An electroencephalogram (EEG) is a test used to detect any abnormalities that may be present in the brain waves of a test subject, a term used to describe the electrical activity present in the brain. Typically, an EEG involves the use of small metal electrodes attached directly to the scalp of the subject being tested. Since neurons, which are the cells that make up the brain, constantly communicate with each other through electrical impulses, this electrical activity will be recorded by the electrodes to provide an EEG reading.
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Animal models for electrophysiology
Different electrophysiological signals can be measured and evaluated for animal research studies focused on the evaluation of brain function and drug toxicity. These signals include EEG, electrocardiograms (ECG), electromyography (EMG), and electrocorticogram (ECoG). In the field of neuropsychopharmacology, animal models are often used to study neuronal activity and drug response.
Various neurological disorders have also been studied, including schizophrenia, depression, anxiety, all of which can be used to advance the development of adequate treatments.
One of the best animal models for studying electrophysiology is the dolphin. These mammals have a unique auditory system and well-developed brain that resembles both the size and functionality of the human brain. In fact, recent studies have shown that dolphins also possess a highly differentiated central nervous system responsible for the high level of intelligence often associated with these animals. Despite their usefulness, dolphins often exhibit unpredictable and uncontrollable behaviors that can interfere with the efficient obtaining of electrophysiological signals. Additionally, the speed at which dolphins can swim, often between 7.2 and 9.3 meters per second, can also hamper signal acquisition efforts.
Invasive electrophysiological devices in animal research
To obtain an accurate electrophysiological recording of dolphins, researchers often prefer an invasive recording device. One of the first applications of this type of experiment was carried out in 1977, when researchers implanted intracortical electrodes into the bony opening of dolphins under anesthesia.
These EMG electrodes, which had a harpoon shape, were then attached to the neck and extraocular muscles to allow invasive signal recording. Although this type of invasive method allowed researchers to obtain pure and very precise electrophysiological signals, due to their proximity to the brain, surgical techniques and animal anesthesia were administered. In addition, as with any surgical procedure, the invasive placement of an electrode also increases the risk of the animal suffering from infection or brain damage.
Non-invasive electrophysiological devices in animal research
Compared to the invasive methods that can be used, several non-invasive approaches are also available. Typically, these approaches will involve the non-surgical placement of electrodes on the scalp surface of the subject being tested. Typically, a non-invasive recording system will consist of several EEG electrodes embedded in suction cups and a signal amplifier, an A / D converter, and a ground station.
Various non-invasive electrophysiological systems have been tested and evaluated for their utility in animal research. For example, an EEG recording system used to study the neurological activity of zebrafish includes multiple active electrodes, as well as a single reference electrode placed on a flexible printed circuit board (PCB) to allow better contact with the zebrafish head during signal acquisition.
A group of researchers have reported a new, long-term, multi-channel EEG recording device that could be used on small aquatic animals, such as zebrafish, to study epilepsy. This research was published in the journal Scientific reports June 8e 2017. In their approach, a four-channel electrode array was printed on a flexible PCB based on a polyimide film, which is biocompatible, flexible and chemical resistant. The array contained four gold electrodes that could successfully acquire brain signals from the telencephalon and midbrain of each hemisphere of the zebrafish.
In Tokyo, Japan, an MT-11 telemetry system was developed, consisting of several vinyl chloride suction cups that are placed near the eyeballs, vent, and dorsal fin of dolphins. Experiments using this system revealed that the power ratios of the frequency bands were associated with the action of the dolphin.
The future of technological devices in animal research
There is a need to develop non-invasive fixed electrophysiological devices that will not restrict animal movements during behavioral brain studies. The methods will have to overcome the large cables of terrestrial devices connected to the electrodes on the scalp of the animals – the main restrictors of movement.
A study published in Sensors recently discussed the development of a portable, portable and waterproof EEG acquisition device tested on dolphins. Here, a collective signal device was made up of a silicon belt, electrodes, and a device box made up of all the electrical parts. Silicone suction cups with a diameter of 8 centimeters (cm) were used to stick gold-plated EEG electrodes to the skin of the dolphin.
The researchers separated their device into a collection box and a ground station to eliminate the need for a large earth system, connected via Bluetooth communication. If there is an interruption in this communication system, all acquired signals are written to an on-board memory reader.
When evaluating the effectiveness of their new system, the researchers in the present study found that their device could successfully record and send the dolphin’s signals while the dolphin was in different states of motion. Although further testing on the device is yet to be performed, the present study found that their device supports long-term portability and, therefore, the ability to collect EEG signals from dolphins in their natural environment.
References and further reading
Mayoclinic.org. (2020) EEG (electroencephalogram) – Mayo Clinic. [online] Available at: https://www.mayoclinic.org/tests-procedures/eeg/about/pac-20393875
S. Aston-Jones, G. and R. Siggins, G., (2000) Electrophysiology. [online] Acnp.org. Available at: https://acnp.org/g4/GN40100005/Default.htm