Spearman wrote: “The theory of ‘two factors’ just delineated, though primarily of psychological origin, has shown itself capable of translation into terms of cerebral physiology.” The “specific factors” Spearman would identify with some “particular cortical region, or other neural characteristic, coördinated to the particular performance in question.” The “general factor” is derived from the fact that all neurones of the cortex arise from the same heredity, and must resemble each other, as “the hair in one region of a person’s scalp normally resembles that on the other regions” (a somewhat precarious analogy); also, from the fact that all parts of the brain are nourished by the same blood supply; and from the supposition that “each momentary focus of cortical activity receives continual support from energy liberated by the entire cortex (or some still wider neural area).” Thomson said: “Let us suppose that the mind, in carrying out any activity such as a mental test, has two levels at which it can operate. The elements of activity at the lower level are entirely specific; but those at the higher level are such that they may come into play in more than one kind of activity, in more than one mental test.... The difference between the levels may be physiological, as between cortex and spinal cord, or it may be the difference between conscious and non-conscious, or what not. The theory may later be reduced to a less harsh dichotomy and there may be gradations from the one level to the other.” These attempts to find a neural basis for the “Two Factor Theory” and the “Two Level Theory” are obviously not very complete. VI. PRESENT STATUS OF THE PROBLEM The conclusion is that at present experimental neurology has nothing secure to offer by way of establishing the neural basis of the special talents and defects, which we wish to consider. We must suppose that in some way unknown they are connected with neural activity, but localization of each function in a restricted area of the brain structure has never been established.