Love is in the... striatum!

愛	Romantic love is an emotion that stirs our souls. Just by looking at the beloved person, it causes strong feelings like butterflies in the stomach. If love produces so strong emotions one may wonder what it does to the brain.

Bartels and Zekin (2000) wanted to know which regions of the brain are activated when someone in love observes the face of the beloved person. They recruited 17 normal subjects 'truly, deeply and madly in love,' and examine their brains with functional magnetic resonance imaging (fMRI) as the subjects observed pictures of their loved ones and friends. Then, they compare the activation in brain areas induced by the beloved person in relation to the friends. To the surprise of the authors, very few regions were selectively activated; medial insula, anterior cingulate cortex, and striatum (nucleus caudate and putamen). All areas were activated in both hemispheres (bilateral).

The activation of the insula and cingulate cortex did not surprise Bartels and Zekin. These areas are related to several emotions. The unexpected result was to find activation of the corpus striatum, an area involved in motor planning. Would this mean that just by seeing the beloved person we want to run to her? The authors were also puzzled:

"Collectively, these results call for a reappraisal of the role of the putamen and caudatus in emotional states and as part of the extrapyramidal system."

Sometimes, however, relationships are broken, and there is grief, especially when there is separation from the beloved. Najib et al., (2004) studies the brain of 17 women experiencing grief, and who were turning their situation over and over in their mind (i.e. "ruminating"). They used fMRI to show that acute grief increases the activity in several posterior brain regions, and decreased the activity in the thalamus, striatum, and cingulate cortex. For women that experience a larger grief, the decrease in activity in these regions was larger.

In another study, Aron et al., (2005) studied the activation of the brain regions, similar to the study of Bartels and Zekin (2000), but at early stages of the relationship. This time, the subjects were in love for 1–17 months. They found activation of the ventral tegmental area, right postero-dorsal body, and medial nucleus caudatus. Interestingly, the higher the love (in a passionate love scale) is, the larger the response of the nucleus caudatus.

What could be the meaning of striatal activation? Perhaps it is related to the dopamine-reward system, i.e. the brain knows that she can make me happy. Or, it may be related to the eye movements; when one stare at the beloved person, the eyes make saccades to scan her face.