The exploration of the mind is one of the main concerns in Buddhist thought, beginning in early Buddhism, sectarian Buddhism, and in Mahāyāna Buddhism. There are many differences in the theory of mind held by the sectarian Buddhist schools as compared to that of the Mahāyāna Mind-only School. These differences include the following questions: 1. Is there one consciousness, or many? 2. If there are many consciousnesses, can they arise at the same time? 3. Are there mental concomitants outside of the mind? Because different Buddhist schools cite passages in early Buddhist texts to support their respective interpretations, and there is no clear definition of the mind and mental concomitants in early Buddhist scriptures, it is thus impossible to resolve these questions on the basis of Buddhist canonical texts. Therefore the present article is an attempt to use modern cognitive psychology in the discussion of these questions. Among sectarian Buddhist schools, Sarvāstivāda holds that the mind is one with the consciousness and that there are mental concomitants outside of the mind. The Sautrāntikas, as represented in the Tattvasiddhi, believe that there are six consciousnesses, which cannot arise at the same time, and that there are no mental concomitants outside of the mind since so-called mental concomitants are nothing but different states of mind. According to the Mind-only School, there are eight consciousnesses, which can arise simultaneously, and mental concomitants outside of the mind can arise with the mind. According to research in Cognitive Psychology, the cerebrum processes each type of sensory data in a different region, and is able to process different sensory data simultaneously rather than dealing with data from one sense organ at a time. The neural network in the brain is like a large-scale parallel computer, which contains numerous processing units closely connected to deal with information simultaneously. Thus, the answer to the question whether different consciousnesses arise simultaneously is affirmative. Additionally, based on the research in contemporary Neuroscience, there are separate systems responsible for emotions and sleep in the cerebrum. Emotions and sleep are discussed as mental concomitants in Buddhism. Because emotions and sleep are functions different from the cognition arisen through sense organs responding to the external world, and they can arise at the same time. Therefore, the assertion about the mind made by the Mind-only school is consistent with the perspective of modern psychology.
