In jnana mudra, the thumb symbolizes Brahman, or the Supreme Reality. The index finger symbolizes the individual self, the inner reality, or the jiva. The connection of the thumb and the index finger means the union of the supreme and inner reality. The remaining three fingers represent the three qualities, or gunas, of nature: sattva, raja and tamas ("balance, action and inaction").
Jnana mudra regulates the flow of prana in the fingers. Normally the prana goes out through the hands, feet or the head. By connecting the thumb and index finger, some of the flow is redirected, bringing the energy inward. This calms the mind, allowing yogis to sit in meditation for long periods of time.
It is believed that practicing jnana mudra helps with insomnia, improves creativity, increases mental peace and spirituality, and stabilizes the mind. It is also benefitial for the memory and regulates the flow of air in the body.