Last Updated on June 11, 2021
Sleep research frequently relies on EEG (Electroencephalography) and EMG (electromyography) to discern between different sleep and wake states of the mice and rats used as models. The combination of EEG and EMG is powerful enough to discern not just between the different sleep and wake states, but also between the different stages within sleep and wake states.
In this article, we’ll show you how to reliably record EEG and EMG, with neural stimulation in untethered mice and rats.
EEG is also frequently used to record seizures in mouse and rat models of epilepsy, as well as for studying Huntington’s, Alzheimer’s, schizophrenia, migraine, and other disorders. Typically epidural EEG, aka Electrocorticography (ECoG), where the electrodes are placed directly on the cortex, is used.
1. Consider alternatives to tethers in EEG experiments
Equipment choice affects the success or failure of many EEG experiments. Typically, a tethered system is used, with implanted electrodes connected via a long cable to the recording system. Tethers are often the weak link in EEG experiments. Tethered mice become tangled, especially during seizures, severely limiting normal mice behavior. Slip rings, swivels, and balance arms can help prevent tangling, but mice do not create enough torque when they move to rotate many slip rings. Rats also chew on the cables, frequently damaging or destroying them. Complete disconnections also occur when animals pull on the cables, ending the recording and injuring the animals.
As an alternative to tethered animals, wireless EEG equipment helps reduce altering the normal actions of freely moving and behaving animals. Wireless EEG equipment also reduces the limitations of environments available for studying behavior.
2. Eliminate electrical noise and artifacts
Tethered EEG equipment often suffers from poor signal-to-noise ratios. Cables act as antennae, picking up electrical noise from AC power lines, motors, and other sources. This leads to artifacts in the data, complicating interpretation. Faraday cages can limit noise from external sources but become awkward and inconvenient when working with multiple animals. Faraday cages also do not protect against motion artifacts caused by the movement of the tether itself. Even connecting a preamplifier directly to the electrodes, so that amplified signals are sent through the tether, does not always eliminate AC and other noise from the system. A preamplifier can also make the system too heavy for use with mice. Additionally, multiple tethered systems in the same room can also lead to interference and noise.
3. Eliminate system limitations that affect your EEG experiment
The issues surrounding tethers have led to a shift to wireless EEG equipment. Wireless inductive telemeters addressed many of the problems of tethered systems, but bring with them other challenges.
Limits to Size and Type of Environment – Inductive systems require the animals to remain directly on top of a special charging pad or platform, limiting the size and type of environments which can be used during behavioral research.
Limits to Channel Bandwidth – Some telemetry systems also limit the bandwidth or number of channels available for EEG signals.
Limits to Sensitivity and Scale Up – Surprisingly, some wireless systems are still vulnerable to AC noise, possibly because of inadequate shielding. The number of frequencies available also limits wireless systems using radio to send data, capping the number of animals that can be monitored in one room.
As an alternative, researchers can use a lightweight data logger small enough to sit on the head of a mouse. The electrodes connect directly to the well-shielded data logger, preventing electrical noise from power lines.
Since data is stored onboard using a microSD card, there is less chance of signal interference and scaleup to more animals is unlimited.
The rechargeable data loggers are as small as 2g, allowing mice to behave normally during chronic recording sessions in any size cage or chamber.
4. Reduce electrode implant surgery time and complexity
PCB-based electrodes can make implantation surgery more complicated and time-consuming, leading to higher failure rates. A simple, flexible electrode design, such as the one shown below, makes for easy implantation.
The Amuza standard electrode set uses a universal 1.27 mm pitch pin and socket connector, making it easy to create your own electrode sets. Our standard electrode has two screws for EEG, two silver wires for EMG, and one screw for GND.
5. Look for universally compatible EEG data processing and analysis
As part of a research team, or in a collaborative setting, it is important to consider using EEG equipment that makes for seamless sharing of data. Proprietary data formats and readers can complicate sharing and processing your data. Incompatible systems can become an unexpected expense when you need one software license to run your EEG system and another for the PC in your office where you process the data.
Amuza’s EEG data analysis software combats these unplanned expenses in four ways:
- Amuza’s EEG data analysis software is included with the system free of charge
- Amuza’s EEG data analysis software can be installed on multiple computers without extra licensing fees.
- Through an intuitive platform, Amuza’s EEG data analysis software enables a quick overview of your data, as well as
filtering and simple (FFT-based) alpha, theta, delta power calculation. It can also create hypnogram plots for sleep analysis.
4. Data from Amuza’s EEG data analysis software is also compatible with MatLab and Octave and can be exported to EDF or TXT. No dedicated reader or software is required.
Amuza’s EEG data analysis software combats these unplanned expenses in four ways:
- Amuza’s EEG data analysis software is included with the system free of charge
- Amuza’s EEG data analysis software can be installed on multiple computers without extra licensing fees.
- Through an intuitive platform, Amuza’s EEG data analysis software enables a quick overview of your data, as well as
filtering and simple (FFT-based) alpha, theta, delta power calculation. It can also create hypnogram plots for sleep analysis.
4. Data from Amuza’s EEG data analysis software is also compatible with MatLab and Octave and can be exported to EDF or TXT. No dedicated reader or software is required.
There is no other system which meets my requirements for wireless operation, channel count, and usability with mice.
Share your work! Tell us how you have struggled with tethered research animals in the comments below.