Methods

Please find below a summary of experimental methods I use(d) for my research either directly or through collaborations with other researchers.

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(Functional) Magnetic Resonance Imaging ([f]MRI)

fMRI(Functional) magnetic resonance imaging ([f]MRI) is used to visualize brain structure, as well as to indirectly measure brain activity through changes in the magnetic properties of blood, and more precisely hemoglobin.

During the resting state, oxygen concentration at a specific brain location is relatively low, so that blood contains a high concentration of deoxy-hemoglobin. After neuronal activation, which leads to increased local oxygen consumption, more oxygen is trans-ported to the site of activation via heightened cerebral blood flow (CBF). This increased CBF entails a washout of deoxy-hemoglobin and an increased concen-tration of oxy-hemoglobin.

Importantly, deoxy-hemoglobin and oxy-hemoglobin have different magnetic properties – the former is paramagnetic while the latter is diamagnetic. Furthermore, the brain tissue that is surrounding blood vessels usually is diamagnetic. This means that during the resting state, there are more magnetic field inhomogeneities at the interfaces of vessels and brain tissue than after neuronal activation – or in other words, an increase in oxy-hemoglobin (and a concomitant decrease in deoxy-hemoglobin) makes the magnetic properties of blood and brain tissue more similar.

By detecting such changes in magnetic field inhomogeneities between blood vessels and adjacent brain tissue as a function of CBF and increased oxygen consumption, fMRI allows the detection of the so called blood-oxygen-level-dependent, or BOLD, signal. The higher the BOLD signal, the more a certain brain area is thought to have been activated by a certain experimental task. In comparison to other neuroimaging methods, fMRI offers a high spatial resolution and can measure brain activation in areas deep within the brain. In turn, fMRI has a relatively poor temporal resolution, because the BOLD signal unfolds within a time window of approximately 20 seconds.

See here for more details and further reading regarding fMRI.

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Functional Near-Infrared Spectroscopy (fNIRS)

fnirs_2This method is similar to fMRI (see above) because it also measures blood oxygen levels – although it derives separate signals from oxy- and de-oxygenated blood. And there are some more differences.

Crucially, fNIRS detectors and emitters are placed on the scalp surface in a similar fashion to EEG electrodes (see below). Furthermore, fNRIS uses infrared light to measure changes in blood oxygenation, which is in contrast to the requirement of a strong magnetic field to measure BOLD with fMRI. Compared to EEG, fNIRS has a better spatial resolution. Compared to fMRI, fNIRS can only obtain measures from areas close to the scalp surface.

The main advantage of fNIRS, over both fMRI and EEG, is its relatively weak susceptibility to movement artifacts. Moreover, fNIRS can be used in more naturalistic environments, particularly in two (or more) people directly interacting with each other (i.e. hyperscanning). We are therefore mainly employing fNIRS to look at brain-to-brain synchrony in adult as well as parent-child dyads within the greater context of investigating bio-behavioral synchrony. 

See here for more details and further reading.

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Electroencephalography (EEG)

This method measures electrical activity on the scalp surface.

EEG signal represents a more direct measure of brain activity, as it stems from ionic currents that flow within the nerve cells (neurons) – and not the indirect measure of brain activity relying on blood flow as used in fMRI and fNIRS. However, only the sum of synchronous activity of thousands or more neurons can be measured with EEG, because the electrical potentials of single neurons are too weak to be captured.

Usually, so called event-related potentials (ERPs) are derived from the EEG signal, which represent brain activity time-locked to the onset of a stimulus, i.e. an image or a sound.

While the spatial resolution or EEG is rather poor as compared to fMRI or fNIRS, it has a very high temporal resolution in the order of milliseconds.

See here for more details and further reading.

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Psychological Questionnaires & Personality Assessment

This method assesses individual differences and psychological traits of a person.

Every person reacts differently to his/her environment or thoughts and emotions arising within the mind and body. Although fMRI, fNIRS, and EEG normally measure effects averaged over a group of participants, it is also of great interest to see how behavioral and/or brain activation patterns differ as a function of individual differences in personality traits.

One way to acquire variables reflecting individual differences in personality is to give participants a set of self-report questionnaires to fill in some time before or after measuring their behavior and/or brain activity. Another way, particularly in the context of my research on attachment, is to use age-appropriate semi-structured interviews such as the adult attachment interview (AAI) or the Story Stem Battery (SSB). These measures can furthermore be combined with behavioral coding of video-sequences, for example acquired during social interaction tasks. 

The psychological trait of main interest in my current research is attachment. Other measures include trait anxiety, behavioral inhibition vs. approach, positive and negative affect, internalization vs. externalization, empathy, resiliency, etc.

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Biological Markers of Well-Being and Health

crpThis method uses immunoassays to determine the concentration of different blood markers of well-being and health, including immune system function (i.e. IL-6 and CRP), and neural growth (i.e. BDNF). It also uses quantitative PCR (qPCR) to determine telomere lenght. Further markers are salivary and hair cortisol / cortisone.

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epigenetics-and-genetics2Genetics and Epigenetics

Through blood or saliva samples, this method either establishes the participants’ genetic profile in terms of gene polymorphisms, or looks at epigenetic modification related to changes in gene function by means of methylation, particularly in the promoter region of genes of interest. Candidate genes include OXTR, NR3C1, DRD4, OPRM1, etc.

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Linguistic Inquiry and Word Count (LIWC)

This method uses computerized text analysis to measure the relative frequency of words used in a written sample. For more information, see here.