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Scientists identify 100-millisecond window to process visual events

A study examining early visual processing in mice could have implications for conditions that affect perception and visual attention, according to researchers at the National Eye Institute (NEI) in the US.

Published online in the Journal of Neuroscience, the study found inhibiting a specific region of the brain in genetically modified mice hindered their event perception, which could aid in better understanding conditions like schizophrenia and attention deficit hyperactivity disorder (ADHD).

Researchers defined a specific 100-millisecond window that mice need to process visual events. They found that as the brain processes visual information, a region known as the ‘superior colliculus’ notifies other regions of the brain that an event has occurred. Inhibiting this particular brain region during the crucial window inhibited event perception in mice.

Senior author of the study Dr Richard Krauzlis said: “One of the most important aspects of vision is fast detection of important events, like detecting threats or the opportunity for a reward. Our result shows this depends on visual processing in the midbrain, not only the visual cortex.”

The authors noted that although they had to be cautious translating data from mice to humans, because of the difference in visual systems, mice have many of the same basic mechanisms for event detection and visual attention as humans.

In the study, Krauzlis and colleagues used a technique called optogenetics to tightly control the activity of the superior colliculus over time.

They used genetically modified mice so that they could turn neurons in the superior colliculus on or off using a beam of light. This on-off switch could be timed precisely, enabling the researchers to determine exactly when the neurons of the superior colliculus were required for detecting visual events.

The researchers trained their mice to lick a spout when they’d seen a visual event, and to avoid licking the spout otherwise.

The researchers found that the deficits with superior colliculus inhibition were much more pronounced when the mice were forced to ignore things happening elsewhere in their visual field.

Essentially, without the activity of the superior colliculus, the mice were unable to ignore distracting visual events. This ability to ignore visual events, called visual attention, is critical for navigating the complex visual environments of the real world.