Recording an Electroencephalograph
The following directions need to be confirmed and cleaned up, but should allow tracings to be performed using the Biopac Student Lab software and a computer. Pictures should follow as soon as we perform the experiment in the lab (around 3 February 2005):
RECORDING AN EEG Using BioPac Student Lab, Version 3.6.7
Using BioPac Student Lab, Version 3.6.7
1) Turn on computer, login: USERBL (a faculty member will log in for you)
2) Plug electrode lead into Channel 1.
2) Open software: BioPac MP30 Student software
3) Choose Lesson: click on LO3- EEG-1
4) Create your file: Type your file name (LASTNAME_X) where X = first name initial, ENTER
5) Connect electrodes: (They MUST have excellent contact with skin for success.)
a) If skin is moist or oily, wipe skin at electrode placement sites with 95% EtOH, dry well.
b) Part the hair so you see the scalp and apply electrodes over the R and L edges of the occipital bone, about 3 inches apart. Press the third electrode on the inside R wrist.
c) Clip lead harness securely to belt or clothing, attach leads to electrodes:
i) red lead to left occipital electrode
ii) white to right occipital electrode. Place snug fitting cap to hold in place (panty hose?)
iii) black lead to inside of wrist. (If necessary, tape down with masking tape.)
6) CALIBRATE: Darken the room, lie the subject down and relax, breathing regularly. Click CALIBRATE. Double check electrode position, click OK. Look for even, flat line, no spikes. If it contains erratic “static,” recheck to secure electrode placement (more gel?) and repeat calibration.
7) After calibration has been successfully completed, proceed to next step.
8) With complete silence of observers, have subject lie completely still with no facial movements.
9) RECORD: With subject’s eyes open, click on RECORD. You should see high frequency (15-60 Hz) low amplitude (5-10 mV) beta waves, typical of the alert brain.
10) After 15 seconds with eyes open, have subject close eyes closed for 30 QUIET seconds (RELAXED…). You should see occasional low frequency (8-10 Hz) high amplitude (50 mV) alpha waves (if the subject is truly relaxed).
11) After 30 seconds in deep meditation, have subject open eyes for 15 seconds.
12) After 60 seconds total, click button STOP.
13) If the tracing is satisfactory (look especially for alpha waves when eyes closed), click on DONE.
14) It asks if you want to stop recording, click YES.
15) A new menu appears, highlight ANALYZE CURRENT DATA FILE to select, click OK.
16) Click FILE, select DISPLAY PREFERENCE, highlight SHOW GRIDS, click OK.
17) Click arrow button in lower right side of screen
18) Left click the space below the graph (next to “seconds”).
19) A menu appears, enter time in the seconds you wish to print for upper scale range, set time division lines at 2 seconds, click OK.
20) Left click voltage space to the right of the graph, set voltage range -50 to +50 mvolts, set voltage division lines at 10 mV, click OK.
21) Click FILE, select PRINT.
22) Select PRINT GRAPH, click OK.
23) The Print Options menu appears. Enter “4″ in the plots per page space.
24) Click on PRINT.
25) Collect printed tracing from the Lab printer. Label when eyes were open or closed, and indicate beta and alpha EEG waves. At the print conditions described in #16-20, 1 interval equals 2 seconds. Mark the one second intervals below the graph (ignore the printed numbers, they are erroneous…) Indicate how many hertz (cycles per second). Cut in half and mount in notebook.
PREVIOUS EEG RECORDING EQUIPMENT:
The following are instructions for recording brain waves usng relatively primative equipment we have used for previous years. Even with the age of the equipment, good tracing can be recorded with proper attention to the idiosyncrasies of the equipment and an understanding of the principles involved.
Equipment and supplies (using Thorton Electronics instruments): strip chart recorder (type-462)
isolated preamp (type-410)
EEG amplifier (type-418)
BNC cable, 24 inch
lead wire assembly: +, -, and ground
three electrode plates
two rubber straps, 16 and 30 inches
electrode cream (Medi-Trace EKG sol)
- Assemble and pre-set apparatus:
Connect amplifier complex by pushing together:
- a) preamplifier
- b) EEG amplifier
- c) Bio-amp/supply
Connect BNC cable from EEG amplifier output to Strip chart recorder signal input jack.
Turn off the power in both strip chart recorder and bio-amp/supply, then plug each into a 110 volt line.
Pre-set the initial settings as follows:
|Strip chart settings:||During Setup||When running a tracing|
|vertical amplifier:*||10 mV/cm|
|Chart Drive:||5 mm/SEC||25 mm/SEC|
|Drive Power Switch:||OFF||ON|
|Pen position & heat:||both at mid-settings||adjust for darkness and position|
- Plug lead wires into preamp: Check that three lead wires are not tangled, then plug into isolated preamp receptacle labeled “electrodes”. Handle with care (do not pull).
- Attach ground electrode to wrist: Attach an electrode plate to the end of the 15 inch strap, apply electrolyte cream, and strap snugly to the inside of a wrist, with the thumb screw toward the hand.
- Attach two electrodes to scalp: Attach 2 electrode plates to the 30 in. strap, the first at the end, and the second 4-5 inches from the first. Place a drop of electrolyte cream the size of a pea on each. With assistance, part hair on lateral occipital portions of subject’s head, 2.5 inches from midline. With thumb screw inferior, press the first electrode so cream smushes into scalp. Hold in place. Part hair on other side of midline, slightly stretching rubber band and smush second electrode into scalp (also with thumb screw inferior). Hold the second in place also. Have assistant gently stretch rubber band around front of head, and attach to first electrode. Make sure it is not too tight.
- Connect wires to electrodes: Attach the ground (G) wire to the ankle electrode, tighten with thumb screw. Repeat with the “+” and “-” wires on the R and L electrodes on scalp. The wire fittings are fragile, handle with care (DO NOT PULL THE WIRES).
- Adjust settings on machine: With subject in a relaxed, comfortable position, change settings to those in the table above: When you switch the coupling on the recorder to AC, the needle should now be moving up and down. (If no needle movement, check connections and wiggle switches.)
- a) Adjust moving pen position to middle of paper.
- b) Turn on chart drive.
- c) Adjust pen heat so tracing is a thin black line.
- Record beta waves of alert subject: When satisfied with preparations and the quality of the tracings at 5 mm/sec, switch chart speed to 25 mm/sec. These high frequency (15-60 Hz) low amplitude (5-10 mV) waves are beta waves, typical of the alert brain. Switch off chart drive. (This image has beta at the left, alpha at the right)
- Record alpha waves of meditating subject: Have subject lie down in dark, close eyes, breath slowly and deeply to relax for several minutes. Set chart drive at 5 mm/sec. Maintain silence. Run for about a minute. Notice the periodic episodes of alpha waves. Alpha waves are low frequency (8-10 Hz) high amplitude (50 mV) waves. When they appear, switch the chart speed to 25 mm/sec. After a minute, without turning off the machine, have subject open eyes and converse, but not move around, press event button to indicate this change in parameters. The EEG pattern should return to the beta pattern.
- Illustrate apparatus, label all features used with appropriate numbers. Cut out examples of alpha and beta waves to mount in your notebook (using scotch tape at the edges, not contact paper). Label and discuss characteristics and significance of each type brain wave recorded.