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136 T. Warbrick and D. Kadlec
11.4.3 Post Measurement
. Remove the EEG cap/net/headset and sensors.
. Offer the participant options for washing their hair.
. Complete post-test questionnaires (where needed).
. Debrief: explain the study, especially if some aspects couldn’t be explained
the experiment. Ask if the participant has any questions. Also, ask the
before
participant for their feedback on how the study was, it could be useful for
planning future studies.
. Clean the EEG cap/net/headset and sensors and store appropriately for drying.
. Tidy the lab and leave it ready for the next measurement.
. Store your data appropriately.
. Complete the lab book and document any issues with hardware or software that
need
to be addressed or could be useful for other lab users (see Sect. 1.2).
. Analyse the recorded data. You don’t have to do this immediately after the
session
than leave it all until the end of the study. By exploring your data, you can spot
any problems with your recording setup, e.g. trigger codes that are incorrect or see
whether your paradigm is working, e.g. expected behavioural effects are seen. If
anything is wrong, you can fix it for the next participants rather than find out at the
end of your study.
but it’s a good idea to keep on top of data analysis as you go rather
11.5 Conclusion
In this chapter, we outlined strategies for establishing study workflows and
implementing effective lab manag ement. Thorough planning and systematic organisation are essential for running a successful EEG experiment and maintaining an
efficient EEG lab. The paper by Boudewyn et al. (
ew of factors to consider when planning and running an EEG study. Although
overvi
2023) provides a valuable
the paper is primarily aimed at large-scale multicentre studies, many principles apply
to studies of any scale.
Other chapters in this book offer complementary guidance on planning and execut-
in
g your studies: Chap. 10 Pilot Testing, Chap. 15 Getting Clean EEG Data: Artifacts
an
d How to Prevent them, and Chap. 16 Practical aspects of EEG Data Analysis.
References
Baker, M. (2016). 1,500 scientists lift the lid on reproducibility. Nature, 533, 452–454.
Boudewyn, M.
Silverstein, S. M., Gold, J., Macdonald, A. W., 3rd, Carter, C. S., Barch, D. M., & Luck, S. J.
(2023). Managing EEG studies: How to prepare and what to do once data collection has begun.
Psychophysiology, 60, e14365.
A., Erickson, M. A., Winsler, K., Ragland, J. D., Yonelinas, A., Frank, M.,
11 Study Workflow and Lab Management 137
Higgins, S. G., Nogiwa-Valdez, A. A., & Stevens, M. M. (2022). Considerations for implementing
electronic laboratory notebooks in an academic research environment. Nature Protocols, 17,
179–189.
Monaghan, J., Brady, S. M., Haswell, E. S., Roy, S., Schwessinger, B., & Mcfarlane, H. E. (2023).
Running
research with values-driven leadership. Journal of Experimental Botany, 74, 1– 6.
Vandendorpe, J., Adam, B.,
for implementing electronic lab notebooks (ELNs). PLoS Computational Biology, 20,
e1012170.
Wright, J.
a research group in the next generation: Combining sustainable and reproducible
Wilbrandt, J., Lindstadt, B., & Forstner, K. U. (2024). Ten simple rules
M. (2009). Make it better but don’t change anything. Automated Experimentation, 1, 5.
Part III
EEG Data Acquisition
Chapter 12
Hardware for Recording EEG
and Peripheral Physiology
Tracy Warbrick and Cilia Jaeger
Abstract In this chapter, we describe the components of a system for recording
EEG
and peripheral physiology, how they work, and how they influence the
recorded data. We cover electrode types and features that affect data quality,
preparation time, and participant comfort. We introduce some examples of peripheral physiology sensors and the technology behind them. We consider the role of the
amplifier and what parameters are important to the recorded data. Finally, we
consider adding triggers to the setup for recording event markers. At the end of
the chapter, you should be able to identify the components of your system, explain
what they do, and make decisions about your own setup.
Keywords EEG amplifier · Electrodes · Peripheral physiology · Sensors · EEG
urement principles · EEG hardware · Peripheral physiology hardware · EEG
meas
recording principles
12.1 Introduction
As an EEG researcher, knowing how your system works and how it influences the
data you acquire is essential. It is also crucial to accurately report the equipment used
in your studies (Keil et al.,
param
eters and their roles. In this chapter, we will cover the components of a system
for recording EEG and peripheral physiology, the different technologies available,
and the important parameters associated with each of them. Our aim is to help you
make the right decisions about your hardware and recording parameters. A good
place to start is to think about the requirements of your study; for example, what’s
your signal of interest, who are your participants, do you have any special recording
conditions (e.g., mobile or multimodal recordings) ? We encourage you to think
about these questions and keep your requirements in mind throughout the chapter.
T. Warbrick (*) · C. Jaeger
Brain Products GmbH, Gilching, Germany
e-mail:
tracy.warbrick@brainproducts.com
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2026
T.
Warbrick (ed.), The EEG Handbook,
https://doi.org/10.1007/978-3-032-20450-9_12
2014), and to do this you need to be aware of relevant
141
142 T. Warbrick and C. Jaeger
12.2 Components of the System
To record EEG data, we need something to detect the signal, something to measure
it, a way to record it, and, when needed, a way to integrate an experimental paradigm
(Fig. 12.1). Here we consider the role of electrodes, peripheral physiology sensors,
amplifiers and the technical features that influence your data. Note that record ing
and
software is covered in Chap. 13: Software for Recording EEG and Peripheral
Physio
logy.
12.2.1 Detecting the Signal: EEG Electrode Technology
The variety of electrode options available can seem overwhelming: gel, salt water,
dry, active, passive, cap, headset, low/high density. The choice can be made easier
by thinking about the desired data quality, participants, and recording environment
for your study. These factors will influence acceptable electrode impedance, comfort, duration of preparation, and duration of recording.
The purpose of the electrode is to detect the electrical signal generated by the
ying neural populations. Here, we will focus on surface EEG electrodes placed
underl
on the scalp. To record a signal, we need to make a connection between the scalp and
Fig. 12.1 The components of an EEG recording setup. (a) EEG electrodes and peripheral physiology sensors are used to detect the signal. (b) The amplifier converts the signal from analog to
digital, amplifies, and filters the signal. (c) Event markers can be co-registered with the data using
triggers. (d) Data (and triggers) are recorded using dedicated software
12 Hardware for Recording EEG and Peripheral Physiology 143
the electrode surface. To achieve this , we need a conductive medium or to apply light
pressure. To appreciate the different electrode types and associated conductive
medium, we need to cover the concept of impedance.
Impedance is the opposition to alternating current, in other words, how easily can
a current pass through. When we talk about electrode impedance, we mean impedance between the electrode and the skin. We aim for a low impedance value because
we want the EEG signal to ‘pass through’ with as little opposition as possible. A low
impedance also helps to reduce susceptibility to environmental electromagnetic
noise. This is important because the electrode and lead wire act as an antenna and
pick up environmental electromagnetic noise. Therefore, the signal reaching the
amplifier is a mix of EEG signal and noise. Much of the noise arriving at the
amplifier will be attenuated by amplifier features such as input impedance and
common mode rejection (see Sect.
the
amount of noise will improve our signal-to-noise ratio and enhance the signal.
We can of course reduce the amount of noise in the environment (see Chap.
al Aspects of EEG Data Acquisition) but we cannot eliminate it all, therefore
Practic
12.2.3). However, anything we can do to reduce
16:
reducing electrode impedance is important.
It’s good practice to have a target impedance for your study and to stay under this
thresh
old consistently across your measurements. To measure impedance a low
voltage alternating current is applied and resistance to this current is measured. It’s
important to note that in most systems where impedance values are displayed, the
value is an approximation within the impedance measurement range rather than an
accurate, specific value. So having a target threshold or range rather than a specific
target value is recommended.
Electrode impedance is influenced by the electrode type (active versus passive),
the conductive medium used (gel, salt water, direct contact), and the human head
(skin, sweat, hair, moisture).
Human Factors Effective electrode preparation can help to reduce the influence of
human head. The optimal preparation strategy will depend on the electrode type
the
that you use. Practical tips for different electrodes and applications are provided in
Chap.
16: Practical Aspects of EEG Data Acquisition.
Electrode Type Active electrodes include a small electronic circuit that performs
imped
ance conversion. This makes active electrodes more robust against cable
motion and noisier environments than passive electrodes. It also means that higher
electrode impedance can be tolerated with active compared to passive electrodes.
This reduces preparation time, which might be beneficial under some circumstances
or in certain populations.
Connection Between Electrode and Scalp We will cover three ways of
connect
ing the electrode to the scalp: electrolyte gel, saline solution, and direct
skin contact.
For each
combination of electrode type and contact method, we will consider
target impedance, preparation time, and recording duration. It is also important to
consider data quality expectations, the population being studied, and the study
environment.
144 T. Warbrick and C. Jaeger
12.2.1.1 Passive Electrode Plus Gel
A low impedance is needed for passive electrodes (see Table 12.1), and an abrasive
gel
is usually used to help reduce impedance. Reducing impedance can be timeconsuming and is less well tolerated by some groups such as children and some
clinical populations. Furthermore, care must be taken to avoid breaking the skin
(Ferree et al., 2001). The low impedance and conductive gel mean that excellent
can be achieved, and complex analyses on small signals of interest are possible.
SNR
This combination is suitable for standard lab environments and electromagnetically
quiet locations as well as special applications where active electrode technology is
not appropriate, e.g., for EEG-fMRI.
12.2.1.2 Active Electrodes Plus Gel
For active gelled electrodes we can tolerate a higher impedance (see Table 12.1), so
we
don’t need an abrasive gel, and we don’t need to work as hard as for passive
electrodes. Therefore, we can save time with the preparation. It is also possible to
achieve excellent SNR and do complex analyses on small signals of interest with this
combination. However, some caution is advised for very fast changes in the signal
(Laszlo et al.,
than 8 h and is suitable for lab-based studies, especially noisier environments,
more
2014). This combination of electrode and gel also allows recordings of
mobile studies, and studies involving movement.
12.2.1.3 Passive Electrode and Saline Soaked Sponges
Sponge-based electrode systems use saline solution to conduct the EEG signal. The
whole
electrode net is soaked in saline solution and this allows an even quicker
preparation because you don’t need to put gel in each individual electrode. Therefore, this combination is suitable for those less tolerant of long preparations and any
study where quick preparation is required. However, it isn’t possible to achieve
impedances as low as with gel-based electrodes (see Table 12.1). Furthermore,
ter sponges are usually used with passive electrodes, consequently, there is a
saltwa
risk of picking up more environmental noise and having a lower signal-to-noise
Table 12.1 Target impedance, estimated preparation time, and approximate recording duration for
commonly used combinations of electrode type and conduction method
Electrode and
conduction
Gelled passive 5–10 30 >8 h
Gelled active 25 5–10 >8 h
Saline solution passive 60–100 5 60–90 min
Dry active 500–2500 5 45 min
method
Target
impedance (kΩ)
Preparation time for
32 channels (minutes)
Recording
duration
12 Hardware for Recording EEG and Peripheral Physiology 145
ratio. Good SNR is possible, and you can expect to reliably measure ERPs and
frequencies up to 100 Hz. Salin e nets are suitable for the lab and environments where
active electrodes are not possible, e.g., EEG-fMRI.
12.2.1.4 Dry Electrodes
Dry electrode technologies don’t use any conductive gel or saline. The most
comm
on type of dry EEG electrodes relies on direct contact between the electrode
and the scalp (for further information on contact and non-contact dry electrodes, see
Shad et al., 2020). Contact between the scalp and electrode surface is achieved using
small amount of mechanical pressure. Preparation is usually very quick, making it
a
suitable for those less tolerant of long preparation. Impedance remains high due to
the lack of conductive medium to stabilize the connection between scalp and
electrode (see Table
active
electrode technology. Acceptable SNR is possible, you can expect to measure
ERPs and lower EEG frequencies, e.g., up to 45 Hz. Dry electrode technologies are
often used in EEG headsets popular for mobile EEG applications due to the need for
quick preparation time in non-standard measurement environments.
12.2.1.5 Electrode Positions
12.1). For this reason, dry electrodes are often combined with
While the choice of electrode technology is important, so is where you put the
electrodes
and studies. The most commonly used is called the 10–20 system (Jasper,
Electr
landmarks on the head and named with a letter representing the lobe of the brain
(e.g., F ¼ frontal) and a number (odd numbers left, even numbers right), see
Fig. 12.2. Due to an increasing number of electrodes being used in EEG research,
Oostenf
Electr
adhesive to fix the electrodes in place. A cap or net can also be used where the
electrode positions are predefined. Of course, head shapes and sizes differ so this is
to some extent an approximation, but you can improve accuracy by using an
appropriately sized cap or net and fitting it properly (see Chap.
of
. A standard positioning system allows comparison across measurements
ode positions are defined by percentages of distances between anatomical
eld and Praamstra (
odes can be positioned individually by measuring the distance and using an
EEG Data Acquisition).
2001) extended the 10–20 system to the 10–5 system.
16: Practical Aspects
1958).
12.2.2 Detecting the Signal: Sensors for Other Measures
Peripheral physiology can be a useful addition to an EEG study or a valuable
measure on its own. A variety of measures are possible, and some applications are
described in Chap.
34: Bridging Brain and Body: Complementing EEG with
146 T. Warbrick and C. Jaeger
Fig. 12.2 The 10–20 system for naming EEG electrodes (Jasper, 1958). Electrode positions are
defined by percentages of distances between anatomical landmarks on the head. They are named
with a letter representing the lobe of the brain (F frontal, P parietal, C central, T temporal,
O occipital) and a number (odd numbers left, even numbers right). The lines connecting anatomical
landmarks, as well as the circumference, are shown. These lengths are defined as 100%. Electrodes
are placed at distances of 10% or 20% of these lines
Peripheral Physiological Signals. Some have different measurement principles from
EEG and require specific sensors. It is also possible to record non-physiological
signals such as force and acceleration alongside your physiological measure. This
section explains the measurement principles used to record some commonly used
physiological signals.
12.2.2.1 Bipolar Peripheral Electrophysiology
Let’s begin with the peripheral signals that use similar measurement principles as
EEG to record electrical activity. These include measuring activity either from the
heart (electrocardiography, ECG), the muscles (electromyography, EMG), or the
eyes (electrooculography, EOG). The principal measurement technique involves a
bipolar recording principle, in which the differential electrical signal is taken
12 Hardware for Recording EEG and Peripheral Physiology 147
between two electrodes. Bipolar measurements are described in Sect. 12.2.3. The
types of electrodes that can be used are the same as for EEG. This includes gel-based
and dry electrodes as well as active or passive electrodes. Depending on the type of
activity recorded, the electrodes should be placed in certain locations to obtain an
optimal difference wave to be recorded by the electrodes.
EOG For vertical eye movement one electrode is placed above the eyebrow on the
forehead and one electrode is placed below the lower eyelid. For horizontal eye
activity, one electrode is placed on the outer canthus of the eye and one electrode is
placed on the outer canthus of the opposite eye (Fig. 12.3a). The EOG electrodes
meas
ure polarity changes of the eye as the eye moves vertically and horizontally
(López et al.,
2022).
EMG For recordings of skeletal muscle, one electrode pair should be placed on the
le belly, which entails the motor unit (Fig. 12.3c). The other electrode should be
musc
placed on midline of the tendinous insert of the muscle (Zaheer et al., 2012).
ECG There are several electrode placement layouts for ECG recordings that range
a 3-lead layout to a 12-lead layout. Here we will cover the simpler 3-lead
from
layout, which places electrodes based on the Einthoven Triangle (Barold,
This
involves a bipolar electrode pair, with one electrode on the left arm and the
2003).
other on the right arm. A third electrode, that often functions as the ground electrode,
is placed on the left ankle (Fig. 12.3b).
Fig. 12.3 Placement of electrodes for peripheral electrophysiology recordings. (a) Indicates
placement of bipolar pair of electrodes for vertical EOG, vEOG, recordings and horizontal EOG,
hEOG; (b) Placement of bipolar electrodes and ground (GND) electrode for ECG recordings; (c)
indicates muscle body tendon placement for EMG recordings. The example shows the bicep muscle
of the arm; and (d) electrode placement for skin conductance with GSR sensor