Can the Police Require a Brain Scan?

Can the government compel an individual to undergo brain-based memory detection tests? Is there a constitutional right to keep memories or thoughts private? Would such methods implicate the Fourth Amendment right against unreasonable search and seizure or the Fifth Amendment protection against self-incrimination? Professor Emily Murphy explores the concept of cognitive liberty and bodily integrity when it comes to brain-based memory detection and its potential uses in the criminal justice system.



Emily Murphy is a professor at UC Hastings Law School. Her research focuses on the intersection of neuroscience, behavioral science, and law.

Can the Police Require a Brain Scan?  Brief Transcript

An Interview with Neuroscience Law Expert  – Professor Emily Murphy


Is there a constitutional right to keep unexpressed thoughts private?  

Joel Cohen (Host): Does the government have a right to, assuming they can, do they have a right to open the curtains and look deep into your brain?

Prof. Emily Murphy: These are questions that start to fall under the rubric of what people are calling “cognitive liberty.” It raises questions of Fourth Amendment search and seizure. So does the Fourth Amendment right to be “secure in our papers houses and effects” extend to the right to have our unexpressed thoughts remain private? It butts up against the Fifth amendment right against self-incrimination under which we are not compelled to testify against our own interests. Are unexpressed thoughts or automatic thoughts detected by brain imaging technology with no outward testimonial sign, are they testimonial for purposes of the Fifth Amendment? We don't really know, but I think the Fourth and Fifth amendment rights, whether we have particular rights to cognitive liberty when if in the hypothetical situation brain imaging technology could extract the truth, the truth as it was undisputed and important to what happened, I don't know how that would come out.


Is compelled brain imaging comparable to a compelled blood draw? 

Host: It seems like the Fifth Amendment right to not incriminate would at least be triggered if you were I suppose the suspect or the target of an investigation? There, I think it jumps out to me, without having done much research, that you might be able to claim that right.

Prof. Murphy:  Yes, although when it showed up in the Supreme Court case of Schmerber where your blood alcohol content is not considered testimonial evidence such that your Fifth Amendment right against testifying against yourself is not triggered by a compelled blood draw in order to preserve evidence of your blood alcohol content. So are our thoughts covered by the Fifth Amendment? I mean it seems to be a much closer right because it's testimonial things we say or write or express. It seems much much closer to our thoughts than our blood alcohol content, but blood alcohol content can be incredibly incriminating, right? That could be the slam dunk case for a DUI. So where does that line of bodily integrity and cognitive liberty lie especially in the face of public safety? 


Forced Bran Scans and the Ticking Time Bomb Terrorist 

Prof. Murphy: This has come up as a hypothetical in cases of terrorism or the the ticking bomb where we have a certain amount of time in order to prevent a mass tragedy. Do we then, does the government then have an overwhelming interest in invading the mental privacy of someone who has said I'm not saying anything.

Host:  Interesting so you're envisioning a situation where perhaps it's not for proving guilt or innocence but, you know, if we could use that this technology to know which train car has the dangerous substance and you could just show the images and detect it in the brain, does the government have the power to force that? 


A Technical Limit to Compelled Memory Detection

Prof. Murphy: Yeah, I mean right now these questions are still hypothetical and they may remain so for some time but you know at some I would not be surprised at some point to see this type of question being brought forth to a court. But even if they had that right, it is technologically infeasible to do it without a pretty cooperative subject. There are differences between the types of technologies that are used to look at brain imaging, but the more powerful one, in my opinion, of functional magnetic resonance imaging requires extremely expensive equipment that cannot be used with anybody who has any kind of ferrous or magnetic metal in their body, so eliminates some proportion of people. And what would eliminate anybody who didn't want to cooperate currently requires people to hold incredibly still in a loud clanging machine for a long period of time. If anyone has ever had an MRI, you are rolled into a fairly small tube and have to hold very very still. This is particularly true for functional brain imaging. There is now an understanding that functional brain imaging research can be distorted by slight head movements, by swallowing, by thinking about different things, by moving off task. It would require a highly compliant subject to be able to do fMRI with our current technology. 

Host: So a hostile witness would have to do little more than twitch their head a little bit to game the system? 

Prof. Murphy: For now, quite right, yeah, at least of the technology currently exists.