Memory is the retention of [images of] sense objects that have been experienced
The Yoga Sutras - Chapter 1, Sutra #11
Anubhuta-visayasampramosah smrtih (in Sanskrit)
Let us continue our study of the Yoga Sutras.
Five types of “vrttis” or changing states of mind such as right knowledge, error, imagination, sleep, and memory, constantly absorb the pure consciousness or our soul away from its pure nature. Today we will focus on the fifth vrtti - memory (“smrtih”).
Memories are generated from and thus depend on the other types of vrttis, they are the retention of objects of experience. Every object that has ever been experienced, forms an imprint in the mind. The mind forms an impression of an object through the senses. Even if an active image of this object is no longer of interest to the mind, it does not disappear, it just becomes inactive, but is retained. In this way, memories are the reactivation of the imprints of sense objects that one has experienced and recognized in the past.
According to the Yoga Sutras, all five vrttis are either detrimental or nondetrimental, beneficial to the goal of yoga. Detrimental vrttis must be restrained and stilled by the yoga practice and dispassion, which we will learn more about in the next Yoga Sutra.