The Neurological Fifth Amendment: Reassessing Self-Incrimination in the Age of Brain-Computer Interfaces
The Fifth Amendment’s protection against self-incrimination stands as one of the most profound constitutional barriers against government intrusion, protecting the sanctity of human thought from compelled discourse. This constitutional safeguard was established to prevent the state from forcing a defendant into a confession. However, what occurs when the government is able to access the mind directly, superseding speech entirely?
The once-hypothetical concept of mind-reading is rapidly becoming scientifically feasible due to the development of Brain-Computer Interfaces (BCIs). Although this technology offers revolutionary breakthroughs in human augmentation and medicine, it also poses a formidable threat to established constitutional protections. For over half a century, American jurisprudence, guided by the Supreme Court's decision in Schmerber v. California, has distinguished between testimonial evidence (the contents in one’s mind, protected under the Fifth Amendment) and physical evidence (bodily characteristics like fingerprints or blood, not protected under Fifth Amendment). Today, this framework is in grave danger of becoming obsolete. Neural data, the fundamental basis of cognition and volition, defies this simplistic categorization. It is not merely a physical attribute; neural data is a direct reflection of the mental processes that the Fifth Amendment was enacted to protect. Compelling an individual to undergo a BCI scan is constitutionally tantamount to coercing a confession. To preserve the right against self-incrimination in this era of neurotechnology, the law must recognize that data obtained from the human brain is intrinsically testimonial and thus beyond the government’s authority to compel.
In Schmerber v. California (1966), the Supreme Court established a doctrinal divide between testimonial and physical evidence that has shaped self-incrimination law for decades. The Court determined that the Fifth Amendment was not violated by compelling a defendant to provide a blood sample which constitutes physical, not testimonial, evidence. The Court ruled that the privilege of the Fifth Amendment only protects an accused from being forced to produce evidence of a “testimonial or communicative nature.” [1] This framework, developed long before neurotechnology, is currently collapsing under scrutiny. BCIs do not merely record neural activity, they also decipher cognitive information. Unlike static biological identifiers, they capture the brain's dynamic electrical patterns,which encode the very memories, intentions, and thoughts protected by the Fifth Amendment. Classifying neural data as "physical evidence” misrepresents its fundamental nature and invites serious constitutional risks. A compelled BCI scan is analogous to forcing someone to transcribe their own thoughts and emotions. Therefore, this practice would render the Schmerber distinction obsolete. Neural data is both physical and emotional, a duality that necessitates a new constitutional approach as it violates the existing dichotomy dictating the right against self-incrimination.
Legal precedent for the protection of neurological data comes from the Fourth Amendment, which protects against unreasonable searches and seizures, reinforcing its constitutional protection. The Supreme Court consistently acknowledges that constitutional interpretation must evolve in tandem with evolving technologies. In Kyllo v. United States (2001), the Supreme Court determined that employing a thermal imager to detect heat patterns in the interior of a home constituted a search. This was due to the fact that the “sense-enhancing” technology could reveal “details of a private home that would have previously been unknowable without physical intrusion.” [2] A BCI scan functions on the same principle but targets an even more personal domain. It is an invasive endeavor to penetrate the depths of an individual’s consciousness, uncovering information otherwise inaccessible. As thermal signatures of a home necessitate constitutional protection from technological intrusion, neural signatures that constitute thought demand an even stronger safeguard.
Similarly, in Carpenter v. United States (2018), the Supreme Court determined that the government must obtain a warrant to examine a person’s historical cell-cite location data. The rationale behind this is that such records provide an “intimate window” into “privacies of life,” revealing people’s movements, associations, and habits. [3] Because monitoring an individual’s physical location requires judicial authorization, utilizing a technology that directly accesses an individual's thoughts, memories, and intentions should be similarly regulated as it invades an even more intimate domain. The Fourth Amendment decisions in both Kyllo and Carpenter delineate a definitive principle: in order to protect the private spheres of human existence, constitutional safeguards must evolve as technology becomes more intrusive. The mind represents the most sacred frontier of privacy, and the information it harbors needs the strongest constitutional safeguards against involuntary governmental intrusion.
The constitutional threat presented by BCIs is not speculative; it is grounded in current neuroscientific evidence. The argument that neural data is fundamentally testimonial is substantiated by recent studies, which have demonstrated the capability of BCIs to access and interpret the contents of the mind. Researchers have successfully decoded imagined speech from brain activity, effectively translating thoughts into text without physical utterance. This ability extends beyond lie detection and into the realm of direct mind-reading, accessing the very communicative acts that the Fifth Amendment safeguards. Additionally, a “guilty knowledge test” was recently developed that is capable of detecting a subject’s recognition of crime-specific information by measuring neural responses, thereby compelling the individual to disclose their knowledge. [4]
In addition to challenging existing legal boundaries, these developments in neurotechnology also shape juries' perceptions of neuroscience. The temptation to use BCI’s for invasive purposes is worsened by the “CSI effect,” which fosters a desire for technological certainty in the courtroom due to increasing public fascination with forensic science. [5] This influence has the potential to evolve into a neuroscience “CSI effect,” in which juries and judges develop an expectation of brain-based evidence, forcing the legal system to confront neurotechnology before a constitutional framework is in place. The age of neurotechnology is no longer a distant hypothetical; it is a tangible reality that tests the boundaries of the American legal system.
The existing Fifth Amendment doctrine, grounded in Schmerber v. California, cannot adequately account for neural data. The solution is not to invent a new constitutional right entirely, but rather to properly apply the existing privilege to the classification of neural data. Methods that can reveal an individual’s private thoughts, memories, or intentions should be deemed testimonial. The legal standard should hold that any compelled government extraction of neural information that reveals the subjective contents of an individual’s consciousness is a violation of the right against self-incrimination. This approach maintains the fundamental principle of the Fifth Amendment: the state is prohibited from compelling an individual to become the means of their own conviction by exposing the contents of their mind.
The once-clear line between physical and testimonial evidence has been blurred by new technologies that can read the human mind. The continued application of this antiquated binary to neural data risks the erosion of one of the most fundamental protections in the Bill of Rights. Our constitutional law must evolve to safeguard the mind, which represents the final and most important refuge of individual autonomy and privacy. Regardless of the technological means of extraction, the courts and legislature must take a proactive approach to guarantee that the contents of human consciousness are beyond the government’s ability to compel. The Fifth Amendment must be employed to protect not only our words but also the thoughts that motivate them.
Edited by Sarah Guttman
Endnotes
[1] Schmerber v. California, 384 U.S. 757 (1966).
[2] Kyllo v. United States, 533 U.S. 27 (2001).
[3] Carpenter v. United States, 585 U.S. 136 (2018).
[4] Christian Herff and Tonio Ball, “Decoding Speech from Brain Signals,” Frontiers in Neuroscience 16:908678 (2022).
[5] Francis X. Shen, “Neurotechnological Decoding and the Law,” SSRN (2017).