by Zachary Shapiro
While there is considerable enthusiasm for incorporating neuroimaging technologies in the courtroom, it must be balanced with an understanding of the very real limitations of available neuroimaging data at present. I will focus on the use and study of one such technology, functional magnetic resonance imaging (fMRI), to explore some of these limitations.
Many fMRI studies have small participant groups, which means that the data may lack the statistical power needed to allow generalization of results. There are several reasons for this. Even though fMRI machines have decreased in price, they are still expensive, and since the fMRI machine is very large, it requires specialized space in order to function. Conducting a scan is also quite time consuming. For these reasons many neuroimaging experiments utilize subject groups that were not selected due to concerns related to statistical power, but rather due to practical concerns such as how much scanning time, space, and money has been allocated to the experiment.
Furthermore, the size and technology of fMRI machines necessitates running experiments in a very particular way that could affect the outcomes. Because participants are required to lie still in a small space, there is a limit to what tasks and activities they can be expected to perform. It is impossible to assess the effects that lying still in a giant scanner may have on normal behavior, meaning that fMRI machines may not accurately tell us about the human brain under normal conditions. Experimental design is especially problematic if we want to bring fMRI experiments into a criminal legal context, as it is currently impossible to design an experiment that accurately recreates the dynamic conditions of stress that are likely to occur during the undertaking of a criminal action.
A further issue has been the limited available data concerning what “normal” brain activity looks like. This is important if neuroimages are to carry weight in a criminal law setting, as data concerning an individual’s mindset is of little value without a “normal” data set with which to compare. Such comparisons will be essential for defense attorneys and prosecutors, who are interested in evidence that demonstrates that an individual does or does not fall outside the norms of everyday behavior.
In order to establish what is normal, researchers use fMRI to measure brain activation from a control group. These results are added together and then averaged. This averaged data is presented as normal, even though no single individual tested may actually conform to the average of the group. This is problematic, as research has shown that variance in brain imaging and neuroanatomy may be the norm, rather than the exception. One study found that brain anatomy can vary significantly between different individuals, especially in cortical areas. This could mean that any comparison to group data is inappropriate, as the relevance would be limited if every individual is expected to present unique variations. Variations are compounded by the small control group size discussed above, as any variance in an individual could disproportionately affect the outcome of the study.
This presents a complication to the legal admissibility of fMRI studies. For any study to be admissible, it must be clear that the data is relevant to the individual. If no two people are expected to have the same brain scans, this would cast doubt on any attorney who tried to use fMRI studies to show that an individual falls outside of the “normal” brain activity map. In fact, an “ideal fit” may never exist, as the data results from averages of trials, rather than any individual image showing real world, non-analyzed brain function.
The general lack of normative data highlights the total absence of group-specific neuroimaging data. There have been few comprehensive studies that investigate the presence of differences in fMRIs across gender, race, age, handedness, and other factors that could contribute to expected variations. For example, a recent study found that similar behavioral performance can correspond to significantly different patterns of brain activation in males and females, a non-surprising finding that highlights the limits of our current understanding of brain function.
These are just a few of the limitations of currently available studies using fMRI, and I am in the midst of a yearlong project to better study the limitations of neuroimaging from a legal perspective. In a future post, I will discuss how the limitations of fMRI present significant problems for the evidentiary admissibility of fMRI studies in a courtroom.
 Stephan Hamann & Turhan Canli, Individual Differences in Emotion Processing, 14 CURRENT OPINION IN NEUROBIOLOGY 233 (2004)
 Gabriele Lohmann & D. Yves von Cramon, Automatic Labeling of the Human Cortical Surface Using Sulcal Basins, 4 MED. IMAGE ANALYSIS 179, 179 (2000)
 Emily C. Bell et al., Males and Females Differ in Brain Activation During Cognitive Tasks, 30 NEUROIMAGE 529, 529 (2006)