Washington, Oct 3 : When an object moves fast, you follow it with your eyes. Now, a new study sheds light on how the brain correspondingly calculates the speed of the object and adapts eye movement to it.
The control of eye movement responds more sensitively to changes in the speed of fast moving objects than slow moving objects, phenomena called "Gain control".
The research team including Stefan Glasauer from the Bernstein Centre for Computational Neuroscience and Ludwig-Maximilians-Universitat (LMU) Munchen determined the location in the brain where 'gain control' is calculated, and what neuronal networks are behind this complex process.
It is already known that different regions of the cerebral cortex are involved in eye tracking movements.
These include "Area MST" and the so-called frontal eye fields, or FEFs for short. Nerve cells in Area MST mainly reflect the speed of the eye or target motion, whereas cells in the FEFs mainly respond to changes in speed.
In the new study, the researchers amalgamated these findings into a computer model that actually explains this eye movement control.
The new model simulates the most important circuits required for controlling eye-tracking movement.
In Area MST, the speed of the target object is calculated and compared with the momentary eye speed in order to adapt it accordingly. The FEFs are the actual location where the gain control takes place; this is where the sensitivity of eye movement to changes in speed is defined.
For further analysis, the scientists along with a team from University College in London, asked the subjects to follow a dot on a screen with their eyes. The activity of the FEFs was briefly disrupted by so-called "transcranial magnetic stimulation".
This technology can influence individual, targeted areas of the brain for a few seconds. The experiments did indeed confirm the predictions of the models: as long as the observed object was moving at a constant speed, a disruption of the FEFs had little effect on eye movement control.
The sensitivity of the eye movement to changes in speed, on the other hand, did not increase sufficiently at higher speeds when the FEFs were disrupted. It follows that the gain control is determined in the FEFs depending on the speed of the eye or the target.
In short, the faster an object moves, the greater the adaptability.
"With this, we have managed for the first time to explain the purpose of parallel anatomic paths in neuronal processing for eye tracking," said Glasauer.
The results could be of great help in the diagnosis of eye movement disorders.