This work was supported by the Australian Research Council grants CE110001021, DP170103148 and DP170102407. Wei He was supported by a Macquarie University Research Fellowship (MQRF, IRIS Project: 9201501199). Hannah Rapaport was supported by the Australian Government&#39;s Research Training Program (RTP) and the Macquarie University Research Excellence Scholarship (MQRES). Robert A Seymour was supported by PhD scholarships from Aston University, Birmingham, UK and Macquarie University, Sydney, Australia. Paul F. Sowman was supported by the National Health and Medical Research Council (1003760) and the Australian Research Council (DE130100868). The authors acknowledge the collaboration with the Kanazawa Institute of Technology and the Yokogawa Electric Corporation in establishing the KIT-Macquarie Brain Research Laboratory.

This research protocol has been approved by the Macquarie University Human Research Ethics Committee.
1. MEG Familiarization Resources
<ol>
	<li>Provide families with resources to learn about MEG prior to visiting the MEG laboratory, such as a child-friendly scientific article7 explaining MEG and the MSR, a story-board detailing the steps involved in completing the MEG experiment (e.g., Supplementary Figure 1 and an MEG information sheet for parents or caregivers (e.g., Supplementary Figure 2).</li>
</ol>
2. MEG Familiarization Session
NOTE: The familiarization session typically runs for 30 min, including an introduction to the MSR (5 minutes), a practice digitization (5 min), and MEG simulator training, including practice on the experimental task (20 min). Conduct the familiarization session between one-to-seven days prior to data acquisition.
<ol>
	<li>MSR introduction
	<ol>
		<li>Take the child on a tour of the MSR (&#34;spaceship&#34;) which is decorated in space-related wall art to reinforce the space mission theme.</li>
		<li>Ask the child to practice lying back with their head in the helmet dewar.</li>
		<li>Tell the child to lie as still as possible so that the spaceship stays on course and can reach its final destination.</li>
	</ol>
	</li>
	<li>Digitization:
	<ol>
		<li>Seat the child on a high chair and fit them with a polyester swimming cap (&#34;astronaut helmet&#34;) containing five marker coils. Adapt loose-fitting caps by folding up the sides. NOTE: The coils send data to a continuous motion tracking unit.</li>
		<li>Place a transmitter and three receivers around the child&#39;s neck.</li>
		<li>Ask the child to demonstrate their best &#39;statue&#39; pose and offer frequent positive reinforcement when they stay still. 
		NOTE: This serves to minimize head movement during digitization that may compromise the accuracy of the subsequent co-registration with the MEG sensors8.</li>
		<li>Use a pen digitizer (see Table of Materials) to record the position of three fiducial points (the nasion and left and right pre-auricular points) and the five marker coils, as well as the shape of the surface of the head. NOTE: This data is used to later determine the position of the child&#39;s head in relation to the MEG sensors.</li>
		<li>Remove the cap, transmitter and three receivers from the child&#39;s neck.</li>
	</ol>
	</li>
	<li>MEG simulator:
	<ol>
		<li>Take the child to the room housing the MEG simulator (see Table of Materials and steps 9 and 10 in Supplementary Figure 1), a full-size replica of an MEG system. The MEG simulator is decorated with space-themed stickers and is equipped with a mock helmet dewar, a bed, a button box and, for visual displays, a screen situated above the mock dewar</li>
		<li>Briefly describe the MEG scanning procedures (i.e., lying still and participating in the practice experimental task) through the narrative of a practice space mission.</li>
		<li>Fit the child with an &#39;astronaut helmet&#39; &#8212; a polyester swimming cap which has a motion detector attached at the front (see Table of Materials).</li>
		<li>Invite the child to lie in the simulator and watch a video of their choosing. If the child appears nervous, first demonstrate the experimental procedures with a toy. 
		NOTE: Whenever the child&#39;s head movement exceeds a pre-determined threshold (e.g., 5 mm), the motion tracking system (see Table of Materials) will automatically pause the video and wait for the experimenter to manually restart the video and restore the movement baseline.</li>
		<li>When the child completes this part of the simulator training, provide the child with training on the experimental task using a separate set of unique stimuli.</li>
		<li>At the end of the task training, offer the child an astronaut training certificate.</li>
	</ol>
	</li>
</ol>
3. MEG Data Acquisition Session
NOTE: The data acquisition session typically runs for approximately 30 min, including digitization (5 min), setting up the participant inside the MSR (5 min) and data acquisition (approximately 20 min, depending on the length of the experimental paradigm).
<ol>
	<li>Preliminary procedures
	<ol>
		<li>Conduct a 30-to-60 s empty room recording approximately 15 min before the child arrives to identify any significant external noise that is detected by the MEG system8.</li>
		<li>When the child arrives, confirm that they are not wearing any magnetic material on their clothes or carrying any in their body, as magnetic materials can distort the MEG signal (see Figure 1B for an example of signal noise due to metal on the participant). 
		NOTE: If the parent or caregiver wishes to accompany their child inside the MSR, the removal of magnetic materials applies to them too.</li>
	</ol>
	</li>
	<li>Digitization
	<ol>
		<li>Check whether the child needs to go to the toilet before commencing digitization, as once the digitization step is completed, the cap cannot be removed until the MEG acquisition session has finished.</li>
		<li>Repeat the digitization procedure outlined in the &#34;MEG familiarization session&#34; section above. 
		NOTE: If the cap moves more than 5 mm over the course of the experiment, perform a second digitization at the end of the experiment</li>
	</ol>
	</li>
	<li>MSR set-up
	<ol>
		<li>Take the child to the MSR (&#34;the spaceship&#34;). 
		NOTE: Two researchers are required for this procedure &#8212; one to accompany the child inside the MSR as the &#34;assistant researcher&#34; (along with the parent or caregiver, if desired) and one to run MEG data acquisition outside the MSR as the &#34;main researcher&#34;. The MSR set-up typically takes 5 min.</li>
		<li>Set up equipment inside the MSR (assistant researcher)
		<ol>
			<li>Ask the child to place their head into the helmet dewar.</li>
			<li>Check that the child&#39;s head is centrally aligned such that the crown of the head is as close as possible to the back of the helmet dewar without touching.</li>
			<li>Ensure that the child is comfortable, relaxed, and remains as still as possible during MEG recording.</li>
			<li>During the set-up, keep the child entertained by playing a video of their choosing on a screen above the dewar.</li>
		</ol>
		</li>
		<li>Set up equipment outside the MSR (main researcher)
		<ol>
			<li>Conduct a pre-experiment/baseline marker coil measurement to record the initial head position with respect to the helmet dewar.</li>
			<li>Conduct a co-registration between the child&#39;s head and the sensor array using both the initial marker coil measurement and the digitization head shape data. 
			NOTE: These preparatory measurements enable visual inspection of head position inside the dewar to ensure that the child&#39;s head is correctly positioned. If these conditions are not met, re-position the child and conduct another co-registration before starting data acquisition.</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>Data acquisition
	<ol>
		<li>Once satisfied with the head position with respect to the helmet dewar, start the MEG recording and the experimental task.</li>
		<li>Record ongoing head movements with a pediatric MEG software system called Real-Time Head Movement (ReTHM)9.</li>
	</ol>
	</li>
	<li>Ending the experiment
	<ol>
		<li>When the experimental task is finished, turn off ReTHM and end the MEG recording. Conduct a post-experiment marker coil measurement to measure the final head position with respect to the helmet dewar. 
		NOTE: This measurement provides a simple visual inspection of overall head movements during the experiment.</li>
		<li>Offer the child a gift bag (&#34;astronaut kit&#34;) for their participation and remunerate the family for their time and travel costs.</li>
	</ol>
	</li>
</ol>

<ol>
	<li>Baillet, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Magnetoencephalography+for+brain+electrophysiology+and+imaging.">Magnetoencephalography for brain electrophysiology and imaging.</a> Nature Neuroscience. 20, 327-339 (2017).</li><li>Gaetz, W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Magnetoencephalography+for+clinical+pediatrics:+Recent+advances+in+hardware,+hethods,+and+clinical+applications.">Magnetoencephalography for clinical pediatrics: Recent advances in hardware, hethods, and clinical applications.</a> Journal of Pediatric Epilepsy. 04, 139-155 (2015).</li><li>Stolk, A., Todorovic, A., Schoffelen, J. -. M., Oostenveld, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Online+and+offline+tools+for+head+movement+compensation+in+MEG.">Online and offline tools for head movement compensation in MEG.</a> Neuroimage. 68, 39-48 (2013).</li><li>Tesan, G., Johnson, B. W., Reid, M., Thornton, R., Crain, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Measurement+Of+Neuromagnetic+brain+function+in+pre-school+children+with+custom+sized+MEG.">Measurement Of Neuromagnetic brain function in pre-school children with custom sized MEG.</a> Journal of Visualized Experiments. (36), 2923-2934 (2010).</li><li>Johnson, B. W., Crain, S., Thornton, R., Tesan, G., Reid, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Measurement+of+brain+function+in+pre-school+children+using+a+custom+sized+whole-head+MEG+sensor+array.">Measurement of brain function in pre-school children using a custom sized whole-head MEG sensor array.</a> Clinical Neurophysiology. 121, 340-349 (2010).</li><li>He, W., Brock, J., Johnson, B. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Face-sensitive+brain+responses+measured+from+a+four-year-old+child+with+a+custom-sized+child+MEG+system.">Face-sensitive brain responses measured from a four-year-old child with a custom-sized child MEG system.</a> Journal of Neuroscience Methods. 222, 213-217 (2014).</li><li>Brock, J., Sowman, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Meg+for+kids:+listening+to+your+brain+with+super-cool+SQUIDs.">Meg for kids: listening to your brain with super-cool SQUIDs.</a> Frontiers for Young Minds. 2, 10-13 (2014).</li><li>Gross, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Good+practice+for+conducting+and+reporting+MEG+research.">Good practice for conducting and reporting MEG research.</a> Neuroimage. 65, 349-363 (2013).</li><li>Oyama, D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Real-Time+coil+position+monitoring+system+for+biomagnetic+measurements.">Real-Time coil position monitoring system for biomagnetic measurements.</a> Physics Procedia. 36, 280-285 (2012).</li><li>de Cheveign&#233;, A., Simon, J. Z. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Denoising+based+on+spatial+filtering.">Denoising based on spatial filtering.</a> Journal of Neuroscience Methods. 171, 331-339 (2008).</li><li>Cheyne, D., Jobst, C., Tesan, G., Crain, S., Johnson, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Movement-related+neuromagnetic+fields+in+preschool+age+children.">Movement-related neuromagnetic fields in preschool age children.</a> Human Brain Mapping. 35, 4858-4875 (2014).</li><li>N&#228;&#228;t&#228;nen, R., Pakarinen, S., Rinne, T., Takegata, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+mismatch+negativity+(MMN):+towards+the+optimal+paradigm.">The mismatch negativity (MMN): towards the optimal paradigm.</a> Clinical Neurophysiology. 115, 140-144 (2004).</li><li>He, W., Brock, J., Johnson, B. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Face+processing+in+the+brains+of+pre-school+aged+children+measured+with+MEG.">Face processing in the brains of pre-school aged children measured with MEG.</a> Neuroimage. 106, 317-327 (2015).</li><li>Wehner, D. T., H&#228;m&#228;l&#228;inen, M. S., Mody, M., Ahlfors, S. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Head+movements+of+children+in+MEG:+quantification,+effects+on+source+estimation,+and+compensation.">Head movements of children in MEG: quantification, effects on source estimation, and compensation.</a> Neuroimage. 40, 541-550 (2008).</li></ol>

The authors have nothing to disclose.

In recent years, MEG has been established as a valuable non-invasive neuroimaging technique for investigating the neural mechanisms underpinning brain development1. However, in-scanner head movements pose a notorious barrier to obtaining good quality MEG data, particularly when assessing pediatric populations. To overcome this problem, this article presented a pediatric MEG research protocol which builds upon procedures outlined in a previous paper from the KIT-Macquarie Brain Research Laboratory 4.
The critical procedures include (1) providing children with MEG familiarization resources from which they can learn about the MEG experiment prior to visiting the lab, which include a child-friendly research article7 explaining the MEG system and the magnetically shielded room (MSR), a story-board outlining 10 simple steps for completing the MEG experiment (Supplementary Figure 1), and an MEG information sheet for parents and caregivers (Supplementary Figure 2); (2) Preceding the MEG acquisition session with a familiarization session, wherein children are acquainted with MEG procedures and are trained to keep their heads still whilst lying inside an MEG simulator; (3) using passive or &#34;gamified&#34; experimental paradigms to minimize head movement due to boredom and restlessness; and (4) tracking ongoing head movements during online data acquisition using a Real-Time Head Movement (ReTHM) system9. Data obtained from ReTHM can be used to conduct offline correction of head movement artefacts when pre-processing the MEG data.
The acquisition of high-quality MEG data critically depends upon the child feeling at ease in the novel MEG environment. To foster this sense of ease, researchers are encouraged to devote time to familiarizing children and their families with the MEG environment and procedures prior to commencing data acquisition. This can be achieved through offering children and their parents MEG resources which explain the MEG procedures in simple, accessible language. Furthermore, families can be invited to visit the MEG laboratory before the data acquisition session to meet the researchers and practice the MEG testing procedures. Through training on the MEG simulator, children implicitly learn the importance of keeping their heads still whilst lying in the MEG. While the MEG familiarization requires both the researchers and the families to devote additional time to the data collection process, the advantages of improving MEG data quality, as well as minimizing the time and cost of conducting subsequent MEG data acquisition sessions, arguably outweighs this downside. Furthermore, performance and compliance during the familiarization session can be used to indicate whether the child is or is not suitable to invite back for an actual MEG data acquisition session.
To minimize in-scanner head movement due to restlessness, it is preferable to use a passive experimental paradigm which does not require instructions, overt attention or active participation. For example, a reliable evoked response can be obtained with an auditory oddball paradigm12, whereby the participant passively listens to a sequence of auditory tones whilst entertained by a silent video. For studies requiring an overt response, the researcher should aim to embed the experimental task in an engaging game-style paradigm11. This improves cooperation and minimizes restlessness during the task. In visual experiments, the use of an MEG-compatible eye-tracker entails little additional set-up time but is necessary in ensuring that children have fixated on the position of the visual stimulus13.
Any residual head movement artefacts can be corrected for using real-time head motion tracking. For example, data obtained from ReTHM can be stored in the MEG recording file and used to compensate for head movement during data acquisition in such a way that head-to-sensor localization can be restored to the pre-movement level to allow for an optimal source reconstruction which is essential for subsequent source level data analyses14.
The implementation of this protocol seeks to improve the quality of pediatric MEG data, minimize participant attrition rates in longitudinal studies, and ensure that families have an enjoyable experience of MEG research participation, with the overarching goal of improving our understanding of early brain development in both typical and atypical populations.

Magnetoencephalography (MEG) is a non-invasive functional neuroimaging technique which measures magnetic fields produced by the electrical activity of the human brain1,2. MEG offers excellent temporal resolution and superior spatial resolution compared with electroencephalography (EEG) due to the lack of signal smearing from the biological tissues between the brain sources and the sensors. In addition, MEG does not involve exposure to loud noises, radiation or magnetic fields. Set-up time is rapid and participants can be accompanied by a parent or caregiver throughout testing. Taken together, these features make MEG a promising tool for investigating the development of typical and atypical brain function in young children2.
To measure brain responses using MEG, research participants must insert their heads into a helmet housing a fixed array of superconducting sensors. It is crucial that the participants keeps their heads still throughout the MEG recording, as changes in the head position relative to the sensors both degrade the neuromagnetic signal distribution and impede accurate source estimation. Inaccurate source estimation inevitably leads to inaccurate statistical inferences in source power, functional connectivity and network analyses3.
Minimizing head movement can be particularly challenging during pediatric MEG assessment for a number of reasons. First, assessing young children in an adult MEG system is problematic as children&#39;s heads are much smaller than those of adults, and the increased space between the helmet and the child&#39;s scalp allows for unconstrained head movement. Second, the novel MEG environment &#8212; a large machine locked inside a windowless magnetically shielded room &#8212; can be intimidating for young children, and head movement may be a consequence of anxiousness. Third, without training, children may not fully understand or comply with the requirement to remain still for the duration of the experiment. Finally, children who have a limited capacity to tolerate boredom may find that some MEG experiments take too long or are tedious, resulting in restlessness and head movement artefacts.
To tackle the long-standing challenge of head movement in pediatric MEG research, this article presents recent hardware and methodological advances that are implemented in the child-friendly MEG protocol used at the KIT-Macquarie Brain Research Laboratory (Macquarie University, Sydney, Australia). As outlined in a previous paper from this laboratory4, the problems involved in the use of a loose-fitting adult-sized helmet dewar have been addressed by installing a world-first, whole-head pediatric MEG system with a bespoke helmet dewar to better fit the heads of young children between approximately three-to-six years of age. This hardware adaptation improves the signal-to-noise ratio, as the sensors are physically closer, on average, to the child&#39;s scalp5,6. More recently, the KIT-Macquarie Brain Research Laboratory has developed several new and novel procedures to overcome the aforementioned antecedents of head movement and hence to improve data quality.
All of the procedures in this protocol are explained through a narrative in which the child participant actively engages in an &#34;astronaut space mission&#34;. This narrative ensures that the child&#39;s MEG research experience is not only less intimidating, but also exciting. Implementing these procedures into a child-friendly MEG protocol is important for improving data quality, minimizing participant attrition rates in longitudinal studies, and ensuring that families have a positive experience in their research participation.

<table border="0" cellpadding="0" cellspacing="0" style="width:1073px;" width="1074">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="42">
			<td height="42" style="height:42px;width:215px;">5 marker Coil set</td>
			<td style="width:505px;">Kanazawa Institute of Technology (KIT) and Yokogawa Electric Corporation, Japan</td>
			<td style="width:119px;">PQ11MKA</td>
			<td style="width:235px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:215px;">Fastrak Digitizer &#8211; 3D</td>
			<td style="width:505px;">Polhemus Cochester, VT, USA</td>
			<td style="width:119px;">1A0383-001</td>
			<td>Pen digitizer</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:215px;">Magnetoencephalography (MEG)</td>
			<td style="width:505px;">Kanazawa Institute of Technology (KIT) and Yokogawa Electric Corporation, Japan</td>
			<td style="width:119px;">PQ1160C</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:215px;">MEG simulator</td>
			<td style="width:505px;">Fino, NSW, Australia</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:215px;">MoTrack system</td>
			<td>Psychological Software Tools, PA, USA</td>
			<td style="width:119px;">MTK-09314-1307</td>
			<td>Motion tracking system</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:215px;">Polyester caps</td>
			<td style="width:505px;">Speedo</td>
			<td style="width:119px;">N/A</td>
			<td>product code: SPE11733.435</td>
		</tr>
	</tbody>
</table>

studying brain function in children using magnetoencephalography

Magnetoencephalography (MEG) is a non-invasive neuroimaging technique which directly measures magnetic fields produced by the electrical activity of the human brain. MEG is quiet and less likely to induce claustrophobia compared with magnetic resonance imaging (MRI). It is therefore a promising tool for investigating brain function in young children. However, analysis of MEG data from pediatric populations is often complicated by head movement artefacts which arise as a consequence of the requirement for a spatially-fixed sensor array that is not affixed to the child's head. Minimizing head movements during MEG sessions can be particularly challenging as young children are often unable to remain still during experimental tasks. The protocol presented here aims to reduce head movement artefacts during pediatric MEG scanning. Prior to visiting the MEG laboratory, families are provided with resources that explain the MEG system and the experimental procedures in simple, accessible language. An MEG familiarization session is conducted during which children are acquainted with both the researchers and the MEG procedures. They are then trained to keep their head still whilst lying inside an MEG simulator. To help children feel at ease in the novel MEG environment, all of the procedures are explained through the narrative of a space mission. To minimize head movement due to restlessness, children are trained and assessed using fun and engaging experimental paradigms. In addition, children's residual head movement artefacts are compensated for during the data acquisition session using a real-time head movement tracking system. Implementing these child-friendly procedures is important for improving data quality, minimizing participant attrition rates in longitudinal studies, and ensuring that families have a positive research experience.

Common Magnetoencephalography signals 
Common MEG signals are displayed in Figure 1, including a normal MEG signal (Figure 1A), as well as MEG signal noise due to metal on the participant (Figure 1B), in which case unlock the sensors, open the MSR door and ask the participant to remove any metal from their body, then take the metal object out of the MSR and perform an auto-tune before repeating the procedures outlined in section 3.5; interference from an electronic device (Figure 1C, most often from a mobile phone), in which case turn off any electronic devices or move them away from the MSR; a clenched jaw (Figure 1D), in which case remind the participant to relax their jaw for the duration of the MEG recording; alpha waves (Figure 1E; these are defined by eight to 12 continuous waves in a 1 s interval), in which case check that the participant is not asleep (it is fine to continue if they are awake); and trapped magnetic flux (Figure 1F); in which case unlock the sensors and turn on the coil heaters on for 5 min. If the flux persists after a subsequent auto-tuning, mark affected channel for removal from subsequent data analysis.
Head movement during data acquisition 
Pediatric MEG data before and after ReTHM correction is displayed in Figure 2. Data was collected from a three-year-old boy who passively listened to auditory tones for 15 min. Data was de-noised10, band-pass filtered11 (1-15 Hz), baseline-corrected and averaged. Root-mean-square (RMS) magnetic waveforms (in the right column) were computed from all sensors. Averaged in-scanner head movements were 44.3 mm. As demonstrated, ReTHM compensated for motion-related artefacts, resulting in more focal isofield contour maps (at the peak of the RMS waveforms; (A), less distorted RMS magnetic waveforms (B), and more meaningful source reconstruction (C) in the bilateral auditory lobes.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/58909/58909fig1.jpg" /> 
Figure 1: Examples of common MEG signals. (A) A normal MEG signal. (B-F) MEG signal noise due to (B) metal on the participant (specifically, noise caused by a small metal buckle on a singlet strap), (C) interference from an electronic device, (D) a clenched jaw, (E) alpha waves, and (F) trapped magnetic flux. For panels C, E, and F, the time scale on the x-axis is in 10-second intervals, and amplitude scale on the y-axis is 32768 A/D. <a href="https://www.jove.com/files/ftp_upload/58909/58909fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/58909/58909fig2.jpg" /> 
Figure 2. Pediatric MEG data before and after Real-Time Head Movement (ReTHM) correction. Data was collected from a three-year-old boy who passively listened to auditory tones for 15 min. Averaged in-scanner head movements were 44.3 mm. (A) More focused isofield contour maps at the peak of the root mean square (RMS) waveforms; (B) less distorted RMS magnetic waveforms, and (C) more meaningful source reconstruction in the bilateral auditory lobes are revealed after ReTHM correction. <a href="https://www.jove.com/files/ftp_upload/58909/58909fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Supplementary Figure 1" src="/files/ftp_upload/58909/58909supfig1.jpg" /> 
Supplementary Figure 1: A story board outlining 10 simple steps for completing the &#34;astronaut training&#34; (i.e., the MEG experiment). This is sent to families prior to visiting the MEG laboratory in order to guide children&#39;s expectations for the acquisition session, as well as to build excitement in anticipation of the &#34;astronaut training&#34;. On data acquisition day, the children follow the story as the experiment progresses and collect stamps after completing each step. Photographs reproduced with informed written parental consent. <a href="https://www.jove.com/files/ftp_upload/58909/58909supfig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Supplementary Figure 2" src="/files/ftp_upload/58909/58909supfig2v2.jpg" /> 
Supplementary Figure 2: An MEG information sheet for parents or caregivers explaining the MEG, the MSR, what to expect on data acquisition day and what to wear. Photograph reproduced with informed written parental consent. <a href="https://www.jove.com/files/ftp_upload/58909/58909supfig2v2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Studying Brain Function in Children Using Magnetoencephalography at JoVE.com

Studying Brain Function in Children Using Magnetoencephalography

This article introduces a child-friendly research protocol designed to improve data quality by reducing head movement during pediatric magnetoencephalography (MEG). We familiarize families with the MEG environment, train children to remain still using an MEG simulator, and correct for residual head movement artefacts using a real-time head movement detection system.

Magnetoencephalography (MEG) is a non-invasive neuroimaging technique which directly measures magnetic fields produced by the electrical activity of the ...

studying-brain-function-in-children-using-magnetoencephalography

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JoVE Journal

Neuroscience

9.0K Views.  Macquarie University. This article introduces a child-friendly research protocol designed to improve data quality by reducing head movement during pediatric magnetoencephalography (MEG). We familiarize families with the MEG environment, train children to remain still using an MEG simulator, and correct for residual head movement artefacts using a real-time head movement detection system.

Video: Studying Brain Function in Children Using Magnetoencephalography

Studying Synaptic Vesicle Pools using Photoconversion of Styryl Dyes

The fusion of synaptic vesicles with the plasma membrane (exocytosis) is a required step in neurotransmitter release and neuronal communication. The vesicles are then retrieved from the plasma membrane (endocytosis) and grouped together with the general pool of vesicles within the nerve terminal, until they undergo a new exo- and endocytosis cycle (vesicle recycling). These processes have been studied using a variety of techniques such as electron microscopy, electrophysiology recordings, amperometry and capacitance measurements. Importantly, during the last two decades a number of fluorescently labeled markers emerged, allowing optical techniques to track vesicles in their recycling dynamics. One of the most commonly used markers is the styryl or FM dye 1; structurally, all FM dyes contain a hydrophilic head and a lipophilic tail connected through an aromatic ring and one or more double bonds (Fig. 1B). A classical FM dye experiment to label a pool of vesicles consists in bathing the preparation (Fig. 1Ai) with the dye during the stimulation of the nerve (electrically or with high K+). This induces vesicle recycling and the subsequent loading of the dye into recently endocytosed vesicles (Fig. 1Ai-iii). After loading the vesicles with dye, a second round of stimulation in a dye-free bath would trigger the FM release through exocytosis (Fig. 1Aiv-v), process that can be followed by monitoring the fluorescence intensity decrease (destaining).

Although FM dyes have contributed greatly to the field of vesicle recycling, it is not possible to determine the exact localization or morphology of individual vesicles by using conventional fluorescence microscopy. For that reason, we explain here how FM dyes can also be used as endocytic markers using electron microscopy, through photoconversion. The photoconversion technique exploits the property of fluorescent dyes to generate reactive oxygen species under intense illumination. Fluorescently labeled preparations are submerged in a solution containing diaminobenzidine (DAB) and illuminated. Reactive species generated by the dye molecules oxidize the DAB, which forms a stable, insoluble precipitate that has a dark appearance and can be easily distinguished in electron microscopy 2,3. As DAB is only oxidized in the immediate vicinity of fluorescent molecules (as the reactive oxygen species are short-lived), the technique ensures that only fluorescently labeled structures are going to contain the electron-dense precipitate. The technique thus allows the study of the exact location and morphology of actively recycling organelles.

FM dyes have been of invaluable help in the understanding of synaptic dynamics. FMs are normally followed under the fluorescent microscope during different stimulation conditions. However, photoconversion of FM dyes combined with electron microscopy allows the visualization of distinct synaptic vesicle pools, among other ultrastructure components, in synaptic boutons.

The fusion of synaptic vesicles with the plasma membrane (exocytosis) is a required step in neurotransmitter release and neuronal communication. The ...

In utero Electroporation followed by Primary Neuronal Culture for Studying Gene Function in Subset of Cortical Neurons

In vitro study of primary neuronal cultures allows for quantitative analyses of neurite outgrowth. In order to study how genetic alterations affect neuronal process outgrowth, shRNA or cDNA constructs can be introduced into primary neurons via chemical transfection or viral transduction. However, with primary cortical cells, a heterogeneous pool of cell types (glutamatergic neurons from different layers, inhibitory neurons, glial cells) are transfected using these methods. The use of in utero electroporation to introduce DNA constructs in the embryonic rodent cortex allows for certain subsets of cells to be targeted: while electroporation of early embryonic cortex targets deep layers of the cortex, electroporation at late embryonic timepoints targets more superficial layers. Further, differential placement of electrodes across the heads of individual embryos results in the targeting of dorsal-medial versus ventral-lateral regions of the cortex. Following electroporation, transfected cells can be dissected out, dissociated, and plated in vitro for quantitative analysis of neurite outgrowth. Here, we provide a step-by-step method to quantitatively measure neuronal process outgrowth in subsets of cortical cells.
The basic protocol for in utero electroporation has been described in detail in two other JoVE articles from the Kriegstein lab 1, 2. We will provide an overview of our protocol for in utero electroporation, focusing on the most important details, followed by a description of our protocol that applies in utero electroporation to the study of gene function in neuronal process outgrowth.

In utero Electroporation followed by Primary Neuronal Culture for Studying Gene Function in Subset of Cortical Neurons

In utero electroporation is a valuable method for transfecting neuronal progenitor cells in vivo. Depending upon the placement of the electrodes and the developmental timepoint of electroporation, certain subsets of cortical cells can be targeted. Targeted cells can then be analyzed in vivo or in vitro for effects of genetic alteration.

In vitro study of primary neuronal cultures allows for quantitative analyses of neurite outgrowth. In order to study how genetic alterations affect ...

Assessment of Cerebral Lateralization in Children using Functional Transcranial Doppler Ultrasound (fTCD)

There are many unanswered questions about cerebral lateralization. In particular, it remains unclear which aspects of language and nonverbal ability are lateralized, whether there are any disadvantages associated with atypical patterns of cerebral lateralization, and whether cerebral lateralization develops with age. In the past, researchers interested in these questions tended to use handedness as a proxy measure for cerebral lateralization, but this is unsatisfactory because handedness is only a weak and indirect indicator of laterality of cognitive functions1. Other methods, such as fMRI, are expensive for large-scale studies, and not always feasible with children2.
Here we will describe the use of functional transcranial Doppler ultrasound (fTCD) as a cost-effective, non-invasive and reliable method for assessing cerebral lateralization. The procedure involves measuring blood flow in the middle cerebral artery via an ultrasound probe placed just in front of the ear. Our work builds on work by Rune Aaslid, who co-introduced TCD in 1982, and Stefan Knecht, Michael Deppe and their colleagues at the University of M&uuml;nster, who pioneered the use of simultaneous measurements of left- and right middle cerebral artery blood flow, and devised a method of correcting for heart beat activity. This made it possible to see a clear increase in left-sided blood flow during language generation, with lateralization agreeing well with that obtained using other methods3.
The middle cerebral artery has a very wide vascular territory (see Figure 1) and the method does not provide useful information about localization within a hemisphere. Our experience suggests it is particularly sensitive to tasks that involve explicit or implicit speech production. The 'gold standard' task is a word generation task (e.g. think of as many words as you can that begin with the letter 'B') 4, but this is not suitable for young children and others with limited literacy skills. Compared with other brain imaging methods, fTCD is relatively unaffected by movement artefacts from speaking, and so we are able to get a reliable result from tasks that involve describing pictures aloud5,6. Accordingly, we have developed a child-friendly task that involves looking at video-clips that tell a story, and then describing what was seen.

Assessment of Cerebral Lateralization in Children using Functional Transcranial Doppler Ultrasound fTCD

Functional transcranial Doppler sonography (fTCD) is a simple and non-invasive ultrasound technique which can be used to assess the lateralization of cognitive functions, especially language, and is suitable for use with children.

There are many unanswered questions about cerebral lateralization.  In particular, it remains unclear which aspects of language and nonverbal ability are ...

Mosaic Analysis of Gene Function in Postnatal Mouse Brain Development by Using Virus-based Cre Recombination

Normal brain function relies not only on embryonic development when major neuronal pathways are established, but also on postnatal 
development when neural circuits are matured and refined. Misregulation at this stage may lead to neurological and psychiatric disorders such as autism 
and schizophrenia1,2. Many genes have been studied in the prenatal brain and found crucial to many developmental processes3-5. However, their 
function in the postnatal brain is largely unknown, partly because their deletion in mice often leads to lethality during neonatal development, and partly because their requirement in early development hampers the postnatal analysis. To overcome these obstacles, floxed alleles of these genes are currently being generated in mice 6. When combined with transgenic alleles that express Cre recombinase in specific cell types, conditional deletion can be achieved to study gene function in the postnatal brain. However, this method requires additional alleles and extra time (3-6 months) to generate the mice with appropriate genotypes, thereby limiting the expansion of the genetic analysis to a large scale in the mouse brain.
Here we demonstrate a complementary approach that uses virally-expressed Cre to study these floxed alleles rapidly and 
systematically in postnatal brain development. By injecting recombinant adeno-associated viruses (rAAVs)7,8 encoding Cre into the neonatal brain, 
we are able to delete the gene of interest in different regions of the brain. By controlling the viral titer and coexpressing a fluorescent 
protein marker, we can simultaneously achieve mosaic gene inactivation and sparse neuronal labeling. This method bypasses the requirement of 
many genes in early development, and allows us to study their cell autonomous function in many critical processes in postnatal brain development,
 including axonal and dendritic growth, branching, and tiling, as well as synapse formation and refinement. This method has been used successfully 
in our own lab (unpublished results) and others8,9, and can be extended to other viruses, such as lentivirus 9, as well as to the expression of 
shRNA or dominant active proteins 10. Furthermore, by combining this technique with electrophysiology as well as recently-developed optical 
imaging tools 11, this method provides a new strategy to study how genetic pathways influence neural circuit development and function in mice 
and rats.

An in vivo method to test gene function in postnatal brain is described. Recombinant AAVs expressing Cre and/or a fluorescent protein are injected into neonatal mouse brain. Mosaic gene inactivation and sparse neuronal labeling are achieved, allowing rapid analysis of gene function in processes critical to neural circuit development.

Normal brain function relies not only on embryonic development when major neuronal pathways are established, but also on postnatal 
development when ...

In ovo Electroporation in Chick Midbrain for Studying Gene Function in Dopaminergic Neuron Development

Dopaminergic neurons located in the ventral midbrain control movement, emotional behavior, and reward mechanisms1-3. The dysfunction of ventral midbrain dopaminergic neurons is implicated in Parkinson's disease, Schizophrenia, depression, and dementia1-5. Thus, studying the regulation of midbrain dopaminergic neuron differentiation could not only provide important insight into mechanisms regulating midbrain development and neural progenitor fate specification, but also help develop new therapeutic strategies for treating a variety of human neurological disorders.
Dopaminergic neurons differentiate from neural progenitors lining the ventricular zone of embryonic ventral midbrain. The development of neural progenitors is controlled by gene expression programs6,7. Here we report techniques utilizing electroporation to express genes specifically in the midbrain of Hamburger Hamilton (HH) stage 11 (thirteen somites, 42 hours) chick embryos8,9. The external development of chick embryos allows for convenient experimental manipulations at specific embryonic stages, with the effects determined at later developmental time points10-13. Chick embryonic neural tubes earlier than HH stage 13 (nineteen somites, 48 hours) consist of multipotent neural progenitors that are capable of differentiating into distinct cell types of the nervous system. The pCAG vector, which contains both a CMV promoter and a chick &beta;-actin enhancer, allows for robust expression of Flag or other epitope-tagged constructs in embryonic chick neural tubes14. In this report, we emphasize special measures to achieve regionally restricted gene expression in embryonic midbrain dopaminergic neuron progenitors, including how to inject DNA constructs specifically into the embryonic midbrain region and how to pinpoint electroporation with small custom-made electrodes. Analyzing chick midbrain at later stages provides an excellent in vivo system for plasmid vector-mediated gain-of-function and loss-of-function studies of midbrain development. Modification of the experimental system may extend the assay to other parts of the nervous system for performing fate mapping analysis and for investigating the regulation of gene expression.

In ovo Electroporation in Chick Midbrain for Studying Gene Function in Dopaminergic Neuron Development

To assess the function and the regulation of genes during the development of midbrain dopaminergic neurons, we describe a method that involves in ovo electroporation of plasmid DNA constructs into embryonic chick ventral midbrain dopaminergic neuron progenitors. This technique can be used to achieve efficient expression of genes of interest to study different aspects of midbrain development and dopaminergic neuron differentiation.

Dopaminergic neurons located in the ventral midbrain control movement, emotional behavior, and reward mechanisms1-3. The dysfunction of ventral midbrain ...

Functional Neuroimaging Using Ultrasonic Blood-brain Barrier Disruption and Manganese-enhanced MRI

Although mice are the dominant model system for studying the genetic and molecular underpinnings of neuroscience, functional neuroimaging in mice remains technically challenging. One approach, Activation-Induced Manganese-enhanced MRI (AIM MRI), has been used successfully to map neuronal activity in rodents 1-5. In AIM MRI, Mn2+ acts a calcium analog and accumulates in depolarized neurons 6,7. Because Mn2+ shortens the T1 tissue property, regions of elevated neuronal activity will enhance in MRI. Furthermore, Mn2+ clears slowly from the activated regions; therefore, stimulation can be performed outside the magnet prior to imaging, enabling greater experimental flexibility. However, because Mn2+ does not readily cross the blood-brain barrier (BBB), the need to open the BBB has limited the use of AIM MRI, especially in mice.
One tool for opening the BBB is ultrasound. Though potentially damaging, if ultrasound is administered in combination with gas-filled microbubbles (i.e., ultrasound contrast agents), the acoustic pressure required for BBB opening is considerably lower. This combination of ultrasound and microbubbles can be used to reliably open the BBB without causing tissue damage 8-11.
Here, a method is presented for performing AIM MRI by using microbubbles and ultrasound to open the BBB. After an intravenous injection of perflutren microbubbles, an unfocused pulsed ultrasound beam is applied to the shaved mouse head for 3 minutes. For simplicity, we refer to this technique of BBB Opening with Microbubbles and UltraSound as BOMUS 12. Using BOMUS to open the BBB throughout both cerebral hemispheres, manganese is administered to the whole mouse brain. After experimental stimulation of the lightly sedated mice, AIM MRI is used to map the neuronal response.
To demonstrate this approach, herein BOMUS and AIM MRI are used to map unilateral mechanical stimulation of the vibrissae in lightly sedated mice 13. Because BOMUS can open the BBB throughout both hemispheres, the unstimulated side of the brain is used to control for nonspecific background stimulation. The resultant 3D activation map agrees well with published representations of the vibrissae regions of the barrel field cortex 14. The ultrasonic opening of the BBB is fast, noninvasive, and reversible; and thus this approach is suitable for high-throughput and/or longitudinal studies in awake mice.

A technique is described for broadly opening the blood-brain barrier in the mouse using microbubbles and ultrasound. Using this technique, manganese can be administered to the mouse brain. Because manganese is an MRI contrast agent that accumulates in depolarized neurons, this approach enables imaging of neuronal activity.

Although mice are the dominant model system for studying the genetic and molecular underpinnings of neuroscience, functional neuroimaging in mice remains ...

Co-analysis of Brain Structure and Function using fMRI and Diffusion-weighted Imaging

The study of complex computational systems is facilitated by network maps, such as circuit diagrams. Such mapping is particularly informative when studying the brain, as the functional role that a brain area fulfills may be largely defined by its connections to other brain areas. In this report, we describe a novel, non-invasive approach for relating brain structure and function using magnetic resonance imaging (MRI). This approach, a combination of structural imaging of long-range fiber connections and functional imaging data, is illustrated in two distinct cognitive domains, visual attention and face perception. Structural imaging is performed with diffusion-weighted imaging (DWI) and fiber tractography, which track the diffusion of water molecules along white-matter fiber tracts in the brain (Figure 1). By visualizing these fiber tracts, we are able to investigate the long-range connective architecture of the brain. The results compare favorably with one of the most widely-used techniques in DWI, diffusion tensor imaging (DTI). DTI is unable to resolve complex configurations of fiber tracts, limiting its utility for constructing detailed, anatomically-informed models of brain function. In contrast, our analyses reproduce known neuroanatomy with precision and accuracy. This advantage is partly due to data acquisition procedures: while many DTI protocols measure diffusion in a small number of directions (e.g., 6 or 12), we employ a diffusion spectrum imaging (DSI)1, 2 protocol which assesses diffusion in 257 directions and at a range of magnetic gradient strengths. Moreover, DSI data allow us to use more sophisticated methods for reconstructing acquired data. In two experiments (visual attention and face perception), tractography reveals that co-active areas of the human brain are anatomically connected, supporting extant hypotheses that they form functional networks. DWI allows us to create a "circuit diagram" and reproduce it on an individual-subject basis, for the purpose of monitoring task-relevant brain activity in networks of interest.

We describe a novel approach for simultaneous analysis of brain function and structure using magnetic resonance imaging (MRI). We assess brain structure with high-resolution diffusion-weighted imaging and white-matter fiber tractography. Unlike standard structural MRI, these techniques allow us to directly relate anatomical connectivity to functional properties of brain networks.

The study of complex computational systems is facilitated by network maps, such as circuit diagrams. Such mapping is particularly informative when ...

Imaging Serotonergic Fibers in the Mouse Spinal Cord Using the CLARITY/CUBIC Technique

Long descending fibers to the spinal cord are essential for locomotion, pain perception, and other behaviors. The fiber termination pattern in the spinal cord of the majority of these fiber systems have not been thoroughly investigated in any species. Serotonergic fibers, which project to the spinal cord, have been studied in rats and opossums on histological sections and their functional significance has been deduced based on their fiber termination pattern in the spinal cord. With the development of CLARITY and CUBIC techniques, it is possible to investigate this fiber system and its distribution in the spinal cord, which is likely to reveal previously unknown features of serotonergic supraspinal pathways. Here, we provide a detailed protocol for imaging the serotonergic fibers in the mouse spinal cord using the combined CLARITY and CUBIC techniques. The method involves perfusion of a mouse with a hydrogel solution and clarification of the tissue with a combination of clearing reagents. Spinal cord tissue was cleared in just under two weeks, and the subsequent immunofluorescent staining against serotonin was completed in less than ten days. With a multi-photon fluorescent microscope, the tissue was scanned and a 3D image was reconstructed using Osirix software.

Supraspinal projections are important for pain perception and other behaviors, and serotonergic fibers are one of these fiber systems. The present study focused on the application of the combined CLARITY/CUBIC protocol to the mouse spinal cord in order to investigate the termination of these serotonergic fibers.

Long descending fibers to the spinal cord are essential for locomotion, pain perception, and other behaviors. The fiber termination pattern in the spinal ...

Chronic Implantation of Whole-cortical Electrocorticographic Array in the Common Marmoset

Electrocorticography (ECoG) allows the monitoring of electrical field potentials from the cerebral cortex with high spatiotemporal resolution. Recent development of thin, flexible ECoG electrodes has enabled conduction of stable recordings of large-scale cortical activity. We have developed a whole-cortical ECoG array for the common marmoset. The array continuously covers almost the entire lateral surface of cortical hemisphere, from the occipital pole to the temporal and frontal poles, and it captures whole-cortical neural activity in one shot. This protocol describes a chronic implantation procedure of the array in the epidural space of the marmoset brain. Marmosets have two advantages regarding ECoG recordings, one being the homologous organization of anatomical structures in humans and macaques, including frontal, parietal, and temporal complexes. The other advantage is that the marmoset brain is lissencephalic and contains a large number of complexes, which are more difficult to access in macaques with ECoG, that are exposed to the brain surface.These features allow direct access to most cortical areas beneath the surface of the brain. This system provides an opportunity to investigate global cortical information processing with high resolutions at a sub-millisecond order in time and millimeter order in space.

We have developed a whole-cortical electrocorticographic array for the common marmoset that continuously covers almost the entire lateral surface of cortex, from the occipital pole to the temporal and frontal poles. This protocol describes a chronic implantation procedure of the array in the epidural space of the marmoset brain.

Electrocorticography (ECoG) allows the monitoring of electrical field potentials from the cerebral cortex with high spatiotemporal resolution. Recent ...

3D Kinematic Analysis for the Functional Evaluation in the Rat Model of Sciatic Nerve Crush Injury

Compared to the Sciatic Functional Index (SFI), kinematic analysis is a more reliable and sensitive method for performing functional evaluations of sciatic nerve injury rodent models. In this protocol, we describe a novel kinematic analysis method that uses a three-dimensional (3D) motion capture apparatus for functional evaluations using a rat sciatic nerve crush injury model. First, the rat is familiarized with treadmill walking. Markers are then attached to the designated bone landmarks and the rat is made to walk on the treadmill at the desired speed. Meanwhile, the posterior limb movements of the rat are recorded using four cameras. Depending on the software used, marker tracings are created using both automatic and manual modes and the desired data are produced after subtle adjustments. This method of kinematic analysis, which uses a 3D motion capture apparatus, offers numerous advantages, including superior precision and accuracy. Many more parameters can be investigated during the comprehensive functional evaluations. This method has several shortcomings that require consideration: The system is expensive, can be complicated to operate, and may produce data deviations due to skin shifting. Nevertheless, kinematic analysis using a 3D motion capture apparatus is useful for performing functional anterior and posterior limb evaluations. In the future, this method may become increasingly useful for generating accurate assessments of various traumas and diseases.

We introduce a kinematic analysis method that uses a three-dimensional motion capture apparatus containing four cameras and data processing software for performing functional evaluations during fundamental research involving rodent models.

Compared to the Sciatic Functional Index (SFI), kinematic analysis is a more reliable and sensitive method for performing functional evaluations of ...