How does intranasal oxytocin affect empathy? What is the role of the human endogenous opioid system?
This type of questions can be addressed by giving people drugs and measuring the effects. Psychopharmacology allows us to directly address the causal effects of drugs or neurotransmitter systems in humans. These methods are generally very safe: we screen participants thoroughly to minimise risk. With intranasal oxytocin most people feel no effect at all, yet we can still produce statistically significant changes in social behaviour at the group level. In our large study to map out the role of the endogenous opioid system for human reward behaviours, we employed moderate doses of an agonist (morphine, to stimulate the receptor) and the antagonist naltrexone (to block the receptor). This ensured that we could measure the effects of the brain’s own opioid system as opposed to the effects of the drugs themselves. Psychopharmacological work from my lab includes Chelnokova et al, 2014, Ellingsen et al, 2014 and Leknes et al, 2013.
Eye-tracking and pupillometry
With eye-tracking methods we can measure where people are fixating their gaze. This reveals how much overt attention people pay e.g. to different parts of the face. Most relevant information about who someone is and what their intentions are is found in the eye region (i.e. if they want to speak to us, whether they are likely to be friendly, if their smile is sincere or not, etc). This video shows a typical gaze pattern to a photograph of a face. How much people look at the eyes of others can also predict whether they have autism spectrum disorder.
Eye-tracking equipment also measures the size of the pupil. The pupil constricts with light and is enlarged in the dark. However, when light levels are constant, the size of the pupil can tell us about people’s interest levels or how much effort they are expending. The pupil also dilates when we feel attracted to others; conversely, we find large pupils attractive. This was exploited by Victorian women who used the poison belladonna to artificially dilate the pupil.
Neurons in the brain communicate through neurochemical signals. Dopamine, opioids (endorphins) and many other compounds make up the brain’s neurotransmitter systems. Hormones such as testosterone, oestrogen and oxytocin also act on receptors on neurons in the brain.
Levels of neurochemical compounds in the brain can be measured via PET scanning or by extracting cerebrospinal fluid (CSF) from the spinal cord. A less costly and invasive method is to measure levels of neurochemical compounds in the blood. In collaboration with Steven Ray Wilson and Elin Johnsen at the Department of Chemistry, UiO, we have developed a new method for quantifying compounds in small amounts of blood.
Neuroimaging methods such as functional magnetic resonance imaging (fMRI) are useful tools to identify brain mechanisms underpinning subjective feelings. In a typical pain experiment, we apply heat pain to the skin for a few seconds, then wait for a while, then apply more pain. And so on for 15-2o minutes. Correlating the timing of the heat pain with the signal over time from voxels (3D pixels) in the brain allows us to create maps of brain regions involved in various aspects of pain. The image to the left depicts Dan-Mikael Ellingsen and Marie Eikemo preparing to scan healthy volunteers in our study of placebo improvement of pain and pleasant touch, published in PNAS.