Name: assessing pupil-linked changes in locus coeruleus-mediated arousal elicited by trigeminal stimulation
Uploaded: 2019-11-26T12:30:00
Description: Watch this Scientific Journal Video about Assessing Pupil-linked Changes in Locus Coeruleus-mediated Arousal Elicited by Trigeminal Stimulation at JoVE.com

The research was supported by grants of the University of Pisa. We thank Mr. Paolo Orsini, Mr. Francesco Montanari, and Mrs. Cristina Pucci for valuable technical assistance, as well as the I.A.C.E.R. S.r.L. company for supporting Dr. Maria Paola Tramonti Fantozzi with a fellowship. Finally, we thank the OCM Projects company for preparing hard pellets and performing hardness and spring constant measurements.

All steps follow the guidelines of the Ethical Committee of the University of Pisa.
1. Participant Recruitment
<ol>
	<li>Recruit a subject population according to the specific goal of the study (i.e., normal subjects and/or patients, males and/or females, young people and/or elders).</li>
</ol>
2. Material Preparation
<ol>
	<li>Prepare a soft pellet; use commercially available chewing gum (Table of Materials; initial hardness = 20 Shore OO).</li>
	<...

<ol>
	<li>Hirano, Y., 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=Effects+of+chewing+on+cognitive+processing+speed.">Effects of chewing on cognitive processing speed.</a> Brain and Cognition. 81 (3), 376-381 (2013).</li><li>Hirano, Y., Onozuka, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chewing+and+cognitive+function.">Chewing and cognitive function.</a> Brain and Nerve. 66 (1), 25-32 (2014).</li><li>Allen, A. P., Smith, A. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effects+of+chewing+gum+and+time-on-task+on+alertness+and+attention.">Effects of chewing gum and time-on-task on alertness and attention.</a> Nutritional Neuroscience. 15 (4), 176-185 (2012).</li><li>Johnson, A. 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The protocols presented in this study address the acute effects of sensorimotor trigeminal activity on cognitive performance and the role of the LC in this process. This topic has some relevance, considering that 1) during aging, the deterioration of masticatory activity correlates with cognitive decay32,33,34; people that preserve oral health are less prone to neurodegenerative phenomena; 2) malocclusion and teeth extraction in...

In humans, it is known that chewing quickens cognitive processing1,2 and improves arousal3,4, attention5, learning, and memory6,7. These effects are associated with shortening of the latencies of cortical event-related potentials8 and an increase in the perfusion of several cortical and subcortical structures2,9.
Within cranial nerves, the most relevant information sustaining cortical desynchronization and arousal is carried by trigeminal fibres10, likely due to strong trigeminal connections to the ascending reticular activating system (ARAS)11. Among ARAS structures, the locus coeruleus (LC) receives trigeminal inputs11 and modulates arousal12,13, and its activity covaries with pupil size14,15,16,17,18. Although the relation between LC resting activity and cognitive performance is complex, task-related enhancement of LC activity leads to arousal-associated19 pupil mydriasis20 and enhanced cognitive performance21. There is reliable covariation between LC activity and pupil size, and the latter is currently considered a proxy of central noradrenergic activity22,23,24,25,26.
Asymmetric activation of sensorimotor trigeminal branches induces pupil asymmetries (anisocoria)27,28, confirming the strength of the trigemino-coerulear connection. If the LC participates in the stimulating effects of chewing on cognitive performance, it may affect parallel task-related mydriasis, which is an indicator of LC phasic activation during a task. It may also affect performance, so a correlation can be expected between chewing-induced changes in performance and mydriasis. Moreover, if trigeminal effects are specific, chewing effects should be larger than those elicited by another rhythmic motor task. In order to test these hypotheses, two experimental protocols are hereby presented. They are based on combined measurements of cognitive performance and pupil size, performed before and after a short period of chewing activity. These protocols utilize a test consisting in finding target numbers displayed in numeric attentive matrices29, alongside with non-target numbers. This test verifies attentive and cognitive performance.
The overall goal of these protocols is to illustrate that trigeminal stimulation elicits specific changes in cognitive performance, which cannot be ascribed aspecifically to the generation of motor commands and are related to pupil-linked changes in LC-mediated arousal. Applications of the protocols extend to all behavioral conditions in which performance can be measured and involvement of the LC is suspected.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Anti-stress ball</td>
			<td>Artengo, Decathlon, France</td>
			<td>TB600</td>
			<td></td>
		</tr>
		<tr>
			<td>Chewing gum</td>
			<td>Vigorsol, Perfetti, Italy</td>
			<td>Commercially available product</td>
			<td></td>
		</tr>
		<tr>
			<td>Infrared Camera-Wearable pupillometer</td>
			<td>Pupil Labs, Berlin, Germany</td>
			<td>Pupil Labs headset</td>
			<td></td>
		</tr>
		<tr>
			<td>Pupillographer</td>
			<td>CSO, Florence, Italy</td>
			<td>MOD i02, with chin support</td>
			<td></td>
		</tr>
		<tr>
			<td>Silicon rubber</td>
			<td>Prochima, Italy</td>
			<td>gls50</td>
			<td></td>
		</tr>
		<tr>
			<td>Software for pupil detection - wearable pupillometer</td>
			<td>Pupil Labs, Berlin, Germany</td>
			<td>Pupil Labs headset</td>
			<td></td>
		</tr>
		<tr>
			<td>Tangram Puzzle</td>
			<td>Citt&#224; del Sole srl, Milano, Italy</td>
			<td>Tangram Puzzle</td>
			<td></td>
		</tr>
		<tr>
			<td>Wearable pupillometer</td>
			<td>Pupil Labs, Berlin, Germany</td>
			<td>Pupil labs model</td>
			<td>Dimension of the frame: 13.5 x 15.5cm</td>
		</tr>
	</tbody>
</table>

assessing pupil-linked changes in locus coeruleus-mediated arousal elicited by trigeminal stimulation

Current scientific literature provides evidence that trigeminal sensorimotor activity associated with chewing may affect arousal, attention, and cognitive performance. These effects may be due to widespread connections of the trigeminal system to the ascending reticular activating system (ARAS), to which noradrenergic neurons of the locus coeruleus (LC) belongs. LC neurons contain projections to the whole brain, and it is known that their discharge co-varies with pupil size. LC activation is necessary for eliciting task-related mydriasis. If chewing effects on cognitive performance are mediated by the LC, it is reasonable to expect that changes in cognitive performance are correlated to changes in task-related mydriasis. Two novel protocols are presented here to verify this hypothesis and document that chewing effects are not attributable to aspecific motor activation. In both protocols, performance and pupil size changes observed during specific tasks are recorded before, soon after, and half an hour following a 2 min period of either: a) no activity, b) rhythmic, bilateral handgrip, c) bilateral chewing of soft pellet, and d) bilateral chewing of hard pellet. The first protocol measures level of performance in spotting target numbers displayed within numeric matrices. Since pupil size recordings are recorded by an appropriate pupillometer that impedes vision to ensure constant illumination levels, task-related mydriasis is evaluated during a haptic task. Results from this protocol reveal that 1) chewing-induced changes in performance and task-related mydriasis are correlated and 2) neither performance nor mydriasis are enhanced by handgrip. In the second protocol, use of a wearable pupillometer allows measurement of pupil size changes and performance during the same task, thus allowing even stronger evidence to be obtained regarding LC involvement in the trigeminal effects on cognitive activity. Both protocols have been run in the historical office of Prof. Giuseppe Moruzzi, the discoverer of ARAS, at the University of Pisa.

Figure 4 shows a representative example of the results obtained when protocol 1 was applied to a single subject (46 years old, female). PI was increased soon after having chewed (T7) both a hard (from 1.73 numb/s to 2.27 numb/s) and soft pellet (from 1.67 numb/s to 1.87 numb/s) (Figure 4A). However, 30 min later (T37), the increased performance persisted only for the hard pellet. On the other hand, both a lack of activity and the handgrip exerci...

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Assessing Pupil-linked Changes in Locus Coeruleus-mediated Arousal Elicited by Trigeminal Stimulation

To verify whether trigeminal effects on cognitive performance involve locus coeruleus activity, two protocols are presented that aim to evaluate possible correlations between the performance and task-related pupil size changes induced by chewing. These protocols may be applied to conditions in which locus coeruleus contribution is suspected.

Current scientific literature provides evidence that trigeminal sensorimotor activity associated with chewing may affect arousal, attention, and cognitive ...

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