In the 1920s, German electrophysiologist and psychiatrist G. Berger (1873-1941) for the first time registered the bio electric activity (in the form of potential fluctuations) of the human brain. Since then, a lot of effort has been made to understand whether such oscillations have any functional significance or just accompany neural activity and serve as an indicator of the state of the brain. Today, we know that the work of this most important human organ is based on the transmission of electrical signals, which are simultaneously generated by many nerve cells. The electrical activity of the entire brain can be imagined as the noise of a huge crowd, billions of members of which are talking at the same time. No one doubts that the voice of an individual neuron is important in this general noise - it is the nerve cell that participates in the analysis and processing of information. But there is still no clarity regarding the entire polyphony.
The total electrical activity of the brain (the noise of a huge crowd) is recorded with the help of an electroencephalograph, which records fluctuations in electrical potentials in several frequency ranges, or rhythms.
Here we are talking about only one of its functions - the visual - and one type of electrical activity reflected on the EEG, the so-called alpha-rhythm, i.e. fluctuations in electrical potentials with a frequency of 8 to 13 Hz. In this range, the rhythm frequency is individual, but it is present in almost every person and is particularly powerful in the visual area (located in the occipital region of both hemispheres) of the cortex of the large brain in a state of calm waking with the eyes closed.
Alpha rhythm, as well as the electrical activity of the brain in the range of other frequencies, has been the subject of fundamental research for many years but has now migrated to applied and sem applied for work. This is apparently due to the fact that most approaches to the analysis of his role have exhausted themselves and proved unproductive. Despite many specific guidelines and a number of journals filled with articles on EEG, the importance of alpha rhythm for brain function is still debatable, if not questionable.
The mechanisms for generating this rhythm are also unclear. Thus, the view that alpha-rhythm is still prevailing is that it is a potential fluctuation that is synchronously developing throughout the visual cortex, i.e. a standing wave. Meanwhile, many years ago, American researchers - mathematician W. Pitts and neurologist W. McCullough - proposed a scanning hypothesis related to this very rhythm [1]. In their opinion, the alpha-rhythm reflects the scanning of the visual cortex and the reading of information from it by the moving wave of excitation. Recall that in the primary projection area of the visual cortex, where the signals from the retina through the subcortical visual center arrive, the so-called retinotopy is observed. This means that the visible world projected onto the retina by the optical system of the eye is reflected in the cortex by the same excitation pattern. Not without reason, the visual cortex is called the cortical screen structure.
The authors of the hypothesis of scanning assumed that every 100 ms in the center of this cortical screen there is a wave of excitation, which spreads at the same time before its borders. This moving wave is summed up in each neuron with excitation coming from the retina, thereby increasing the level of depolarization of nerve cells, located further and further from the center of the visual cortex. As a result, the cortical screen structure sequentially reads, scans, and transmits visual information to other areas of the cortex, where it is further analyzed and the images are identified. The authors attached great importance to alpha-rhythm and without undue modesty called their article "How we know the universe. Perception of auditory and visual information.
The idea of a scanning wave did not arise from anything. The authors noticed the similarity of the structure of the main nerve fiber bundles in the visual and auditory cortex with the schemes of devices for automatic control of anti-aircraft fire, developed at the end of the Second World War.
Undoubtedly, this idea, if it were true, would be very important both for understanding the sequence of visual information processing and for evaluating the functional value of alpha-rhythm. However, there was no strong evidence of the hypothesis. The scanning process itself was not detected experimentally, and the indirect data turned out to be contradictory - some of them confirmed the consequences of the hypothesis, others - not.
It's known that a man can better identify the centripetal direction. (This is apparently related to the greater biological significance of signals that appear on the periphery of the field of vision due to their novelty and possible danger.) This was the case in control. But in the experience this preference was changed to the opposite: the subjects recognized the centrifugal direction better - towards the alpha-wave. Such a preference in recognition is quite understandable. It is known that perception of movement is based on activation of neurons of the visual cortex with high sensitivity to its direction. And since activation depends on the spatial and temporal gradient of the input signal, which is the largest in the counter movement of two waves (centripetal alpha-wave and light-induced centrifugal wave), it is natural that in this case the recognition indicators improve.