Neuron activation is a process that changes the activity of neurons in the brain. It can have a range of effects, from changing the perception of stimuli to altering the behavior of a monkey.
The neural basis for this process is unclear. However, it is known that a particular type of neuron in the primate visual cortex has a distinct firing pattern and is more stimulus selective than other cell types.
What is it?
Activation is the process by which neurons communicate with other neurons. These communication processes are essential for animals to adapt and survive, and they are also the basis of many other biological systems, such as the immune system.
Neurons are cells that contain specialized elongated extensions, called dendrites, which receive messages from other neurons. They also have a long, finer extension that reaches out from the cell body, called an axon, which carries nerve signals to other neurons.
The axon is an important part of the nervous system as it allows information to be sent across great distances. In nerves, the axons of neurons can be tens, hundreds or even thousands of times the diameter of the soma (the main part of the cell that receives and sends chemical messages).
Each neuron has a specific membrane potential: an electrical potential across its cell membrane that arises from different distributions of positively and negatively charged ions within and outside the neuron’s cell membrane. This potential is normally a negative number, i.e. -70 mV, but it can be positive, or more negative, depending on inputs from other cells.
When a neuron receives a signal from another neuron, it generates an action potential in the axon hillock and releases a chemical, known as a neurotransmitter, into the synapse. The neurotransmitter can then stimulate or inhibit the target neuron.
For example, in a muscle neuron, the release of acetylcholine triggers the muscles to contract, enabling the animal to move its body. This is a key function of the somatic nervous system, which is responsible for voluntary or conscious movement, such as walking and talking.
However, a number of autonomic nervous system (ANS) cells, such as the sympathetic nervous system, do not respond to stimuli but instead produce other physiological changes that regulate bodily functions. This can include a rise in heart rate and blood pressure, for example.
These ANS cells are known as sympathetic neuronal cells and they are critical to regulating a wide range of bodily functions. They are also the cells responsible for arousal, sleep, hunger, thirst and urination.
How does it work?
Activated neurons receive electrical signals, which can be transmitted over long distances. These electrical signals are called action potentials and can travel down axons to cause the release of neurotransmitters. The transmitters then bind to receptors on other cells, causing them to activate. The chemical signal then opens up channels that allow ions to flow into the receiving cell.
Typically, these ions are Sodium (Na+) ions. Those ions are then electrostatically bumped up along dendrites and other areas of the cell, converting the chemical message into an electrical signal that can be sent down axons to other neurons.
This process of conversion happens quickly but weakly. This is what explains why the neuron only responds to the initial spike from the other cell, but loses strength as it travels down its axon.
In addition to sending a signal down an axon, a neuron can also send signals to other neurons via a special type of chemical signal that changes the electrical charge across its membrane. These changes are called synapses, and they can connect cells anywhere in the brain.
These synapse are connected to axons by a series of postsynaptic receptors, which allow ions to pass from one neuron to the next, and vice versa. These synapse are critical for transmitting messages and controlling the behavior of the neurons that send them.
For example, when a neuron in the motor cortex of a monkey is stimulated by an external stimulus, it will begin to send out chemical signals that travel down its axon to other neurons. These chemicals then bind to postsynaptic receptors on the other neurons, causing them to activate.
When the other neuron is stimulated, it will then send out its own chemical signal that binds to its own postsynaptic receptor. This causes a neurotransmitter release in the other neuron, triggering another spike from the first neuron, which then starts a new circuit of chemical signals in the other neuron.
The combination of these chemical signals can make a neuron’s activity dynamic and unpredictable, much like an individual’s brainwaves. Depending on how the chemical signal changes, the neuron may either start to move in a particular direction or stop moving entirely.
What are the possible applications?
Monkey neuron activation is a technique that allows researchers to use light to activate specific neurons. This could have applications in treating epilepsy or Parkinson’s disease, which affect the brain’s ability to send messages or make decisions.
It could also help understand how certain neuron types are important for certain behaviors, such as controlling the hands of monkeys who play video games. And it might lead to new treatments for mental health problems like anxiety or depression, according to Science News.
The researchers used optogenetics, a method that involves using light to activate certain proteins in nerve cells, to stimulate neurons in the motor cortex of macaque monkeys. The animals then played a video game that required them to move a cursor to different targets on a screen.
After identifying the neurons that controlled each direction of movement, the researchers flipped a switch that allowed them to control the motion without the animals’ knowledge. The neurons then sent their signals to the computer, directing the cursor towards the target.
This approach has been used in nematode worms and mice to stimulate brain cells, but this was the first time it had been applied to the motor cortex of a monkey. The method is a promising tool for studying the brain’s complex signaling network, but it’s limited to single neurons.
Rather than activate all of the neurons, the team focused on just the ones that had been identified as controlling hand movement, and they found that only about six to 30 were needed for this to work. These were primarily located in the primary motor cortex and its surrounding area, called the premotor cortex (PM).
Their study was published in Nature Neuroscience.
These results suggest that certain neuron types may be more important for some tasks than others, and that some cells in the brain have an innate preference for one type of input over another. For example, the researchers observed that axon-carrying dendrites in neurons in the inferotemporal cortex of monkeys were more likely to transmit visual information than non-axon-carrying dendrites, a finding that has implications for how humans perceive faces and other complex objects.
What are the limitations?
In the realm of neuroscience, there are many subtle differences between human and nonhuman primates. For example, the human brain is more efficient in processing information than a monkey’s. But it also has several limitations, including the inability to render its neurons light sensitive.
Researchers are still working on the best approach to this problem. One option is to implant tiny electrodes inside the neurons themselves, but that involves invasive surgery. Alternatively, researchers can use techniques such as neuron activation to manipulate the electrical activity of individual neurons in the brain without disrupting normal function.
But this technique isn’t cheap or easy to do in humans, and the results can be mixed. For example, some of the experiments have shown that the most effective way to activate neurons is through manipulation of their environment — not by injecting chemicals or other substances into the brain.
Another way to achieve this is by implanting tiny radio waves into the neurons themselves. This is known as transcranial magnetic stimulation (TMS), and it has been used to control behavior in a variety of animal models, from dolphins to zebrafish.
However, this technique is expensive and difficult to implement in a large number of patients, so it hasn’t been widely applied in the medical field. To get around this barrier, a team of scientists at the University of California at Los Angeles and Argonne National Laboratory used existing data from single-neuron recordings in humans with epilepsy who were undergoing neurosurgery.
Using the data, they compared two different types of connections in the human brain: excitatory and inhibitory. The resulting data was impressive enough to be the basis for a scientific paper published in Science last year.
The most important finding was that the most effective way to stimulate the monkey’s neurons was to use a combination of signals from different regions of the brain, as opposed to just using one type of signal. The trick was to choose the signal that would be most useful in a specific situation and then amplify it to the appropriate size and strength.