Functional Mri (fMri)
The technique uses an MRI scanner to measure the blood oxygenation level-dependent (BOLD) signal. The BOLD changes are generally correlated with the underlying synaptic activity. Spatial resolution is 1–10 mm, and temporal resolution is 1–10 s. In general, the higher the spatial resolution, the lower the temporal resolution. Of the three imaging technologies described in this Box, fMRI has a substantial advantage in resolving small structures and those that are deep in the brain. However, some important brain regions, especially the orbitofrontal cortex, are affected by signal artefacts that may reduce the ability to obtain useful information. State of the art MRI scanners cost approximately US$1 million per Tesla and have annual operating costs of $100,000–$300,000.
EEG uses electrodes applied to the scalp and measures changes in the electrical field in the brain region underneath. EEG has very high temporal resolution (milliseconds) and can therefore detect brief neuronal events. Because the skull disperses the electrical field, EEG has low spatial resolution (~1 cm) that depends on how many electrodes are used. The number of electrodes can be as few as two or range up to hundreds in high-density arrays. The greater the number of electrodes, the better the spatial resolution. Apart from the low spatial resolution, EEG has poor sensitivity for deep brain structures. Equipment costs can be low (<$10,000) but increase with high-density arrays and the concomitant resources needed to process the data. A common technique is to measure the left–right asymmetry of the frontal EEG78. This is typically measured by the power in the alpha band (8–13 Hz). This research has suggested that relatively greater activity in the left frontal region is associated with either positive emotional states or the motivational drive to approach an object79. Although there are strong correlations between frontal EEG asymmetry and...
Please join StudyMode to read the full document