The purpose of the study is to establish the specifics of spectral, amplitude-time characteristics and localization of sources of cortical responses during the implementation of motor tasks in the paradigms of Stop-Signal task and Stop-Change task in men and women. To achieve this purpose, the following research methods have been set: the determination of the profile of manual and auditory asymmetries, neurodynamic examination, the determination of the event-related synchronization / desynchronization of human EEG spectral power (ERS / ERD), the event-related brain potentials, three-dimensional localization of the sources of brain activity, parametric and non-parametric statistical methods of processing the obtained results.
35 men and 40 women, aged 18–23 years, volunteers, healthy, with the right profile of manual and auditory asymmetries, were examined. The right profiles of manual and auditory asymmetries were evaluated by the nature of responses during the survey and the performance of motor and psychoacoustic tests. Time of sensorimotor responses of simple visual-motor reaction and reaction in the choice of one of three objects as signals (triangles, circles, squares) was determined. EEG experiment procedure envisioned the use of two successive series. In the first series, the Stop-Signal task paradigm was used. Prior to the beginning of the test, the subject obtained the following instruction: after hearing a low-frequency tone signal (600 Hz), s/he should rapidly press a left button on the panel by the right-hand forefinger and then to release the button. After the appearance of a high frequency tone signal (1600 Hz), the tested person should avoid the pressing movement. All sound signals were presented in pairs. In some such pairs, both sounds were low-frequency (600 Hz); in other pairs, the first sound was low-frequency, while the second one was high-frequency (1600 Hz, Stop). In all cases, the participants began realization of the movement after presentation of the first sound (Go). The second sound in the stimulus pair was important for the subject as either a confirmation for realization of the just begun movement or for cessation of the latter, i.e., the signal sequence corresponded to the Stop-Signal task paradigm. In the course of the second series, the tested persons responded to the stimuli under conditions of the Stop-Change task paradigm. With the appearance of the high-frequency signal, the subject had to rapidly press the right button of the panel by the middle finger of the right hand and to release the button. In the case where the stimuli in the pair differed from each other, the triggered motor program (for pressing the left button on the panel by the right-hand forefinger) should be inhibited with subsequent switching over to the alternative abovementioned program (Stop-Change).
In both series of the experiment, the prevalence of ERS response especially in the range of 7-10 Hz EEG has been noted. In the series with a stop of the started motor program followed by switching to the alternative one (Stop-Change paradigm) of the examined subjects altogether, a higher level of manifestation of activation processes in the separate subbands of α- and β1-activity of EEG in the frontal, central and parietal cortical areas in comparison with Stop-Signal task has been determined. The detected longer latency period of the P3 component in the Stop-Signal task situation can be caused by a multi-stage complete stop of movements, whereas in the Stop-Change task situation only one motor installation could be stopped and there could be initiated the alternative one, which respectively affected the shorter latency period and the lower amplitude of components N2 and P3 under these conditions. The peculiarities of the evoked electrical activity and the localization of their generators in brain established in women in both experimental situations may indicate the prevalence of inhibitory and to some extent nonspecific processes, while in men the areas responsible for monitoring conflicts and response selection activated more locally. The right hemisphere localization of sources of brain activity under the conditions of Stop-Signal task has been revealed. Instead, the relative enhancement of the cognitive control in the Stop-Change task situation determined the bilateral left-hemispheric vector of brain activity generators localization in the examined subjects.
