Recording EEG in Animals

Historically, research protocols in animals have relied on invasive approaches such as subdural or intracranial recordings to target neuronal activity.

In contrast, surface recordings like EEG and fNIRS are non-invasive: they do not require surgical procedures or anesthesia. Instead, recording with surface sensors is safe and painless for the animal participant, thus contributing to animal welfare. Furthermore, using high density recordings with lots of small sensors on the animal’s head can overcome issues of sparse sampling, which is a typical limitation of invasive recordings.

As in humans, EEG recordings in animal models can be utilized to provide information on brain activity in a multitude of contexts: in basic research, in comparative neurobiology and in applied fields such as veterinary medicine. Understanding topics such as mammalian biology and evolution, disease and remedy development, and interactions with environments inevitably motivate the study of brain activities in our animal relatives.

Individual research questions may include:

• Investigating brain dynamics in sensory processing, cognition, learning and memory
• Targeting disease-related issues such as pain perception, or diagnosis-related topics such as seizure activity in epilepsy
• Exploring therapy effects as in pharmacological treatment or brain stimulation
• Determining (depth of) anesthesia
• Studying sleep stages and sleeping patterns
• Scanning brain behavior in combination with other imaging modalities, e.g., fMRI

The animal kingdom is an abundant and multifaceted domain, yet some animal species are more often investigated with EEG or fNIRS recordings:

When discussing how neurophysiological signals in animals can best be realized, we first want to look at situational factors of the data acquisition:

Depending on the research question and animal model, a recording with single electrodes, applied in the fur with electrolyte paste, may be a sufficient and elegant solution. Easycap offers several very small electrodes that are best suited for recordings on very small heads (B15 sensor, B29 sensor).

For a larger number of sensors to be applied, we recommend organizing the electrodes in a structured, bundled way, in the form of an electrode patch or a cable tree. For example, combining sensor wires in a cable tree with cable lengths tailored to the desired recording sites can be a good solution. This solution is also well suited for bumpy and irregular head surfaces as present in some animal models. Using sensor patches can offer an easy, quick and reliable application.

Finally, in addition to caps for human EEG, Easycap also provides bespoke cap designs for various recording protocols in animal models.

The core feature of a recording cap is that it can be positioned repeatedly and reliably in the same place by aligning it to anatomical landmarks, i.e., Nasion, Inion, Vertex, eyes and ears. Next to EEG recording caps, simple animal caps – with marks or with openings –also allow for easy, reliable sensor placement for other techniques (e.g., fNIRs or stimulation).

For animals with more oblong head shapes such as horses and dogs, our cap solutions represent a fabric covering the core recording sites, with additional straps for easy and safe cap placement. For dogs and horses, we offer conventional sizes (small / medium / large).

Next to the fabric cap, we also offer default suggestions for electrode placements. For NHPs, we offer an equidistant layout as well as an electrode layout inspired by the 10/20 system as derived from human EEG. Please note: as animal brain anatomy is somewhat different than human, the ‘names’ of the 10-20-system do not fully apply here. Still, to be in line with the familiar nomenclature as in humans, the same abbreviations are often utilized in animal EEG. This also applies for example to EEG in horses, dogs, cats, etc.

EEG setup and impedance minimization in animals is very similar to setting up EEG recordings in humans. However, a few aspects must also be considered.

First, animals need to get accustomed to the recording situation so that they become comfortable with the procedure and environment in which the research is conducted. To simplify this habituation step, Easycap offers sensor-free mock caps for habituation training, allowing investigative population to get comfortable with the cap before real recordings.

Second, impedance minimization is more difficult in furry animals with thicker and more dense hair than humans. More effort may be required to reach similarly low impedances. There is no need to shave the hair, with sufficient patience and sufficient electrolyte gel or paste, good signals can be accomplished. Our electrolyte gels and pastes are non-toxic and water soluble, so they can be easily rubbed or rinsed off after the recording.

Lastly, eye movement (electroocular, EOG) or muscle (electromyographic, EMG) artifacts in animal recordings may be of higher magnitude and amplitude compared to those recorded in humans. EOG artifacts may be larger as many animals have large eyes located in closer proximity to recording sensors. Moreover, compared to humans, the mobility of animals’ ears is far greater and may happen with high responsiveness. EMG artifacts induced by muscles around animal ears may occur in nearby EEG sensors. Nonetheless, like in human EEG recordings, removing and reducing artifacts in the EEG signals can be overcome with the help of conventional postprocessing methods.

We hope you like our small overview, and we are looking forward to working with you on new endeavors in animal research!