Trystan Casey
The brain is an incredibly complex organ, and its electrical activity is a key indicator of its functionality. Electrical activity in the brain is measured through electroencephalography (EEG), which involves placing electrodes on the scalp to detect electrical charges resulting from brain cell activity. This process is non-invasive and helps in understanding brain disorders, emotions, thoughts, and sensations. Scientists have also developed innovative techniques such as using light-sensitive proteins and voltage-sensing molecules to study electrical activity in the brain more effectively. These advancements allow researchers to gain deeper insights into the brain's electrical behaviour and its impact on our overall health and well-being.
| Characteristics | Values |
|---|---|
| Method to record electrical activity in the brain | Electroencephalography (EEG) |
| How does EEG work | Electrodes are pasted onto the scalp to detect tiny electrical charges that result from the activity of brain cells |
| Purpose of EEG | To detect abnormalities in brain waves or electrical activity of the brain |
| Frequency range | 1-30 Hz |
| Amplitudes | 20-100 μV |
| Frequency subdivisions | Alpha (8-13 Hz), Beta (13-30 Hz), Delta (0.5-4 Hz), and Theta (4-7 Hz) |
| Alpha waves | Observed when a person is in a state of relaxed wakefulness |
| Beta waves | More prominent during intense mental activity |
| Theta and Delta waves | Not generally seen in wakefulness; if present, it is a sign of brain dysfunction |
| Calcium imaging | Allows dense sampling of electrical activity but measures calcium, which is an indirect and slow measure |
| Voltage imaging | Allows imaging of electrical activity at the timescale of milliseconds |
| tDCS | Transcranial direct current stimulation; uses an electrical current to alter the electrochemical activity of a particular brain region |
| Neurons | Cells in the brain that use electrical charges and chemicals (ions) to communicate with each other |
| Neurons at rest | Have more negative ions inside and more positive ions outside, giving the neuronal membrane a negative charge |
| Neurons during activity | Positive ions rush into the neuron and negative ions rush out, changing the voltage and causing the neuron to send a signal to nearby neurons |
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What You'll Learn
Electroencephalography (EEG)
EEG is typically non-invasive, with the electrodes placed along the scalp, a method commonly known as "scalp EEG". This technique provides a safe and comfortable procedure for patients, causing no discomfort or sensation during the process. The placement of electrodes follows the International 10–20 system or its variations.
The electrical signals detected by EEG represent the activity of neurons in the underlying brain tissue. These signals are then transmitted and amplified to be displayed as graphs on a computer screen or printed on paper. The resulting waveforms, or graphoelements, are then visually inspected by a clinical neurophysiologist or neurologist to interpret the readings.
EEG is particularly useful for evaluating brain disorders, such as epilepsy, brain lesions, Alzheimer's disease, psychoses, and narcolepsy. For epilepsy, seizure activity is visible as rapid spiking waves. Lesions from tumours or strokes can result in very slow EEG waves, depending on their size and location. EEG can also be employed to assess trauma, drug intoxication, brain damage, and comas.
Furthermore, EEG can be used to monitor blood flow in the brain or neck blood vessels during surgery. It is also beneficial for stimulation therapy, helping to resolve problematic brain activity patterns in individuals with brain damage or disorders. EEG results can be influenced by certain factors, such as caffeine consumption and body or eye movement during the test, although these rarely interfere significantly with interpretation.
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Measuring electrical activity
A more advanced approach is calcium imaging, which allows for dense sampling of neural electrical activity. This technique involves genetically engineering neurons to contain a fluorescing molecule, such as Archon1 or SomArchon, that reveals electrical activity. Calcium imaging, however, operates on a slower timescale compared to the rapid voltage changes in the brain.
To overcome this limitation, researchers at Boston University and MIT have developed a new imaging technique that uses a voltage-sensing molecule. This molecule fluoresces when brain cells are electrically active, providing a clearer picture of individual neuron activity. This method has been successfully tested on mice, zebrafish larvae, and worm Caenorhabditis elegans.
Another way to measure electrical activity in the brain is through electroencephalography (EEG). This non-invasive technique uses electrodes placed on the scalp to record electrical activity. The signals detected by EEG represent the electrical activity of neurons in the underlying brain tissue. EEG can be used to detect abnormalities in brain waves, diagnose disorders such as Alzheimer's disease and psychoses, and evaluate trauma or drug intoxication.
In summary, measuring electrical activity in the brain can be achieved through various techniques, each with its own advantages and limitations. These methods provide valuable insights into how the brain functions and facilitate the diagnosis and treatment of neurological disorders.
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Brain stimulation
Direct electrical stimulation is an invasive procedure that requires surgery. It allows for the precise targeting of specific brain regions and is often used when other treatments have failed. Indirect electrical stimulation, on the other hand, is non-invasive and does not require surgery. It can be achieved through techniques such as transcranial direct current stimulation (tDCS), which uses rubber electrodes positioned on the head to target the brain area of interest. tDCS alters the electrochemical activity of a particular brain region by changing the charges in populations of neurons, making them more or less likely to send signals.
Another form of indirect brain stimulation is electroconvulsive therapy (ECT), which has been cleared by the FDA to treat severe depressive episodes in individuals 13 years and older with depression or bipolar disorder. ECT involves using an electric current to induce seizure activity in the brain and has a long history of use in the treatment of depression.
In recent years, researchers have been developing new techniques to image and stimulate the brain. One such technique involves using voltage-sensing molecules that fluoresce when brain cells are electrically active, providing a clearer picture of brain cell activity. Another approach involves embedding light-sensitive proteins into neuron membranes, which emit fluorescent signals that indicate the voltage a particular cell is experiencing. These techniques offer new ways to study how neurons behave and communicate with each other, providing valuable insights into the electrical activity of the brain.
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Imaging techniques
Several imaging techniques are used to measure and map electrical activity in the brain. Electroencephalography (EEG) is a well-known technique that records electrical activity in the brain through electrodes placed on the scalp. It is non-invasive and can be used to determine the brain's electrical response to a stimulus. However, it has poor spatial resolution and cannot be used to study certain regions of the brain, like the hippocampus.
Another technique, electrocorticography (ECoG), provides improved localisation of the source of electrical activity and records higher-frequency electrical activity. It is, however, too invasive to be used in humans who do not require brain surgery. Functional magnetic resonance imaging (fMRI) is widely known for recording neural activity and provides an unrivalled view of where and to what extent different functions are localised within the brain. Unlike EEG, fMRI records blood flow, a proxy for neuron activation, rather than directly recording electrical activity.
Other imaging methods include positron emission tomography (PET), computed tomography (CT) scans, magnetoencephalography (MEG), nuclear magnetic resonance spectroscopy (NMR or MRS), single-photon emission computed tomography (SPECT), near-infrared spectroscopy (NIRS), and event-related optical signal (EROS).
More recently, researchers have developed techniques to image electrical activity using fluorescent molecules and proteins. One such molecule, Archon1, can be genetically inserted into neurons, and its fluorescence, visible under a standard light microscope, increases with electrical activity. This technique has been used to image electrical activity in zebrafish embryos, mouse brain slices, and live mice. Another molecule, SomArchon, has been used in live mice to monitor electrical activity in many neurons simultaneously while correlating their activity with movement.
Calcium imaging is another technique that allows for dense sampling of neural electrical activity, although it measures calcium, which is an indirect and slow measure.
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Neurons and their functions
Neurons are nerve cells that transmit electrical and chemical signals to other cells. They are the key players in the brain and are responsible for sending and receiving signals to coordinate behaviour, sensation, thoughts and emotions. Neurons are born in areas of the brain that are full of neural stem cells or precursor cells. They have a lot in common with other types of cells but are structurally and functionally unique.
There are many different types of neurons, and they serve many different functions in the body. They vary in size, shape and structure depending on their role and location. For example, Purkinje cells are a special type of neuron found in a part of the brain called the cerebellum. These cells have highly developed dendritic trees, which allow them to receive thousands of signals.
Dendrites are fibrous roots that branch out from the cell body and act as antennae, receiving and processing signals from the axons of other neurons. Axons are specialized projections that allow neurons to transmit electrical and chemical signals to other cells. Neurons can have more than one set of dendrites, known as dendritic trees. The number of dendrites a neuron has generally depends on its role.
The creation of new nerve cells is called neurogenesis. This process is much more active when an individual is an embryo, but evidence suggests that some neurogenesis occurs in adult brains throughout life. Scientists are intrigued by current research on neurogenesis and the possible role of new neurons in the adult brain for learning and memory.
In the past, scientists have used electrodes inserted into the brain to measure electrical activity in neurons, but this technique is labor-intensive and only allows for the recording of activity from one neuron at a time. More recently, researchers have developed a light-sensitive protein that can be embedded into neuron membranes, emitting a fluorescent signal that indicates how much voltage a particular cell is experiencing. This new approach is believed to be much easier and more informative, allowing scientists to study how neurons behave millisecond by millisecond as the brain performs a particular function.
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Frequently asked questions
Electrical activity in the brain refers to the electrochemical charges and signals that are sent between neurons, enabling the brain to perform its functions.
Electrical activity in the brain can be measured through a test called an electroencephalogram (EEG). This involves attaching electrodes to the scalp to detect electrical charges and brain waves.
An EEG is used to detect abnormalities in brain waves and electrical activity. It can be used to diagnose disorders such as epilepsy, Alzheimer's disease, psychoses, and sleep disorders.
Yes, another method is to use electrodes inserted into the brain, although this technique is labour-intensive and can only record activity from one neuron at a time. More recently, researchers have developed light-sensitive proteins that can be embedded into neuron membranes to measure electrical activity through fluorescence.
Yes, electrical brain activity can be altered through techniques such as transcranial direct current stimulation (tDCS), which uses electrical currents to modify the electrochemical activity of specific brain regions. This can be used to treat brain damage or disorders and improve emotion regulation, attention, learning, problem-solving, and memory abilities.
