October 8, 2009

More On Amygdala, Anxiety, and MRIs

After the last post, I thought, "perhaps I was too broad.  Maybe too political, maybe I didn't have enough concrete examples."

Then I opened my mail.

What I found was the most recent issue of Primary Psychiatry, in which appears Imaging and Genetics: Future Applications in the Emergency Room

It reviews the literature on the neurobiology of aggression in precisely the way I was railing against in the earlier post: sufficiently vague that it makes people think this is alerady established, common knowledge.

The amygdala, located in the temporal lobe, has been shown to be associated with aggression and violence. Studies(29) have found a high rate of atrophy, as much as 20%, of the amygdala in aggressive and violent patients.
Note: studies (plural) but one reference.  Note: you can't tell if 20% is a high rate of atrophy, or if it means "high rate of people who have 20% atrophy."  And you're not supposed to know, because the point is simply to make you feel secure that his overall thesis is well supported.

But, according to reference 29, in a study of aggressive patients, only 20% of them had any amygdala atrophy (e.g. the other 80% didn't.)  The amount of atrophy was fairly small. 

Furthermore, that reference was a study of aggressive vs. non-aggressive epileptics.  In addition to differences in aggression, the subjects also differed in IQ (lower IQ in aggressive group) and a history of encephalitis (associated with smaller amygdalas.)  The study could well have been resubmitted: "A Couple Of People With Low IQs And A History Of Encephalitis Have Kind Of Smaller Amygdalas.  We Think."

Here is the next sentence:

Imaging studies9,10 have also shown abnormalities in amygdala functioning, including decreased activation of the amygdala during affective stimuli in psychopaths
I'm sure whatever imaging studies they were doing 12 years ago were crackerjack, and based on two of these (which are the same data), the reviewer concludes psychopaths have decreased activation in the amygdala. 

Which isn't what the studies found anyway.

First, the study didn't measure just psychopaths (e.g. antisocial PD), but psychopathic murderers who were incarcerated and legally insane.  Note how the author extends these findings to psychopaths in general.

Second, it didn't find decreased activation in the amygdala, it found the opposite: higher activation on the right, and no difference on the left.  Do you know the relevance of it being right vs. left?  Of course not.
So the studies say: "psychopathic murderers have increased activation on the right."  The reviewer summarizes: "psychopaths in general have decreased activation overall."

You would think that difference matters, but it doesn't, because the point of the review article isn't to teach you information, e.g. what happens to the amygdala, it is to convince you that aggression is biologically mediated. These articles succeed because it is established that no one will check whether it is actually increased or decreased (note that three reviewers did not check), because no one cares whether it is increased or decreased, because we all know those are just silly details.

I may as well point out that the studies referenced here didn't even measure the amygdala, they measured the subcortex (amygdala, hippocampus, midbrain, thalamus, together).  Take that, precision instruments.


In fairness to the psychiatry review author, the authors of the above references jumped to an even worse set of conclusions based on their own data

Raine et al. speculate that excessive subcortical activity contributes to an aggressive temperament in both types of murderers, but that "while predatory violent offenders have sufficient left prefrontal functioning to modulate such aggressive behavior in a way to bully and manipulate others to achieve desired goals, affectively violent offenders lack this prefrontal modulatory control over their impulses, resulting in more unbridled, dysregulated, aggressive outbursts." (bold mine, emphasis theirs)

and then published this in a forensic journal.  Do you see? 

The entire article is filler. All he wants to say is this single sentence:

In effect, research is supporting the notion that repetitive acts of aggression are grounded in a neurobiologic susceptibility.
This is simply not true.  There may be aliens in the universe, but it is false to say, today, "in effect, evidence is supporting the notion that aliens can and do live in the universe."  All we know is that there are studies that show a relationship between specific behaviors and specific anatomical areas.  However, we do not know the nature of that relationship.

We cannot accurately quantify the behaviors and distinguish them from similar behaviors (is it aggression out of fear, anger, horniness, temporary insanity, or a combo?), and we can't adequately control for billions of confounders (3 red wines/d vs. 3 beers/d, bad parents, too many horror movies, frequency of one night stands, etc).  How then can we relate them to inadequately  characterized anatomical regions using machinery with the precision of an icepick, and then conclude "predatory violent offenders have sufficient left prefrontal functioning to modulate such aggressive behavior in a way to bully and manipulate others?"

We tend to focus only on one error, e.g. MRI false positive rate.  But these studies don't take into account all of the other errors.  It is the problem of significant digits: 3.225 x 5.23441 x 7 does not equal 118.16680575.  It equals 100.


You all think I'm exaggerating.  That I am punching windmills.

In keeping with this development, sometime in the future cord bloods will be taken routinely from birth and used to delineate the individual's DNA so that genetic information will be readily available under emergency conditions to assure proper assessment of violent people. Hence, a patient presenting with an episode of violence and a history to support that will have their DNA contrasted with norms to determine if they have a predisposition to aggression and violence...
I have enough rum to get through the rest of my life, but the rest of you would do well to heed my warning: if you do not rein in your social scientists, your civilization is doomed.