A brief review of research using near-infrared spectroscopy to measure activation of the prefrontal cortex during emotional processing : the importance of experimental design

Abstract

During the past two decades there has been a pronounced increase in the number of published research studies that have
employed near-infrared spectroscopy (NIRS) to measure neural activation. The technique is now an accepted neuroimaging tool
adopted by cognitive neuroscientists to investigate a number of fields, one of which is the study of emotional processing. Crucially,
one brain region that is important to the processing of emotional information is the prefrontal cortex (PFC) and NIRS is ideally
suited to measuring activity in this region. Compared to other methods used to record neural activation, NIRS reduces the
discomfort to participants, makes data collection from larger sample sizes more achievable, and allows measurement of activation
during tasks involving physical movement. However, the use of NIRS to investigate the links between emotion and cognition has
revealed mixed findings. For instance, whilst some studies report increased PFC activity associated with the processing of
negative information, others show increased activity in relation to positive information. Research shows differences in PFC
activity between different cognitive tasks, yet findings also vary within similar tasks. This work reviews a selection of recent
studies that have adopted NIRS to study PFC activity during emotional processing in both healthy individuals and patient
populations. It highlights the key differences between research findings and argues that variations in experimental design could be
a contributing factor to the mixed results. Guidance is provided for future work in this area in order to improve consistency
within this growing field.