EEG

Overview:

Electroencephalography (EEG) is the oldest example of a non-invasive medical imaging technology used to record brain activity. Its origins date back to the work of Hans Berger, a German neurologist, who demonstrated in the early 1920s that different behavioral states such as attention and mental effort were related to specific patterns of brain activity.

The technique is made possible by virtue of the organization of the cerebral cortex, which contains densely-packed columns of neurons running perpendicular to the surface of the brain. When neurons in these columns become activated as a result of receiving excitatory inputs, local current flows are generated between the body of the neuron (soma) and its primary source of inputs, the dendritic tree. The current flow causes a potential difference between the two cell compartments creating a temporary dipole. EEG electrodes placed on the scalp are able to read these dipoles when large populations of neurons (e.g., ~106-109 per sensor in humans) become synchronously active. EEG signal amplitude therefore reflects the degree of neuronal synchronization.

Quantitative EEG remains a widespread technique in research and clinical applications. Some examples are:

  • Testing afferent pathways by evoked potentials
  • Monitoring cognitive engagement, alertness, and concentration
  • Investigation of epilepsy and anti-epileptic drugs, or testing convulsive properties of drugs
  • Monitoring normal functional brain development
  • Investigation of sleep disorders
  • Monitoring the effects of biochemical, circulatory, hormonal and metabolic changes

Method:

Electrode placement and preparation

The number of EEG channels recorded from will depend on the requirements of the study and hardware available. ADInstruments EEG systems range from simple single channel applications to multi-channel montages using a standard 10-20 placement electrode cap (Figures 1 & 2). Skin must be prepared prior to electrode placement using mildly abrasive creams to remove skin debris and alcohol to remove oils. Where the electrode cap is to be used, blunt needles can be used to scrape the surface of the skin and a conductive gel can be used to fill each hold prior to electrode placement. Electrodes typically consist of Ag-AgCl disks 1-3 mm in diameter. The integrity of the electrode-skin contact may be easily and rapidly evaluated with the Model 1089 MK III Checktrode®.
 

Fig. 1. Standard 10-20 EEG cap.



10-20 EEG placement

Fig. 2. The standard 10-20 electrode placement system [1]. The electrode sites are geometrically arranged according to proportional distances (indicated in percentages ) relative to skull landmarks (nasion to inion, and periauricular). Electrode sites are labeled according to the corresponding brain areas (T, temporal; F, frontal; Fp, frontal pole; P, parietal; O, occipital), while the letter ‘C’ denotes the center (or vertex). Odd numbering refers to the left side of the head, and even to the right side. Locations along the anterior-posterior midline are denoted with the letter ‘z’ (zero).

EEG systems can be configured for unipolar and bipolar recordings. In the case of simple 1 or 2 channel EEG applications, ADInstruments provides differential Bio Amplifiers that are suitable for bipolar recordings that measure the potential variation at a site between two electrodes. For EEG montages, ADInstruments provides a 16 channel Bio Amplifier that can be used for unipolar (or bipolar) recordings, in which case a single reference site may be chosen, provided it is relatively electrically neutral and symmetrical with respect to between-hemisphere electrode sites (i.e., introduces minimal topographic distortion). Suggested reference sites include: Cz (Fig 1), the nose, or linked ears.

Signal acquisition and analysis

The EEG biopotentials are typically within the µV range1. 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. The following ADInstruments' biological amplifiers are fully isolated for connection to human or animal subjects: A notch filter may be applied to remove unwanted noise in 50-60Hz range. Narrow or wide-band filters can  applied to raw data to obtain specific frequency bands of interest:

Alpha (8 to 13 Hz)
Alpha rhythm is seen when the eyes are closed and the subject relaxed. It is abolished by eye opening and by mental effort such as doing calculations or concentrating on an idea. It is thus thought to indicate the degree of cortical activation; the greater the activation, the lower the alpha activity. Alpha waves are strongest over the occipital (back of the head) cortex and also over frontal cortex.

Beta (13 to 30 Hz)
In awake, alert individuals with their eyes open, the dominant rhythm is beta. It may be absent or reduced in areas of cortical damage and can be accentuated by sedative-hypnotic drugs such as benzodiazepines and barbiturates.

Theta (4 to 8 Hz)
Theta rhythm is said not to be seen in awake adults but is perfectly normal in awake children up to adolescence. It is normal during sleep at all ages. (Note however, that some researchers separate this frequency band into two components, low theta (4 - 5.45 Hz) activity that they correlate with decreased arousal and increased drowsiness, and high theta (6 - 7.45 Hz) activity that is claimed to be enhanced during tasks involving working memory).

Delta (0.5 to 4 Hz)
Delta rhythm is the dominant rhythm in sleep stages 3 and 4 but is not seen in the conscious adult. It tends to have the highest amplitude of any of the component EEG waves. Note that EEG artifacts caused by movements of jaw and neck muscles can produce waves in the same frequency band.

Gamma (30 to 50 Hz)
Some people also recognize gamma rhythm but their existence and importance is more controversial. It may be associated with higher mental activity, including perception and consciousness and it disappears under general anesthesia. One suggestion is that the gamma rhythm reflects the mental activity involved in integrating various aspects of an object (color, shape, movement, etc) to form a coherent picture. Interestingly, recent research has shown that gamma waves are enhanced in Buddhist monks during meditation and are absent in schizophrenics.

Spectral analysis using fast Fourier transformations (FFT) is a popular tool for quantitative EEG analysis. FFT applied to raw or filtered data can reveal the power or density of the signal within frequency bands of interest. Reduction of the frequency-domain series into to a single parameter (e.g., mean μV2) is a useful approach for quantifying the degree of neural synchronization. In the case of montages, functional connectivity across brain areas may be inferred using cross-correlation analysis. 

1. Signal amplitudes during seizure activity may approach low millivolt ranges (1-10 mV) due to the abnormally high level of neural synchronization.

1. Adopted by the International Federation in Electroencephalography and Clinical Neurophysiology

Software:

The LabChart Advantage:

(may require additional Modules and Extensions)

  • Band-pass filtering can be applied to raw EEG data to show frequency bands of interest
  • FFT of raw or filtered EEG data be used to quantify spectral power within EEG each band 
  • Cyclic measurements of peak spectral power can additionally reveal hidden periodicities in the EEG signal, for example during cognitive tasks
  • View EEG cutouts in Scope View based on Cyclic Measurements event detection
  • LabChart data files can be marked with events using the Comments feature
  • Macros can automate many tedious and repetitive analysis tasks
  • Automated extraction of data from recordings using online Timed Add to Data Pad or offline using Multiple Add to Data Pad
  • Extracted parameters in the Data Pad or Cyclic Measurements Table View can be easily exported for further analysis, e.g in Excel or Matlab

LabChart

LabChart 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.

LabChart example EEG recording

Figure 1. LabChart recording of EEG activity. The raw signal (top trace) has been filtered to show alpha and beta frequency bands (respectively, below raw trace). FFT of filtered EEG signals have been applied as channel calculations (lower two traces). Note: the sudden loss of alpha activity is due to the subject having open their eyes. This is referred to as 'alpha blocking'.  

Spectrum View

The Spectrum View is a powerful tool to display and analyze the component frequencies of a signal.  The spectral analysis is represented graphically with the Power Spectral Density (PSD) and the Spectrogram plot (Fig. 2).

LabChart Spectrum View of EEG activity

Figure 2. Spectrum View of EEG activity with PSD (top) and Spectrogram (bottom).

The PSD and Spectrogram panes can be displayed individually or together, in online or offline modes. Spectrum is frequently used to isolate electrical noise components or distinguish component waveforms within a signal such as Alpha, Beta, Delta, Theta and Gamma waveforms within an EEG.

Scope View

Scope View (LabChart Windows) provides the features of a digital oscilloscope to facilitate recording and viewing consecutive sweeps of data. These sweeps, or pages, can be overlaid and averaged within LabChart. Scope View can be used to show real time or event-based raw or averaged EEG waveforms. For analyzing Evoked EEG Potentials, the signal averaging functions are necessary to extract the evoked response from background noise.

There are several powerful features in Scope View that enhance analysis and display including:

  • Provides the ability to display continuous or cutout EEG signals that are time-locked to a stimulus.
  • Synchronizes sweeps with recorded or built-in stimulation patterns.
  • 3D Depth and Saturation Overlay feature in the Scope Overlay Options to help distinguish overlaid traces.
  • Alter the active trace and overlay trace colors.
  • Change the display background to black for better contrast. 

GLP and 21 CFR Part 11

For 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.

Hardware:

PowerLab Data Acquisition Systems

The PowerLab is a high-performance data acquisition unit capable of recording at speeds of up to 400,000 samples per second continuously to disk (aggregate). PowerLab units are compatible with instruments, signal conditioners and transducers supplied by ADInstruments, as well as many other third-party companies. In addition to standard single-ended BNC inputs, 4 differential Pod ports are also available for direct connection of Pod signal conditioners and appropriate transducers. Research PowerLab units include:

Signal Conditioners

Bio Amplifiers

Human EEG

The following ADInstruments' biological amplifiers are independently certified to comply with international safety standards and are fully isolated for connection to human subjects:

FE132 Bio Amp

FE135 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. 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.

Multi-Channel EEG

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)

Animal EEG

The following ADInstruments' biological amplifiers for use with animals (i.e. pithed toad, or anaesthetized rat/mouse) only:

FE136 Animal Bio Amp

Instruments

Multi-Channel EEG

GT201/F 16 Channel Bio Amp

Note: 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.

 

Wireless Animal Electrocorticography (ECoG)

ADInstruments provides implantable wireless solutions for recording ECoG signals in behaving rat and other small animals.

TR50B Telemetry Biopotential Telemeter

  • Suitable for single channel ECoG on animals ≥200 g

TR50BB Telemetry Dual Biopotential Telemeter

  • Suitable for recording ECoG plus another biopotential signal, such ECG for combined neurophysiology and cardiophysiology studies in animals ≥200 g.

Accessories

Bio Amp Cables:

Leads:

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:

Checktrode®:

Model 1089 MK III Checktrode®:

  • Designed to rapidly evaluate the integrity of electrode-skin contact in electrophysiological recordings such as EEG.
  • Aids in reduction of electrode contact impedance with the skin.
  • May be used to investigate the integrity of electrodes used in these applications.

Leads and electrodes that are compatible with the Model 1089 MK III Checktrode®


Consumables:


EEG Caps (Not suitable for use with the ML136 Animal Bio Amp):

The heart rate response to spontaneous arousal from sleep is reduced in children with Down syndrome referred for evaluation of sleep-disordered breathing
O'Driscoll DM, Horne RS, Davey MJ, Hope SA, Walker AM, Nixon GM, American Journal of Physiology: Heart and Circulatory Physiology, H1986-H1990, 2010

Acute administration of typical and atypical antipsychotics reduce EEG gamma power, but only the preclinical compound LY379268 reduces the ketamine induced rise in gamma power.
N C Jones, M Reddy, P Anderson, M R Salzberg, T J O’Brien, D Pinault, International Journal of Neuropsychopharmacology, 1-12, 2011

Citations Database


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.

Research Solutions
Education Solutions
Pharma Solutions
Citations Database
Top Solutions:
Site Feedback
X

Site Feedback

http://www.adinstruments.com/solutions/research/Electrophysiology-and-Cell-Biology/EEG/

* Denotes a required field
* Name
* E-Mail
* Operating System
* Web Browser

* Comments