I have defined the meaningless signification of the true truth as the signifying derivative dS/dt . Now such a derivative makes us think of a certain threshold in a passage where the true truth acts as the gatekeeper. We can identify this threshold precisely as the “rim-like structure” (Seminar 11) that Lacan designates as the source (Quelle) of the drives. According to Lacan, there are four drives; they are oral, anal, scopic, invocatory drives and their rims are respectively the mouth, the anus, the eye, and the ear.
For Lacan, these rims delineate a field of ‘objectality’ that is distinct from the usual objectivity of modern science. But Lacan has a mythical and tragic notion of this distinct field: “Objectality is the correlate to a pathos of the cut” (Seminar 10). As if humans were whole at the beginning, and then they were pathetically castrated, when the God cut their four rims. What is thereby supposedly cut from the pathetic humans is presumably the mythical Lamella.
Instead of the “pathos of the cut” let us conceive of these rims as the consequence of a long process of neuro-biological evolution: Each of these rims is a port that is located at the threshold of a passage. Each port neurally internalizes, assumes and ‘computes’ (metaphorically) a certain signifying derivative dS/dt. These drive rims work and are able to embody a true truth only insofar as they are neurally ‘differentiable’ in the mathematical sense, which means that they should be sufficiently smooth so that one can compute a finite limit that delineates the threshold of the rim.
This brings us to the definition of autism as the foreclosure of the rim . Foreclosure of the rim means that the source of the drive is not neurally differentiable, so that the signifying derivative dS/dt is intractable, which is why the true truth becomes inaccessible. One cannot reach a finite limit that delineates the threshold of the rim, which leads to a space “in which infinity and proximity are the same”, so that “the Other is always able to invade the subject’s body with a terrible jouissance, in catastrophic ways, without rims which could mark a regulated pulsation” (Laurent quoted by Brenner).
In the case of the neurotic, the rims of the drives are neurally differentiated through the legitimate handling of mistakes and malfunctions. The conscious negation of mistakes in the sense of disregarding, neglecting, forgetting, repressing, etc. delegates the task of neural differentiation of the rim to the unconscious. This delegation is a great relief for the neurotic, because it’s akin to finding an approximate solution to an infinite series by computing only up to a certain term and ignoring the rest of the series because it’s too costly to compute. This is the essential utility of the passion of ignorance. Anxiety ultimately originates from the challenges and difficulties in the neural differentiation of the rim of a drive. On the other hand, ‘desire’ designates the paradoxical appeal of this infinite task of differentiation. This is why desires are inextricably intertwined with mistakes and malfunctions; and psychoanalysis calls this intertwinement the symptom .
 See Leon Brenner’s The Autistic Subject (2020) page 179 onwards.
 See “Desire and Malfunction”
Image source: The Autistic Subject page 184. Based on the image from Lacan’s 11th seminar.