Event-Related Potential Lab
When brain cells fire, they release tiny amounts of electricity that travel right through the brain and the scalp. This is very convenient because it means that we can measure a person's brain responses from outside their head. We do this by using small sensors that are placed near the scalp. Unfortunately, these sensors do not just pick up electricity from brain cells. They also detect random electricity produced by other types of cells such as muscle cells around the eyes and jaw. To get rid of this unwanted random electricity, we take a continuous recording (called an electroencephalogram or EEG) of the electricity present at a person's scalp (i.e., brain-cell electricity + random electricity) while we present them with the same stimulus over and over again. We then average together time chunks of the EEG that occur when the stimuli occur. When any type of random activity is averaged together, it cancels itself out. So, when we average the EEG chunks, the random electricity cancels itself out, leaving us with the brain-cell electrical potentials that are related to a particular stimulus event (i.e., hence the term event-related potential; ERP).
It is important to note that when electricity travels through the head it gets deflected by the different layers of brain tissue and bone. This makes it difficult to use ERPs to find the location of firing brain cells. However, the deflections do not interfere with the timing of the electrical potentials. So ERPs are good for measuring the temporal processing of perceptual stimuli (e.g., sounds, images, tastes), motor responses (e.g. a button press), and higher level cognitive skills. ERPs are also good for testing children or people with poor attention because they can be measured without a person attending to stimuli. The MACCS ERP Laboratory has been "Harry Potterised" to make it more relaxing for children.
32-Channels SYNAMPS II: technical specifications
The MACCS ERP laboratory uses the latest 32-channel SYNAMPSII amplifier from Neuroscan, which measures ERPs at all frequencies, including brainstem responses. The Neuroscan SynAmps2 32-channel amplifier system is suitable for high-density, low noise recordings. Additional headboxes and System Units may be added to create up to 512 recording channels. Our existing headbox can support 70 channels, consisting of 64 monopolar, 4 bipolar and 2 high-level channels. Participants' electroencephalograms (EEGs) are detected at the scalp using Ag/AGCl sintered electrodes that are held in place by Quik-Caps (small, medium, and large). The EEGs are recorded using SCAN Acquire software and are processed to produce ERPs using the SCAN Analysis software.
The stimuli are presented using Presentation software that drives a SoundBlaster Audigy2 ZS soundcard (for sounds) and NVIDIA GEForce FX 5200 videocard (for images). Sounds are presented through speakers and Sennheiser headphones. Images are presented on a 19-inch CRT Monitor. The resolution of the system (i.e. the time delay between when a stimulus code is recorded on the EEG and when the stimulus is actually presented) is less than 1 ms. The laboratory has a comfortable sofa chair that can be converted into a bed. It also has a DVD/video player that can be used to entertain participants during auditory ERP experiments and while the electrodes are being applied.
Information for Lab Users
If you are working in the ERP lab, please read the ERP Test Guide prepared by Carmen Atkinson. It contains detailed information about how to work with this equipment.
If you are going to work with the ERP equipment for the first time, you will need to fill in this form: ERP-lab training. This form should be returned to Christopher Sewell.
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