How does a baby learn to walk, talk and be social?

These are a few questions developmental researchers aim to answer. fNIRS is an optimal brain imaging technique for studying infant brain functioning non-invasively and, crucially, without requiring the infant to verbally answer questions.

Over the past years, fNIRS has been increasingly used by scientists to tackle different questions on typical and atypical infant development. Research topics include language, speech and visual perception, social communication, parent child interaction and much more.

Testing young babies, between 0 and 2 years of age, is definitely fun, but it also comes with challenges. We asked several developmental researchers to point out the main difficulties they typically encounter and what features an infant-friendly NIRS should have. Based on their feedback, we developed the BabyBrite.

Meet the BabyBrite

So, what are these challenges and what can researchers and technology do to overcome them?

The unpredictable mood of children is certainly one of these challenges. Children may be very calm and compliant, or tired and fussy. In the latter case, putting a funny hat with many sensors and cables on a child's head requires the researcher to be quick and creative. Effective strategies to achieve a successful study include distracting the child while putting the cap on, making the test day a fun experience, and good communication between the baby, the parents and the researcher.

Parents are often happy to help if they are given enough information. They know their child better than anyone else and can provide important information, such as their child's daily schedule! Thus, involving parents in planning the lab visit according to the infant routine is good practice.

Other crucial aspects to consider is the babies’ comfort. When infants feel discomfort, they might start crying, become very agitated or want to take off the headcap. Increased movements can be also observed when infants get too excited about something. Using a comfortable headcap and NIRS system definitely helps the babies forgetting they are wearing fancy hats!

To achieve this, the BabyBrite has soft optodes, holders, and headcaps (Easycap) which are all gentle on the infant skin and easily adapt to different babies' head shapes. The BabyBrite also has an easy and soft click in system allowing researchers to pull out the optodes and move the hair aside to enhance coupling with the skin, in case the infant already has quite some hair.

While NIRS is well known to be less susceptible to movements than other techniques, such as EEG, yet it is not immune to active babies! Motion artifacts mainly occur in NIRS data when the optode moves on the skin causing sensor-skin decoupling.

How can researchers prevent such artifacts to occur? Keeping a baby calm is very important, so testing in a quiet and friendly environment helps not agitating the infant. Next, it is essential to ensure that the headcap is tight and appropriately placed on the infant head. In some cases, adding an extra headcap or bandana on top of the one holding the NIRS optodes is a valid strategy to enhance the stability of the headcap, to ensure good coupling, and to protect optodes as well as cables from being grabbed and pulled by the infant.

Another advantage of the BabyBrite is that it is light-weight, with its main unit being smaller than a donut. The main unit is connected to optode hubs with longer cables which allow the main unit to be placed to accommodate most testing protocols (e.g. carsit; bed; high chair etc.). Another tip that could help avoiding motion artifacts include bundling the cables so they are not easily reachable by the baby.

A final remark focuses on the optode template and distance between light transmitters and receivers (i.e. interoptode distance). When defining these, several factors should be taken into account, such as the aim of the study, age and cortical area of interest. Indeed, the interoptode distance defines how deep from the scalp you can measure with NIRS, e.g. 20mm distance allows to measure at 10mm .ca in depth. One way to choose the template and interoptode distance is to dive into literature that tackled a question similar to your study or infant atlases showing where brain areas are located.

The BabyBrite uses Easycaps which report the EEG 10-20 system locations to help researchers correctly position their favorite templates. The BabyBrite allows to measure everywhere on the head and comes with distance guards of 20 or 25mm; these ensure the interoptode distance to remain constant during and between measurements.