Few Gens ever achieve any conscious control of this body function; however, it does respond to the emotions the Gen experiences. When a Gen feels empathic sympathy for a sime's suffering, selyur nager almost invariably occurs, linking the Gen's selyn field to the sime's selyn field. If the linkage is precise enough, the Gen can control the sime's selyn-consumption rate, thus dispelling much of the discomfort of Need and, to a certain extent, controlling the sime's emotions. This requires great skill and is commonly considered extremely dangerous, and impertinently intrusive.
The mathematics of selyur nager linkage are akin to that of electrical inductance, and it is thus a reciprocal relationship; the sime can control the state of the Gen body if a precise attunement can be reached.
A selyur nager linkage is a condition brought about by the ability of a Gen to, consciously or unconsciously, match his/her selyn production rate with the Selyn consumption rate of a sime. This can create a synchronized couple for Transfer, and is the aim of a Companion who is dedicated to a particular sime. A Gen with a high production rate working to serve more than one sime should not try to establish Selyur Nager as it is impossible to do with more than one sime at a time. Selyur Nager is not necessary to provide good Transfers. (See also: Companion & Donor)
See also the dangers and advantages of pairing a Sime and a Gen for transfer where the inherent (genetic) basal selyn consumption and production rates are exact matches: Lortuen, Orhuen, Torluen The rare, and usually accidental match of basal rates is even more rare in the Interstellar era when humanity is so spread out.