  It is shown that there is no standard spiking neural P system that simulates
Turing machines with less than exponential time and space overheads. The
spiking neural P systems considered here have a constant number of neurons that
is independent of the input length. Following this we construct a universal
spiking neural P system with exhaustive use of rules that simulates Turing
machines in linear time and has only 10 neurons.
