Vestibular Testing Results in a World-Famous Tightrope Walker

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This is an interesting work, worth puplishing. It needs a minor revision just to make some points clearer, so as to be more instructional to readers interested in vestibular test battery.

Comments for author File: Comments.pdf

Author Response

Revision Points:

Introduction: none

 

Methods: Experimental setup. An introductory reference to the tests that have been performed should be made, together with a simple note about the point of each test, for example to classify your investigation into diagnostic tests of the five peripheral vestibular organs ( Caloric, v- HIT, VEMPs ), video oculography as a means of tracing central and peripheral dysfunctions and functional tests of gaze stability (DVA) and balance (Equitest and static balance).

 

Reply by the authors: We thank the reviewer for his/her suggestion. We have added an introductory sentence at the beginning of the methods section, summarizing the different type of quantitative tests applied. We separated the tests into those assessing brainstem reflexes and functional tests.

 

“By combining various tests, semicircular canal function and otolith function was assessed both at the level of brainstem reflexes (angular vestibulo-ocular reflex [aVOR] as assessed by the video-head-impulse test [vHIT] [4] and caloric irrigation, otolith-dependent reflexes such as vestibular-evoked myogenic potentials [5] and gravity-dependent ocular torsion [6]) and by use of functional tests evaluating postural stability (as assessed by static and dynamic posturography [7]), verticality perception (as assessed by the subjective visual vertical [SVV] [8]), and dynamic visual acuity [DVA] [9]).“

 

 

Otolith testing

At this point a reference could be made to the diagnostic target of the MRI as a means of tracing the rubro- spinal and cortico-spinal pathways, explaining their role in balance and why this investigation was of interest to your study.

 

Reply by the authors: As suggested by the reviewer we have added a comment related the diagnostic target of the MR-imaging applied. We refer to the physiologic role of both systems citing a recent review (PMID 34177458) and discussing the value of assessing these pathways in our study subject.

 

“In order to assess the structural integrity of those tracts that are eminent in motor control, i.e. the corticospinal tract and the rubrospinal tract [23], fiber tracking was performed.“

 

 

Line 91: described by [4], it should be better expressed as: described by Weber et al [4].

 

Reply by the authors: We have changed this to “…as described by Weber and colleagues [11].”

 

 

Line 106: explain the symbol @V

 

Reply by the authors: This should be mV. It has been changed accordingly.

 

 

Semicircular canal testing

Line112: as a reduction in VOR gain (omit the article)

 

Reply by the authors: We have removed the article (“a”) as suggested.

 

 

Line 124: Why did you perform ocular stability tests in the supine position?

Please explain.

 

Reply by the authors: This was done in order to assess any positional nystagmus. This has now been added to the sentence (in italics):

 

“Then ocular stability was measured while in supine position with the head roll-tilted 60° to either side in order to search for any positional nystagmus.“

 

 

Line 151: (utricular and saccular) input

 

Reply by the authors: this was changed as suggested by the reviewer.

 

 

Assessment of Semicircular canal Function

Line 186: “During oscillations marked gain reductions were noted’. Does this refer

to VOR-suppression? (see line 134). Please re-express so as to become clearer.

 

Reply by the authors: This was referring to the VOR-gain during the chair rotations (per-rotatory VOR-gains). This is now stated more clearly:

 

“During oscillations marked per-rotatory VOR-gain reductions were noted and …“

 

 

Figure 1. In the v-HIT diagram the left Anterior is wrongly repeated in the legends

instead of left Horizontal.

 

Reply by the authors: We thank the reviewer for spotting this mistake. We have now corrected the legend accordingly.

 

 

Table 1. The section of Dynamic Posturography is difficult to understand. Should the reader read the lines horizontally or is each column independent? This section should be better aligned. Also, in the legend RT is not explained. Does it stand for Reaction Time?

 

Reply by the authors: We do agree with the reviewer that this part of the table is difficult to read. It was meant to be read by horizontal lines independently. We have now optimized the illustration to increase its readability.

Furthermore, RT does indeed stand for reaction time. We have added this definition to the table legend.

 

 

Discussion

 

Line 272: Irregular type I cells

 

Reply by the authors: we have changed this accordingly.

 

Line 292-293: “The absence of abnormalities in these tracts points to a functional origin for the slight asymmetry observed in vestibular responses”. Do you mean that the asymmetry was due to a slight peripheral lesion? Please make your comment in a more detailed way.

 

 

Reply by the authors: We have rephrased this sentence to make the statement more clear:

 

“The absence of structural abnormalities in the cortico-spinal and rubro-spinal tracts further supports the assumption of a peripheral-vestibular origin for the slight asymmetry observed in vestibular responses with excellent central compensation.“

Reviewer 2 Report

Comments and Suggestions for Authors

This manuscript provides an interesting insight into tightrope walking and vestibular function, and also gives an interesting insight into the mechanisms of compensation.  It has clinical value as it is a real life example that goes against clinical beliefs and teachings that “compensation is never perfect”.  It also illustrates how little concrete knowledge we have about the compensation process.  A further contribution could be that it could be used as an example for patients recovering from vestibular injury (and perhaps struggling to compensate effectively.   

 

There are two factors missing in this manuscript that would have “completed the story”.  It would have been interesting to have had air conducted OVEMPs carried out, as they are more side specific.  The other factor is his unfortunate death, as it would been fascinating to have followed him over the years to document any age-related decline in his skills.   

 

 

Author Response

This manuscript provides an interesting insight into tightrope walking and vestibular function, and also gives an interesting insight into the mechanisms of compensation.  It has clinical value as it is a real life example that goes against clinical beliefs and teachings that “compensation is never perfect”.  It also illustrates how little concrete knowledge we have about the compensation process.  A further contribution could be that it could be used as an example for patients recovering from vestibular injury (and perhaps struggling to compensate effectively.   

 

There are two factors missing in this manuscript that would have “completed the story”.  It would have been interesting to have had air conducted OVEMPs carried out, as they are more side specific.  The other factor is his unfortunate death, as it would been fascinating to have followed him over the years to document any age-related decline in his skills. 

 

Reply by the authors: in our laboratory, we do only collect bone-conducted oVEMPs. Thus, we do not have air-conducted oVEMPs available. Indeed, it is very sad that the patient passed away.