Near-InfraRed Spectroscopic Imaging

See the brain working through diodes

Thanks to a grant from the Fondation pour la Recherche sur le Cerveau in cooperation with the Rotary Club of France (call for tender “Espoirs en tête 2015“), the Neurofunctional Imaging Group recently acquired a new brain imaging technique called NIRS, for Near-InfraRed Spectroscopy. NIRS is based on the use of a set of light-emitting diodes (LEDs) and photodiodes (light detectors) placed on the scalp. When light is emitted by LEDs, with wavelengths close to that of infrared light, it passes through the skull and penetrates into the brain. Some of these light rays will interact with blood circulating in the cerebral arteries and veins, this interaction being different for venous blood (rich in deoxygenated hemoglobin) and arterial blood (saturated with oxygenated hemoglobin). By collecting the reflected rays with the photodiodes and analyzing their wavelengths, it is possible to measure the proportions of oxygenated blood and deoxygenated blood of the cerebral cortex. When the cortex is activated by a task, the local blood oxygenation increases and can be detected. Compared to other brain imaging techniques, the NIRS offers incomparable advantages: lightweight, portable system, easy to implement, it can be used in very small children, and is totally non-traumatic for the subjects.

To carry out NIRS experiment in, a cap is placed on the head of the participant in which are inserted diodes that emit light in the near infrared. This light passes through the scalp and the skull and is reflected on the blood molecules, but in different ways depending on whether it is oxygenated or deoxygenated. The reflected light is captured by photodiodes also inserted in the cap and converted into maps giving the relative concentration of oxygenated blood. When a region of the brain activates, the NIRS detects the increase in oxygenated blood that accompanies this activation.


The CoMoNIRS project

This project brings together researchers from IMN, GIN’s ones, the Physiology and Physiopathology of Executive Functions team (Thomas Boraud), and the Clinical IMN (Wassilios Meissner), to study active brain regions during motor activities and during tasks requiring to make decisions and/or to make choices (executive tasks). The goal is to study both healthy volunteer control subjects and Parkinsonian patients with this completely non-invasive NIRS imaging device that allows the subjects participating in these studies to work in “ecological” conditions. We will study the regions that deactivate during hand movements to understand the mechanisms of manual preference, being right-handed or left-handed. We will then measure the brain areas that work as the subjects walk and bring new information about the mechanisms involved in gait freezing, one of the disabling symptoms of Parkinson’s disease. Finally, we will compare the cerebral regions at work during executive tasks in healthy subjects, parkinsonian patients with treatment and patients without treatment to better understand the mechanisms involved in this disease.



Team 4