The cerebral cortex contains large numbers of neurons. Activity of these neurons is to some extent synchronized in regular firing rhythms (‘brain waves’). Electrodes placed in pairs on the scalp can pick up variations in electrical potential that derive from this underlying cortical activity. The electroencephalogram (EEG) and electrocorticogram (ECoG) are recordings of the electrical activity of the brain that occurs between pairs of electrodes in contact with the scalp and represents the sum of a large amount of underlying neural activity.
These EEG signals are affected by the state of arousal of the cerebral cortex, show characteristic changes in different stages of sleep and can be used in the diagnosis of several diseases.
EEG/ECoG recording is technically difficult, mainly because of the small size of the voltage signals (typically 50 µV peak-to-peak). The signals are small because the recording electrodes are separated from the brain’s surface by the scalp, the skull and a layer of cerebrospinal fluid. A specially designed amplifier, such as the Bio Amplifier front-end, is essential. It is also important to use electrodes made of the right material, and to connect them properly. Even with these precautions, recordings may be spoiled by a range of unwanted interfering influences, known as ‘artifacts’.
Simple EEG activity can be recorded with two electrodes: a frontal electrode on the forehead, and an occipital electrode on the scalp at the back of the head and a third (ground or earth) electrode is also attached, to reduce electrical interference.
A simple setup to record of an EEG signal.
Single or dual channel recordings may be useful for the simple recording and identification of alpha activity in conscious subjects or specific waveforms representative of the sleeping subject, whilst multiple channel EEG is used for the identification of neurological functioning and/or abnormalities. Therefore, in clinical EEG, it is usual to record many channels of activity from multiple recording electrodes placed in an array over the head using EEG caps.
Multiple channel EEG recorded using an EEG cap.
ADInstruments EEG Electro-Cap systems includes a cap for EEG, electrode adapter (suits the MLA2540 5-Lead Shielded Bio Amp Cable), body harness, quick insert electrode, ear electrodes (one pair), disposable sponge disks (100), needle/syringe kit, electro-gel (16 oz), head measuring tape, ivory cleaning liquid and a manual. The system is suitable for use with the ADInstruments ML135 Dual Bio Amp, ML138 Octal Bio Amp or the GT201 16 Channel Bio Amp except the ML136 Animal Bio Amp.
To ensure high quality, low noise recordings of EEG/ECoG good subject preparation and application techniques are essential. Excessively high skin impedances (due to inadequate preparation) will cause signal artifacts that can interfere with EEG/ECoG recordings. Therefore, impedances of all electrodes should be checked with a suitable device (i.e. CheckTrode MkIII from UFI) to ensure they are below 10 kOhm.
The EEG signal can be separated and classified into a few distinct waveforms of different frequencies. These waveforms include the Alpha, Beta, Delta, Theta, Gamma and SMR (Sensorimotor Rhythm) waves.
Note: When recording EEG/ECoG it is important to differentiate between "referential" and "differential" recording systems. A "referential system" measures the biopotential of a single electrode site in relation to an electrophysiologically silent electrode (reference). An absolute biopotential is then obtained for each active electrode and the difference between any pair of active electrodes is software-derived at a later stage. In contrast, the ADInstrument's "differential" Bio Amps directly measure the difference between a pair of electrodes and the absolute biopotential at each single electrode site is not provided. The desired channels are determined by hardware electrode connections and cannot be interchanged with software controls. The absolute potential of a single electrode may be obtained with ADInstrument's Bio Amps by linking the negative inputs of all channel connections.
LabChartLabChart software (for Windows and Macintosh) combines the familiar simplicity of a traditional strip chart recorder with the powerful analysis features of a digital acquisition system. LabChart software and a PowerLab data acquisition unit provide data integrity, easy selection of hardware settings, powerful online and offline analysis, procedure automation, seamless extraction of experimental data and flexible display options. Acquisition and analysis capabilities can be further increased with LabChart Extensions and LabChart Modules. LabChart Modules are available as part of
LabChart Pro and LabChart Extensions are free for download from the website for existing LabChart users.
In addition, LabChart software can:
- Rectify and integrate the raw EEG signal and display the results on a separate channel.
- Calculate and display the RMS power content of the signal.
- Display the power spectrum (FFT) of a selected region of data using Spectrum command
- Include a digital filter that allows the user to record at the highest sampling rate and apply filtering online or offline.
- Apply filtering options such as low-pass, high-pass, notch, narrow band-pass, band-pass and band-stop. This is very useful for EEG recording and analysis because specific waveform frequencies such as alpha, delta and theta etc can be easily identified.
Scope Scope software, supplied with PowerLab systems, provides powerful display, recording and analysis features to transform your computer into a two-channel storage oscilloscope, XY plotter or Power Spectrum (FFT) analyser. Scope is used commonly to measure any high-frequency signal that is time-locked to a stimulus such as action potentials and evoked responses. For analyzing Evoked EEG Potentials, the Scope Software is recommended because it provides signal averaging functions that are necessary to extract the evoked response from background noise.
This software:
- Provides the ability to record, display and analyze any high frequency signal that is time-locked to a stimulus
- Synchronizes sweeps with recorded or built-in stimulation patterns
- Provides a range of real-time and offline analysis features
- Generates stimuli of differing intensities and waveform structures (i.e. single-pulse, multiple pulse, simple ramps) and controls an external stimulator using the analog output on the front of the PowerLab.
GLP and 21 CFR Part 11For those researchers working within a laboratory requiring GLP and 21 CFR Part 11 compliance the
GLP Client and GLP Server are available for use with LabChart (Windows only) and PowerLab data acquisition systems. For more information, visit the
Good Laboratory Practice application page or contact your nearest ADInstruments representative.
Bio Amplifiers The EEG biopotentials are typically very small in amplitude (µV). Therefore accurate recording, display and analysis of an EEG requires a suitable bioamplifier. ADInstruments offer a range of Bio Amplifiers that when connected to a PowerLab data acquisition unit are certified safe for use with humans or animals. These bioamplifiers are fully software-controlled using LabChart or Scope. The following ADInstruments' biological amplifiers are fully isolated for connection to human or animal subjects:
Human EEGThe following ADInstruments' biological amplifiers are independently certified to comply with international safety standards and are fully isolated for connection to human subjects:
ML132 Bio Amp ML135 Dual Bio Amp ML408 Dual Bio Amp/Stimulator The Bio Amp, Dual Bio Amp and Dual Bio Amp/Stimulator are manufactured for use with PowerLab data acquisition systems and are fully software-controlled by LabChart or Scope. These Bio Amps cannot be used for recording 3 or more biopotentials on a single subject; however, they may be used for multiple subjects that have separate grounding leads. For recording more than 3 biopotentials from a single subject see below:
Multiple-Channel EEG/ECoG RecordingsADInstruments also provides multiple channel bioamplifiers that connect directly to PowerLab data acquisition systems. These units are also fully-isolated, and independently certified, for connection to human subjects.
ML138 Octal Bio Amp - A differential amplifier that consists of eight electrically isolated differential input AC amplifiers
- A shared ground connection across all eight inputs.
- Supplied with two packets of MLA0310 Lead Wires (1.8 m, 10 snap on)
GT201/F 16 Channel Bio Amp - A fully isolated, 16 channel stand-alone biological amplifier that consists of 8 modules, with each module containing two channel amplifiers that share a common ground input
- Suitable for unipolar and bipolar recordings
- Electrodes are NOT supplied and must be ordered separately
- Suitable electrodes and lead wires include the:
Animal EEGThe following ADInstruments' biological amplifiers for use with animals (i.e. pithed toad, or anaesthetized rat/mouse) only:
ML136 Animal Bio Amp - An isolated, high performance and software-controlled differential amplifier
- Has three 2mm input sockets allow the direct connection of electrodes to this amplifier
- Supplied with MLA1215 Animal Bio Lead Wires
- Also suitable for use with
Multiple channel EEG may be recorded using the ML138 Octal Bio Amp or GT201/F 16 Channel Bio Amps that connect directly to the MLA1505 Lead Wires that terminate in alligator clips or the MLA1203 Needle Electrodes.
AccessoriesBio Amp cables:
Leads compatible with both shielded (MLA2340 & MLA2540) and unshielded (MLA1340 & MLA1540) cables:
Leads compatible with shielded cables (MLA2340 & MLA2540) only:
Leads that directly connect to the Dual Bio Amp
Leads that directly connect to the Animal Bio Amp
Electrodes:
Consummables:
EEG Caps (Not suitable for use with the ML136 Animal Bio Amp):