EyeProprio

Poster:

Cortical and subcortical proprioceptive contribution to oculomotor control in humans
Daniela Balslev¹, Graeme A. Keith², Ross Hardaker³, Frances Crabbe³, and Alessio Fracasso^3
1School of Psychology and Neuroscience, University of St. Andrews, Scotland, UK ²Imaging Centre of Excellence, University of Glasgow, Scotland, UK ³School of Psychology and Neuroscience, University of Glasgow, Scotland, UK

Our poster reports the results of a small pilot study using ultra-high field (7 Tesla) functional magnetic resonance imaging (fMRI). We show the feasibility of parallel, brain and brainstem data acquisition.

We did this research because we have previously observed that stretching the extraocular muscles of the right eye is associated with an increase of neural activity in the brainstem extraocular motor nuclei that move the left eye (Balslev et al., Human Brain Mapping, 2022). Understanding the proprioceptive coupling between the two eyes is important, because it may shed light on the disease mechanisms of strabismus, a common and disabling condition in children characterised by misaligned ocular axes. The objective is to find out which brain or brainstem structure drives this proprioceptive coupling between the two eyes. Is this a short reflex via the brainstem (like a crossed stretch reflex in the skeletal muscles) or does it reflect a longer feedback loop via the brain?

One can answer this question using fMRI connectivity. The first step in this research, however, is to acquire fMRI data from both brain and brainstem at the same time. This was not possible in our previous study at 3 Tesla where we had to zoom in on the brainstem. Imaging the brainstem is challenging because of the small nuclei and the proximity of the pulsating blood vessels. Most studies tackle this challenge by limiting the field of view to the structure of interest. Our innovative approach was to use the higher streghth of the magnetic field to increase signal-to-noise ratio. We replicate previous results, and this time around, we manage to image both brain and the brainstem at the same time, enabling future connectivity analyses.

The poster is scheduled for presentation on Wednesday June 26 and Thursday June 27 13:45-15:45 at COEX Seoul, South Korea. This small pilot was funded by the University of St Andrews (LIFTS award to Daniela) and the University of Glasgow. We are now applying for funds to complete this research (UPDATE 1.07.2024 – I just heard that the UK Medical Research Councils funded this project. I’m so happy and grateful that we get to finish this research!) .

Gaze and attention: mechanisms underlying the therapeutic effect of optokinetic stimulation in spatial neglect by Chan, Mitchell, Sandilands and Balslev, Neuropsychologia, 2024 (in press)

I am delighted to announce that our paper has just been accepted for publication. The contributions from Hilary Chan and Eilidh Sandilands, who were undergraduate students at the University of St Andrews when they completed this research, deserve a special recognition.

In brief, we investigated how left optokinetic stimulation, which is a rehabilitation method in spatial neglect works. Spatial neglect is a common and disabling neuropsychological condition after a right hemisphere lesion characterised by inattention to people and objects in the contralesional space. Optokinetic stimulation is the exposure to large field visual motion, for instance when watching dots that move in the same direction on a computer screen in the lab (or in real life, when looking out of the window from a moving train). Optokinetic stimulation induces a type of eye movements called optokinetic nystagmus.

We found that in healthy participants optokinetic stimulation altered the proprioceptive (stretch) input from the extraocular muscles. The misperception of own gaze direction was associated with a bias in spatial attention. Both changes outlasted the period of optokinetic stimulation.

We are therefore proposing that the change in the eye position signals underlies the therapeutic effect of optokinetic stimulation. If so, then the effect of left optokinetic stimulation in spatial neglect could be improved by combining it with other interventions that affect eye proprioception, such as repetitive transcranial magnetic stimulation over the somatosensory cortex.

I have uploaded our accepted-for-publication manuscript here.

We could not fill this position so I am re-advertising the project.

A PhD studentship (competition funding, EASTBIO/BBSRC) is available with start on September 2024. The project investigates the neural substrate of motor eye dominance (the stable preference for one of the two eyes when sighting).

A full project description and information about the application process are available here.

You can contact me at daniela.balslev@st-andrews.ac.uk if you have questions.

Extraocular muscles graffiti, on my way to Imaging Excellence Center, Queen Elizabeth University Hospital, Glasgow for a pilot project on the 7T scanner (cortco-subcortical interaction in the control of ocular alignment). No, it wasn’t me, I’m not that talented 🙂

Proprioceptive coupling between the two eyes. A brief, passive stretch of the right eye’s lateral rectus muscle in humans is associated with an increase in the BOLD response in the left oculomotor and abducens nuclei, which innervate the extraocular muscles of the left eye. In complete darkness the left eye’s active movement mirrors the passive movement of the right eye, suggesting a role of extraocular muscle proprioception in ocular alignment (Cover illustration based on Balslev, Mitchell, Faria, Priba, Macfarlane. Proprioceptive contribution to oculomotor control in humans  https://onlinelibrary.wiley.com/toc/10970193/2022/43/16)

Proprioceptive contribution to oculomotor control in humans

We have a new paper accepted for publication at Human Brain Mapping. We argue that in humans the afferent input from the extraocular muscles (EOM proprioception) facilitates yoked movements of the two eyes.

Thanks go to my co-authors Jen Macfarlane, Lukasz Priba, Alexandra Mitchell, and Patrick Faria. Shout-out to Patrick who was only a Masters student at the time he completed a very demanding eye-tracking experiment.

The highlights are:

• A brief, passive stretch of the right eye’s lateral rectus muscle in humans was associated with an increase in the BOLD response in the left oculomotor and abducens nuclei, which innervate the extraocular muscles of the left eye.
• The left eye’s active movement mirrored the passive movement of the right eye.
• Both neuroimaging and eye tracking suggest a proprioceptive coupling between the two eyes.

I will add a link to the open-access paper and the publicly available dataset as soon as I get a free moment.

Here is a 3-minute video presentation of this research (presentation at the Annual Conference of the Organisation for Human Brain Mapping in June 2022)

It’s been a great pleasure to record a lecture on “Ocular Proprioception and Attention” this week, at the invitation of the organizers of the International Society for Proprioceptive Disorders.

The lecture is available here.

The lecture has three parts. The first part, “Oculoproprioception: Anatomy” presents the anatomy of the oculoproprioceptive system and allows me to offer a first glimpse into new, yet unpublished, results from my lab showing an oculoproprioceptive projection in the brainstem’s oculomotor nuclei in humans likely to play a role in inter-ocular alignment.

The second part, “Oculoproprioception: Methods” details the methods that are available to study this sensory modality in humans.

The final part “Attention” presents the contribution of the oculoproprioceptive signals to the allocation of attention in space and a new hypothesis about disease mechanisms in spatial neglect, which is a disorder of spatial attention in stroke patients.

I just realised that the lecture compresses thirteen years of research into just 90 minutes. I feel very privileged to have worked on a topic I am curious about and to meet great mentors, colleagues and students along the way.

If you are interested to join the lab as an Undergraduate, Master or PhD student or as a postdoctoral researcher please get in touch with Daniela at db87@st-andrews.ac.uk.