Instinctual pressure is of the impulses associated according to Lacan with the mirror stage. for Freud, pressure is characteristic of all impulses and is their essence. The amount of pressure can be theoretically quantified, and it the measure of pressure which determines the strength of the conflict it imposes on the subject. In relating to the mirror stage, Lacan describes aggression as an impulse which operates on the subject and can dictate his behavior. Lacan suggested that the extent of pressure operating on the subject during the mirror stage can shape the manner in which any instinctual pressure can become threatening and dangerous for the subject.
see: Lacanian Terminology