Optimized perception in the twilight zone

April 11, 2018, Goethe University Frankfurt am Main
a) The variance in resting activity decreases significantly during twilight in the brain areas shown. The variance describes the change in brain activity during measurement. (1) visual, (2-4) somatosensory and (5) auditory cerebral cortex. b) The variance in resting activity -- shown here in the visual cortex by way of example - is reduced at 8:00 and 20:00 in comparison to other times of the day. c) Parallel to a reduction in the variance in resting activity, weak visual stimuli are more easily detected during twilight under the same light conditions. The test persons miss less visual stimuli at 8:00 and 20:00. Credit: GU

In the pre-industrial age, twilight was a dangerous time for humans due to higher risk of encountering nocturnal predators. The ability to see in weak light conditions was therefore at a clear evolutionary advantage. Neuroscientists at Goethe University Frankfurt have now discovered that the human brain prepares for dawn and dusk by ending resting activity in the visual cortex at these times so that weak visual stimuli are not overwhelmed by the brain's background noise.

The transition from night to day, light and dark, has a greater influence on perception that previously known. The time of day has a particularly significant impact on the quality of visual signals around us. In the course of evolution, our visual system has adapted perfectly to light conditions during the day. It has, however, also developed a strategy for twilight—evidently, the predicts these periods and prepares the visual system for periods of low-quality visual signals.

"Whilst the cogs of our inner clock have already been studied in depth, it was not known to date which mechanism optimises visual perception at times when poor signal quality can be expected," explains Dr. Christian Kell from the Brain Imaging Center of Goethe University Frankfurt. Lorenzo Cordani, his doctoral researcher, examined how 14 healthy subjects reacted to at six different times of the day in the framework of a complex fMRI study.

The main idea of the study was to relate the perception of sensory signals to the brain's resting activity. Such preoccupies the brain even in the complete absence of external stimuli. The international team led by Christian Kell, Lorenzo Cordani and Joerg Stehle showed that the body independently downregulates resting activity in the sensory areas during dawn and dusk. The more resting activity was reduced, the better the subjects were able to perceive weak when measured afterwards.

This means that humans can perceive weak visual stimuli during dawn and dusk better than at other times of the day. In other words, during twilight, the signal-to-noise ratio in the sensory areas of the brain improves. Since resting activity during twilight decreases not only in the visual but also in the auditory and somatosensory regions of the brain, the researchers assume that perception also sharpens in areas besides the visual system. An earlier study showed that weak auditory during twilight were perceived better. The mechanism now discovered, which was published in the latest issue of Nature Communications, could therefore represent a key that ensured survival in the pre-industrial era.

Explore further: Why the world looks stable while we move

More information: Lorenzo Cordani et al, Endogenous modulation of human visual cortex activity improves perception at twilight, Nature Communications (2018). DOI: 10.1038/s41467-018-03660-8

Related Stories

Why the world looks stable while we move

March 12, 2018
Head movements change the environmental image received by the eyes. People still perceive the world as stable, because the brain corrects for any changes in visual information caused by head movements. For the first time, ...

Thalamus found to add contextual information to visual signals

December 23, 2015
The thalamus not only relays visual signals from the eye to the visual cortex as previously thought, but also conveys additional, contextual information. Integrating these different signals is essential to understand and ...

How neural circuits implement natural vision

May 24, 2016
At any given moment, the neuronal circuits in the brain receive and process sensory information that permits us to perceive and interact with the environment. Yet it remains unclear how the visual brain processes natural ...

Synapses in the brain mirror the structure of the visual world

July 12, 2017
The research team of Prof. Sonja Hofer at the Biozentrum, University of Basel, has discovered why our brain might be so good at perceiving edges and contours. Neurons that respond to different parts of elongated edges are ...

After blindness, the adult brain can learn to see again

October 25, 2016
More than 40 million people worldwide are blind, and many of them reach this condition after many years of slow and progressive retinal degeneration. The development of sophisticated prostheses or new light-responsive elements, ...

Recommended for you

Animal study connects fear behavior, rhythmic breathing, brain smell center

April 20, 2018
"Take a deep breath" is the mantra of every anxiety-reducing advice list ever written. And for good reason. There's increasing physiological evidence connecting breathing patterns with the brain regions that control mood ...

Mechanism behind neuron death in motor neurone disease and frontotemporal dementia discovered

April 20, 2018
Scientists have identified the molecular mechanism that leads to the death of neurons in amyotrophic lateral sclerosis (also known as ALS or motor neurone disease) and a common form of frontotemporal dementia.

When there's an audience, people's performance improves

April 20, 2018
Often, people think performing in front of others will make them mess up, but a new study led by a Johns Hopkins University neuroscientist found the opposite: being watched makes people do better.

Signaling between neuron types found to instigate morphological changes during early neocortex development

April 20, 2018
A team of researchers from several institutions in Japan has found that developing neocortex neurons in mammals undergo a morphological transition from a multipolar shape to a bipolar shape due at least partially to signaling ...

MRI technique detects spinal cord changes in MS patients

April 20, 2018
A Vanderbilt University Medical Center-led research team has shown that magnetic resonance imaging (MRI) can detect changes in resting-state spinal cord function in patients with multiple sclerosis (MS).

Gene variant increases empathy-driven fear in mice

April 20, 2018
Researchers at the Center for Cognition and Sociality, within the Institute for Basic Science (IBS), have just published as study in Neuron reporting a genetic variant that controls and increases empathy-driven fear in mice. ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.