[Electroencephalographic changes in response to the equilibrium test and rhythmic light flashes]

Reliable diagnosis of CNS noise resistance is very important in the selection of operators, pilots and cosmonauts. This dictated a study the purpose of which was to investigate neocortex biopotentials of 74 test subjects during equilibrium tests in the presence or absence of 12 Hz light flashes. Electrocardiographic and stabilographic recordings were taken from 6 sites of the left neocortex during equilibrium tests (standing on toes) and during light stimulation. EEGs were processed through correlation-spectral analysis by means of Electronika-60 and EC-1035 computers. During light stimulation 35 "nonsusceptible" subjects maintained equilibrium for as long as 80-100% of the normal time while 39 "susceptible" subjects maintained it for only 10-30% of the normal time. In response to light stimulation susceptible subjects showed distinct rearrangement of the autospectral and coherence functions. The spectral density increased by 115-170% and the coherence of biopotentials that corresponded to the light stimulation frequency grew by 42-70% (p less than 0.01). Peaks of the function maxima occurred at 12 Hz. At the same time the density and coherence of biopotentials in the frequency range 6-8 Hz decreased by 50-58% and 15-28%, respectively (p less than 0.01). The above changes were more pronounced in the neocortex areas related to movement organization, viz. premotor, motor and sensorimotor areas. In the non-susceptible subjects light stimulation induced no changes in EEG. It is concluded that noise resistance of the motor control system depends on the CNS capacity to prevent the rhythm of light stimulation to occur in EEGs of motor areas.