  The Sanskrit term most commonly associated with sensory activity,  indriya (‘sensation’ or ‘power’), is found in the Rg Veda (I, 55; II, 16), a collection of hymns  dealing with various religio-philosophical topics central to the  Brahmanical tradition. Here the senses are likened to lesser deities  acting on behalf of Indra, the king of the gods, as messengers to the lower realms. As manifestations of Indra's specific powers, the  senses thus understood correspond to his capacity for knowledge  (buddhīndriya) and action (karmendriya). This  early mythological narrative in which lesser deities are the agencies of sensory activity in humans bears some structural similarity to  Descartes’ account in his Treatise of Man and  Passions of the Soul of the animal spirits which flowing  from the pineal gland control the activity of sensation, imagination, as well as bodily movements. In the Upaniṣads, this  mythological account gives way to a philosophically nuanced view of  sensory activity as the direct result of contact between the self and the world. According to the Upaniṣadic understanding of  perception, the senses are created from the substance of  sense-objects and with the specific purpose of revealing the latter.  The revealing agent, however, is the self (see Kaṭha  Upaniṣad, I, iii, 4).