[Chaotic non-linear dynamics of alpha-band of the EEg and organization of the cortical activity of P300 wave].

Variations of non-linear dynamic operations in of alpha-band of the EEG are reflected in the peculiarities of the P300 wave cortical field organization. In high-dimensional chaotic processes this field is characterized with high values of integral indices of its activity, the spatial synchronization of generating process as well as with the prevalence of P3a wave generation. The diversity of spatial combinations of P-wave sources reflects the high rate of their spatial complexity organization. The main contribution into this activity is made by symmetrical points of anterior and temporal cortical portions. In low-dimensional dynamics the spatial structure of the positive wave is simplified. It becomes less global and more differentiated. P3b wave generation prevails in this case. The values of integral indices of wave cortical field activity are reduced. The focal topography of positive waves and their sources changes. Chaotic systems of alpha-band wave generators demonstrate good controllability and high plasticity in contingent acoustic stimulation. They change their dynamic characteristics due to biofeedback control, determining thereby P-wave field organization.

[Chaotic nonlinear dynamics of prestimulus EEG and the structure of auditory evoked potentials ]. / Khaoticheskaia nelineinaia dinamika prestimul'noi EEG i struktura slukhovykh vyzvannykh potenthialov.

The dynamic pattern of a prestimulus EEG was studied by the fractal analysis technique. The character of this pattern was shown to affect the structure of cortical auditory evoked potentials (EP). A monoperiodic pattern in the control frequency band was accompanied by a formation of several new attractors with low dimensionality attributed to simultaneous functioning of several weakly connected dynamic systems with an indefinite trend of a leading process. During development of multiperiodic processes in EEG segments, the fractal analysis revealed a tendency for a formation of a single complex dynamic system with high dimensionality of the attractor. Characteristic changes in parameters of the primary and middle-latency EP components, their correlation, and factor models are related with the character of nonlinear patterns. Analysis of variance revealed the most effective role of pattern changes in the EEG alpha control band. The structure of combination of parameters of the EP primary components into connected complexes depends on the nonlinear prestimulus EEG patterns. The above predictors determine differently directed and differently pronounced changes in parameters of the middle-latency positive waves.

Adaptive regulation of the nonlinear dynamics of electrical activity of the brain.

A programmable system was used to provide contingent reinforcement of EEG cycles corresponding to a selected criterion in a dynamic regime. Use of automated reinforcing stimulation of emotionally positive zones of the hypothalamus led to a significant increase in the number of cycles with the characteristics specified by the dynamic regime within the dominant EEG frequency bands. This effect lasted for some time after withdrawal of reinforcing stimulation, and then died down gradually. These changes in the EEG activity structure did not occur in conditions of nonassociated hypothalamic stimulation. Pseudoreinforced background EEG cycles showed complex nonlinear dynamics with competitive interactions between processes in which the large dimensionality of the attractor was difficult to interpret because of indeterminacy in the trends of the dominant process. In contingent hypothalamic stimulation, the form of the correlation integral changed towards a predominance of a single nonlinear process determining all the activity recorded. In fact, a single dominant nonlinear process was formed, which became responsible for the entire dynamics of the system with concordance of its internal structure.

[The adaptive regulation of the nonlinear dynamics of brain electrical activity]. / Adaptivnaia reguliatsiia nelineinoi dinamiki élektricheskoi aktivnosti golovnogo mozga.

The reinforcing automated stimulation of the emotional positive hypothalamic areas which was contingent upon the multiperiodical events in the EEG structure increased the number of episodes with non-linear dynamics. It resulted in an increase in the frequency of the intracranial self-stimulation. Under conditions of controlled experiment a possibility was shown of the intentional experimental formation of the EEG episodes with different types of non-linear dynamics. At the stages preceding the associative learning, the application of fractal analysis enabled revealing a complex character of non-linearity in the bands of the EEG dominant frequencies with a slight tendency to a dominant process. The associative learning produced one dominant non-linear process which determined the dynamics of the whole system. The neurophysiological characteristics of the given adaptive process were determined as well as the difference between this process and the response to control stimulation.