Activetwo

While driving, the EEG (biosemi active system, Active two, BioSemi, NL) was recorded from 64 scalp electrode sites. EEG electrodes were arranged on the basis of the International 10–10 system and two additional electrodes were placed on the left and right mastoids. The Biosemi’s Active two amplifier uses a 2-wire active electrode system with a Common Mode Sensing and Driven Right Leg (CMS/DRL) principle. Data were sampled at 2048 Hz and a bandwidth of DC– 140 Hz. Additionally, six electro-oculography (EOG) electrodes were positioned around the two eyes to record horizontal and vertical eye movements. Electrode impedance was kept below 10 kΩ. The current position of the vehicle was continuously recorded by the EEG system.

In an electrically shielded room, EEG data was continuously recorded (DC–104 Hz; sampling rate (SR) 512 Hz) using Biosemi ActiveTwo amplifier, with 128 active electrodes mounted in a fitted flexible cloth cap according to the Biosemi 128 montage. Offline reference electrodes were attached at the mastoids. Electrooculography was measured with two bipolar electrode sets, mounted horizontally at the outer canthi of each eye, and vertically above and below the left eye.
Additionally, electrocardiography was measured from chest-mounted electrodes at the manubrium and lower left rib. Electrodermal activity was measured from the proximal phallanges of the index and forefinger on the non-dominant hand. These autonomic nervous system signals are not analysed herein.
Biosemi ActiveTwo equipment reduces the need for impedance measurement (http://www.biosemi.com/faq/cms&drl.htm). Instead, the quality of contact between electrode and skin was monitored using running average voltage offset at each electrode, which was kept below ±25 mV.

The requirements for voltage recording are parallel data collection, low noise and the ability to save data for offline processing. EEG amplifiers offer an effective off the shelf solution with high performance systems such as the BioSemi ActiveTwo (Biosemi, Amsterdam, The Netherlands), actiCHamp (Brainproducts GmbH, Gilching, Germany) and g.tec HIamp (g.tec Medical Engineering GmbH, Graz, Austria) offering 24-bit resolution and a channel count up to 256. Each system offers a PC GUI for saving data to disk, data streaming over TCP/IP and the option to write custom software to interface with the device. These specifications come at the expense of maximum bandwidth, which in practice is limited by hardware anti-aliasing filters with typical cut off frequencies a tenth or a fifth of the sampling rate, Table 3. While this is sufficient for all brain EIT applications, Table 2, it may preclude use of the system in applications such as lung ventilation, which typically employ frequencies at 50 kHz or above [2 (link)]. For the experimental work presented here, either the BioSemi ActiveTwo (Biosemi, Amsterdam, the Netherlands) or actiCHamp (Brainproducts GmbH, Gilching, Germany) system was used for voltage recording.