fNIRS Tool Measures Brain’s Response to Acute Pain

Functional near-infrared spectroscopy (fNIRS) — an optical imaging tool for monitoring regional blood flow and tissue oxygenation — is being explored as an option to track the brain's response to acute pain in adults and infants.

A block diagram illustrates the cold pressor protocol applied in a Drexel University study on functional near-infrared spectroscopy in assessing pain response in the brain. Courtesy of study authors: Zeinab Barati, Issa Zakeri, and Kambiz Pourrezaei.

Researchers from Drexel University used cold pressor tests (CPT) at different temperatures to assess whether pain perception is proportional to hemodynamic response — the response of the circulatory system to stimuli such as exercise or emotional stress — at a given water temperature.

The fNIRS technique is portable and noninvasive, which is an advantage over other hemodynamic-based imaging techniques. It also does not require ionizing radiation or drug injection and can withstand a certain amount of motion, which is desirable for patients such as infants, small children, and elders with involuntary movement disorders.

"This is one of a few recent studies demonstrating that fNIRS can afford noninvasive, objective measures of cortical responses at the prefrontal region to noxious pain resulting from either cold or hot thermal stimulations," said Hanli Liu, professor of bioengineering at the University of Texas at Arlington. "Interestingly, this is the first scientific report on gender difference in hemodynamic responses to noxious cold stimuli seen in the prefrontal cortical region, although no gender difference was found in pain threshold, tolerance, or scores. It sheds light on hidden differences in biological variables in the human brain."

Applications of the technique could include pre- and postoperative uses, study of spontaneous pain under natural conditions, examination of patients who cannot remain motionless in a magnet or positron emission tomography (PET) scanner, assessment of patients under sedation or who may have reduced perception of pain, and study of conditions affecting pain tolerance, such as drug abuse, smoking, and alcohol use.

Advanced brain imaging methods such as PET and functional magnetic resonance imaging (fMRI) have revealed the activation of brain regions during physical or psychological experiences of pain. Previous studies have found a relationship between the intensity of perceived pain and the neuronal activation in several cortical areas.

The Drexel study, titled "Functional near-infrared spectroscopy study on tonic pain activation by cold pressor test," has been published in the SPIE journal Neurophotonics (doi:10.1117/1.NPh.4.1.015004).