fNIRS (functional near-infrared spectroscopy) and EEG (electroencephalography) are both frontrunners in the neurofeedback field. So why does Mendi use fNIRS?
Here are some benefits of fNIRS:
Forgives movement
- While it’s ideal that you stay relatively still during your neurofeedback sessions for the best signal, fNIRS is fairly robust to movement.
- If a group of scientists were running a study, this would make it a good choice for studies that require moving around, or for studies with child participants (kids are fidgety).
- EEG is less forgiving of movement than fNIRS. This is because every time we move, the electrical conductance on our skin changes. EEG picks up on this.
- Whereas EEG measures electrical signals, fNIRS uses light to “peer into” brain activity. You should still remain as still as you can to make sure the fNIRS device gets the cleanest signal possible, but the movement is less of an issue than with EEG.
Quick and easy to put on (and take off!)
- Unlike EEG, there is no need for any gels or pastes to make the sensors stick to your head.
- fNIRS typically uses an elastic band or cap that fits around the head.
- This is a bit different from EEG. With EEG, electrodes must be attached to the scalp using a gel or paste. In addition to making the electrodes stay in place, the gel or paste also helps with conductivity.
- These electrodes are completely safe (they only receive a signal — they’re not putting out any electricity), but it can be a bit uncomfortable! Not to mention that the person will have to remove the substance from their skin later.
Better at telling where a signal came from
- fNIRS has what we call high “spatial resolution.” This means it is better than EEG at telling where in the brain a signal came from. (However, fMRI is even better at this than fNIRS).
- Remember, though, that this spatial resolution depends on what type of fNIRS is being used. For example, Mendi looks only at the prefrontal cortex. So, it will give insight into what the prefrontal cortex is doing, but not other brain areas.
Okay, fNIRS sounds pretty good so far. Why would anyone use EEG then?
- EEG and fNIRS have their own time and place. One is not objectively better or worse than the other because they both have pros and cons.
- What you’re investigating: EEG lends itself well to research studies that examine a variety of topics, including attention, sleep/wake states, language, decision-making, and facial recognition, to name a few.
- Temporal resolution: EEG is really good at picking up when the brain registered something. This is called having a high “temporal resolution.” It can capture neural events within milliseconds after they have occurred. This is super fast!
What else should I know?
Safety: fNIRS is extremely safe. Unlike a CT or a PET scan, fNIRS doesn’t use ionizing radiation. Instead, it uses low-energy (infrared) light to gather information.
EMFs: We received a question recently about whether electromagnetic fields (EMFs) are something to be concerned about with Mendi.
- As you know, Mendi uses fNIRS. fNIRS itself does not emit EMFs. It emits low-energy light but doesn’t emit any electric currents, ionizing radiation, or magnetic fields.
- While Mendi uses fNIRS technology to collect data about the brain, the Mendi headband needs a way to send this data to your phone so that you can see what your brain is doing in the on-screen game. Mendi uses Bluetooth to do this.
- The power levels of Bluetooth devices are typically low. In our daily environment, most Bluetooth devices emit lower EMFs than your cell phone.
- So while Bluetooth does emit EMFs, this is not more exposure than you would receive on a daily basis from other Bluetooth devices.
I hope that you understand a little better from this why Mendi uses fNIRS. It’s extremely safe, forgiving of movement, and easy to put on and take off. EEG is also a reliable, valid method of measuring brain activity (and so is fMRI, albeit a much more expensive one). Each of these has its own important role in research and the medical field, but fNIRS has a lot of pros that make it a good candidate for use in the home.
About the author
Hannah Claussenius-Kalman earned her Ph.D. in Cognitive Neuroscience from the University of Houston (UH), where she was a graduate researcher in the Laboratory for the Neural Basis of Bilingualism. During her three years as an instructor for upper-division courses in Cognitive Psychology as well as Neuroscience at UH, she discovered a love for sharing and communicating science. She can be found on Instagram as (@doctorhannah_).
