PASSIVE AND ACTIVE P300 – TWO SYSTEMS OF GENERATION (P300 IN PATIENTS WITH FOCAL BRAIN DAMAGES) L.Oknina, E. Sharova, O.Zaitsev, E.Masherow INSTITUTE OF HIGHER NERVOUS ACTIVITY AND NEUROPHYSIOLOGY, BURDENCO NEUROSURGERY INSTITUTE, MOSCOW, RUSSIA MOSCOW, RUSSIA METHOD Р300 recorded in the simple oddball paradigm. 'Passive' P300 = No instruction 'Active' P300 = Instruction to count rare low sounds To the dipole sources location on step-by-step method and their structural attachment were made by BrainLoc (MBN, Russia). This program allows finding of the location and orientation of dipole sources in the head model so that the difference between the recorded data and the calculated surface data of the dipole model is to a minimum. In the one-dipole model a moving dipole are used. Search of an optimum arrangement of dipoles was conducted on all volume of a brain. The goodness of fit is expressed by the dipole coefficient (Kd) as a percentage of the signal variance which is achieved 100% during the procedure. Definition of spatial coordinates and orientations of the equivalent dipole sources both for the separate moments of time, and for the given intervals of the initial data were done. Estimation of reliability of calculated parameters and selection of authentic sources were done. The BrainLoc allowed to locate the dipole neuroanatomically. Difference waveform were obtained by subtracting event-related potentials elicited by the "standard" tone from the event- related potential by "target" one. The correlation function of the obtained difference with the sample of the curve were constructed with using a positive half-cycle. On the basis of these data the approximation of potential was under construction. The quality of approximation were evaluated as the attitude of the dispersions of the subtraction and approximation curves taken in percentage, time shift on which the maximal correlation between these curves was achieved and mean amplitude of approximating curve. BACKGROUND Many studies have been attempted to identify the dipole source localization of the P300 of the acoustic evoked potential. Although, the P300 generators are not known certainly. More often in clinic at impossibility of contact with the patient it is necessary to record P300 in "passive condition. The going of present study was analysis of Р300 of the acoustic evoked potential at healthy examinees and patients with focal damages during the "passive" and "active" oddball paradigm. RESULTS Healthy subjects (control research) Analysis of P300 at healthy subjects revealed that active P300 had an amplitude maximum in the fronto-central or parieto-central area more often in the left hemisphere. Two waveforms - simple and complex, correlating with features of the alpha-rhythm in background EEG were allocated: the answer of the most simple waveform was marked at the examinees with highly synchronous alpha-rhythm. The analysis of dipole sources has shown the involving of the brainstem structures, limbic system (hippocampus) and frontal lobes in generation of the wave. The determining role at all examinees the brain stem structures in generation of the active P300 were marked. The easing of the frontal lobes contribution to the generative process at the persons with highly synchronous alpha-rhythm was marked. At passive P300 the authentic differences of its parameters were observed in 46% of cases (at the persons with not hyper synchronous alpha-rhythm). The simplification of the waveform, displacement of the amplitude maximum zone to the right hemisphere and reduction the number of the equivalent dipole sources was marked at the expense of reduction of the contribution frontal and limbic structures in generation P300. Patient with focal brain damage Specific changes of P300 was revealed for each type of brain damage. Although shifts of amplitude- time parameters was not depended on topography of damage and had similar type of changes at any cases: the prolong of latency, reduce of amplitude and tendency to decrease of half-cycle took place in the all cases. These parameters had significant changes from norm in all groups with the brain damage. Significant correlation between the degree of P300 changes and clinical severity took place in all cases. Topography had more specific to the brain damage to contrast the amplitude-time parameters. The localization of the maximal amplitude in occipital area without asymmetry was typical to patients with frontal lobe damage; at damage of the temporal lobe some foci frequently taking place in different hemispheres of a brain were registered; at patients with brainstem damage the amplitude maximum was in fronto-polar area of the right hemisphere. The relatively not depended behaviour P300 in the active and passive situation was shown in patients. Moreover, passive P300 had more sensitivity to the brain damage in compare to the active one. It was changed in all patients even though active P300 had no changes. CONCLUSION The existence of two brain systems for "passive" and "active" P300 were assumed. For formation "passive" P300 a left frontal lobe and middle-stem structures of the brain are more important then others. These structures answer in a greater degree for involuntary kinds activation. In maintenance "active" P300 the primary importance has safety of a right frontal lobe (or both lobes) ensuring stability of any attention, and also structures of a limbic system, in particular, hippocampus. SPATIO-TEMPORAL MAPS IN THE P300 LATENCY, AVERAGED POTENTIAL FOR TARGET STIMULI IN THE ELECTRODES OF THE MAXIMAL EXPRESSIVENESS OF ONE AND DIPOLE LOCALIZATION IN THE ACTIVE (LEFT) AND PASSIVE (RIGHT) EXPERIMENTAL SITUATIONS IN THE HEALTHY SUBJECTS IN PATIENTS WITH FOCAL DAMAGE OF THE LEFT FRONTAL LOBE¹ ¹ - for patient with right or both-side frontal damage is more typical the maps like as in the passive condition of presented IN PATIENTS WITH FOCAL DAMAGE OF THE TEMPORAL LOBE IN PATIENTS WITH FOCAL DAMAGE OF THE ORAL BRAINSTEM SUBJECT 29 healthy subjects 9 patients with focal damages of the brainstem 13 patients with focal damages of the frontal lobe 10 patients with focal damages of the temporal lobe