Trystan Casey
The human brain is a complex network of nerve fibres that facilitates the constant transmission of electrical signals, which gives rise to our thoughts, emotions, and behaviours. The brain is made up of small cells called neurons that communicate electrochemically to enable us to think, feel, and interact with the world around us. Neurons generate electric signals using the motion of ions across cell membranes, and these signals are passed from cell to cell through channels called 'gap junctions'. Scientists have been studying the electrical activity of neurons to understand how electricity flows through the brain. This involves measuring the electrical activity of neurons using electrodes, imaging techniques, and models of the brain's physical wiring. Electrical brain stimulation is also being explored as a treatment for various disorders and to improve cognitive functions.
| Characteristics | Values |
|---|---|
| How electricity is generated by neurons | The motion of ions across cell membranes |
| Number of neurons in the human brain | Over 86 billion |
| How electrical signals are communicated | Through a complex network of nerve fibres that interlinks all brain regions |
| How electrical activity is measured | By inserting an electrode into the brain, using multielectrode arrays, or a technique called calcium imaging |
| How electrical activity is imaged | Using a voltage-sensing molecule that fluoresces when brain cells are electrically active |
| How electrical brain stimulation is achieved | By using transcranial direct current stimulation (tDCS) or repetitive transcranial magnetic stimulation (rTMS) |
| How tDCS works | By sending an electrical current through the skin and skull to alter the electrochemical activity of a particular brain region |
| How electrical stimulation can be used | To treat mood disorders and stress, improve emotion regulation, attention, learning, problem-solving, and memory |
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What You'll Learn
Brain stimulation therapy
The brain is made up of networks of small cells called neurons, which communicate electrochemically to enable humans to think, feel, and interact with the world. Neurons generate electric signals using the motion of ions across cell membranes. The difference in electrical charge across the cell membrane is called the membrane potential. The grouping of ions on either side of the cell membrane causes this potential. In a rested state, sodium cations (Na+) and chloride anions (Cl-) are more prevalent outside the cell membrane, while potassium cations (K+) and various organic anions (A-) are present in greater numbers on the inside.
During brain stimulation therapy, electricity is used to alter the electrochemical activity of a particular brain region. This can be done non-invasively, as in electroconvulsive therapy (ECT), where electrodes are placed on the scalp to induce a controlled seizure. ECT is the oldest and one of the most widely used brain stimulation therapies, with a long history of use for depression. It has been approved by the FDA to treat severe depressive episodes in people 13 years and older with depression or bipolar disorder. Other non-invasive procedures include repetitive transcranial magnetic stimulation (TMS or rTMS), where an electromagnetic coil is placed on the scalp to deliver magnetic pulses to areas of the brain associated with mood. TMS may reduce symptoms of anxiety, OCD, depression, and other conditions. Magnetic seizure therapy (MST) is similar but operates at a higher frequency, aiming to induce a controlled seizure.
Some brain stimulation therapies are invasive and require surgery. Deep brain stimulation (DBS) involves implanting electrodes in the brain, which are then connected to a small generator placed in the patient's chest. Another procedure, transcranial direct current stimulation (tDCS), involves placing two rubber electrodes on the head to target the brain area of interest. The electrodes create an electrical circuit by sending a current through the skin and the skull, affecting the brain underneath.
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The role of neurotransmitters
The brain is made up of networks of small cells called neurons that communicate electrochemically to enable us to think, feel, and interact with the world around us. Neurotransmitters are the body's chemical messengers, and they play a crucial role in this electrochemical communication. They are the molecules used by the nervous system to transmit messages between neurons or from neurons to muscles.
Communication between two neurons occurs in the synaptic cleft, the small gap between the synapses of neurons. Here, electrical signals that have travelled along the axon are briefly converted into chemical signals through the release of neurotransmitters, causing a specific response in the receiving neuron. A neurotransmitter influences a neuron in one of three ways: excitatory, inhibitory, or modulatory. Excitatory neurotransmitters excite the next neuron by binding, while inhibitory neurotransmitters prevent the next neuron from firing.
There are several types of neurotransmitters, each with its own unique role and function. For example, acetylcholine, the first neurotransmitter to be discovered, is released by most neurons in the autonomic nervous system, regulating heart rate, blood pressure, and gut motility. It also plays a role in muscle contractions, memory, motivation, sexual desire, sleep, and learning. Another neurotransmitter, dopamine, is involved in the body's reward system, including feeling pleasure, achieving heightened arousal, and learning. It also helps with focus, concentration, sleep, mood, and motivation.
Imbalances in neurotransmitter levels can have significant effects on the body and have been linked to various diseases and disorders. For example, low levels of endorphins, which are the body's natural pain relievers, may play a role in fibromyalgia and certain types of headaches. Similarly, imbalances in acetylcholine levels are associated with Alzheimer's disease, seizures, and muscle spasms.
In summary, neurotransmitters are essential chemical messengers that facilitate communication between neurons and play a crucial role in various cognitive and physiological functions. Understanding their role is vital for developing medications that can influence these chemical messengers to treat a range of health conditions.
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Measuring electrical activity
Measuring the electrical activity of the brain is crucial for understanding its functioning and diagnosing disorders. Here is a detailed overview of some techniques used to measure brain electrical activity:
Electroencephalography (EEG)
Electroencephalography is a widely used technique for recording the brain's electrical activity. It involves placing electrodes on the scalp to detect tiny electrical charges resulting from brain cell activity. These electrodes are small metal disks with thin wires, and they don't cause any discomfort or sensation during the procedure. The recorded activity is then amplified and displayed as graphs or printed on paper for interpretation by healthcare providers. EEG is useful for detecting abnormalities in brain waves and diagnosing disorders like Alzheimer's disease, psychoses, and narcolepsy. It also helps evaluate trauma, drug intoxication, and brain damage.
Functional Magnetic Resonance Imaging (fMRI)
FMRI is a popular technology for mapping brain activity. It provides an unrivalled view of where different functions are localized within the brain. However, it does not directly record neuronal activity but instead measures blood flow as a proxy for neuron activation. fMRI produces multicolour images that reflect the relative presence of oxygenated versus deoxygenated blood, as active brain regions require more oxygenated blood. Researchers are working on improving fMRI's spatial and temporal resolution by making it more sensitive to neuronal changes.
Electrocorticography (ECoG)
ECoG is similar to EEG in that it measures the activity of millions of neurons. However, it requires the insertion of electrodes under the scalp, making it an invasive procedure. Due to its invasiveness, ECoG is typically only suitable for patients already scheduled for brain surgery. One advantage of ECoG is its improved localisation of the activity source and the ability to record higher-frequency electrical activity, making it useful during epilepsy surgery.
Calcium Imaging
Calcium imaging allows for dense sampling of neural electrical activity by measuring calcium levels. However, it is an indirect and slow measure of electrical activity. This technique involves genetically engineering neurons with fluorescing molecules, such as Archon1 or SomArchon, which reveal electrical activity. SomArchon is an improved molecule that accumulates in the centre of neuron cell bodies, preventing interference from neighbouring neurons.
Event-Related Potentials (ERP)
ERPs are brain waves recorded while the subject is exposed to specific sensory or cognitive stimuli. They provide sensitive measures of brain functions, reflecting subtle, dynamic, real-time transactions. ERP mapping is useful in studying the effects of alcohol on brain function and identifying risks for developing alcoholism. Computerized mapping techniques produce graphs or colour-coded images to summarize data about ERP generation.
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Brain cell activity imaging
One of the most common approaches to imaging brain cell activity is through microscopy, which captures activity-dependent fluorescence from fluorescent proteins expressed in neurons of transgenic animals. This involves using genetically-encoded sensors derived from fluorescent proteins, such as the GCaMP family of indicators, to image large populations of neurons in genetically accessible animals. Calcium imaging is another technique that allows dense sampling of neural electrical activity, albeit indirectly and slowly.
Recent breakthroughs have enabled whole-brain recording in small behaving animals, such as the nematode Caenorhabditis elegans, the fruit fly Drosophila melanogaster, and the larval zebrafish Danio rerio. These whole-brain experiments capture neural activity with cellular resolution across sensory, decision-making, and motor circuits.
Additionally, researchers at Boston University and the Massachusetts Institute of Technology have developed a new imaging technique using a voltage-sensing molecule that fluoresces when brain cells are electrically active. This method has allowed them to visualize the activity of many individual neurons in mice brains, providing a clearer picture of brain cell activity than ever before.
Furthermore, a new method called JEDI-2P, developed by researchers at Baylor College of Medicine, enables long-lasting imaging of rapid brain activity in individual cells deep in the cortex. This technique promises to advance our understanding of how the brain functions in both healthy and neurologically impaired awake, active animals.
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The impact of electrical signals
The human brain is a complex network of nerve fibres, with electrical signals constantly travelling across it. These electrical signals are generated by the motion of ions across cell membranes. The difference in electrical charge across the cell membrane is called the membrane potential. The membrane potential is caused by the grouping of ions, with sodium cations (Na+) and chloride anions (Cl-) more prevalent outside the cell membrane of a neuron, and potassium cations (K+) and various organic anions (A-) present in greater numbers inside the cell membrane.
The brain's electrical activity is facilitated by neurons, which send and receive information in the form of electrical signals from sensory organs, enabling communication with the brain. Each neuron receives multiple incoming signals from many cells at a time through different neurotransmitters. Neurotransmitters are chemical substances that bind to receptors on dendrites, converting incoming chemical input into electrical signals in the neuron, generating an action potential. Excitatory neurotransmitters excite the next neuron by binding, while inhibitory neurotransmitters prevent the next neuron from firing.
The electrical signals in the brain can be measured through various techniques, including the use of electrodes, multielectrode arrays, and imaging techniques. Electrical brain stimulation, such as transcranial direct current stimulation (tDCS), can be used to safely and effectively alter brain activity without the need for brain surgery. tDCS uses an electrical current to modify the electrochemical activity of a particular brain region, affecting the electrical signals responsible for brain activity. This can be used to treat mood disorders, stress, and to improve emotion regulation, attention, learning, problem-solving, and memory abilities.
The impact of these electrical signals is profound, as they give rise to our thoughts, emotions, and behaviours. When something goes wrong with these electrical signals, it can potentially lead to mental health and neurological issues. By understanding the electrical activity in the brain, scientists can develop treatments for brain disorders and improve overall brain functioning.
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Frequently asked questions
Electrical signals are constantly travelling across the brain through a network of nerve fibres. These signals are generated by the motion of ions across cell membranes.
Electrical activity in the brain can be observed through various techniques such as using electrodes, MRI scans, and new imaging techniques that use voltage-sensing molecules.
Understanding the flow of electricity in the brain can help us develop treatments for mental health and neurological disorders. It can also improve our ability to regulate emotions, attention, learning, problem-solving, and memory.
Techniques like transcranial direct current stimulation (tDCS) use electrical currents to alter the electrochemical activity of specific brain regions. This can be done non-invasively, with electrodes placed on the head to target the desired brain area.
