BOLD Signal
Definition
Blood-oxygen-level-dependent signal; the measure in fMRI that captures changes in the ratio of oxyhaemoglobin to deoxyhaemoglobin as a proxy for neural activity. Forms the raw data for fMRI-based deception detection.
- Full name
- Blood-oxygen-level-dependent signal
- Measured by
- Functional MRI (fMRI)
- Physiological basis
- Ratio of oxyhaemoglobin to deoxyhaemoglobin
- Forensic application
- Raw data for fMRI-based deception detection
Common questions
Does the BOLD signal directly measure neural activity?+
No, it is an indirect proxy. It reflects local blood flow and oxygenation changes that follow neural activity by a few seconds, so fMRI infers activity from this haemodynamic response rather than recording electrical or metabolic activity in neurons directly.
Why is BOLD-based lie detection controversial in court?+
Courts have generally excluded it under admissibility standards because the link between a BOLD pattern and the specific claim of deception, as opposed to general cognitive load, anxiety, or other mental states, has not been established with the reliability required for legal proof.
Related terms
- AI Act Article 5(1)(F)
- The EU AI Act prohibition on AI systems that infer emotions, intentions, or characteristics from biometric data in law-enforcement and related contexts....
- BEOS / Brain Fingerprinting
- Lawrence Farwell's EEG-based method using the P300 event-related potential to detect concealed knowledge of crime-relevant items. Addressed by the Indian Supreme Court...
- Cephos Corporation
- A US company that offered commercial fMRI lie-detection services from approximately 2006. Its technique was excluded from evidence in US v. Semrau...
- Daubert Standard
- The US federal evidentiary standard (Daubert v. Merrell Dow Pharmaceuticals, 1993) requiring that expert testimony be based on scientifically valid methods with...
- Ecological Validity
- The degree to which a measurement or test procedure produces results that generalise from the controlled laboratory context to the real-world condition...
- Greely-Illes Critique (2007)
- Henry Greely and Judy Illes's 2007 analysis in the American Journal of Law and Medicine identifying five categories of problem with fMRI...
- No Lie MRI
- A San Diego-based company offering fMRI lie-detection services during the same period as Cephos. No court has admitted No Lie MRI evidence...
- P300 ERP
- A positive-going scalp electrical potential peaking approximately 300 ms after presentation of a significant, infrequent, or unexpected stimulus. Used in EEG-based concealed-information...
- US V. Semrau (2010/2012)
- The US district court Daubert hearing (2010) and Sixth Circuit affirmance (2012) excluding Cephos fMRI lie-detection evidence on grounds of insufficient testability,...