This CBC news story describes a brain surgery simulator that doctors in Halifax, Canada use for practice before cutting open real patients. It simulates not a generic human brain, but the brain of the specific patient:
First, patient data from functional magnetic resonance imaging (fMRI) is rendered into a 3-D, high-resolution model of an individual's brain. After the model is loaded into the system, doctors can touch and manipulate tumors and other virtual objects on screens in real time using a physical instrument resembling a scalpel. The instrument has six degrees of freedom and re-creates the force-feedback of the real tool and the varying resistance of tissue in brain regions with differing toughness. Meanwhile, photo-realistic on-screen imagery shows the simulated surgery, including bleeding and pulsing gray matter.
Link via Popular Science