fNIRS

Functional Near Infrared Spectroscopy (fNIRS)

As part of the Cognitive Neuroscience Hub at the Melbourne School of Psychological Sciences, we are using functional near-infrared spectroscopy (fNIRS) to measure brain activity in children and adults.

How does fNIRS work?

This techniques involves using emitter optodes set up in a neoprene cap to shine near-infrared light into the head. Near-infrared light can go through the skin and the skull and illuminates the top 2-3 cm of the brain. This is a bit like when you shine a torch light into your hand and some light goes through your finger.

The light is reflected by the brain differently depending on oxygen concentration in the blood (blood with more oxygen is redder, and blood with less oxygen is bluer). When parts of the brain are more active, the neurons are working harder and the cardio-vascular system sends more blood rich in oxygen to this brain region (this relationship between neuron activity and blood flow is called neurovascular coupling.

Receiver optodes also fixed in the neoprene cap receive the reflected light and we can use specialise software to assess concentration of oxy- and deoxyhemoglobin over time, while participants are performing a task (for example additions and multiplications). Higher level of oxyhemoglobin indicate the underlying brain region is more active.

Illustration of neurovascular coupling, whereby neuronal activity (the grey cells with lots of branches) leads to changes in blood flow and oxygenation in the blood.

Why fNIRS?

FNIRS has increasingly been used to study the brain of infants, children and adults all over the world. While it has a less good spatial resolution than functional magnetic resonance imaging (fMRI), it is portable, cheaper and less sensitive to movement than other neuroimaging techniques. This is an advantage when studying younger children or when we want to put our participants in more realistic situations.

What does it look like?

These are pictures of adult and child wearing an fNIRS cap to measure brain activity. Light is shone into the head and is then reflected by the brain differently depending on oxygen concentration in the blood (blood with more oxygen is redder and blood with less oxygen is bluer). This allows us to measure changes in activity in different parts of the brain depending on what task you are performing. These participants are wearing the Artinis system we use in our lab.

What happens during fNIRS data collection?

When participants take part in an fNIRS study, we first measure the circumference of their head, so we can choose a cap that is the correct size.
We then put the cap on their head making sure it is in the right position, so we can have similar measurements across all our participants.
Then we connect the device to a laptop and check whether the light seems to be emitted and received well. If it is not, we try to move the hair out of the way of each optode using a plastic stylus, and try again.
Once the quality of the signal is good, we can start the recording, while the participant completes some computerised or pen and paper tasks. fNIRS does not make any noise.
At the end of the session, we remove the neoprene cap.

Are there any risks to fNIRS?

fNIRS has been thoroughly tested prior to use with any populations.

Decades of research and rigorous safety testing procedures have been applied in order to ensure the system to be safe and comfortable for infants, children and adults. The amount of light that goes into the participant’s brain is comparable to the amount of light that goes into the brain when you walk outside on a sunny day (see here), no harmful radiation is employed. This means that fNIRS is completely safe.

The light intensity is also kept well below safety limit to avoid the risk of thermal damages. No cumulative harmful effects are known so that measurements can be applied repeatedly or in a continuous manner (see here).

The main risk of using fNIRS is that participants may find wearing the fNIRS cap uncomfortable, and they may get some pressure marks on their skin from wearing the fNIRS cap, similar to when they wear a tight hat or helmet.

Which fNIRS system do we use?

In our lab, we use fNIRS equipment designed by a Dutch company, Artinis. The light sources of the Artinis Brite comply with the International Standard IEC 62471 “Photobiological safety of lamps and lamp systems” based on the maximum power that they can deliver and their output has been measured as well.

The maximum emitted energy at each pair of light sources is 2 mW. It is not possible to accidentally raise the intensity of the light beyond the maximum power by accidentally touching either fNIRS system or even by changing the existing settings.

The Artinis Brite is a wearable and wireless continuous wave fNIRS system which is very easy and fast to set up. It is designed to be lightweight and extremely comfortable to wear, making it a system ethat is particularly attractive for research with children, so they can move about freely and easily.

Google Sites

Report abuse