The Vedanta Sutras of Badarayana, Commentary by Sankara (SBE38), tr. by George Thibaut [1896] at sacred-texts.com
12. It is designated as having five functions like mind.
The chief vital air has its specific effect for that reason also that in scripture it is designated as having five functions, prâna, apâna, vyâna, udâna, samâna. This distinction of functions is based on a distinction of effects. Prâna is the forward-function whose work is aspiration, &c.; apâna is the backward-function whose work is inspiration, &c.; vyâna is that which, abiding in the junction of the two,
is the cause of works of strength 1; udâna is the ascending function and is the cause of the passing out (of the soul); samâna is the function which conveys the juices of the food equally through all the limbs of the body. Thus the prâna has five functions just as the mind (manas) has. The five functions of the mind are the five well-known ones caused by the ear, &c., and having sound and so on for their objects. By the functions of the mind we cannot here understand those enumerated (in Bri. Up. I, 5, 3), 'desire, representation,' &c., because those are more than five. But on the former explanation also there exists yet another function of the mind which does not depend on the ear, &c., but has for its object the past, the future, and so on; so that on that explanation also the number five is exceeded.--Well, let us then follow the principle that the opinions of other (systems) if unobjectionable may be adopted, and let us assume that the five functions of the manas are those five which are known from the Yogasâstra, viz. right knowledge, error, imagination, slumber, and remembrance. Or else let us assume that the Sûtra quotes the manas as an analogous instance merely with reference to the plurality (not the fivefoldness) of its functions.--In any case the Sûtra must be construed to mean that the prâna's subordinate position with regard to the soul follows from its having five functions like the manas.
90:1 Viz. the holding in of the breath; cp. Kh. Up. I, 3, 3-5.