We will question the scope of the concept of excitation as a plausible point of intersection between psychoanalysis and biology, from the epistemological paradigm of interdisciplinary dialogue, suggested by François Ansermet and Pierre Magistretti. We shall examine the fact that, in spite of the great importance of excitation as the somatic origine of drive within the metapsychological structure, a strict analysis of the epistemological foundations of the Freudian conception of excitation, and also a study of the model of backing impulse on the need, both would lead us to consider, in another way, the excitation as a major abutment point introducing a radical incommensurability between the two disciplines. Thus, excitation would appear, not as a concept at the intersection in psychoanalysis and biology, but, on the contrary, as a frontier-concept between these two areas, because it would feature a discontinuity related to the epistemological break proposed by Sigmund Freud, in his concept of sexual impulse, the cornerstone of the psychoanalytical theory. The difference established by Jacques Lacan, throughout his formalization of the graph, between the need, the demand and the excitation, will be also a heuristic tool that will be able to enlighten the emergence of a radical hollowness between biological excitation and its representation of the psychic drive. Excitation could embody the impossible relationship between a merely biological conception and the impulse defined by psychoanalysis as the impulse structurally sexual. Whether any dialogue points could be started between neurobiology and psychoanalysis, the aporia that is opened by the problem of excitation from an epistemological point of view leads us to consider the impossibility for the biological science to take account of the sexual understanding of the impulse, to which biology would resist across any possibility of dialogue.