National Brain Mapping Lab

EEG

EEG

 

 

EEG Lab Facilities(Top)

g.USBamp(Top)

g.USBamp is g.tec’s 16 channel biosignal amplifier with CE & FDA approval. The device has a wide input range which allows the acquisition of different biosignals such as EEG, EOG, EMG and ECG without saturation. Moreover, various additional sensors can be connected to amplifier's input channels. g.USBamp has 4 potential separated groups with 4 input channels each. This allows to simultaneously record EEG, EMG, EOG and ECG without interference. The 4 groups can be interconnected to record 16 EEG channels with the same ground and reference potentials. Multiple g.USBamp can be used to build multi-channel system with more than 16 channels. A synchronization cable guarantees that all devices are sampling with exactly the same frequency.

A powerful floating point DSP performs the real-time filtering of the biosignal data. Real-time analysis is enabled through the g.tec high-speed processing library for simulink which is important for BCI and neurofeedback studies.

The g.USBamp amplifier can be connected directly to a PC with an USB connector. The g.USBamp has 8 trigger channel, 4 digital output and a SC input to quickly connect amplifier inputs to ground potential. Furthermore, the device can be used with both active/passive electrodes and has an internal calibration unit and impedance check. Also a driven right leg (DRL) signal for the suppression of power line interference can be generated.

 

Highlights

  • Up to 32 channels perfectly synchronized with 24 bits
  • 4 potential separated groups
  • 8 digital trigger inputs/ 4 digital output
  • DC coupled & wide range input channels
  • Digital filtering of all channels
  • Real-time analysis through simulink
  • Can be used with active/passive electrodes
  • Impedance check for passive electrodes

 

g.HIamp(Top)

g.HIamp is g.tec’s 80 channel biosignal amplifier with CE & FDA approval. The device has a wide input range which allows the acquisition of different biosignals such as EEG, EOG, EMG and ECG without saturation. Moreover various additional sensors can be connected to amplifier's input channels.

A powerful floating point DSP performs the real-time filtering of the biosignal data. Real-time analysis is enabled through the g.tec high-speed processing library for simulink which is important for BCI and neurofeedback studies.

The g.HIamp amplifier can be connected directly to a PC with an USB connector. The g.HIamp has 16 trigger channel and a HOLD input to suppress artifacts amplifier inputs to ground potential. Furthermore, the device can be used with both active/passive electrodes and has an internal impedance check unit for both.

 

Highlights

  • Up to 80 channel perfectly synchronized with 24 bits (64 channels can be used for EEG recording)
  • 16 digital trigger inputs
  • DC coupled & wide range input channels
  • Digital filtering of all channels
  • Real-time analysis through simulink
  • Can be used with active/passive electrodes
  • Impedance check for active/passive electrodes
  • HOLD channels during magnetic/electric stimulation

 

g.Nautilus(Top)

g.Nautilus is g.tec's biopotential amplifier with wireless data transmission technology and CE approved. The device can acquire up to 32 channel EEG data with 24 Bit resolution and a sampling rate of 250 or 500 Hz. Each analog to digital converter operates at 1.024 MHz. This oversampling and consequent averaging results into a high signal to noise ratio.

The tiny and lightweight device is attached to the EEG cap and is responsible for EEG data collection and transmission to the base station. The device is completely water-proof, which allows easy cleaning of the electrodes together with the cap. g.Nautilus avoid cable movements and allow completely free movements of subject. g.Nautilus reduces set-up time due to available 10-20 standard montage of active electrode cap.

g.Nautilus transmits data via 2.4 GHz band in an indoor operating range of 10 meter. The base station sends the received digitized data to the PC via USB. An electrode Impedance check can be performed automatically via software and a 3 axis acceleration sensor provides online head movement information along with the biosignal. Moreover, the input sensitivity range of all channels is adjustable. 8 digital trigger lines can be connected to the base station to record event trigger timing information.

g.Nautilus has a built-in lithium Ion battery, which allows for continuous recording up to 8 hours.

 

Highlights

  • Up to 32 channel perfectly synchronized with 24 bits
  • 8 digital trigger inputs
  • Adjustable input sensitivity range
  • 2.4 GHz digital transmission, range 10 meters indoor
  • 8 hours continuous recording and 2-3 hours charging
  • 3 axis acceleration sensor provides online head movement information
  • Reduce setup time
  • Digital filtering of all channels
  • Real-time analysis through simulink
  • Impedance check

 

g.TRIGbox(Top)

The g.TRIGbox is a device to generate trigger pulses from various sensor or input signals. Input and output lines are isolated from each other. The trigger outputs can be connected to digital or analog inputs of a data acquisition system such as g.USBamp, g.HIamp or g.Nautilus.

Thus, g.TRIGbox provides exact detection and recording of almost any type of stimulation in experimental paradigms. Its wide range of possible input signals and sensors allows use of various trigger sources such as sound card outputs, microphones, piezoelectric or individual sensors, response buttons, various logic signals (TTL, C-MOS…) provided by external stimulator, visual markers from computer monitor, LED indicator, flash lamps or slide projectors.

Each channel has a separate threshold level adjustment and a trigger output indicator LED. The trigger output signals are provided at two different voltage levels: 5 V (for TTL or CMOS logic inputs) and 200 mV (for the connection to analog unfiltered amplifier inputs). In addition to the single trigger output signals, an encoded 4-bit analog output signal can be used to record all 16 possible output combinations in one analog channel.

 

Highlights

  • 4 isolate input/output lines
  • Simple use of PowerPoint to presents stimulus/paradigm
  • Possible use of various trigger sources such as visual, auditory and somatosensory
  • Distinct adjustable threshold for each channel
  • Can be connected to digital inputs of recording amplifiers
  • Use one coded trigger channel for up to 16 different experimental conditions

 

g.STIMbox(Top)

The g.STIMbox is used to generate and record trigger signals. Arbitrary paradigms can be programmed easily using the 16 digital outputs and are executed with high temporal precision. At the same time, trigger signals from external devices can be recorded using the 14 digital inputs of the device. Therefore the g.STIMbox is an ideal extension for electrophysiological research systems which require additional digital input and output possibilities. The g.STIMbox can be connected to PC via a USB cable. The device has synchronous or asynchronous operational modes. In order to elicit steady-state visual evoked potentials (SSVEP), optical stimulus presentation is performed with an additional device which is connected to g.STIMbox’ outputs via cable and the parameters of paradigm can be adjusted by software.

 

Highlights

  • Controlled inputs and outputs for accurate timing
  • Digital outputs can be used to produce precisely-timed paradigms
  • Digital inputs can be acquired and used within the recording system
  • Direct control of inputs/outputs from a computer via USB
  • Digital outputs usable for tactile or visual stimulation

 

Sensors(Top)

SPO2 Sensor(Top)

A photoelectric sensor which is placed on the index finger (mostly) and uses two light sources with different wavelengths to measure the saturation of oxygen in the blood. Moreover, the sensor provides heart rate and plethysmography signal.

 

Pulse Sensor(Top)

A lightweight photoelectric sensor which is placed mostly on finger and utilizes plethysmography to record pulsatile blood flow.

 

Skin Temperature Sensor(Top)

A sensor that is attached to the skin and measures the skin temperature in the range of 20 – 45 ℃ with 0.2 ℃ precision.

 

Galvanic Skin Response Sensor(Top)

This sensor consists of two electrodes which are placed on the fingers and through current application, monitors and records electrical activity of skin (or changes of skin conductance). This sensor is used widely in polygraph or emotional studies.

 

Flow Sensor(Top)

A thermistor sensor that is place in front of the nose and mouth and measures temperature changes in inhaled and exhaled air. The resultant respiration signal is very robust against movement artifacts.

 

Respiration Effort Sensor(Top)

A piezoelectric sensor that is placed in a belt system and records chest and abdominal respiration waveforms independently.

 

Acceleration sensor(Top)

A sensor that is placed on body or directly on the moving object to measure the 3-axis acceleration in the range of ± 3g.

 

Limb Movement Sensor(Top)

A piezoelectric sensor that is placed on ankle to detect feet movements during sleep. This sensor can be used to study Restless Leg Syndrome (RLS) or Periodic Limb Movements (PLM).

 

Snoring Sensor(Top)

A piezoelectric sensor that is placed on the subject’s neck to record trachea’s sounds and can be used in sleep studies.

 

Lab Services(Top)

EEG(Top)

Data processing in central neural system is done via electrical activity of neurons. This continuous electrical activity generated by the brain itself, can be measured and recorded by electrodes placed on the scalp. The resulting traces are known as an electroencephalogram (EEG) and represent a summation of post-synaptic potentials from a large number of neurons.

The use of EEG in neuroscience research delivers a number of benefits. One is that EEG is non-invasive for the research subject. Furthermore, the need to restrict the subject‘s movements is clearly lower than in other fields of neuroscience such as functional magnetic resonance imaging (fMRI). A further benefit is that many EEG applications record spontaneous brain activity, which means that the subject does not need to be able to cooperate with the researcher (as is necessary, for instance, during behavioral testing in neuropsychology). Also, EEGs have a high temporal resolution compared with techniques such as fMRI and PET and are capable of detecting changes in electrical activity in the brain on a time scale in the millisecond region.

The results of EEG can be used to identify abnormal electrical activities of brain which may be related to disorders such as epilepsy, brain tumor, Alzheimer, brain stroke and dementia. The EEG recording can be utilized to detect brain activity during comma or patient monitoring in a brain surgery.

In a conventional EEG recording session, an electrode cap is placed on the subject’s head and to obtain high quality EEG signal conductive gel is used to decrease the skin-electrode impedance.

 

Lab Facilities in this field:

  • 16 & 32 channel biosignal amplifier (g.USBamp)
  • 80 channel biosignal amplifier (g.HIamp)
  • 32 channel wireless EEG amplifier (g.Nautilus)
  • The g.tec Highspeed Online Processing Library for Simulink

 

Event- Related Potential Recording(Top)

An event-related potential (ERP) is any stereotyped electrophysiological response to an internal or external stimulus. In simple terms it is any measured brain response that is the direct result of a thought process or perception. While evoked potentials may reflect the processing of the physical stimulus, they may also be modulated or even mediated by the higher processes involving memory, expectation, attention, or changes in mental state.

Experimental psychologists and other neuroscientists have revealed many different stimuli and paradigms to elicit reliable ERPs from their subjects. The timing of these responses is thought to represent timing of the brain‘s communication during information processing.

ERPs can be reliably measured using electroencephalography (EEG). This method utilizes surface electrodes to measure the electrical activity of the brain (specifically the cortex) through the skull and scalp. As the EEG reflects many thousands of simultaneously ongoing neuronal processes, the brain’s response to a specific stimulus or event of interest is rarely visible in the ongoing EEG. In actual recording situations, even the most robust ERPs emerge only after many dozens of individual presentations of the stimulus of interest are averaged together. This technique cancels out noise and spontaneous EEG and enhances the voltage response to the stimulus making it stand out clearly from the averaged out background. As ERPs are temporally locked to stimuli, therefore EEG amplifiers need to be equipped with trigger inputs capable of registering markers related to stimulus events occurring during continuous and ERP like EEG acquisitions.

 

Lab Facilities in this field:

  • 16 & 32 channel biosignal amplifier (g.USBamp)
  • 80 channel biosignal amplifier (g.HIamp)
  • 32 channel wireless EEG amplifier (g.Nautilus)
  • g.TRIGbox to generate trigger pulses locked to events
  • g.STIMbox to generate & record trigger pulses locked to events
  • The g.tec Highspeed Online Processing Library for Simulink

 

Sleep Studies(Top)

Sleep progresses throughout the night in cycles of REM and NREM phases. In humans, these cycles are approximately 90 to 120 minutes long and each phase may have a distinct physiological function.

In REM sleep, the brain is active and the body inactive, and this is when most dreaming episodes occur. REM sleep is characterized by an electroencephalography (EEG) that has low voltage and mixed frequencies, similar in appearance to the awake EEG. During REM sleep the sympathetic nervous system is active, but there is a loss of skeletal muscle tone and our muscles are paralyzed so that we don’t act out our dreams.

In NREM sleep, the body is active, while the brain is relatively inactive compared to REM sleep, and there is relatively little dreaming. Non-REM encompasses four stages; stages 1 and 2 are considered ‚light sleep‘, and 3 and 4 ‚deep sleep‘. They are differentiated solely using EEG and unlike during REM sleep which is characterized by rapid eye movements and relative absence of muscle tone, during NREM sleep limb movements are quite frequent and sleep walking (parasomnia) can occur in non-REM sleep.

EEG is the most commonly used method to detect REM/NREM Stages, complemented by additional physiological parameters like ECG, EMG, EOG, respiration or heart rate.

 

Lab Facilities in this field:

  • 16 & 32 channel biosignal amplifier (g.USBamp)
  • 80 channel biosignal amplifier (g.HIamp)
  • Sensors
  • The g.tec Highspeed Online Processing Library for Simulink

 

Neurofeedback Studies(Top)

Neurofeedback is a way to quantify and train brain activity; it is brainwave biofeedback. During a neurofeedback session, the electrical activity of brain is recorded by measurement electrodes placed on target area in respect to neurofeedback's goal. Intended measures are extracted online from EEG signals and are compared to their goal values. Sounds or images corresponding to comparisons result tell subjects immediately when they reaches their goal or not while activating or suppressing the target area of the brain. Through this method, subjects learn how to increase or decrease brainwaves to enhance brain function.

 

Lab Facilities in this field:

  • 16 & 32 channel biosignal amplifier (g.USBamp)
  • 80 channel biosignal amplifier (g.HIamp)
  • 32 channel wireless EEG amplifier (g.Nautilus)
  • The g.tec Highspeed Online Processing Library for Simulink

 

Brain-Computer Interface System Design(Top)

A Brain-Computer Interface (BCI) is a system that measures CNS activity and converts it into artificial output that replaces, restores, enhances, supplements, or improves natural CNS output and thereby changes the ongoing interactions between the CNS and its external or internal environment.

 

Lab Facilities in this field:

  • 16 & 32 channel biosignal amplifier (g.USBamp)
  • 80 channel biosignal amplifier (g.HIamp)
  • 32 channel wireless EEG amplifier (g.Nautilus)
  • The g.tec Highspeed Online Processing Library for Simulink

 

EEG-fMRI(Top)

EEG-fMRI is a multimodal neuroimaging technique which enables the acquisition of EEG and fMRI data synchronously. Scalp EEG reflects the brain‘s electrical activity, more specifically it represents post-synaptic potentials in the cerebral cortex. fMRI detects hemodynamic changes throughout the brain known as the BOLD effect (Blood Oxygen Level Dependent). EEG-fMRI therefore enables the direct correlation of these two important measures of brain activity.

 

Lab Facilities in this field:

  • BrainAmp MR Series amplifiers - from non-magnetic materials - dedicated for use inside the scanner bore.
  • Offline as well as real-time gradient and pulse artifact correction software.
  • special "MR safe" electrode

 

EEG-TMS(Top)

EEG (or ERP) recording during TMS stimulation is an important technique providing support in the determination of cognitive processes, but it is also a well-known technically challenging task. TMS stimulation induces a very strong electrical field that can saturate the recording amplifiers for a long duration. Furthermo¬re, even if the amplifier does not reach saturation point, the TMS pulse induces an artifact in the EEG data that can last for hundreds of milliseconds. The existing EEG amplifier in our lab is able to hold the channels during the magnetic stimulation to suppress artifacts or amplifier saturation.

 

LAB Facilities in this field:

  • 80 channel biosignal amplifier (g.HIamp)
  • The g.tec Highspeed Online Processing Library for Simulink

 

What is Hyperscanning?(Top)

Social communication skills are considered vital for humans. Due to developed social skills such as language, they are capable of establishing highly organized society. Neural correlates of social communication usually are investigated through studies of brain lesions, patients with communication disorders and moreover with combination of psychological experiments and neuroimaging techniques on healthy subjects engaged in social interactions. One of the limitations of conventional studies is that they are mainly concentrated on aspects of offline social cognition, while most of human’s social behavior are described by online mutual interactions and forms a two-in-one system. The two-in-one system in social communications is a complex nonlinear system that cannot be simplified by the summation of effects in single distinct brains. So it seems reasonable to measure the two brain activity at the same time during the social interactions.

The term “hyperscanning” refers to concurrent brain activity recording from two or more subjects. Some “hyperscanning” studies have only assessed single brains activity during the social interaction. Social communications are appeared when two individuals are reacting to each other or interacting together, and this communication consists a nonlinear complexity due to inter-subject correlation of neural activation and behavior. Therefore, in order to characterize the social interaction the most efficient method is to utilize hyperscanning neuroimaging data to calculate inter-brain effects such as correlative (functional connectivity) and casual (efficient connectivity) relationships across areas in the two brains.

 

EEG Hyperscanning

EEG is the most common neuroimaging technique in hyperscanning studies. EEG hyperscanning is a way to record electroencephalography simultaneously from two or more individuals and analyze the resulting data to clarify the mutual changes in neural activation due to social and behavioral interactions.

In compare to fMRI, the greatest advantage of EEG, is its high temporal resolution. This good temporal resolution in millisecond scale might be helpful to estimate casual relationships between brain activations obtained from two subjects. Furthermore, it provides the opportunity to assess the frequency dependency in inter-brain neural synchronization and investigate instantaneous inter-brain synchronization. The other advantage of EEG is that the social activities which subjects can be engaged are not limited due to recording device. This feature enables the researcher to study the inter-brain neural synchronization in a more natural situation.

The big disadvantage of EEG is its limited ability to locate epicenter of brain activity. EEG measures the electrical potentials generated by the neural currents near the surface of scalp and its spatial resolution is approximately in range of 1-2 centimeters due to inhomogeneous conductivity profile of the head. Although nowadays estimation of brain activity sources is more possible with high-density EEG recording and mathematical methods, but source estimation still remains an ill-posed problem and EEG cannot be used to localize the deep brain sources including those engaged in social communication. So EEG is not suitable to determine spatial pattern of inter-brain networks involved in social interactions.

 

EEG Hyperscanning Setup in NBML

The synchrony between EEG amplifiers in EEG hyperscanning studies is a problem. To figure this out in a forward approach an external trigger can be sent to the EEG amplifiers to synchronize the recorded data in respect to this time marker. There is a point about this approach that each EEG amplifier uses a distinct sampling clock for data recording and subsequently time of trigger detection can be different among the amplifiers in the range of one sample time. This difference can be decreased through increasing the sampling rate. Another approach is to feed the data into a same unit. Another challenge about EEG hyperscanning is the different sensitivity of various amplifiers that can be solved with calibration of all EEG amplifiers through sending a signal with fixed amplitude to all of them. Although the latter problem is not a concern with EEG amplifiers which provides the recorded activity in scale of microvolt.

Multiple EEG amplifiers that are available in the EEG laboratory of NBML provides the opportunity to do EEG hyperscanning studies and we invite all of the researcher in this field to use the lab service.

 

EEG-fMRI(Top)

Functional magnetic resonance imaging (fMRI) and electroencephalography (EEG) detect two fundamentally different physiological phenomena reflecting brain activity. fMRI typically measures the changes in the blood oxygenation (as known by BOLD) due to neuronal activity, whereas EEG measures the electric potential directly generated by neuronal activity and outlines the same timescale as the underlying cognitive processes.

The fMRI (hemodynamic) and EEG (electromagnetic) measurements are complementary in their spatiotemporal resolutions. EEG records electrical brain activity on a millisecond timescale and thus enables analyzing temporal dynamics of brain function. However, and especially for deeper cerebral structures, attempts to localize the neural sources of the surface electric field are compromised by the “inverse problem: a given electromagnetic field registered by scalp EEG can result from an infinite number of different intracranial sources. Therefore, the topographical analysis of surface EEG is limited in terms of its localizing capabilities. The utilization of fMRI evidence to better constrain solutions of the inverse problem of source localization of EEG activity is an exciting possibility. Conversely, fMRI allows an anatomically detailed measurement of neuronal activity including that of deeper cerebral structures, but temporal resolution of fMRI is bound by the time constants of neurovascular coupling. It is obvious that a combination of both techniques is a very attractive aim in neuroscience, in order to achieve both high temporal and spatial resolution for the non-invasive study of cognitive brain function.

The combination of EEG with fMRI forms a powerful tool for the investigation of brain function, but concurrent implementation of EEG and fMRI poses many technical challenges. Simultaneous EEG-fMRI recordings require the presence of MRI compatible EEG amplifiers and electrodes and because of the large artifacts generated in the EEG recording from the switching on-off of the MRI gradients, particular care has to be taken for artifact removal in the recordings.

 

BrainAmp MR Amplifier(Top)

The BrainAmp MR was manufactured by Brain Product for EEG/fMRI simultaneous acquisition. The device provides 64 channel EEG recording inside the scanner with up to 5 kHz sampling rate and 16 bit resolution.

The digitized signal is transmitted via fiber optic cable from the amplifier to the USB interface placed in the control room. Therefore no artifacts are being added along the way to the outside of the MRI chamber. The short length of the electrical cables used to connect the electrode cap with the amplifier fulfills all safety requirements for the experimental subject and, at the same time, guarantees an outstanding quality.

The BrainAmp MR is powered by the rechargeable PowerPack battery which enables typically 15 hours of EEG recording. Also the integrated impedance measurement could be done for passive electrodes. Moreover, trigger pulses received from PC parallel port can be used to record external events such as stimuli presentation and subject response.

Furthermore, the BrainAmp MR can be combined with the BrainAmp ExG MR to co-register other types of physiological data such as bipolar and peripheral signals (e.g. EOG, ECG, EMG and GSR) up to 16 channels in the MRI environment. The amplifier can be used inside the MRI chamber and placed right next to the subject.

 

Highlights

  • Up to 64 channel perfectly synchronized with 16 bits
  • Powered with rechargeable PowerPack
  • 15 hours continuous recording
  • Digital filtering of all channels
  • Real-time analysis with BrainVision RecView
  • Impedance check
  • can be combined with the BrainAmp ExG MR