and keep all distractions away from the volunteer.

2. Start recording. Record for 30 seconds. Prepare a comment with “open;” do not enter it yet. Tell the volunteer to open both eyes. Immediately press Return/Enter to add the comment.

3. Record with the volunteer’s eyes open for 10 seconds. Do not stop recording.

4. Prepare a comment with “shut.” When the 10 seconds are complete, tell the volunteer to close both eyes. Immediately press Return/Enter to add the comment.

5. Repeat steps 3 and 4 twice, to give you three sets of results. Save your data.

Analysis Exercise 1: Recognizing Artifacts

1. Examine the vertical scale at the left of the Chart View, and note the positions corresponding to +50 µV and –50 µV. True EEG signals rarely exceed these limits.

2. Examine the entire data trace and Autoscale, if necessary. There may be some large signals outside the ±75 µV range. Such large signals are artifacts.

Exercise 2: Alpha Waves in the EEG 1. Examine the entire data trace. Use the View Buttons to change the

horizontal compression to see data with eyes open and shut. Make a data selection that includes some data from both eyes open and eyes shut conditions. View this selection in Zoom View. This should make it easier to see the alpha wave activity (Figure 3). Now Autoscale, if necessary.

Figure 3. EEG signal with eyes shut and open. Note alpha waves during eyes shut.

2. In Chart View scroll through the parts of the recording that were made with the volunteer’s eyes shut to look for alpha waves. Use the View Buttons to change the horizontal compression if necessary. The alpha waves can be recognized by their amplitude (usually 30 to 50 µV peak-to-peak, although it can be quite variable) and their frequency. Each cycle of an alpha wave should last approximately 0.1 s.

3. Use the Marker and Waveform Cursor to measure the amplitude of the alpha waves. Place the Marker at the lowest point of the wave and move the Waveform Cursor to the peak of the wave. Measure the amplitudes of five waves from when the volunteer’s eyes were closed. Record the values in Table 1 of the Data Notebook.

4. Now measure wave amplitudes when the volunteer’s eyes were open. Record these values in Table 2 of the Data Notebook.

The amplitude of the waves is affected by the quality of the EEG signal. Therefore, it is useful to examine the frequency and power of the wave activity. Spectral analysis can be used to examine these features of a signal. Before examining your EEG signal you will complete a short tutorial on Spectral Analysis.

Spectral Analysis

A spectrum is a representation of data based on the frequency distribution of its

component sine waves. Spectra indicate the strength of the various frequencies in a time-

varying waveform. Spectrum View allows you to observe the frequency distribution of

data that might not otherwise be easily seen. For example, it could be used to break down

an EEG waveform into its various components: beta waves, alpha waves, theta waves and

delta waves. A mathematical technique known as the Fast Fourier Transform is applied to

the raw data. The results of this analysis can be displayed as a plot of the power (vertical

axis) of different frequencies (horizontal axis) relative to each other in the input signal.

This is called a Power Spectrum Density (PSD) plot. The data can also be displayed as 3-

dimensional color plot of spectral power, frequency, and time called a Spectrogram.

Open the Welcome Center and in the Experiments tab browse the “EEG

Spectral Analysis Tutorial.” It will be in the Settings folder for this experiment.

Open this file.

Examine the Chart View. Use the View Buttons to view each block. You should

see five blocks of data. The first record is a slowly oscillating sine wave.

Open Spectrum view by clicking on the Spectrum View button in the Toolbar

(Figure 4).

Figure 4. Spectrum View Toolbar button

A. Click the Smart Tile button in the LabChart Toolbar to display both windows in full screen mode.

B. In Chart View Select the first record by double clicking in the Time axis. This will perform a spectral analysis for this record and displays the result in the Spectrum view. Adjust the horizontal scaling of plots to view the results:

Set the horizontal scaling for the Power Spectrum Density (PSD) plot to 50 Hz (Figure 5). Use the horizontal scroll bar to display the 0 Hz to 50 Hz region of the plot.

Figure 5. Spectrum PSD Scale

Set the horizontal scaling for the Spectrogram to 50:1.

Examine the PSD plot and then the first section of the Spectrogram. Expand the vertical axes if necessary. Use the waveform cursor to identify the frequency in Hertz (Hz) of the peak in the PSD plot and the band in the Spectrogram. Values are displayed at the top of each plot.

1. Use the View Buttons to change the horizontal compression to 10:1 (Figure 7).

2. Find the part of the recording when the volunteer had his/her eyes shut. Click-and-drag across this part of the data trace to select it. From the Window menu, select Spectrum. In the Spectrum View choose Selected (Figure 8).

3. Find the part of the recording when the volunteer had his/her eyes shut. Click-and-drag across this part of the data trace to select it. From the Window menu, select Spectrum. In the Spectrum View choose Selected (Figure 8).

Figure 7. Alpha Waves with 10:1 Compression

4. Find the part of the recording when the volunteer had his/her eyes shut. Click-and-drag across this part of the data trace to select it. From the Window menu, select Spectrum. In the Spectrum View choose Selected (Figure 8).

Figure 8. Spectrum of an EEG

5. Alpha activity shows up in the PSD plot as a clear peak in the 8-12 Hz range. Then print the PSD plot.

6. Alpha activity shows up in the Spectrogram as a band of color in the 8-12 Hz range. If you cannot see the alpha activity as a clear peak in the 8-12 Hz range, scale the horizontal and vertical axes. Note that Spectrogram displays all the recorded data and that the selection you have made is highlighted in a darker blue color.

7. Make a data selection of several seconds from when the volunteer had their eyes open. Select Spectrum. Note that in the PSD plot the peak in the alpha activity range of 8-12 Hz is small or absent and in the Spectrogram the band of color in the alpha activity range of 8-12 Hz is weak or absent. Print the PSD plot.

8. In the Spectrogram scale the horizontal axis so that all the data is visible. Note the presence and absence of the band of color in the alpha activity range of 8-12 Hz which correspond with the eyes shut and eyes open conditions. Print the Spectrogram.

5) ConclusionHere we analyzed that the alpha and beta rhythms are affected by different parameters like eyes shut, eyes open, arithmetic calculation, various types of music etc.

When eyes are open, the alpha amplitude of the wave is very much low than the amplitude in case of closed eyes.

When eyes are open, the beta amplitude of the wave is low than the amplitude in case of closed eyes but the difference between the two cases are less as compared to alpha wave amplitude.

When eyes are open, the alpha frequency of the wave is higher than the frequency in case of closed eyes.

There is very slight difference in the beta frequencies in both the cases. The amplitude of alpha wave is more without arithmetic than with arithmetic. As with

arithmetic the subject has to do some mental exercise. There is very less variation in the frequencies both alpha and beta frequency. Also there is not much variation in the beta amplitude with and without arithmetic. There is a visible change in the amplitudes of wave (alpha and beta both) as the music is

presented to a subject. This is so because the subject is not familiar to the music, but as the subject becomes familiar and starts enjoying the music then the difference between the amplitude starts improving.

No doubt there is change in frequency, but change in frequencies is not that large.