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

fMRI(Functional) magnetic resonance imaging ([f]MRI) is used to visualize brain structure, as well as to indirectly measures 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 is transported to the site of activation via heightened cerebral blood flow (CBF). This increased CBF entails a washout of deoxy-hemoglobin and an increased concentration 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 as well. 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 concomittant 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 increase 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.


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). This detector location makes experimental settings much more naturalistic and data less susceptible to movement artifacts. 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.

See here for more details and further reading.


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.


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, fNRIS and EEG normally measure effects averaged over a group of participants, it is also of great interest to see how brain activation patterns differ as a function of individual personality traits.

Normally, participants are given a set of self-report questionnaires to be filled in some time before or after measuring their brain activity. Questionnaire scores are then correlated with brain data.

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


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.


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.