Excerpt from the first chapter 'Aldous' in "Aldous Huxley, An English Intellectural" by Nicholas Murray:

In the 1940s, Huxley was smitten by the classification of human types drawn up by Dr William Seldon in The Varieties of Human Physique and The Varieties of Temperament. In this scheme, Huxley was a 'cerebrotonic', a term that would crop up regularly in his later works. In an article which appeared in Harper's Magazine in November 1944, with droll illustrations by James Thurber, Huxley explained the characteristics of his own type:

The cerebrotonic is the over-alert, over-sensitive introvert, who is more concerned with the inner universe of his own thoughts and feelings and imagination that with the external world. . .In posture and movements, the cerebrotonic person is tense and his physiological responses uncomfortably intense. . .Extreme cerebrotonics. . .have a passion for privacy, hate to make themselves conspicuous. . .In company they tend to be shy and unpredictably moody. . .Their normal manner is inhibited and restrained and when it comes to the expression of feelings they are outwardly so inhibited that viscerotonics suspect them of being heartless.