The Deep by Isaac Asimov — Read

Theory, thought Gan, always theory. The folk of the surface, a million or more years ago, could see the Universe, could sense it directly. Now, with eight hundred miles of rock above their heads, the Race could only make deductions from the trembling needles of their instruments;

It was only theory that brain cells, in addition to their ordinary electric potentials, radiated another sort of energy altogether. Energy that was not electromagnetic and hence not condemned to the creeping pace of light. Energy that was associated only with the highest functions of the brain and hence characteristic only of intelligent, reasoning creatures.