In this use case we present the results of an EEG measurement in a completely mobile setup. We demonstrate that SAGA32/64+ is able to record high quality EEG in an outdoor sports experiment. The data from the recording is available for download. Active shielding keeps out mains interference as well as cable movement artifacts, which are challenging in experiments that involve activities such as walking or even running.
SAGA64+ was used for a 32 channel EEG recording using the BrainWave head cap with integrated Ag/AgCl electrodes with active shielding technology. The SAGA Data Recorder was mounted to the subject as shown in the picture above using the SAGA Bracket, which is a standard accessory to the SAGA system. The cable from the head cap was not fixated to allow optimal freedom of movement.
Firstly, we show the data obtained while the subject was walking normally. The data is band pass filtered between 1 and 40 Hz. The steps during walking can be recognized from the signal trace recorded using the internal 3D accelerometer. A few phenomena can be clearly observed: • Jumps in voltage mainly on channels Fp1, Fpz and Fp2. These are caused by eye movements following the rhythm of steps: the eyes keep their focus so when rapid changes in vertical body position occur, they move in the opposite direction to keep focus on the same point. • High frequent noise, mainly on channels M1, M2, T7, T8, O1, O2 and Oz. These are caused by muscle activation (jaw muscles and neck muscles). • During walking, hardly any movement artifacts can be observed.
This data is obtained whilst running and logged on the onboard memory of the SAGA Data Recorder. Again, the data is filtered between 1 and 40 Hz. Clear EEG data among minor artifacts can be observed. Data from the internal 3D accelerometer could be used for compensation of the movement artifacts and muscle artifacts due to the running using advanced signal analysis techniques. So running induces some artifacts, most probably coming from 'heel strike'. This most probably causes minor movements of the electrode resulting in a small artifact.
In contrast to many devices available on the market, we show that SAGA is able to truly record high quality EEG data without clear instructions to sit as still as possible. SAGA allows mobile recordings, even in sports exercises. The active shielding minimizes any cable movement artifacts and 50 or 60 Hz mains interference. We could have further increased the signal quality by properly bringing impedance further down to < 5 kOhm. Higher electrode impedance may increase the probability and amplitude of electrode movement artifacts. Minor artifacts from muscles on the head whilst running could be observed.
Our vision is to provide data as clean and pure as possible, so that is why we decided not to do that in this case study and present the data in its purest form.
The combination of high-quality amplifier systems and active shielding technology gives you the best possible data quality and the best possible outcomes of your research.
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