MEG Acquisition
From MEGwiki
Contents |
Subject exclusion criteria
Subjects in the Pittsburgh MEG should fit the following criterion:
- Head size must be less than 63 cm diameter. Subjects with larger heads will be unable to fit in the MEG bore.
- Subjects should be 6' 2" or shorter. Taller subjects will either not fit or will experience significant discomfort in the scanner.
- Subjects must weigh less than 290 lb.
Additionally, researchers should be aware that subject height can play a non-trivial role in the amount of biological noise detected by the scanner. In particular, significantly short subjects possess a shorter distance between the top of the head (the area touching the MEG helmet) and their heart and chest, both possible sources of noise (heartbeat and breathing artifacts). This shorter distance may also decrease the effectiveness of noise removal techniques such as SSS. As such, if given the choice, MEG researchers should generally use taller subjects rather than short ones.
Data Acquisition
Continuous HPI (Head-movement Monitoring)
Please see http://www.megwiki.org/images/b/b1/Guide_cHPI.pdf for a quick guide to continuous head movement compensation.
The Trigger System
Read about the CABMSI Trigger System Setup
Triggers Stuck
If you look at the Trigger Box and some of the lights seem to be stuck on, then run the following
program to clear them:
On the Desktop of cabmsi login: RESEARCH EXPERIMENTS/Administrative/ClearChannels/ClearChannels.ebs
Paradigm Development
E-Prime
Read about Using E-Prime with the Elekta Neuromag System
MATLAB
Paradigms can be written in MATLAB, as well. The computer used to display the paradigms has Psychtoolbox installed, as well as a number of MATLAB toolboxes.
EEG
Here is the EEG Net Layout (64) we use at UPMC CABMSI.
Sound Mixer
A new sound mixer was recently installed at UPMC CABMSI. This new mixer offers new functionalities to researchers using sounds in their paradigms, such as fine tuning of different settings for individual channels. The left and right channels with the sounds coming from the E-prime computer were set up as individual channels in the mixer, and a microphone was also set up so that the subjects can hear instructions better when wearing the earplugs. The mixer was calibrated so that the sound is approximately equally loud coming from the two ear plugs (about 85dB, measured with the sound pressure meter), so It is important that people only change the current settings if they know what they are doing. If that happens, it would be nice if they put everything back to the settings currently set up when they're done, and also tell Anna that changes were made.
You can also plug in headphones or even a small speaker to the mixer so to hear what the subject is listening to if necessary. It can be any speaker/headphone, as long as it has the thicker audio connector (to connect to the mixer), or at least the corresponding adapter.
For your reference, you can see a picture of the current setup on the right.
These are the changes that made to the zeroed out setup, as seen in the first picture in the mixer manual, if it ever needs to be setup up again.
- All controls in the PC should be in maximum.
- Channel 1: microphone plugged in, mute button unpressed, sound control at +10dB (above U). See picture for gain control.
- Channel 3/4: left channel plugged in, mute button unpressed, sound control at 10dB (below U). See picture for gain control.
- Channel 5/6: right channel plugged in, mute button unpressed, sound control at 20dB (below U). See picture for gain control.
- Main sound control at 10db (below U).
Please turn the microphone off using the button in the microphone if not used. The power switch to the mixer is on the back. If the volume of the input to the subject should be changed, please use only the Main sound control, always putting it back to 10dB when done.
Let us (Erika or Gustavo) know if any questions arise.
