In recent decades, significant changes have occurred in views on the cerebral organization of the processes of speech, reading and memory. More than 100 years ago P. Broca and K. Wernicke based on data on speech disorders with focal brain lesions created ideas about the cortical organization of speech functions. Since then, it is known that speech recognition occurs in the Wernicke area, located in the back of the left upper temporal gyrus. The motor mechanisms of speech are realized upon activation of the Brock center, localized in the posterior third of the lower frontal gyrus of the left hemisphere.
Modern methods for studying local cerebral blood flow and the intensity of glucose consumption by the brain, as well as computerized EEG and evoked potentials associated with events, have shown that much wider areas of the cortex are involved in speech processes than previously thought. Speech activates the cerebral cortex bilaterally, although activation of the left hemisphere prevails in right-handed people. The perception of speech and pronunciation of words occurs with the participation of the prefrontal and frontal areas of the cortex.
Reading processes also involve broader areas of the cortex than previously thought. Reading aloud and to oneself causes the right-handed people to activate energy metabolism and increase cerebral blood flow in the occipital and prefrontal areas, mainly in the left hemisphere, parieto-temporal, middle and upper temporal regions of the left and, to a lesser extent, the right hemisphere.
Changes in the EEG in the form of the appearance of slow-wave activity of the delta and theta range during reading occur primarily in the right hemisphere. Reading aloud is more pronounced than reading inwardly, increasing the power spectral beta1 and theta activity in the temporal region x .
In accordance with these data, a new model of the cortical organization of speech functions was proposed. According to this model, written and oral speech messages arrive through the visual and auditory systems in the secondary sensory areas of the cortex and are transmitted almost instantly via powerful phylogenetically new paths to the prefrontal and frontal areas. Here, the identification and interpretation of sound signals with the participation of motor speech programs takes place .
When retelling the material read, i.e. during mnemonic processes, in addition to the centers involved in providing reading, the anterior prefrontal region of the right and left hemispheres is activated, and in some observations the right hippocampal and parahippocampal regions are activated . The general activation of the energy metabolism of the brain, especially the occipital regions, during the tests on memory is shown .
In a number of diseases of the central nervous system, in some cases at the preclinical stage, the pattern of changes in cerebral energy metabolism is violated during mnemonic tests. It was shown that in clinically healthy people genetically predisposed to Alzheimer’s disease, there is an excessive increase in local cerebral blood flow in the structures of the brain involved in the provision of memory processes, subsequently these structures were subjected to atrophy and . Thus, the state of energy metabolism and cerebral blood flow when performing mnemonic tests can be a predictor of the development of the disease.
Data on significant changes in energy metabolism during speech and mnestic processes have suggested that brain SCP may also change. This section discusses the dynamics of SCP in healthy people when reading aloud and retelling the text read.
We examined 15 healthy test right-handed subjects aged 24 to 59 years (average age 44.9 + 3.1 years). Registration of SCP was carried out in 5 standard leads. In the process of recording, skin resistance was controlled, the changes of which did not exceed 1 kOhm. SCP was recorded for 5 minutes in a state of calm wakefulness and then for 5 minutes in the process of reading aloud. At the end of the reading, the SCP was recorded for 5 minutes without load, after which the subjects were asked to retell the text fragment they had read. Registration of SCP was continued during the retelling of the text and after its completion also for 5 minutes.
After the recording is completed, the soft-starter values recorded in each mode. Since during the tests the SCP parameters changed gradually, only the SCP indicators recorded 2.5 minutes after the start of reading or retelling the text were taken into account. After the reading, there was also a gradual restoration of SCP, in connection with which, when averaging, only data from the second half of the rest period before retelling the text were taken into account. Thus, for each subject, the SCP parameters were averaged in the background before reading (5 min), when reading (2.5 min), in the background before retelling the text (2.5 minutes) and during retelling of the text (2.5 min). Then, statistical processing of the data for the group was carried out, including analysis of the standard SCP parameters in the above modes. The reliability of changes in SCP under loads was evaluated using one-way analysis of variance. SCP data at rest and while reading are presented.