Fruit fly offers new insights into attention and sleep

27 November 2020



As you are reading or listening to this article, your brain is focusing attention on these words while filtering out other stimuli in your surroundings. Yet precisely how our brains do this is not understood.

Research on human brains has shown that when we focus our attention, groups of neurons involved in processing the relevant information synchronise their electrical neural activity; they fire in rhythm with one another.

These synchronised oscillations help to integrate important information, explains Dr Martyna Grabowska of UQ’s Queensland Brain Institute.

For example, they help to increase the activity for certain visual features while suppressing the other, more irrelevant visual features, she says.

“As a result, you get a higher signal to noise ratio for a particular visual object or feature.”

It is unclear if this occurs only in more complex brains or if it’s a general feature of neuronal networks, including less complex brains, she says.

If the latter is true, then studying the smaller, simpler brains of fruit flies could reveal how this mechanism works.

Does the brain of fruit fly behave like ours?

So Dr Grabowska and Associate Professor Bruno van Swinderen decided to find out.

“First we needed to determine what the flies even pay attention to, or want to pay attention to,” says Dr Grabowska.

She placed tethered fruit flies in a virtual reality visual environment so they were surrounded by a wraparound digital screen. Images of simple objects then appeared on the screen and the flies’ behavioural choices were tracked. If a fly attempted to walk toward a particular object, this indicated it was focusing on that object.

The bigger the better for attention 

By observing the flies’ behavioural choices, Dr Grabowska discovered that the flies were attracted to and focused on large objects. By contrast, they seemed to be repulsed by smaller objects, and tried to avoid them.

With the help of advanced research techniques such as optogenetics, which make it possible to turn neural circuits on and off with light, she was able to activate reward centres in the flies brains when they looked at repulsive objects. Sure enough, the flies now paid more attention to those objects.

Dr Lucy Tainton-Heap and Dr Martyna Grabowska.

She also monitored the flies’ brain activity for the whole duration of those experiments.

“We observed that when the flies were focusing on attractive objects or objects that were rewarded, there was a stronger brain signal for that object, suggesting to us that groups of neurons were oscillating together when flies were paying attention.”

Associate Professor van Swinderen says the frequency range of the underlying oscillations was particularly exciting.

“They were in the 20-30Hz frequency range, which is a similar frequency range employed by the human brain to pay attention to specific objects.”

The findings, which have been published in The Proceedings of the National Academy of Sciences, reveal a valuable approach for understanding how perception works in any brain, says Professor van Swinderen.

“This work also shows that we can, in a way, know a fly’s mind, and infer what it is paying attention to by reading its brain activity.”

What can a sleeping fly teach us?

Associate Professor van Swinderen and his colleague Dr Lucy Tainton-Heap have also investigated the link between sleep and attention in fruit flies. In an intriguing study published this week in Current Biology, they revealed that a fly’s brain activity during a specific sleep stage influences its ability to pay attention when awake.

Sleep is found throughout the animal kingdom, but it’s still largely an enigma, says Dr Tainton-Heap.

“It’s a thing we do so much of our lives and we have so little understanding of it,” she says.

In humans, sleep has been linked to a variety of important biological functions, including metabolism and immunity, and there is increasing evidence of a strong relationship between sleep and cognition.

Dr Tainton-Heap developed a method to track thousands of neurons simultaneously while flies spontaneously fell asleep.

“We discovered that sleep in the fly brain comprises distinct stages, including a more active ‘wake-like’ stage followed by a deep sleep stage,” she says.

“During both sleep stages, flies are significantly less responsive to external stimuli, hence asleep.”

Sleeping patterns key to maintaining attention

Interestingly, a similar paradox of wake-like brain activity coupled with low responsiveness is observed during REM sleep in humans, which is when vivid dreams are often experienced.

To investigate the effect of sleep stages on flies’ ability to pay attention, Dr Tainton-Heap and her colleague Dr Leonie Kirszenblat used optogenetics to activate a part of their brain that seemed to be involved in promoting wake-like sleep. Later, when the flies were awake, they monitored their behaviour.

They discovered that when they artificially increased the amount of wake like sleep, the flies were less distractible and better at paying attention to attractive objects. In particular, prolonged wake-like sleep corrected attention defects that were associated with sleep deprivation.

The findings shed new light on the links between certain sleep stages and the ability to pay attention.

Moreover, the remarkable similarities between fruit flies and humans when it comes sleep stages offers new insight into the evolution of sleep itself, says Dr Tainton-Heap.

“It seems like sleep is complex even in the smallest animal brains, which allows us to more easily study the reason for this complexity.”

It may be that to pay attention properly requires an optimal balance of different kinds of sleep, and this seems to be just as important for a fly as for a human.