Yes, in fact, rhythmic sensory/motor activity of many kinds--flashing lights, music, repetitive movement, will induce or alter oscillations in brainwaves. Even imagining finger tapping can have this effect (DOI: 10.1016/j.brainres.2018.04.013 ). A number of studies have experimented with using finger tapping therapeutically by altering brainwave rhythms. Also, flashing lights at the gamma frequency has been shown to remove the toxic beta amyloid protein in a mouse model of Alzheimer’s disease https://www.quantamagazine.org/stimulated-brain-waves-offer-a-possible-treatment-for-alzheimers-20200527/ . Effects on brain rhythms are, in part, how music and dance therapy can be helpful for people with Parkinson’s disease.

Experimental research on this question is lacking, but any experience that alters mood would be accompanied by characteristic changes in brainwaves. Alpha wave activity, for example, is greater in a relaxed state.

Neurons communicate by generating brief electrical impulses (action potentials) and by brief alterations in voltage at their synapses (synaptic potentials) that cause release of neurotransmitters. These very weak electrical signals can be detected by inserting a microelectrode into the brain to penetrate or come into very close contact with a neuron. When a large number of neurons operate in synchrony, the combined effect of these small voltage signals builds, like the thunderous applause in an auditorium from people clapping hands in synchrony. Electrical activity in thousands of neurons operating together in the cerebral cortex (the outermost layer of the brain), builds to the extent that the electricity can penetrate the skull and be detected by electrodes on the scalp. Surprisingly, these electrical fluctuations are oscillatory (thus the name ‘brainwaves’). The rhythmic electrical activity oscillates at characteristic frequencies, from less than one cycle per second (delta waves) to over 60 cycles per second (gamma waves). Since this electrical activity reflects information processing going on in neural networks, normal and abnormal operation of cognitive functions can be assessed by monitoring brainwaves, and brain function can be altered by electrical or other means to change brainwaves. Moreover, as waves of all types interact in complex ways, brainwaves can couple together electrical activity in populations of neurons without them being wired together by synaptic connections. Coupling neurons in this way can form dynamic functional assemblies of neurons that synchronize, filter, and manipulate information processing in the brain.

Neurofeedback works by providing the participant feedback (usually an auditory tone) to signal when their brainwave activity shifts in a desired way. For example, the power of alpha waves increases in a relaxed state, and this relaxed state can be promoted by neurofeedback. The process does not require intentional effort. Cued that brainwave patterns have shifted in the intended direction, the brain will act to induce those changes to receive the ‘reward’ tone.

Yes, neuroplasticity can be increased by neurofeedback that alters brainwave activity in specific brain regions. The principle here is that neural plasticity, for example in recovering from brain injury or disease, is in part directed by functional feedback. Brainwaves are altered by functional activity and by brain dysfunctions, so neural plasticity can be promoted by altering brainwaves. In Parkinson’s disease, for example, neural oscillations are perturbed in brain circuits that control movement. In experimental research, patients with Parkinson’s disease benefit by monitoring changes in these brainwaves (mainly beta waves) and using neurofeedback to que the patient as to when the brainwave activity is shifting in the desired direction (for example see: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6877348/). Similar approaches can be used to alter cognitive and emotional states; for example, to heighten arousal, promote relaxation, or for cognitive enhancement. In addition to altering brainwaves by neurofeedback, electrical or electromagnetic stimulation of specific brain regions through the skull can be used.
There are many devices sold on the internet to enable people to monitor their own brainwaves for such purposes. These can be fun to use and are often effective; however, these devices are much less sophisticated than instrumentation used in scientific laboratories. Also, what some of these commercial gadgets are actually detecting and how the signals are analyzed is obscure and proprietary. A person wishing to explore neurofeedback for therapeutic benefit would do well to consult medical professionals and certified neurofeedback practitioners for the best outcome.

Brainwave analysis and other methods of monitoring brain activity, such as fMRI and near infrared spectroscopy, can be used to gain insight into what a person is thinking, but probably not in the way your question implies. Because different thoughts activate a different constellation of brain circuits and brain regions, it is possible to analyze the brain’s activity using machine learning techniques, and identify specific thoughts. Marcel Just at Carnegie Mellon University has pioneered this technique to reveal if a person is having thoughts of suicide, for example (https://www.nature.com/articles/s41562-017-0234-y). Similarly, people can be instructed to imagine engaging in an activity, clenching their fist or playing tennis, for example, and the brain’s response can be recognized. Using this approach, it is possible to identify a person’s answers to true-false questions, by instructing them to imagine playing tennis if the answer is true (https://www.frontiersin.org/articles/10.3389/fnins.2020.00105/full). That mental imaginary activates vigorous brain activity in sensory-motor and visual regions of the cerebral cortex, which is readily distinguished from the brain’s ongoing activity. This can be extremely useful in determining the extent to which a person in a coma may be conscious of their surroundings, but unable to move or talk to communicate to caregivers that they are consciously aware. Such studies have revealed that a significant fraction of people in comas or who are presumed to be in vegetative states after brain trauma are in fact conscious (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6059097/ ).
Prosthetic limbs operate in a similar manner. The patient with an electrode array implanted in their motor cortex to record neuronal firing, or by monitoring brainwave responses using EEG, imagines moving a limb and the sudden alteration in brain activity can be recognized to trigger a computer to respond. When we move or even think about moving, brainwave activity in the motor cortex suddenly diminishes. This response is so robust that it was observed in the very earliest studies of brainwaves performed in the 1800’s. People who are completely paralyzed can communicate with this type of brain-computer interface, by mentally typing out their thoughts on a computer keyboard (https://www.scientificamerican.com/article/wireless-brain-implant-allows-ldquo-locked-in-rdquo-woman-to-communicate/ ).
But if you are asking if it is possible to read a person’s thoughts by brainwave analysis in the way we can read a computer program, or as depicted in fictions like the TV series Black Mirror, the answer is no. Current understanding of how the brain encodes information is much too rudimentary to accomplish this SciFi feat, and the complexity of the brain far exceeds our ability to extract and comprehend the complex information processing going on in our brains.

Neurofeedback is considered quite safe; especially in comparison to alternatives, such as drug therapies. Transcranial stimulation by passing electrical or electromagnetic pulses through the scalp is also considered safe, but carries greater risk. Transcranial stimulation will suppress or excite specific brain regions and this could promote transient impairments or possibly seizure. Even watching flashing lights, which can synchronize brainwaves, causes seizures in some people.

Researchers are able to monitor brainwaves in one person to transmit signals to a person in a remote location to impose a response by beaming electromagnetic, electrical, or ultrasonic pulses of energy through the skull. For example, Rao and colleagues working in the laboratory of Andrea Stocco and Chantel Prat at the University of Washington, have used this method to allow a person in one location who is watching a video game to team up with another person in a remote location through brain-to-brain transmission. When the person watching the video game imagines pulling a trigger, that brainwave response is detected and a signal is transmitted over the internet to energize an electromagnet positioned above the recipient’s head to activate the brain region that causes the recipient’s hand to pull a trigger (https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0111332 ). Such brain-to-brain transmission has even been done between humans and animals.

Human behaviors, thoughts, moods, and specific memories in vivid detail can be evoked by using electrodes to stimulate specific brain circuits that carryout these functions. A person can be driven into a violent rage, for example by stimulating the amygdala, or be overcome with sexual desire by stimulating the appropriate brain regions. However, fears of ‘mind control’ are not grounded in fact. It is not possible to direct a person’s thoughts or direct behaviors in a programmed way. The responses evoked by brain stimulation are not predictable, in part because everyone’s brain is different. Moreover, the methods used to stimulate neural circuits are far too crude to control a person’s thoughts or actions. Brain stimulation most often acts as a monkey wrench thrown into the works, and disrupts normal activity, preventing a person from being able to talk, for example. Our understanding of the brain is nowhere near what it must be to provide the capability of mind control. Technology that could do this remotely from a distance is also beyond current capabilities. However, attention has been drawn to the potential misuse of such methods in warfare to disrupt an enemy’s brain functions remotely by perturbing electrical activity in the brain through various methods.

PTSD is notoriously difficult to treat, but neurofeedback can enhance treatments. TMS (transcranial magnetic stimulation) to alter brainwaves is also being used to treat veterans with PTSD.

I believe brainwave analysis will transform medicine and change society in profound ways. When you go to the doctor, he or she takes a blood sample and has a biochemical analysis performed to diagnose disease. Then, chemicals (drugs) are given to correct the biochemical abnormalities to treat the condition, or you can take other measures, like reducing fats in your diet if you have high cholesterol. We are on the threshold of being able to analyze and treat neurological and psychological conditions in a similar way—by monitoring and manipulating the fundamental way our nervous system operates, which is through electricity. Precision therapy will be provided by direct stimulation the appropriate neural circuits that are responsible for the conditions.
The ability to evaluate cognitive function and know the strengths and weaknesses of your brain by monitoring its activity by EEG and other non-invasive means, will be helpful in education and considering career choices. Forewarned by brain monitoring that your preschool child is likely to have difficulty learning to read, for example, you can undertake early educational measures to strengthen the brain circuits involved in reading before the child enters school.
At present, most of this research is being carried out in scientific laboratories, but the day is coming soon when this capability will be applied by doctors and therapists in their offices and hospitals. As our understanding of how specific neural circuits are involved in cognitive functions and behavior increases, brainwave analysis will become an increasingly powerful tool to enable each of us to attain our maximal potential.

TMS boosts or squelches neuronal firing (depending on the polarity of the voltage delivered), and this alters brainwave activity at a focused point in the brain. This is a powerful experimental approach for determining which parts of the brain and which circuits are involved in specific brain functions, and this method has many therapeutic applications. When rhythmic TMS stimulation is applied, the frequency of brainwave oscillations can be altered.