Do sheep with human brains dream of origami chickens?

From the "nightmarish future" department, this AP story on MSNBC about stem cell experiments creating human tissue inside of other species.

On a farm about six miles outside this gambling town, Jason Chamberlain looks over a flock of about 50 smelly sheep, many of them possessing partially human livers, hearts, brains and other organs.

The story uses this research farm as a touchstone to consider the current science of animal-human chimeras. As for the sheep themselves: "Most of the adult sheep in his experiment contain about 10 percent human liver cells, though a few have as much as 40 percent."

Particularly worrisome to some scientists are the nightmare scenarios that could arise from the mixing of brain cells: What if a human mind somehow got trapped inside a sheeps head?
The "idea that human neuronal cells might participate in 'higher order' brain functions in a nonhuman animal, however unlikely that may be, raises concerns that need to be considered," the academies report warned.

This is my favorite part:

In January, an informal ethics committee at Stanford University endorsed a proposal to create mice with brains nearly completely made of human brain cells. Stem cell scientist Irving Weissman said his experiment could provide unparalleled insight into how the human brain develops and how degenerative brain diseases like Parkinsons progress.
Stanford law professor Hank Greely, who chaired the ethics committee, said the board was satisfied that the size and shape of the mouse brain would prevent the human cells from creating any traits of humanity. Just in case, Greely said, the committee recommended closely monitoring the mices behavior and immediately killing any that display human-like behavior.

Just for the record, there is little reason to think that human neurons themselves have much to do with the human-like aspects of our brains. Although human neurons may bear some lineage-specific adaptations (one might suppose selective pressures to make them more capable of transmitting messages without interference across a very large brain structure, for example), most of the characteristics we know and love come from the structure of our brains rather than the tissue itself. On the other hand, what if some of those structural genes influenced the form of the mouse-sized brain? What if they were capable of making a rudimentary circuit that in a human would be related to social cognition? Could we see more social mice? Mouse the toolmaker? We're probably not headed for the rats of NIMH, but if we were, would it be right to kill them off? I wonder about these "ethics committees," especially the "informal" kind.