I wonder why it's a mix of human & mouse. The novel aspect seems to be that they're lab grown/multiplied, rather than 'freshly donated'? Rat brains have been us

I wonder why it's a mix of human & mouse. The novel aspect seems to be that they're lab grown/multiplied, rather than 'freshly donated'? Rat brains have been used for robot cars & games (like pong in TFA) for well over a decade.