Friday, August 8, 2008

My brain and I interpret you as hostile

My love affair with PLOS continues. Today I saw an interesting study: "Individual Attachment Sytle Modulates Human Amygdala and Striatum Activation during Social Appraisal" by a group in Switzerland. Translated into non-science babel, the group was looking at the biological underpinings behind human bonding, such as mother-child bonding or more broadly how people non-verbally perceive each other. They used functional magnetic resonance imaging (fMRI) to look at which parts of the brain are active during assessment of facial expressions. Basically, the amygdala and striatum were the two primary areas involved, but they were triggered differentlly depending on your 'attachment' style: secure, avoidant, or anxious.
  • Anxious attachment style - "perceive others as unresponsive or inconsistent, worry about being rejected, and show heightened vigilance to signs of support or hostility"
  • Avoidant attachment style - "prefer being distant and detached from others, report no need for close relationships, and tend to distrust affective signals from others"
  • Secure attachment style - "report positive and trustful interactions with others"
Stated differently: the exact same face (such as an angry expression or someone smiling) excites completely different areas of the brain. This pattern can be predicted based on the fundamental style of interaction. This is a great example of correlating basic science with a real-world readout. It may be a bit far-reaching, but the paper states that someday, their methodology could be applied to better create intervention strategies for disorders such as autism and phobias, which are characterized by abnormal and pathologic interactions.

Interestingly, the paper did not touch on any gender differences (with all 16 of its subjects). I would like to know if, even within the same attachment category, there were any inconsistencies between men and women, or if ultimately the style trumped sex.


daedalus2u said...

This is an interesting study. I would like to point out that the signal that fMRI measures is changes in oxyhemoglobin and deoxyhemoglobin levels. They have slightly different magnetic susceptibilities and changes in that cause observable changes in the MRI signals. What they are really measuring is not neuronal activation, but dilation and increased blood flow in that region of the brain (which parallels neuronal activation).

The reason I am such a stickler for pointing this out is that what causes the vasodilation is nitric oxide, the subject of my research. What fMRI is showing is volumes of increased NO levels which cause vasodilation, which change the oxy/deoxy hemoglobin levels.

It turns out that a lot of attachment pathways are mediated by NO. If nitric oxide synthase is blocked in ewes, they don't bond to their lambs. If NOS is blocked but supplemental NO is supplied they do bond.

Basal NO levels are something that is affected by stress and energy status. High stress or low metabolic energy (low ATP levels, not necessarily lack of food supply) causes low NO levels and perturbs physiology in the low NO direction. NO inhibits the cytochrome P450 enzyme that makes testosterone, so low NO will increase testosterone levels. Estrogen causes activation of nitric oxide synthase through the estrogen receptor. There is some thought that higher NO due to estrogen is the reason why pre-menopausal women have less heart disease than men, and why post-menopausal women have the same level.

Making attachment dependent on NO levels couples attachment to stress levels and to energy status. This would show up as differences in the size of the regions observed to be activated by fMRI (low basal NO decreases the range and the magnitude of any NO mediated signal).

In the case of maternal bonding to infants, under conditions of severe metabolic stress, as in famine, disease or war and in "the wild", a woman not bonding to her newborn might be a better reproductive tactic. If she doesn't have the metabolic resources to sustain her infant until the infant is weaned, the infant is going to die eventually anyway. If she survives she may have the opportunity to raise a child successfully.

I think that is what causes postpartum depression, metabolic stress. If it is severe enough it causes postpartum psychosis and infanticide, the evolved technique for a metabolically stressed female to shed the metabolic load of lactation.

Habladora said...

I love this post, btw. I can't wait to read the original PLOS article.