An Electroencephalogram (EEG) measures the electrical activity produced by the brain. In mice, EEG involves placing electrodes on the scalp or within the brain to detect these signals. It is a tool for researchers to study brain function and neurological conditions, monitoring neural activity, tracking disease progression, and assessing treatment impacts.
What Mouse EEG Measures
Mouse EEG measures the collective electrical activity of millions of neurons firing in sync within the brain. These synchronized electrical pulses create rhythmic patterns, commonly referred to as brain waves, which are categorized by their frequency. Different brain wave frequencies correspond to distinct brain states and cognitive processes.
Delta waves (0.5-4 Hz) are slow, high-amplitude waves associated with deep, restorative sleep.
Theta waves (4-8 Hz) are observed during light sleep, drowsiness, or relaxation, and are linked to memory formation and creativity.
Alpha waves (8-12 Hz) appear when an animal is awake but relaxed, particularly with eyes closed, and are associated with a calm state.
Beta waves (13-30 Hz) indicate active, alert, and focused mental states, such as during problem-solving or intense concentration.
Gamma waves (30-100 Hz) are high-frequency oscillations involved in complex cognitive processes like perception, learning, and memory.
The specific patterns and changes in these brain waves provide insights into the functional state of the mouse brain.
How Mouse EEG is Conducted
Conducting mouse EEG involves a surgical procedure to implant small electrodes onto or near the mouse’s brain. These electrodes are made of stainless steel screws or fine wires, positioned on the skull’s surface (epidural placement) or sometimes directly into deeper brain structures. This allows for the detection of faint electrical signals.
The implanted electrodes connect to a headcap secured to the mouse’s skull. This headcap links to recording equipment, including amplifiers and a data acquisition system to convert signals into digital data. Wireless telemetry systems are often used, allowing the mouse to move freely during recording for more natural behavioral data. After implantation, mice recover for 7 to 10 days before recordings begin, ensuring their well-being and stable signal acquisition.
Key Applications in Research
Mouse EEG is a tool in scientific research, offering insights into various neurological conditions and brain functions. It is used to study neurological disorders, such as epilepsy, by detecting abnormal brain activity like seizure-like events. Researchers observe how brain activity changes during seizure onset, progression, and recovery, which helps in understanding disease mechanisms.
The technique also investigates neurodegenerative diseases like Alzheimer’s and Parkinson’s, monitoring brain wave pattern alterations correlating with disease progression or cognitive decline. For example, changes in delta or theta power can indicate neuronal dysfunction. Mouse EEG assesses new drugs or genetic manipulations on brain activity, providing a preclinical platform for drug discovery and therapy development. It is also applied to study sleep patterns and disorders, analyzing different sleep stages (wakefulness, non-rapid eye movement, and rapid eye movement sleep) and identifying disruptions, which allows for a deeper understanding of sleep architecture and its role in health and disease.
What Mouse EEG Reveals About Brain Function
Analysis of mouse EEG data provides insights into brain function, allowing researchers to identify and characterize various brain states. By examining brain wave patterns and frequencies, scientists can distinguish between wakefulness, different stages of sleep, and transitions between these states. For instance, an increase in delta waves signifies deep sleep, while a predominance of theta and gamma waves can indicate active exploration or cognitive engagement.
Mouse EEG also reveals abnormal brain activity, such as epileptiform discharges characteristic of seizure activity. Researchers can pinpoint the onset, duration, and spread of these abnormal electrical patterns, offering information about the underlying pathology of neurological disorders. By correlating changes in brain activity with observed behaviors, researchers investigate the neural underpinnings of various actions and responses. This approach helps understand how the brain processes stimuli, adapts to new environments, and how its activity changes with disease progression or therapeutic interventions.