We introduce in the P systems area a mechanism, inspired from neural-cell behavior, which controls computations by inhibiting and de-inhibiting evolution rules. We investigate the computational power of this mechanism in both generative and accepting P systems. In particular, we prove that universality can be obtained by using one catalyst. If we use only non-cooperative rules and one membrane, then we can obtain at least the family of Parikh images of the languages generated by ET0L systems. Several research proposals are also suggested.