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Abstract
[...]the promise of brain surrogates is such that abandoning them seems itself unethical, given the vast amount of human suffering caused by neurological and psychiatric disorders, and given that most therapies for these diseases developed in animal models fail to work in people. An adult human brain measures roughly 1,350 cubic centimetres, and is made up of 86 billion neurons and a similar number of non-neuronal cells. [...]brain organoids have received sensory input only in primitive form, and connections from other brain regions are limited. [...]with outbound connections severed, isolated tissues can't communicate with other regions of the brain, or generate motor outputs. [...]the possibility of consciousness or other higher-order perceptive properties emerging seems extremely remote. Gray Matters: Topics at the Intersection of Neuroscience, Ethics, and Society (Presidential Commission for the Study of Bioethical Issues, 2015); available at https://go.nature. com/2vdqx5j A full list of author affiliations accompanies this Comment online (see go.nature.com/2hz3ogu).