Novel population of neurons identified that control binocular eye movements in 3D space

Novel population of neurons identified that control binocular eye movements in 3D space

University of Alabama at Birmingham researchers have discovered a previously undescribed population of neurons that help control our eyes as they view in three-dimensional space.

During normal viewing, we direct our eyes between objects in the three-dimensional space many times a minute. With each change, the left and right eyes will rotate, generally in the same direction, but mostly by different degrees of rotation. These unequal movements are known as disjunctive saccades.

Disjunctive saccades differ from two other eye movements: one, called conjugate saccades, where the eyes rotate in unison, and one called symmetrical vergence eye movements, where the eyes rotate in equal but opposite directions. The underlying mechanism for disjunctive saccades is not known.

Several models of eye movement predicted the existence of a population of neurons called saccade-vergence burst neurons, or SVBNs, that would produce a burst of activity solely during disjunctive saccades, while not firing during the other two types of eye movements.

The UAB researchers, led by Julie Quinet, Ph.D., hunted for these putative neurons in a region of the midbrain located near to the oculomotor nucleus called the central mesencephalic reticular formation, or cMRF. Recent anatomical studies had suggested that the cMRF might contain premotor neurons involved in the neural control of disjunctive saccades.

Using brain recordings from trained rhesus monkeys, Quinet and colleagues found and recorded 18 SVBNs in the cMRF. “To our knowledge,” said Quinet, a researcher V in the UAB Department of Ophthalmology and Visual Sciences, “no such class of cells has been reported in prior recording studies.”

This novel population of SVBNs displayed three unique characteristics that were predicted by models: 1) The neurons discharged when animals performed a disjunctive saccade; 2) The neurons remained silent during the unison eye movement called conjugate saccades and also during the eye movement when the eyes rotate in equal but opposite directions, called symmetric vergence eye movement, and; 3) The neurons burst without regard to the direction — rightward or leftward — of the disjunctive saccade. Furthermore, the bursts of spikes during disjunctive saccades were highly correlated with vergence velocity — the speed at which the eyes move toward or away from each other.

Intriguingly, half of the recorded cells increased their firing rate for convergence disjunctive saccades, while half increased their firing rate for divergence disjunctive saccades.

Quinet and colleagues say that further studies of disjunctive saccades in brain areas that may supply input to SVBNs can help explain and advance solutions to treat strabismus, a condition in which eyes do not properly align with each other while looking at an object.

The results of this study and previous studies elsewhere and at UAB, Quinet says, suggest that SVBNs could play a role in all the components of the near triad responses — lens accommodation, pupillary constriction and vergence.

Story Source:
Materials provided by University of Alabama at Birmingham. Original written by Jeff Hansen. Note: Content may be edited for style and length.

XL subscribe to our newsletter banner

Get the latest news and advice on COVID-19, direct from the experts in your inbox. Join hundreds of thousands who trust experts by subscribing to our newsletter.

Send your news and stories to us or and WhatsApp: +447747873668.

Before you go...

Democratic norms are being stress-tested all over the world, and the past few years have thrown up all kinds of questions we didn't know needed clarifying – how long is too long for a parliamentary prorogation? How far should politicians be allowed to intervene in court cases? To monitor these issues as closely as we have in the past we need your support, so please consider donating to The Climax News Room.

Leave a Reply

Your email address will not be published. Required fields are marked *