Vrittis (Mental Modifications)
Vrittis are the continuous modifications, fluctuations, and movements of the mind-field — the ever-changing content of consciousness that yoga practice aims to still.
Vritti (from the root 'vrit' — to turn, to revolve) describes the turning or spinning of the mind-field: the constant arising and passing of thoughts, perceptions, emotions, memories, and imaginings that constitute ordinary mental life. Patanjali identifies five types (1.6): Pramana (correct cognition), Viparyaya (error), Vikalpa (imagination), Nidra (sleep), and Smriti (memory). He further classifies all five as either Klishta (afflicted — reinforcing suffering) or Aklishta (non-afflicted — not reinforcing suffering). The goal of yoga is not to destroy the mind or suppress all thought permanently but to achieve the state of Nirodha — restraint or stilling of vrittis — in which consciousness can rest in its own nature without the distortion of constant mental movement. Between thoughts, in the space of Nirodha, the natural state of consciousness is revealed.
The modifications of the mind are five in kind, and either painful or non-painful.
Psychologist Matthew Killingsworth's experience-sampling research (2010, Science) documented that the human mind wanders from its present activity 46.9% of the time and that this mind-wandering is associated with unhappiness — confirming Patanjali's identification of the vrittis' constant movement as a primary source of human suffering.
Yoga Sutras of Patanjali