The concept of whole brain emulation has been widely discussed in futurism ( Martin 1971 ; Moravec 1988 ; Hanson 1994b , 2008b ; Shulman 2010 ; Alstott 2013 ; Eth et al. 2013 ; Bostrom 2014 ) and in science fiction ( Clarke 1956 ; Egan 1994 ; Brin 2002 ; Vinge 2003 ; Stross 2006 ) for many decades. Sometimes emulations are called “uploads.” Let me now try to be clearer about the technological assumptions whose consequences I seek to explore. When I refer to a “brain” here, I refer not just to neurons in a head, but also to other supporting cells in the head, and to neurons and key closely connected systems elsewhere in the human body, such as the systems that manage hormones. Using that terminology, I assume, following a wellestablished consensus in the cognitive and brain sciences, that “the mind is just the brain” ( Bermúdez 2010 ). That is, what the brain fundamentally does is to take input signals from eyes, ears, skin, etc., and after a short delay produces both internal state changes and output signals to control muscles, hormone levels, and other body changes. The brain does not just happen to transform input signals into state changes and output signals; this transformation is the primary function of the brain, both to us and to the evolutionary processes that designed brains. The brain is designed to make this signal processing robust and efficient. Because of this, we expect the physical variables (technically, “degrees of freedom”) within the brain that encode signals and signal-relevant states, which transform these signals and states, and which transmit them elsewhere, to be overall rather physically isolated and disconnected from the other far more numerous unrelated physical degrees of freedom and processes in the brain. That is, changes in other aspects of the brain only rarely influence key brain parts that encode mental states and signals. We have seen this disconnection in ears and eyes, and it has allowed us to create useful artificial ears and eyes, which allow the once-deaf to hear and the once-blind to see. We expect the same to apply to artificial brains more generally. In addition, it appears that most brain signals are of the form of neuron spikes, which are especially identifiable and disconnected from other physical variables.
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