ELECTROENCEPHALOGRAPHY: EEG FLEX/PRO AND EEG-Z
Sensor Type
To record EEG on the ProComp Infiniti, use an EEG-Flex/Pro or EEG-Z sensor. Unlike the EMG
and EKG sensors, the EEG sensor will not be able to detect a good quality EEG signal without the
use of extender leads and proper electrodes. The EEG-Z is identical to the EEG Flex/Pro, it
incorporates an automated three-lead impedance checking function.
Operating Principle
The EEG sensor detects and amplifies the small electrical voltages
that are generated by brain cells (neurons) when they fire.
Similarly to muscle fibers, neurons of different locations can fire
at different rates. The frequencies most commonly looked at, for
EEG, are between 1 and 40 Hz. The EEG sensor records a “raw”
EEG signal, which is the constantly varying difference of potential
between the positive and negative electrode, and the software
processes that signal by applying a variety of digital filters to the
recorded signal, in order to extract frequency-domain
information. Note: EEG practitioners call the negative electrode
"reference" and the positive electrode "signal."
Measurement Unit
The EEG-Flex/Pro sensor measures microvolts (
μ
V), raw. A normal EEG signal, recorded from the
scalp, will have an amplitude between 0.1 and about 200
μ
V. The raw EEG signal is mainly used
to evaluate the quality of the recorded signal and to do artifact rejection. For biofeedback
purposes, clinicians will usually want to filter out subsets of the whole EEG bandwidth and
measure the real-time changes in the total power generated by all the frequencies in the subset.
Generally, the most frequently observed frequency subsets are defined as: High Beta 20-40 Hz,
Beta 15-20 Hz, Sensorimotor Rhythm (SMR) 13-15 Hz, Alpha 8-13 Hz, Theta 4-8 Hz and Delta 2-
4 Hz. The frequencies above 40 Hz are interpreted as EMG noise from neighboring muscles.
Sensor Placement
The EEG sensor, like the EMG and EKG sensors, has three
electrodes. The positive one is called the "signal" electrode.
The negative one is the reference and the third one is the
ground. For EEG applications, the regular Triode, Single Strip
or Uni-Gel electrodes are not appropriate. Thought
Technology manufactures three types of EEG extender
cables: monopolar, bipolar and monopolar with linked ears.
These extender cables have small tin cups at the end of each
lead. For clinicians who prefer using third-party electrodes
(silver or gold), a fourth type of EEG extender cable, with
