During this formative period of his work, Freud valued and came to rely on the intellectual and emotional support of his friend Wilhelm Fliess, a Berlin-based ear, nose and throat specialist whom he had first met in 1887. Both men saw themselves as isolated from the prevailing clinical and theoretical mainstream because of their ambitions to develop radical new theories of sexuality. Fliess developed highly eccentric theories of human biorhythms and a nasogenital connection which are today considered pseudoscientific. He shared Freud's views on the importance of certain aspects of sexuality – masturbation, coitus interruptus, and the use of condoms – in the etiology of what were then called the "actual neuroses," primarily neurasthenia and certain physically manifested anxiety symptoms. They maintained an extensive correspondence from which Freud drew on Fliess's speculations on infantile sexuality and bisexuality to elaborate and revise his own ideas. His first attempt at a systematic theory of the mind, his "Project for a Scientific Psychology" was developed as a metapsychology with Fliess as interlocutor. However, Freud's efforts to build a bridge between neurology and psychology were eventually abandoned after they had reached an impasse, as his letters to Fliess reveal, though some ideas of the "Project" were to be taken up again in the concluding chapter of "The Interpretation of Dreams".