Re: Oh, that smells. (Neuroscientist spins brain scans.)
In the brain and behavior class I taught last semester, the course project involved the question on whether or not brain scans are sufficient in criminal sentencing if the person's orbitofrontal cortex shows a pattern of activity that is common in psychopaths. It was interesting to read the responses of various students. Some brought up the argument that it is the crime itself that matters since many people with orbitofrontal activity similar to that of a psychopath may not commit criminal offenses and are probably not psychopaths. It's a common argument because most people are still not used to thinking of a non-criminal psychopath.
In any case, I agree with AI that one brain scan should not be the sole arbiter of a diagnosis. However it does give us a hints on whether or not the person is more likely to exhibit psychopathic tendencies (criminal or not) compared with someone with a different brain activity pattern. fMRI measures cerebral blood flow and in both psychopaths and schizophrenics there is hyperfunction in mesolimbic dopamine and hypofunction in orbitofrontal cortex. There are many differences between the two, however, that involves additional analysis that gets into spatial and temporal activity that fMRI is best at giving the spatial part.
Sometimes evoked electrical potential, EEG which gives good temporal data and fMRI can both be used when assessing the relationship between an individual's brain activity and particular disorders. For example, the p3 or P300 is the activity of a population of cortical cells 300 milliseconds after presentation of non-neutral stimulus against background noise stimuli. If I am remembering this correctly, alcoholics and their non-alcoholic offspring show reduced electrical potential at p300. This in turn is used with fMRI to help in selection of possible candidate genes that may be involved. From there the genetic studies can be done. Other things may alter p300 activity which is why researchers use it as either as a springboard for genetic studies or in conjunction with genetic studies. So the fMRI or EEG alone are marker but often not used alone except in experimental studies as opposed to say diagnosis. Also, depending on the stimulus you can actually have increased or decreased activity in individuals whether they are psychopaths or not so it depends on exactly what is looked at in conjunction with other tests. Devil in the detail and the details are often missing in what is made public. For example, fMRI data from one study shows decreased amygdala function in those diagnosed with anti-social disorder and it is deemed a reliable marker. I've also seen data for a subset with that diagnosis that actually shows an increased functioning. Maybe the study was designed badly or something went wrong. In either case, one always need to look at multiple data sets from different types of studies. A former student of mine is now looking at p300 and fMRI in a genetics lab for antisocial disorder so it will be interesting to see his results.
Even with illnesses or injury, brain scans are used in conjunction with other tests; behavioral, biochemical, basic observation ( like knowing that a head injury occurred) etc. I am not aware of biochemical tests for psychopathy, though monoamine differences exists (serotonin, epinephrine, nor-epinephrine and dopamine). There are gene variants that are being looked at as potential markers but not yet accepted as definitive markers. This is because these things usually involve multiple genes in which the contribution from any one gene toward a given disorder is very small. So I think brain scan results just help to narrow down what may be the most likely situation compared to what is considered normal, as well as give an indication of other things to look at if it was not already done. This is when psychometric tests, which include PCL-R among others, behavioral observations, etc. comes into play. Hopefully soon genetic tests.
In essence, brain scans are useful for determining how much an individual's brain activity differ from the estimated population's average score in order to explain the likely neurological basis of the results gleaned from the other assessments. So no, it shouldn't be the only test. I am guessing there is actually a range of scores based on averages from multiple participants, which in turn is used to estimate population norms. So, if they then scan an individual whose pattern of brain activity scores fall above or below the average range of scores by a given amount (often 2 or more standard deviations from the average) then the determination is that the individual is an outlier, ie different from the normal population. That score is then compared to the average range of scores determined from multiple individuals diagnosed as psychopaths. If it falls within the average range of scores for psychopaths, then most likely the person is one but I would say that the inclusion of other data (behavior, psychometric tests) should be included in a definitive diagnosis. If you just want to predict the likelihood, not definitive that an individual may be psychopathic, then sure the brain scan alone is one of any given number of predictors but not the sole determinant. I am interested in knowing how strong a predictor of psychopathy it is. ( percent contribution it provides) and will have to look it up. That gets into all the statistical analysis and such.
It maybe that there is a push to focus on scans because for now, it may be easier to discount the result when it is the only tool used and most have no idea how strong a predictor it is. For example, polygraphs were used extensively for lie detection. Anectdotally people would talk about how easy it was to beat. In the late 1990s their accuracy was looked at in meta analysis of many tests over the years, it was around 60 percent or so. Better than chance, yes, definitive no. There have since been new improved lie detector tests, one of which includes fMRI with a stated 90% accuracy. Interesting that this particular lie detector has been rejected by criminal courts as a tool. hmm.....
For all I know fMRI could be a very strong predictor of psychopathy. If it explains say 80 percent of the variability in psychopaths, then it is very strong and so should be used. I dunno though. Maybe others know this. For the everyday person it may be sufficient to say that there is a common brain activity pattern in psychopaths though for diagnosis..
My opinion as someone who is not expert on brain scans is that converging data accumulated from the use of different types of assessment tools, that also account for the lack of violence in a sub-set of psychopaths, is the way to go. I reckon psychopaths dont' want that. Interesting too that as fMRI are becoming popular, the psychometric tests are coming under attack. They want one to focus on one thing so you don't see the other stuff that is going on.
brainwave.
