Wednesday, February 14, 2007

Brain Physiology of Love and Sex

Elizabeth Cohen posted this story on CNN about what cognitive scientists are learning about love.

We exchanged a few emails on the subject so I figured I'd take one of them and post this blog entry.

Cohen wrote, “In a group of experiments, Dr. Lucy Brown, a professor in the department of neurology and neuroscience at the Albert Einstein College of Medicine in New York, and her colleagues did MRI brain scans on college students who were in the throes of new love.  While being scanned, the students looked at a photo of their beloved. The scientists found that the caudate area of the brain -- which is involved in cravings -- became very active. Another area that lit up: the ventral tegmental, which produces dopamine, a powerful neurotransmitter that affects pleasure and motivation."

"Dr. Brown said scientists believe that when you fall in love, the ventral tegmental floods the caudate with dopamine. The caudate then sends signals for more dopamine....  The more dopamine you get, the more of a high you feel" similar to the effect of cocaine on the nervous system.

The physiology of sex, on the other hand, appears to be quite different.  Cohen explained, “In studies when researchers showed erotic photos to people as they underwent brain scans, they found activity in the hypothalamus and amygdala areas of the brain. The hypothalamus controls drives like hunger and thirst and the amygdala handles arousal, among other things.  In the studies of people in love, 'we didn't find activity in either,' according to Dr. Fisher, an anthropologist and author of Why We Love -- the Nature and Chemistry of Romantic Love.

Let’s examine their findings in more detail and ask some questions.  First of all, how do we know the students they selected were actually in love?  And how do we know that looking at pictures of your beloved evokes the same response as love?  And finally, can we trust their conclusions?

This kind of questioning is a huge part of science.  Is the methodology valid?  Scientists are skeptical.  Unfortunately journalists are less so.  They rarely discuss questions on the methodology of the study or delve into the philosophical underpinnings of the conclusions and report on how scientists challenge one another.  Would that be boring?  Maybe.  But without that discussion, how do we know, really?  And I wonder if you could make it interesting....

In their search for a juicy story, science journalism is often guilty of exaggerating the claims or conclusions of the scientists themselves.  For example, in this case they might have concluded that brain region A was activated when the subject studied images of X while region B was activated when images Y were projected to the subject.  This deductive reasoning is solid:  if A then X and not Y.  If B then Y and not X.   It’s what makes reductionist science work.

But that’s not where it ends.  A good paper might cautiously extend limited conclusions like these beyond the scope of the experiment back to the considerably more complex “real world.”   The synthesis of these results with lots of other experiments on mind, brain AND body systems is actually inductive reasoning.  These results together with lots of other results might support (and do not contradict) a proposed model that accounts for the mechanisms of perception and other kinds of cognitive behavior.  We can’t say that the model is right.  We can only say that it has not been disproved yet.

Naturally, we would have to find and study the original paper to be sure of this.  But it does serve to illustrate this point:  reporters typically skip this intermediate step making it seem like the experiment is deductive reasoning about the real world.  It is not.

Implicit messages and omissions are another problem with scientific journalism.  Cohen wrote, “By studying MRI brain scans of people newly in love, scientists are learning a lot about the science of love: Why love is so powerful, and why being rejected is so horribly painful.”  To the romantic reader, lover of poetry, art or music perhaps, claims like this imply much more than is actually intended by the scientists themselves.  Knowledge of physiology tells us nothing about the subjective  experience of love at all and certainly can’t help us answer questions like “Why should we experience such feelings?”

Reasonable, well adjusted scientists are well aware that the model of the mechanism is interesting but totally distinct from the experience or the meaning of the phenomenon.  E. O. Wilson would suggest that’s exactly why science and literature and art and music are complimentary or even 'consilient' inductions insofar as they 'jump together' and reinforce one another.  It is assumed by scientists. Perhaps we should make it explicit for the rest of us as we ask, "but how do we know?"