Brain signals
The presence of an enormous number of neurons in our brain makes it an important source of electrical signals. These signals reflect our brain activity, previously used only to detect possible abnormalities of functioning, nowadays they have found a new range of applications as our knowledge of the nature of these generated signals increases.
We also learned how to interfere with their behavior by applying external signals, which opens up an increasingly important new range of applications. The direct interaction of the brain with external electronic devices and even brain-to-brain communication with the help of high-tech devices is not far away. But, starting from the known signals of the brain which lead to other applications, we can make a short classification based on what is known today and used in medicine in the electroencephalogram or EEG.
It appears that in different states of brain functioning, it generates signals corresponding to low frequency “waves” which can be detected through external electrodes. These waves are produced by fluctuations in the currents circulating through neurons. Thus, we can detect the stresses generated by placing electrodes on the brain, as they propagate through the conductive medium which is our own body.
We then have the following types of signals:
a. Gamma waves which correspond to signals above 30 Hz, which medicine have not found a practical application yet. They are associated with cognitive processes and certain stages of sleep.
b. Beta waves which have frequencies between 14 and 30 Hz and a typical amplitude below 30 uV and manifest when we are in the state of full surveillance or attention.
c. Alpha waves which have frequencies between 8 and 14 Hz and an intensity below 50 mV when we are at rest.
d. Theta waves with frequencies between 4 and 8 Hz normally associated with sleep and activities involving the imagination. Peaks of these waves can be associated with depression.
e. Delta waves with frequencies between 0.3 and 4 Hz being related to deep sleep.
In fact, the profound interpretation of these waves is still something that deserves much study.
The Signals of the Heart
It is justified for medicine to be concerned with the signals of the heart, as it is a non-invasive way of knowing what is happening to it. The nervous stimuli which make it work and the consequent reaction allow it to detect anomalies with good precision. The heart is a muscle whose cells are negatively charged at rest and with the discharge to zero the muscle contracts. In this process, a potential is generated, which can be detected externally.
Then we have the electrocardiogram or ECG that can be analyzed from the following types of signals:
a. P waves showing the activation of the right atrium. Its approximate duration is 80 ms.
b. Complex QRS showing the rapid depolarization between the right and left ventricles lasting between 80 and 100 ms.
c. T wave which shows the repolarization of the ventricles with a duration of approximately 160 ms.
d. U wave showing the repolarization of the interventricular septum.
For medicine these signals are important, but they can also be used in other applications such as monitoring physical activity. With the use of artificial intelligence algorithms, the signals can be analyzed together, generating information which can improve the physical performance of athletes, improve the quality of life for the elderly and much more. A lot can be developed.
Muscle Signals
Nerve stimuli are responsible for muscle contraction and these signals can be monitored through electrodes and recorded. The muscle membrane has a resting potential maintained by the presence of ions on its two faces. The depolarization and repolarization of neurons results in signals of excitation which cause the muscle fibers to contract and stretch. This effect can be monitored by the generated electrical potentials. The signal recording of many muscle fibers results in the electromyogram or EMG, being used in medicine.
These signals can be used for other purposes such as recording physical activity, tiredness, and even inversely with external excitation. The stimulus generated by the brain, for example, which does not reach a muscle due to a nervous problem, can be transmitted by artificial means. With that, a member with paralysis can return to work. Finally, muscle signals can be used in numerous applications as well as stimulus signals.
Eye Signs (EOG)
Eye signals lead to an electrooculogram which consists of recording eye movement signals. Electrodes placed on the front of the head, close to the eyes can pick up the rest signals between the cornea and the retina produced by the action of nerves. The cornea is usually positive, and the retina is negative, the two functioning as a dipole between which a tension manifest. Eye movements alter this potential, which can vary between -0.06 to +0.06 V. This signal is used in ophthalmology, but it can find other interesting applications.
The possibility of controlling a cursor on a computer screen or even the movements of a wheelchair or artificial arm have already been tested in quadriplegics. For developers, an idea would be a device which allows very seriously ill patients to have no movement, to communicate or trigger distress signals using eye movement. And, in the opposite case, we have already dealt with studies which allow exciting brain regions or appropriate optic as well as auditory nerves to bring the sensations of images and sounds to those who lost them.
Magnetic Brain Signals
The movement of electrical charges in the brain caused by its normal activity generates currents which are responsible for the creation of magnetic fields. These magnetic fields can be detected externally and are used in what is called Magnetoencephalography or MEM. The use of ultra-sensitive magnetometers allows the measurement of these fields, although their decoding is very difficult, since the fields generated by the individual currents are added vectorially due to the diversity of their orientations. But in addition to medical applications, we can mention others involving the control of devices based on signals from the brain, if we do their decoding which, in our day, is still a little far away.
Signals of the Skin
These signals are technically called galvanic skin response. What is analyzed in the case is the fact that the electrical properties of the skin change sensitivity depending on both the person's psychological state and possible changes in organ functioning. This change can be detected by changing its electrical resistance. The process of measuring this resistance is technically called Galvanic Skin Response or GSR with important medical applications.
Outside of medicine we can mention the lie detector or polygraph, but we can go further with the indication of interesting possibilities for the technology of the future. Detection of specific states by simply placing electrodes in contact with the skin can be the basis of applications such as health monitoring, metabolism, stress states and more.
As variations of these signals, several others can be noticed as the electrodermal response or EDR, psychogalvanic reflex (PGR), skin conductance response, among others. Acupuncture uses these signs a lot in its practices. For the developer, the values we should work with are important. The resistance inside the body varies a lot according to the graph obtained in Figure 1.
These resistances are also important in safety, as they indicate currents which can cause sensations and damage to our body.
Conclusion
In fact, our organism is a complex electrochemical machine that generates an infinite number of signals, many of which we are barely aware of. In the same way, we have a sensitivity to signals we barely know. Low frequency fields can cause damage under certain conditions, high frequency fields can cause poorly known stimuli. Light can excite and have specific effects, electromagnetic radiation from the radio range can have the most diverse influences on our body. There is still a lot to study and the findings can lead to incredible innovations. On our website, we have several articles that may be important for the reader who wants to know more.
