g.EEGsys: Specs & Features
A complete EEG/CNS research system, ready-to-go installation on a PC or notebook
Start your EEG research immediately! We provide various complete EEG-research packages with 8 to 256 channels to meet your research needs. The systems include amplifier(s), acquisition software, analysis software and a high-end business PC or notebook with all the software installed and ready to go. Just add your desired sensors, caps, electrodes, consumables and stimulation setup for doing ERPs and your lab is ready to go!
g.Recorder enables easy amplifier configuration, data visualization and storage. You can assign and record triggers and markers, review data, and perform other tasks. For data analysis, g.EEGsys packages include g.BSanalyze (base version plus EEG toolbox).
g.EEGsys can be set up with g.MOBIlab+, g.USBamp, g.HIamp and g.Nautilus. Systems based on g.USBamp can be upgraded for more channels at any time. All g.tec systems can be used with active or passive electrodes using gel, and also work with dry electrodes. Upgrading the system for real-time processing, including BCI reserach, is also no problem at all. Please see the software options.
For ERP research, g.tec offers various stimulation devices: (i) electrical stimulators, (ii) vibro-tactile stimulators, (iii) auditory stimulation for doing BAEPs, MMN, P300, N400, ASSR, SEP,..., and (iv) visual stimulation for VEPs and SSVEPs. Additionally, external stimulators such as heat can send trigger signals to the g.tec system. Visual stimulation can be done with head-mounted displays, computer monitors, VR systems or LEDs. Auditory stimulation is done via in-ear phones on the left and right ear. For ERP analysis, the correct time resolution of the trigger event is very important. Therefore, g.tec sends hardware trigger signals from the stimulator to the digital inputs of the amplifiers, which provides perfect time resolution because the triggers are sampled with the analog channels. Such triggers come from the auditory stimulation system, the electrical stimulator, the tactile stimulator or the g.TRIGbox that detects visual, auditory events or button presses.
- The complete solution for your lab
- All software already installed and tested on a high end business PC/notebook
- Based on g.MOBIlab+ (8 channels), g.USBamp (16 - 64 channels), g.HIamp (80-256 channels) or g.Nautilus (8-64 channels)
- Includes g.Recorder data acquisition software
- Includes g.BSanalyze offline analysis software (base version + EEG toolbox)
- Can be upgraded to a real-time/BCI system at any time
- High resolution ERP acquisition and analysis including statistical analysis
- Records short, middle and late latency ERPs
- Presentation or e-prime can be used as stimulation systems
- Recommended setup for a fully equipped EP lab plan available
g.tec's Setup ERP/EP
If a healthy person is exposed to a stimulus, which might be visual, auditory, or somatosensory, the response from the brain can be detected through positive or negative changes in the potential detected on the skull. Reflecting this relation of cause and consequence, an electrophysiological signal which captures the response to a stimulus is called an Evoked Potential (EP) or Event Related Potential (ERP).
A stimulus can either be a single event or a periodically repeated event which elicits a response of the nervous system. This leads to an important distinction with regard to the evaluation of the captured signals:
- A periodic stimulation, e.g. an LED which flickers with a certain frequency for a couple of seconds, causes a periodic response of the same frequency within the captured EEG data. To measure the response, data is evaluated within the frequency domain.
- A single stimulation event, e.g. an LED which lights up once, elicits a transient response in the EEG. To measure the response, data is evaluated within the time domain.
The paradigms listed below can be performed with a complete system provided by g.tec, including:
The P300 response
||The P300 response is a positive deflection, which occurs approximately 300 ms after a visual, auditory or somatosensory Stimulus. The P300 reflects the brain's processing of the event, and is much larger if the user pays attention to a specific event, called the target.|
|Visual P300||Auditory P300||Tactile P300|
|Many Systems use a matrix of symbols, including letters from A to Z and numbers from 0 to 9. The user is asked to concentrate on a certain letter. Throughout the experiment, all letters are highlighted in a random sequence. As soon as the target letter is highlighted, a P300 response is elicited.||An infrequent target stimulus must be presented within frequently occurring non-target stimuli. For example, a non-target (or “standard”) stimulus can be a pure tone burst with a base frequency of 440 Hz and a duration of 100 ms. The rarely occurring target (or “deviant”) stimulus is again a pure tone burst with a duration of 100 ms, but with an altered base frequency of 660 Hz||Tactile stimulation can be achieved e.g. using mechanical actuators placed to the user's fingertips. An oddball paradigm (e.g. a series of frequently occurring stimuli on one hand is interrupted by an unlikely stimulation on the other hand) is often used to evoke a P300 response.|
Mismatch Negativity - MMN
The MMN (Mismatch Negativity) response occurs approximately 200 ms after a stimulus is presented. The response occurs only if a new stimulus does not match a previously presented one. For example, if a series of tones is presented and one tone is different with regard to duration or frequency, a N200 response occurs.
The stimulation approach seems to be quite similar to the P300 paradigms. However, the experiments are different with regard to the Stimulation Onset Asynchrony (SOA), which is the time gap between the onset of consecutive stimuli. For the MMN response, the SOA should not exceed 300 ms. For the P300, a larger SOA (e.g. 1000 ms) is common.
The two experiments are also different in terms of the participant's mental activity. While a P300 experiment requires active participation of a test subject, an MMN experiment relies on sensory or pre-attentive processing, which means that a tested subject does not have to pay attention to the experiment.
Brainstem Auditory Evoked Potential - BAEP
The response to a short auditory stimulus (e.g. a clicking sound), measured within the first 12 ms after the onset of the stimulus, is known as “early auditory evoked potential” or early AEP. Measured from the vertex to the mastoid, early AEPs are also referred to as Brainstem Auditory Evoked Potentials (BAEPs). A BAEP signal is a characteristic pattern of seven positive waves, which are labeled from I to VII.
Each peak can be related to neurological activity, either within the Cochlea (I,II) or within the brainstem. Clinical applications of BAEPs rely on the interpretation of the measured BAEP pattern.
Compared to the P300 and the MMN response, BAEPs have a very small amplitude (approx. 0.5 µV). Therefore, evaluating BAEPs often requires repeating the procedure many times to collect many trials to average. Due to the low latency between stimulus and the EPs, the accurate triggering of an experiment is crucial. Without reliable professional auditory hardware, which manages stimulus output and signal triggering for subsequent recording equipment with a very low latency, recording BAEPs is impossible.
Steady State Visually Evoked Potential - SSVEP
|The Steady State Visually Evoked Potential (SSVEP) is elicited if a subject is exposed to a visual stimulus which is repeated with a frequency of at least 6 Hz. For example, a flickering LED can be used as stimulating device. If the LED flickers with a frequency of 14 Hz, the response of a subject paying attention to the LED is increased at 14 Hz. A spectral analysis of the captured EEG data shows a clear peak at 14 Hz. If several LEDs flicker at different frequencies and the user pays attention to one of the LEDs, the captured SSVEP can be used as input method for a Brain-Computer Interface.||
Auditory Steady State Response - ASSR
If rapid auditory stimuli are used as inputs, the so-called auditory steady state response (ASSR) may be found in the EEG. Auditory steady-state responses are used for objective audiometry. Hearing thresholds at various input frequencies can be measured without any participation of the tested subject. For example, ASSRs can be used to estimate the hearing threshold in infants or to evaluate hearing aids. ASSRs are recorded with a special auditory Stimulation, which consists of a carrier frequency modulated with a lower frequency.