Module 17

Brain fingerprinting is a technology that involves reading brain waves to determine whether a suspect has the record of a particular crime stored in his mind. The principle behind brain fingerprinting is quite simple: Memory centers of the human brain, when presented with a familiar stimulus, respond with a distinct change in electrical brain activity, a P300 wave or MERMER (memory and encoding related multifaceted electroencephalographic response). This brain wave response is elicited when the brain processes information it recognizes. So, when we present details of a crime that only the perpetrator of the crime would know, a MERMER is emitted by the brain of the perpetrator but it is not emitted by the brain of a falsely accused innocent person.

What is the scientific procedure involved in brain fingerprinting?
A headband containing sensors is placed on the suspect's head.

Above, Oklahoma death row inmate Jimmie Ray Slaughter undergoes "brain fingerprinting."

The sensors measure brain waves in the frontal, central, and parietal areas of the brain. Then a series of pictures or words is flashed on a video monitor. Each stimulus is shown for just a fraction of a second. The Subject's electrical brain responses are stored on a computer disk and analyzed.

The stimuli are of three types:

(1) Targets. These are stimuli given to the Subject just before they take the test because we have to make sure that the subject knows these stimuli. These "targets" are details about the crime that we tell the subject and we are sure that he knows these targets. (He may also have learned about these details from another source as well.) The purpose of the targets is to get a brain response that indicates "yes," the subject knows this and recognizes it so these targets serve as a control for a positive response.

When given the targets to learn, the subject is told they will flash briefly on the screen and he has to be able to recognize them when they come up. So he has to make sure he knows them. When the subject reads the target during the test, his brain should fire a P300 response. The x-axis is "time" in milliseconds (msec) and the y-axis is voltage in microvolts(mv).

Figure 1. The red line is the P300 Response Emitted to Targets

(2) The second kind of stimuli is called irrelevants. The stimuli are words or pictures that are irrelevant to the person: They are stimuli that have nothing to do with the crime. They are things he does not know or will not find significant. They provide a standard for information the subject does not know and, therefore, they serve as control stimuli for the no P300 response waves. This is represented by the green line below:

Figure 2. The Non-P300 Brain Wave Response to Irrelevant Information (green)

(3) The third type is called probes. These are the experimental items: In a situation where a crime has been committed, they are items that only the individual who committed the crime would know. The person would have no way of knowing the items if he was not at the scene of the crime. We can see if the suspect's brain has these details stored in it.

Each time a stimulus appears, the Subject must click the mouse. He must left click when presented with targets, the words he memorized. He is supposed to right click for all other stimuli. This keeps the Subject on task so we can be sure he is attending to the stimuli.

Figure 3 below shows the brain waves for suspect A.

Figure 3. "Information Absent"

In Figure 4 below, we see the brain waves for suspect B.

Figure 4. "Information Present"

We now turn to two specific true cases where brain fingerprinting technology has been used. The first is the Harrington case; the second is the Anhydrous Ammonia case.

Case 1: Harrington Case | Case 2: The Anhydrous Ammonia Case