6 experiments you should do with NIRS (vs fMRI)

4 min read

[last update: 2019-02-20]

Let’s be frank. Compared to fMRI, NIRS has a number of intrinsic weaknesses. The signal to noise ratio is lower, the spatial resolution is (10x) lower, it can’t measure the deep brain, and it only covers a portion of the brain surface. As a result, fMRI, when possible, is still the preferred method to elucidate brain mechanisms. So if we do use NIRS, we’d better do experiments fMRI can’t, or at least very difficult to, do.

Below are 6 experiments NIRS can do, but fMRI can’t (or difficult to do):

  1. Study of the mechanism of BOLD signal
    1. Study of the relationship between oxygenated and deoxygenated hemoglobin concentration
      For a given voxel, fMRI only gives you a single number at a time. The number (BOLD signal) depends on many factors. On the other hand, NIRS can give you two numbers, the concentrations of both oxygenated and deoxygenated hemoglobin. So if you ever want to study the relationship between them, we should use NIRS. For an example, please check out https://www.ncbi.nlm.nih.gov/pubmed/19945536
    2. Study of the fine temporal change of BOLD signal
      In most fMRI settings the temporal resolution of BOLD signal is low (about 2 seconds, or 0.5Hz). That means we only get a number every two seconds. If we want to know the rise and fall of the BOLD signal in much higher temporal resolution, e.g. 10Hz, then NIRS would be a good choice.
  2. Study in naturalistic settings
    If you ever participate in a fMRI study, you will feel the room far from friendly. The scanner is loud, and it looks scary. During the entire experiment, you are lonely inside the confined space. You can’t move, can’t talk (for most experiments), and feel guilty when you swallow saliva as the experimenter probably told you in advance that any motion might distort the signal. What you often see is much simple visuals (such as blocks and circles) on a computer screen. Do we live such a life in reality? On the contrary, NIRS is small, even portable, and can be used in a naturalistic environment.

    1. Sports and exercise
      As long as the optodes are attached to the head nicely to ensure proper signal collection, the participants can move freely. NIRS has been used in a number of sports or exercises studies such as running, squatting, biking, ping-pong, piano playing, and stretching etc. Be sure to check out the videos in https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5434677/

      Source: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5430058/
    2. Face to face communication
      You might see other people’s face on a screen in fMRI, but with NIRS, you can see a real face. We humans are fundamentally social, and to study social behavior in a naturalistic environment is important. NIRS allows you to study face-to-face gaming (video or board), talking, brain storming, cooperation or competition, etc. For example, in one of our studies (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3254802/) participants played a video game together. my colleague Ning Liu et al has an experiment when two people play Jenga games (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4782164/).
    3. Study in a moving environment
      Many NIRS devices are small enough so you can carry it in a car or even a backpack. That means you can study the driver’s brain when he is actually driving! An example would be https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5671603/
  3. Hyperscanning
    fMRI can be used in hyperscanning studies, and in fact the first hyperscanning is done with fMRI by my former advisor Dr Montague (https://www.ncbi.nlm.nih.gov/pubmed/12202103). However, seeing it with first hand, I know hyperscanning with fMRI is technically challenging. You need two fMRI scanners, each costs a few million dollars; and you also need to synchronize them. On the other hand, many NIRS devices are able to do hyperscanning natually. For example, when we used ETG 4000, we simply use one patch on one participant and the other on another participant. It does not add complexity on the hardware part.
    To date there are a number of hyperscanning studies with NIRS. For a list, please refer to https://www.ncbi.nlm.nih.gov/pubmed/?term=(fnirs+OR+nirs)+hyperscanning. If you are patient enough to scroll to the last page, you will find our paper!
  4. Real time (feedback), brain computer interface
    Let’s say you want your participants to move a bar in a computer game mentally (brain computer interface), or you provide a real time neural feedback to your participants to improve cognitive function, in both cases you need the brain signal in real time.  fMRI can do this too, but first you will need to get the data in real time, and second, due to poorer time resolution (2s), there will be some lag. Many NIRS devices allows you to get the measured signal out without delay, and of course the temporal resolution of NIRS is typically much higher (e.g. 10Hz). An recent example can be found at https://www.ncbi.nlm.nih.gov/pubmed/30634177
    Some may argue that higher temporal resolution is not that useful because the BOLD signal is already slow (usually 4-6s from onset to peak). However, with finer temporal resolution, we can use algorithms (e.g. machine learning) to detect signal with much smaller delay. For example, in one of our studies the delay can be reduced by 50% (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2978722/)
  5. Field studies, large scale studies
    You can’t carry an fMRI scanner around for sure, but with NIRS’ portability, you can collect neural data in the field. My colleague Dr Baker took a NIRS device to the rural places in Costa Rica, and scanned the local farmers. Check out his paper.

    In addition, since you may carry NIRS devices around, you can scan a lot of participants, e.g. a few hundred or even thousand. Imagine you are to study the brain and cognitive development of children in rural areas in China in a large scale (say 10,000 participants), then NIRS will become your top choice.
  6. Study on special participants
    Due to safety reason, the following people should not do fMRI experiments (source):

    1. with shrapnel or other metal or electronic implants in their bodies (such as pacemakers, aneurysm clips, surgical devices, metallic tattoos on the head, etc.)
    2. pregnant
    3. with a history of head trauma or fainting
    4. currently using sleeping aids, painkillers (including aspirin), or other agents known to affect brain function (for instance, antihistamines, decongestants, etc.)
    5. with major medical, neurological, or psychological disorders (including depression, generalized anxiety, panic attacks, AD(H)D, strokes, tumors, heart conditions, claustrophobia, etc.)

    In addition to this list, fMRI is also not friendly to infants (but still can be done in fMRI). In contrast, NIRS does not have issues with the participants in the list. Imagine you can do an experiment on claustrophobia with NIRS, but probably not with fMRI.

So, what is the ideal experiment with NIRS? Based on the above list, if one is to use hyperscanning to study the face-to-face communication when two claustrophobia participants are running together along a mountain trail, I would say it’s pretty hard for fMRI to catch on.

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fNIRS Journal Club 视频

546个被试的大型实验是怎么做的?近红外超扫描技术如何揭开群体冲突的神经机制?北京时间2020年5月29日周五上午11点,北京师范大学的马燚娜教授(Yina Ma)为大家讲解了她们组刚刚在Nature Neuroscience发表的文章。下面是报告视频。第一个是在Youtube,第二个是在youku。 Youtube:https://www.youtube.com/watch?v=4qZ7zP-BGz4Youku:https://v.youku.com/v_show/id_XNDY5MTc0MjAxMg==.html 她讲的文献如下: Within-group synchronization in the prefrontal cortex associates with intergroup conflict. Nature neuroscience https://www.storkapp.me/pubpaper/32341541 中文摘要(人工智能翻译,仅供参考):陷入群体的个人有时会失去自己的个性,冒着通常会避免的风险,以无端的敌对态度与外界接触。在这项研究中,我们确定了右侧背外侧前额叶皮层(rDLPFC)和右侧颞顶交界处(rTPJ)的组内神经同步是组间敌对性的潜在机制。我们将546个人组织为91个三对三人小组间比赛,诱导了组内亲和,并使用功能性近红外光谱仪测量了神经活动和组内同步。在组内亲和之后,个人给组内成员的钱比给组外成员的钱多,并且捐出更多的钱来击败竞争对手。组内亲和减少了rDLPFC的活动,并增加了rDLPFC和rTPJ之间的功能连接。尤其是在组外攻击期间,组内亲和还增加了rDLPFC和rTPJ中的组内同步,并且组内rDLPFC同步与组间敌对性正相关。组内同步减少前额活动可能可以解释组内联结如何导致对外界的冲动和集体敌视。
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fNIRS Journal Club 通知 2020/5/29, 11am

546个被试的大型实验是怎么做的?近红外超扫描技术如何揭开群体冲突的神经机制?北京时间2020年5月29日周五上午11点,北京师范大学的马燚娜教授(Yina Ma)将为大家讲解她们组刚刚在Nature Neuroscience发表的文章。 欢迎大家参加并参与讨论。 时间: 北京时间2020年5月29日周五上午11点 地点: https://zoom.com/j/84320310196房间号: 843 2031 0196 密码: 600516 她要讲的文献如下: Within-group synchronization in the prefrontal cortex associates with intergroup conflict....
Xu Cui
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One Reply to “6 experiments you should do with NIRS (vs fMRI)”

  1. Hi Dr. Cui,

    This was very helpful. I am sure someone will ask the same question in my defense (soon to come)! Thank you!

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