A few days ago a woman in India was convicted of murdering her fiance. A prime piece of evidence was a BEOS, Brain Electrical Oscillation Test, of her own brain.
It works like this: Prosecutors read aloud to the suspect a description of the murder, all couched in first person ("I bought arsenic," etc.) while she had electrodes attached to her head that showed which areas of the brain lit up at what point. She was also read neutral statements ("The sky is blue.") The "pattern" of electrical responses in her brain supposedly showed that she had "experiential knowledge" of the murder, rather than merely having heard about it.
This has, understandably, set off a storm of controversy, in and out of India. The specific technology is new, although it builds on a large body of brain-study literature (some of which I refer to in my current ASIMOV'S story, "The Erdmann Nexus.") But this is a new application of brain studies, and it has ethicists shuddering. Proponents point out that the suspect agreed to the test, but the press has speculated that she may have done so to avoid what she thought might be a brutal police interrogation if she refused.
In the United States, not even polygraph results are admissible in court. We also have the Fifth Amendment providing protection against self-incrimination, presumably including by your own brain. This is a draconian version of Big Brother is Watching You:
His Honor the Judge is Watching You. With your help.