A scientific approach to silent consciousness

INTRODUCTION All mammals show the physiological correlates of waking, dreaming and deep sleep. Many contemplative traditions propose a fourth state of consciousness, “silent consciousness,” defined as consciousness without reportable contents. For example, the Mandukya Upanishad, one of the root texts of Vedanta philosophy, explicitly claims a fourth state of “consciousness without content.” (Sharma, 1997) The classical summary of yogic thought, Patanjali’s Yoga Sutras, recommends “Let there be soundless repetition of (the inner mantra) OM and meditation thereon.” (Feuerstein, 1989). The classical texts of Zen Buddhism also cite consciousness without reportable contents many times (Reps and Senzaki, 1998; Hori, 2000). About a fifth of the world population is Hindu or Buddhist. “Silent consciousness” may sound paradoxical to Western ears, but such reports are widespread in Asian, Western, Middle Eastern, and shamanic traditions. While contemplative practices are very diverse, “inner silence” is often taken to be a goal. One common rationale is that silent consciousness exists continuously in the background of the three standard states, and that contemplative practices aim to make that background more easily accessible to the practitioner. Thus, various practice aim to “uncover” what already exists in the mind. The resulting access to silent consciousness is often interpreted in ontological terms as a direct knowledge of metaphysical reality. However, such claims are not considered in this article, which is focused on empirical evidence. Benson (1984) reported such experiences in naive subjects who mentally repeated an arbitrary mantra, the word “one.” Follow-up studies show a host of non-voluntary physiological effects, including changes in stressrelated gene expression, alteration in O2/CO2 exchange, and changes in energy metabolism, insulin secretion and inflammatory pathways (Dusek et al., 2008; Bhasin et al., 2013). These findings support Benson’s proposal that mantra meditation evokes a neurohormonal “relaxation response,” able to counteract the HPA stress reaction homeostatically. The exact relationship between silent consciousness and the relaxation response is not known. An empirical probe for silent consciousness is therefore described below.