Molly Ayala
The human brain is a complex system, with billions of neural cells that transmit electrical signals. These signals are generated by the cooperative action of brain cells, or neurons, and carry information from one place to another in the nervous system. While neurons are not good conductors of electricity, they have evolved mechanisms for generating electrical signals based on the flow of ions across their plasma membranes. Researchers have traditionally measured electrical activity in the brain by inserting electrodes to record the voltage between the inside and outside of nerve cells. However, this technique is labor-intensive and only captures the activity of one neuron at a time. More recently, advanced imaging techniques, such as voltage-sensing molecules and calcium imaging, have enabled scientists to visualize and study the electrical activity of multiple neurons simultaneously. Despite these advancements, there is ongoing debate about the nature of nerve signals, with some evidence suggesting that they are not solely electric but also mechanical pulses.
| Characteristics | Values |
|---|---|
| Nature of electrical signals in the brain | Electrical signals in the brain are nerve signals transmitted in the membrane that makes up the axon's outer wall. |
| Mechanism of transmission | Channels in the lipid layer open momentarily, letting sodium and potassium ions (charged particles) flow through the membrane and then close. As the opening and closing advances down the axon, it creates a traveling voltage pulse. |
| Measurement techniques | Invasive techniques require surgery to implant microelectrodes that record brain signals directly from the cortex's surface. Non-invasive techniques include electroencephalography (EEG) and magnetoencephalography (MEG). |
| Brain cell activity | Researchers have developed a voltage-sensing molecule that fluorescently lights up when brain cells are electrically active, providing a clear picture of brain cell activity. |
| Nature of nerve cells | Nerve cells generate electrical signals that transmit information. Neurons are not intrinsically good conductors of electricity but have evolved mechanisms for generating electrical signals based on the flow of ions across their plasma membranes. |
| Resting membrane potential | Neurons ordinarily generate a negative potential, called the resting membrane potential, that can be measured by recording the voltage between the inside and outside of nerve cells. |
| Action potential | The action potential abolishes the negative resting potential and makes the transmembrane potential transiently positive. Action potentials are propagated along the length of axons and carry information from one place to another in the nervous system. |
| Mechanical pulses | Some researchers argue that brain cells communicate with mechanical pulses rather than solely electric signals. These mechanical pulses are triggered by voltage pulses and travel as shock waves down the axon. |
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What You'll Learn
How electrical signals are generated
Brain cells, or neurons, generate electrical signals that transmit information. Neurons are not naturally good electricity conductors, but they have evolved complex methods for producing electrical signals based on the flow of ions across their plasma membranes.
Neurons typically generate a negative potential, known as the resting membrane potential, which can be measured by recording the voltage between the inside and outside of nerve cells. The action potential eliminates the negative resting potential and causes the transmembrane potential to become transiently positive.
Action potentials are transmitted along the length of axons and are the primary signal that transports information from one location to another in the nervous system. The nerve cell's selective permeability to various ions and the normal distribution of these ions across the cell membrane are responsible for the generation of both the resting potential and the action potential.
The electrical activity of neurons has traditionally been measured by inserting an electrode into the brain, but this method is time-consuming and usually only allows for the recording of activity from a single neuron. Multielectrode arrays can monitor electrical activity from many neurons simultaneously, but they cannot capture the densely packed activities of all neurons within a piece of brain tissue.
Calcium imaging is a technique that allows for dense sampling, but it measures calcium, which is an indirect and slow indicator of neural electrical activity. Researchers have also used voltage-sensing molecules that fluoresce when brain cells are electrically active, providing a clearer picture of brain cell activity.
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Measuring electrical activity in the brain
Electrical signals in the brain are generated by nerve cells, or neurons, which transmit information. These neurons are not good conductors of electricity, but they have evolved to generate electrical signals based on the flow of ions across their plasma membranes.
Electroencephalography (EEG): EEG is a widely used technique for recording neural activity directly. It involves placing electrodes on the scalp to record the brain's electrical activity. EEG can be used to detect abnormalities in brain waves and overall electrical activity. It is also useful for diagnosing disorders that influence brain activity, such as Alzheimer's disease and narcolepsy. One of the limitations of EEG is its poor spatial resolution, which makes it difficult to pinpoint the precise location of signals within the cortex.
Electrocorticography (ECoG): ECoG is similar to EEG in that it measures the combined activity of millions of neurons. However, it requires the insertion of an electrode array under the scalp, making it a more invasive procedure. ECoG provides improved localisation of the activity source and records higher-frequency electrical activity. Due to its invasiveness, ECoG is typically only suitable for patients already scheduled for brain surgery.
Functional Magnetic Resonance Imaging (fMRI): fMRI is widely known for recording neural activity, but it does not directly measure neuron activity. Instead, it provides multicolour images that reflect blood flow in the brain, indicating active regions that require more oxygenated blood. fMRI offers an unrivalled view of where and to what extent different functions are localised within the brain. However, it does not provide a direct measure of electrical activity.
Calcium Imaging: This technique involves genetically engineering neurons to contain fluorescing molecules that reveal electrical activity. Calcium imaging allows for the dense sampling of neural activity but is considered slow compared to voltage imaging.
Voltage Imaging: This technique uses a voltage-sensing molecule that fluoresces when brain cells are electrically active. It provides a clearer picture of brain cell activity and can capture small fluctuations in activity, even when neurons are not firing significant spikes in electrical activity.
These techniques provide valuable insights into the electrical activity of the brain, contributing to our understanding of brain function and enabling the diagnosis and treatment of various neurological disorders.
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The role of neurons in transmitting signals
Neurons play a crucial role in transmitting electrical signals within the brain. They are the key players in the nervous system, conveying information through electrical and chemical means. While neurons are not inherently good conductors of electricity, they have evolved to generate electrical signals through the movement of ions across their plasma membranes. This movement creates a voltage difference, resulting in an electrical charge that carries information from one neuron to another.
The structure of a neuron facilitates the transmission of signals. Each neuron consists of dendrites, a cell body, and an axon. Dendrites are thin fibres that extend from the cell and receive information from other neurons. The cell body, or soma, houses the nucleus and performs essential cellular functions. The axon, a long thin fibre, propagates the signal to the next neuron through specialised endings called axon terminals. Myelination, a process where myelin acts as an insulator along the axon, increases the speed of conduction, ensuring the efficient transmission of the electrical signal.
An essential aspect of neuron signalling is the action potential. This occurs when there is a rapid, temporary change in membrane potential due to the movement of sodium and potassium ions. The action potential abolishes the negative resting potential, resulting in a transiently positive transmembrane potential. Neurotransmitters, such as dopamine, play a crucial role in initiating and propagating the action potential by binding to receptors and acting as ligand-gated ion channels. This process involves the opening and closing of voltage-gated ion channels, which further influence the membrane potential.
The transmission of signals between neurons occurs at synapses, where two neurons come into close contact. Neurotransmitters are released from the axon terminals of the sending neuron, crossing the synaptic cleft to reach the dendrites or dendritic spines of the receiving neuron. This process triggers a cascade of chemical events, resulting in changes in cell function and the initiation of an action potential in the receiving neuron. The complex interplay between electrical and chemical signals allows neurons to transmit information effectively, facilitating various cognitive and physiological processes in the brain.
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Brain signals as mechanical pulses
Brain cells, or neurons, communicate with each other via electrical impulses, allowing the brain to coordinate behaviour, sensation, thoughts, and emotions. However, recent studies have suggested that brain cells also communicate with mechanical pulses, not just electric signals.
In the mid-1900s, researchers learned to insert electrodes into nerve cells to monitor the voltage across the membrane wall. This technique has been used to measure the electrical activity of neurons by detecting the voltage between the inside and outside of nerve cells. However, this method is labor-intensive and can typically only record the activity of one neuron at a time.
In 2018, MIT researchers developed a light-sensitive protein that could be embedded into neuron membranes, emitting a fluorescent signal that indicates how much voltage a particular cell is experiencing. This allowed scientists to study how neurons behave, millisecond by millisecond, as the brain performs a particular function.
Despite these advancements, scientists have struggled to explain how the brain achieves complex tasks such as face recognition and conversation while relying on electrically noisy and unreliable neurons. This has led to the exploration of mechanical waves as a potential explanation for the brain's impressive capabilities.
In 2005, Heimburg and his colleague Andrew D. Jackson proposed a theory that a voltage pulse travelling down a membrane would be accompanied by a mechanical wave, and vice versa. This theory was supported by Matthias Schneider, a biophysicist, who successfully triggered a mechanical wave by applying a voltage pulse to an artificial membrane in 2009. The pulse strength and speed were similar to those found in nerve cells.
The nerve signal is not just a voltage pulse but also a mechanical pulse, as evidenced by the transient widening of the nerve fibre, rearranging of molecules, and heating and cooling effects observed during nerve signalling. These mechanical waves may compensate for the electrical noise in neurons, providing a more robust means of communication for brain cells.
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Visualising electrical signals in the brain
Electrical signals in the brain are generated by nerve cells, also known as neurons. Although neurons are not good conductors of electricity, they have evolved mechanisms for generating electrical signals based on the flow of ions across their plasma membranes.
Visualising these electrical signals in the brain has been a challenge for scientists, who have traditionally measured these signals with electrodes inserted into the brain. This method is difficult, time-consuming, and only allows researchers to record the activity of one neuron at a time.
However, recent advancements in imaging techniques have provided a clearer picture of brain cell activity. Researchers at Boston University and the Massachusetts Institute of Technology (MIT) have developed a voltage-sensing molecule that fluorescently lights up when brain cells are electrically active. This technique has allowed them to visualise the activity of many individual neurons simultaneously, providing a more detailed understanding of brain function.
Another imaging technique, called calcium imaging, allows for dense sampling of neural electrical activity. By genetically engineering neurons to contain fluorescing molecules, such as Archon1 and SomArchon, researchers can visualise electrical activity without the interference of neighbouring neurons. This approach has been used to study the electrical activity in the brains of mice during movement, providing insights into how neurons behave millisecond by millisecond.
Additionally, electroencephalography (EEG) is a non-invasive technology that can record coordinated electrical activity in large groups of neurons. EEG data is often used to create visualisations of brain activity, such as the "Glassbrain Flythrough 2015" video by the Neuroscape Lab at the University of California, San Francisco. These visualisations use 3D models derived from magnetic resonance imaging (MRI) data and depict electrical activity as pulses of light and colour changes, offering a captivating and informative perspective on brain function.
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Frequently asked questions
Electrical signals in the brain are generated by nerve cells, or neurons, and transmit information.
Neurons are not good conductors of electricity, but they have evolved to generate electrical signals based on the flow of ions across their plasma membranes.
Electrical signals in the brain can be measured using invasive or non-invasive techniques. Invasive techniques involve implanting microelectrodes into the brain to record electrical signals. Non-invasive techniques include electroencephalography (EEG) and magnetoencephalography (MEG), which use sensors placed on the scalp to measure electrical activity.
