The analysis of evoked potentials of sensorimotor cortex in response to electrical stimulation of n. ischiadicus shows that the extremal factor hypokinesia has a negative impact on the dynamics of formation of amplitudal and temporal characteristics since eyes openning in 2-weeks old rats. The most vulnerable process to the impact of hypokinesia is the first-positive phase, which disappears in this case and the inhibitory effect of ascending excitation on the brain cortex is observed. This indicates that 2-weeks old rat lies in its most critical period and the onset stage of functional changes that will be eyes opening and formation of motor activity. Hypokinesia has a negative impact not only on the characteristics of the evoked potentials, but as well on biometric values (weight, length) and on the eyes-opening process. Therefore, the presented experimental data showed the impact of hypokinesia on the brain maturation, on the processes of excitation in the brain cortex, and in this way demonstrate the heterochronic morpho-functional maturation of its structures.