Hemodynamic Responses to Thermal Stimulation in the Prefrontal Cortex of the Brain measured by FNIRS

Abstract

Although FMRI has marked its importance in the neurological research by understanding the brain activities, FNIRS has also set a new standard in the brain imaging study research with non-invasive and easy to use technology. FNIRS is a portable, inexpensive optical imaging method that measures the changes in the oxygenated and de-oxygenated hemoglobin of the brain that results from the neurological activity. In this study, FNIRS has been used to study the pain processing in humans by measuring the pre-frontal cortex area of the brain. Eight (n=8) healthy subjects were induced with pain using a thermal stimulator device with temperatures ranging from 45 to 47°C and their temporal profiles of the brain activity were analyzed to see which part of the pre-frontal cortex showed changes in the hemodynamic response. Apart from this, first 2 blocks and the last 2 blocks of the experimental protocol were compared to see if there were any symptoms of pain habituation due to repeated painful stimuli for six times. 13 out of the 64 long separation channels and 3 of the 16 short separation channels showed significant deactivations at the time of the painful stimuli which covered areas of the pain matrix including dorsolateral pre-frontal cortex (BA 9 and 46), frontopolar cortex(BA10), etc. Activations were found during the recovery phase in the areas of dorsolateral prefrontal cortex (BA 9 and 46), frontopolar area (BA 10) and parts of broca area. On the other hand, 10 out of the 64 long separation channels and 4 out of the 16 short separation channels showed less deactivation in the first 2 blocks than the last 2 blocks and hence, it was also proved that repeated painful stimuli leads to adaptation of the signal.