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EEG & ECoG
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| Electroencephalograph (EEG) and electrocorticograph (ECoG) signals can be recorded using a Bio Amp and PowerLab data acquisition system.
The electroencephalogram and electrocorticogram 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. Single or dual channel recordings may be useful for the simple recording and identification of alpha activity during waking or specific waveforms representative of the sleeping subject, whilst multiple channel EEG is used for the identification of neurological functioning and/or abnormalities.
Given that these bioelectrical signals are typically very small in amplitude (μV), an amplifier is required to accurately record, display and analyze the EEG/ECoG. Depending on the hardware and software used, the biological amplifier provides not only amplification of a signal but also apply a range of filtering options for the removal of unwanted signal artifacts. ADInstruments offer a range of Bio Amplifiers suitable for use with animals as well as units certified safe for use with humans. A PowerLab data acquisition system can be used with other brands and models of amplifier to record the EEG/ECoG, provided they have a suitable analog output (Max. ± 10 V). Ask your nearest ADInstruments representative for details.
Human EEG
When connecting any type of biological amplifier to a human subject it is extremely important that an independently-certified, electrically-isolated amplifier is used. This is necessary to prevent any risk of electrical shock to the subject. ADInstruments Bio Amps have been externally certified to comply with international safety standards, ensuring that our biological amplifiers are safe for connection to humans.
The following ADInstruments' biological amplifiers are fully isolated for connection to human subjects: - Bio Amp (ML132): A single channel, differential amplifier that is suitable for recording a range of biopotentials such as EEG, ECG, EMG or EOG. For example, a single channel of EEG such as a central, parietal or occipital lead may be measured between 2 active electrode connections.
- Dual Bio Amp (ML135): A dual channel, differential amplifier that is suitable for recording 2 independent biopotentials that share a common ground. In EEG recordings, any two channels may be recorded (i.e. central, occipital).
- Dual Bio Amp/Stimulator (ML408): A dual channel, differential amplifier that also includes an isolated stimulator suitable for mild electrical stimulation of human subjects (i.e. Evoked EMG studies).
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 Recordings
For recording 3 or more biopotentials from a single subject, ADInstruments provide third-party amplifiers that connect directly to PowerLab data acquisition systems. These units are also fully-isolated, and independently certified, for connection to human subjects. - ADInstruments Octal Bio Amp (ML138): Suitable for measuring up to eight simultaneous biopotential recordings from a single subject (human or animal). The unit is fully isolated and safe for connection to human subjects (certification pending).
- 8 Channel Bio Amp (GT205): An 8-channel biological amplifier supplied with 2 independent ground inputs for recording ECG, EEG, EOG or EMG. Suitable for unipolar and bipolar recordings.
- 16 Channel Bio Amp (GT201): A 16-channel biological amplifier supplied with 2 independent ground inputs for recording ECG, EEG, EOG or EMG. Suitable for unipolar and bipolar recordings.
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.
Animal EEG
To measure EEG/ECoG in animal subjects, we recommend the Animal Bio Amp (ML136) supplied with lead wires that terminate in alligator clips or MLA1204 Needle Electrodes. Alternatively, the MLA1505 unshielded lead wires can be used with the Bio Amp (ML132), Dual Bio Amp (ML135) and Dual Bio Amp/Stimulator (ML408). The MLA1505 lead wires connect to the Bio Amp subject cable and terminate in alligator clips.
Multiple channel EEG may be recorded using the Octal Bio Amp (ML138), 8 or 16 Channel Bio Amps that connect directly to the MLA1505 Lead Wires that terminate in alligator clips or the MLA1203 Needle Electrodes.
Software and Data Analysis
LabChart software can rectify and integrate the raw EEG signal and display the results on a separate channel. The RMS power content of the signal can also be calculated and displayed. The LabChart software Spectrum command displays the power spectrum (FFT) of a selected region of data and can be used to detect alpha rythyms etc. The Evoked Response extension for LabChart (MAC only) analyzes physiological responses to a stimulus and may be used to determine response latency etc.
For analyzing Evoked EEG Potentials, the Scope Software (which operates like a two channel oscilloscope) is recommended as it provides signal averaging functions that are necessary to extract the evoked response from background noise. Both LabChart and Scope software enable researchers to generate stimuli of differing intensities and waveform structures (i.e. single-pulse, multiple pulse, simple ramps) and control an external stimulator using the analog output on the front of the PowerLab.
LabChart also includes a digital filter that, allows the user to record at the highest sampling rate and apply filtering online (Win only) or offline (Win and Mac). The Digital Filter extension provides a number of additional filtering options, including low-pass, high-pass, notch, narrow band-pass, band-pass and band-stop. This is very useful for EEG recording and analysis as specific waveform frequencies such as alpha, delta and theta etc can be easily identified.
Accessories
To ensure high quality, low noise recordings of EEG/ECoG good subject preparation and application techniques are essential. Because EEG/ECoG signals are very low amplitude signals in comparison to ECG and EMG, excessively high skin impedances (due to inadequate preparation) will cause signal artifacts that can interfere with EEG/ECoG recordings. Impedances of all electrodes should be checked with a suitable device (i.e. CheckTrode MkIII from UFI) to ensure they are below 10 kOhm.
A number of accessories to assist in the preparation and recording are available from ADInstruments, including Abrasive Gel (MLA1093B), Electrode Paste (MLA1095) and Electrode Cream (MLA1090).
ADInstruments also supply the EEG Electro-cap Systems that are suitable for use with all ADInstruments Bio Amps (Bio Amp, Dual Bio Amp, Dual Bio Amp/Stim, Octal Bio Amp) as well as 8 and 16 Channel Bio Amp. They are not suitable for use with the Animal Bio Amp. The MLAEC1 EEG Electro-cap System 1 includes a medium cap, electrode adapter, body harness, quick insert electrode, ear electrodes, disposable sponge disks, needle/syringe kit, electro-gel, head measuring tape, ivory cleaning liquid and a manual. The MLAEC2 Electro-cap System 2 includes all of the same components as the MLAEC1 but provides an additional large-sized cap. For more information about any of the above products, please contact your nearest ADInstruments representative.
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| PowerLab (MacLab) citations: |
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| Electroencephalographic activation by fluoxetine in rats: role of 5-HT1A receptors and enhancement of concurrent acetylcholinesterase inhibitor treatment. |
| H. C. Dringenberg and P. Diavolitsis, Neuropharmacology, 42, 154-161, 2002. |
| In adult rats (400–500 g) a chronic neocortical recording electrode (Teflon coated wire, 125 µm diameter) was implanted on the surface of the sensory-motor cortex (AP-1.0 from bregma; L+2.0 from midline). Additional reference and ground connections (jewelry screw attached to a miniature female connector) were placed in the bone over the cerebellum. All electrodes were held in place by dental cement built around the electrodes and anchor screws placed in the bone around the electrodes. Neocortical EEG activity was recorded in awake, freely moving rats placed in a Plexiglas cage. Lightweight cables were connected to the implanted electrodes and cortical activity was recorded differentially against the cerebellar connection. The neocortical signal was amplified using Grass P511 amplifiers (half-amplitude set at 0.3 Hz and 10 kHz). Initial filtering (low pass filter set at 47 Hz) and digitizing (100 Hz) of the raw EEG signal was carried out by a PowerLab/4s system for the Macintosh (ADInstruments, Milford, MA). The digitized EEG signal was displayed on one EEG channel. Further, it was passed through additional software-controlled band-pass filters to separate and display the following frequency bands on four additional channels: delta: 0.5–4 Hz; theta: 4–8 Hz; alpha: 8–12 Hz; beta: 12–30 Hz. |
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| Influence of a dietary n-3 fatty acid deficiency on the cerebral catecholamine contents, EEG and learning ability in rat |
| T. Takeuchi, Y. Fukumoto and E. Harada, Behavioural Brain Research, 131, 193-203, 2002. |
| Newborn rats EEG electrodes were implanted chronically. Recording electrodes, Teflon-coated multi strand stainless-steel wire (7935, A-M Systems Inc, USA), were bilaterally implanted extra-durally over the frontal and occipital areas. Ground and reference electrodes were also implanted over the frontal sinus and at an intermediate position between the frontal sinus and frontal bone, respectively. Each electrode was connected to a socket, and fixed on the surface of the skull with dental resin…….. Monopolar EEG recordings were made from bilateral occipital areas, using a polygraph (1A74, NEC San-ei, Tokyo) with time constant at 0.3 s and high frequency 60 Hz filter. The EEG signals were recorded on paper (3 cm/s) for visual analysis and stored on magnetic tape (MR-10, TEAC, Tokyo) which enabled off-line computer analysis……….. On the basis of visual analysis, parts of the EEG recording lasting 1 min each, were selected for computer (MacLab, AD Instruments, USA) analysis. Prior to spectral analysis, each digitized epoch of EEG was filtered by application of a Hanning window cosine transform. The EEG signal was sampled at a rate of 128 Hz and then digitally low-pass filtered at 60 Hz. Frequency analyses were carried out by means of a fast Fourier transformation. The EEG was sampled and transformed directly in epochs of 2 s. Each digitized 2 s epoch of EEG thereby yielded a power spectrum having a Fourier resolution of 0.5 Hz over a frequency range of 1–30 Hz. The average power spectrum of 30 of these epochs for each 1.5 min EEG sample was plotted in the range from 1 to 30 Hz with a resolution of 0.5 Hz. |
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The material on this page is provided in good faith and believed accurate at the time of writing. No responsibility will be taken, or liability accepted, for damages arising from the use of information herein. Readers are urged to check with respective manufacturers the accuracy of all product related information.
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