The nested hierarchy of consciousness: A neurobiological solution to the problem of mental unity

In spite of a resurgence in interest regarding the nature of consciousness, some puzzling aspects of the relationship between the mind and the brain r emain unexplained, One particularly mysterious feature of consciousness is known in philosophy as the 'grain problem': how does the divisible and hete rogeneous brain produce the subjectively unified and seamless mind? Some mo dels of the brain-mind relationship, such as the one offered by Sperry, ass ume that the brain functions hierarchically like a pyramid, with consciousn ess mysteriously 'emerging' unified at the summit of the hierarchy. This mo del fails to account for the manner in which both lower and higher hierarch ical levels of the brain contribute to consciousness. In this paper, I prop ose an alternative model of the brain-mind relationship in which the brain functions, like all living things, as a nested hierarchy. While the specifi c neurophysiological mechanisms behind cerebral integration require further elucidation, the difficult philosophical problem of the difference between the grain of the brain and the mind has a neurobiological explanation.