Functional near infrared spectroscopy or F nears is a method for measuring the hemodynamic response related to neural activity in the brain by using near infrared laser source detector pairs or optos placed on the participant's head. When neurons in a particular brain region increase their activity, their oxygen consumption also increases. This in turn, promotes increased blood flow into the active brain region.
As oxygenated and deoxygenated blood have different optical absorption properties, the optos placed on the outside of the skull can monitor these subtle changes. These changes correlate with the underlying brain activity and the probability pattern of photons between the source detector pair takes a banana shape. The closer the source detector pairs are placed, the better the spatial resolution, the further apart, the greater depth of penetration.
Hi, I'm Yuli Coman from Dr.Laura and Petito Cognitive Neuroscience of Nurse Brain Imaging and Gene's laboratory for language bilingualism and child development in the Department of Psychology at the University of Toronto. And hello, I'm Dr.Laura Ann Petito. Today, Dr.Lauren Petito, mark Linsky, melody Barens and I will collectively demonstrate the method for data acquisition and analysis using functional neuro infrared spectroscopy.
We use this procedure in our laboratory to study language and brain development in babies'children, and adults. So let's get started. Prior to the participant's arrival, prepare the room to be used for the study.
Remove extraneous articles that may be distracting to the participant. When the room is ready, set up and load the experimental protocol on the F Ns Hitachi ETG 4, 000 system like FMRI. This F NS system assesses hemodynamic response.
That is, it assesses the blood flow to brain regions actively involved in the task at hand. There are many advantages of F N'S over FMRI. For instance, it is quiet, portable, and does not require confinement in a narrow tube.
Importantly, the system allows us to observe awake and behaving infants and young children. F N's temporal resolution is comparable to FMRI and the sampling rate is much greater. The Hitachi ETG 4, 000 samples at 10 hertz.
Thus f nears is optimal for measuring brain activity via hemodynamic response. Experimental paradigms can be programmed with different presentation software, but in this study we will use ePrime. Since timing is key for data analysis, the experimental paradigm must be perfectly timed.
With data collection, the EF nurse Hitachi ETG 4, 000 system has triggering capabilities, which allows the experimental paradigm to trigger the data collection or vice versa. Here we will show triggering via the parallel port. Triggering can also be done using serial or USB ports test the triggering of the presentation program from the F Ners Hitachi ETG 4, 000 system.
Once tested, one is ready for the participant's arrival. Before the experiment can begin, participant's, parent or legal guardian must sign a consent form. A language assessment test is then given.
After the consent form has been signed, the participant is seated close to the F NS testing system. The position of the participant is crucial for standardizing the F Ns recording protocol. To enable consistent data interpretation, the optimal position is to have the participant adult or an older child seated comfortably in a chair.
Babies and young children are best seated on the mother's lap. Once situated, the session can move forward to opto placement. Accurate opto placement is as important as participant positioning for standardizing the F Ns recording protocol.
To achieve both the accurate neuro anatomical placement of probes and the confirmation of regions of interest, we use the International 10 20 system for electrode placement, we will demonstrate the procedure for the adult. The same procedure applies to all ages, babies, children, and adults. To begin, take the following head measurements with a tape measure and record them on the participant's data sheet.
First, measure and record the nain to Indian around next measure and record the Nain to Indian over top. After that measure and record, the ear to ear over top surgical tape can be used to mark specific target locations. In this experiment, we will mark the FP T three, T four, and F eight F seven positions.
Finally, the opto arrays are placed on the participant's head with specific optos anchored at 10 20 points as directed by the purposes of the experiment, which is now represented by the placement of surgical tape. Make sure that the fiber optics are hanging loosely without contact with the participant's body or the chair. When working with children and infants, we recommend playing a cartoon and having an extra person to entertain the child.
During the probe placement procedure, make sure to take digital photos of the probe positions for further verification to confirm stereotactic localization of the probe beret on the participant's skull 3D tracking information is obtained with a polyus fast track system. This information is then overlaid onto an anatomical MRI co-registration scan of the participant conducted with vitamin E capsules placed at each probe location. Once optos are placed on the participant's scalp, the signal quality is tested.
If an opto does not have a clear signal, for example, flat lines will indicate that the optos are not well connected. Gently remove hair from the connection of the opto and the scalp. On occasion, the optos may need to be wiped with an alcohol swab.
After checking that all optos have clear signals, the experiment begins. At least two. Experimenters must be always present during testing.
One, to observe the F nears Hitachi ETG 4, 000 realtime readout and the other. To observe the participant, we highly recommend having a video camera focused on the participant for post-talk observations. So in this experiment, you're going to hear sounds ba da.
So every time you hear da, I would like for you to press this button with your index finger. Ba BB da BB.Okay. You're going to look at the screen and you're gonna see words.
Some of them are gonna be real words and some of them are gonna be fake words, and all you have to do is read the words that you see.Alright? Okay.Alright.Now I'm gonna start When Zero away shade cold. An F near study can employ visual or auditory experimental paradigms.
The system is completely quiet and is thus perfectly suited for auditory experiments. Participants should keep their head and torso still, which doesn't preclude them from giving a verbal or a manual response. Once all the data have been collected, the optos are removed from the participant.
The participant is thanked for his or her time and willingness to participate and leaves the lab. The data collected by the Hitachi ETG 4, 000 is exported to another computer for data analysis. The F n's Hitachi, ETG 4, 000 measures the scattering and absorption of near infrared light from which the changes in concentration of oxygenated and deoxygenated hemoglobin are calculated as indicators of neural activity.
Therefore, the raw attenuation values measured in microvolts must be converted to oxygenated and deoxygenated hemoglobin values. Using the modified Beer Lambert equation, please see our written protocol for detailed explanations of how these equations are used. A typical hemodynamic response results in several distinct characteristics in the oxyhemoglobin response.
First, there is a characteristic dip. This dip occurs as a region of neurons activates and depletes available oxygen as blood flow increases carrying oxygenated hemoglobin, the oxyhemoglobin response rises rapidly above the initial baseline levels to a steady state level. When the region is no longer being activated, the oxyhemoglobin response decays over the next 12 to 15 seconds and slowly drops back to baseline levels.
There is occasionally an undershoot that occurs prior to the hemodynamic response returning to initial baseline levels. In contrast, atypical or bad results are usually the results of ods not properly seated on the scalp or excessive movement. Both oxy and deoxy responses move in a coordinated fashion.
This is demonstrated by shaking the fiber optics. We have just shown you how to use functional neurore spectroscopy to study language development in babies'children, and adults. A method developed here at the University of Toronto by Dr.Lauren Petito and her research team.
When doing this procedure, it's important to remember four things. Number one, make sure the room is clean and tidy, so as not to distract the participants. Number two, make sure the computer system is functioning properly before the participant arrives.
Number three, make sure the odes are positioned correctly using the 10 20 system. And number four, explore signal artifacts and analyze your data correctly. If used correctly, the NER system will allow you to unlock the secrets of the human brain.
If you have any questions, please don't hesitate to contact me. Laura am Petito at the University of Toronto. Thanks for watching and good luck with your experiments.
