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Developmental Neurolinguistics Lab
Electrophysiology and Event-Related Potentials (ERPs)
The brain consists of billions of neurons and connections (axons
and synapses) between these neurons. Neurons communicate with each
other via electrochemical events.
Electrical changes caused by the activity of the neurons can be
recorded at the scalp using electrodes. The signals are very small
(on the order of 1 to 100 millionths of a volt) and must be amplified.
Specialized amplifiers and computer software has been designed to
record this electrical activity, which is called the electroencephalogram,
of EEG.
The EEG has been used to examine brain activity in infants, children
and adults for over 30 years. It is a safe, non-invasive method.
In our laboratory, a net of 65 electrodes is placed on the scalp.
Each electrode is made of tin and makes contact with the scalp via
a sponge soaked in a solution of water and salt.
During a study the infant or child listens to, and/or watches some
stimulus (e.g., speech sounds, or pictures of animals). These stimuli
are called events, and the electrical activity associated with these
events are called ERPs.
Electrical activity from the brain is recorded to a number of these
events. Consistent electrical changes to a category of events can
be seen by averaging together the electrical activity from 15 or
more of these events.
This activity is seen as a series of positive and negative-going
deflections, and shown in figure 1 below in section 3.
The timing and size of these deflections, and the location of this
activity on the scalp is used to make inferences about the time-course
of processing in the brain and the location of the source of this
activity.
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