Activation of the prefrontal cortex during a visual n-back working memory task with varying memory load: a near infrared spectroscopy study

We evaluated frontal brain activation during a Working Memory task with graded levels of difficulty in a group of 15 healthy subjects, by means of fNIRS technique. Brain activation (% signal change with respect to the baseline) was computed and load-related increases of blood oxygenation were found for the four different levels of task difficulty. Generalized Linear Models were applied to the data in order to evaluate the metabolic processes occurring during the mental effort and, possibly, their involvement in short term memorization. The Cognitive Failure Questionnaire was also administered in order to assess its diagnostic relevance in clinics. Results attest a monotous increase of brain oxygenation with WM load during the first half of task, persisting through the central resting period and prevailing in the left hemisphere. Decreasing WM load is also coupled with oxygenated hemoglobin decrease.