Saturday, December 30, 2023
Light color is less important for the internal clock than originally thought
What influences the internal clock?
Ambient light however does not only allow us to see, it also influences our
sleep-wake rhythm. Specialised ganglion cells are significantly involved in
this process, which – like the cones and rods – are sensitive to light and
react particularly strongly to short-wavelength light at a wavelength of around
490 nanometres. If light consists solely of short wavelengths of 440 to 490
nanometres, we perceive it as blue. If short-wavelength light activates the
ganglion cells, they signal to the internal clock that it is daytime. The
decisive factor here is how intense the light is per wavelength; the perceived
color is not relevant.
“However, the light-sensitive ganglion cells also receive information from the cones. This raises the question of whether the cones, and thereby the light color, also influence the internal clock. After all, the most striking changes in brightness and light color occur at sunrise and sunset, marking the beginning and end of a day,” says Dr. Christine Blume. At the Centre for Chronobiology of the University of Basel, she investigates the effects of light on humans and is the first author of a study investigating the effects of different light colors on the internal clock and sleep. The team of researchers from the University of Basel and the TUM has now published its findings in the scientific journal “Nature Human Behaviour”.
Light colors in comparison
“A study in mice in 2019 suggested that yellowish light has a stronger
influence on the internal clock than blueish light,” says Christine Blume. In
humans, the main effect of light on the internal clock and sleep is probably
mediated via the light-sensitive ganglion cells. “However, there is reason to
believe that the color of light, which is encoded by the cones, could also be
relevant for the internal clock.”
To get to the bottom of this, the researchers exposed 16 healthy volunteers
to a blueish or yellowish light stimulus for one hour in the late evening, as
well as a white light stimulus as a control condition. The light stimuli were
designed in such a way that they differentially activated the color-sensitive
cones in the retina in a very controlled manner. However, the stimulation of
the light-sensitive ganglion cells was the same in all three conditions.
Differences in the effect of the light were therefore directly attributable to
the respective stimulation of the cones and ultimately the color of the light.
“This method of light stimulation allows us to separate the light
properties that may play a role in how light effects humans in a clean
experimental way,” says Manuel Spitschan, Professor of Chronobiology and Health
at the Technical University of Munich, who was also involved in the study.
In order to understand the effects of the different light stimuli on the body, in the sleep laboratory the researchers determined whether the internal clock of the participants had changed depending on the color of the light. Additionally, they assessed how long it took the volunteers to fall asleep and how deep their sleep was at the beginning of the night. The researchers also enquired about their tiredness and tested their ability to react, which decreases with increasing sleepiness.
Ganglion cells are crucial
The conclusion: “We found no evidence that the variation of light color
along a blue-yellow dimension plays a relevant role for the human internal
clock or sleep,” says Christine Blume. This contradicts the results of the
mouse study mentioned above. “Rather, our results support the findings of many
other studies that the light-sensitive ganglion cells are most important for
the human internal clock,” says the scientist.
Manuel Spitschan sees the study as an important step towards putting basic
research into practice: “Our findings show that it is probably most important
to take into account the effect of light on the light-sensitive ganglion cells
when planning and designing lighting. The cones and therefore the color play a
very subordinate role.”
It remains to be seen whether the color of the light also has no effect on sleep if the parameters change and, for example, the duration of the light exposure is extended or takes place at a different time. Follow-up studies should answer questions like these.
Night mode on screens – useful or not?
We often hear that the short-wavelength component of light from smartphone
and tablet screens affects biological rhythms and sleep. The recommendation is
therefore to put your mobile phone away early in the evening or at least use
the night shift mode, which reduces the short-wavelength light proportions and
looks slightly yellowish. Christine Blume confirms this. However, the yellowish
color adjustment is a by-product that could be avoided. “Technologically, it is
possible to reduce the short-wavelength proportions even without color
adjustment of the display, however this has not yet been implemented in
commercial mobile phone displays,” says the sleep researcher.
Journal article: https://www.nature.com/articles/s41562-023-01791-7
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Friday, December 29, 2023
NASA’s Juno to Get Close Look at Jupiter’s Volcanic Moon Io on Dec. 30 - UNIVERSE
This image revealing the north polar region of the
Jovian moon Io was taken on October 15 by NASA’s Juno. Three of the mountain
peaks visible in the upper part of image, near the day-night dividing line,
were observed here for the first time by the spacecraft’s JunoCam.
Image data: NASA/JPL-Caltech/SwRI/MSSS, Image
processing by Ted Stryk
The orbiter has performed 56 flybys of Jupiter and documented close
encounters with three of the gas giant’s four largest moons.
NASA’s Juno spacecraft will on
Saturday, Dec. 30, make the closest flyby of Jupiter’s moon Io that any
spacecraft has made in over 20 years. Coming within roughly 930 miles (1,500 kilometers) from the surface of
the most volcanic world in our solar system, the pass is expected to allow Juno
instruments to generate a firehose of data.
“By combining data from this flyby
with our previous observations, the Juno science team is studying how Io’s
volcanoes vary,” said Juno’s principal investigator, Scott Bolton of the
Southwest Research Institute in San Antonio, Texas. “We are looking for how
often they erupt, how bright and hot they are, how the shape of the lava flow
changes, and how Io’s activity is connected to the flow of charged particles in
Jupiter’s magnetosphere.”
A second ultra-close flyby of Io is
scheduled for Feb. 3, 2024, in which Juno will again come within about 930
miles (1,500 kilometers) of the surface.
The spacecraft has been monitoring Io’s volcanic activity from distances ranging from about 6,830 miles (11,000 kilometers) to over 62,100 miles (100,000 kilometers), and has provided the first views of the moon’s north and south poles. The spacecraft has also performed close flybys of Jupiter’s icy moons Ganymede and Europa.
This JunoCam image of Jupiter’s moon Io captures a
plume of material ejected from the (unseen) volcano Prometheus. Indicated by
the red arrow, the plume is just visible in the darkness below the terminator
(the line dividing day and night). The image was taken by NASA’s Juno
spacecraft on October 15.
NASA/JPL-Caltech/SwRI/MSSS
“With our pair of close flybys in December and February, Juno will
investigate the source of Io’s massive volcanic activity, whether a magma ocean
exists underneath its crust, and the importance of tidal forces from Jupiter,
which are relentlessly squeezing this tortured moon,” said Bolton.
Now in the third year of its extended mission to investigate the origin of Jupiter, the solar-powered spacecraft
will also explore the ring system where some of the gas giant’s inner moons
reside.
Picture This
All three cameras aboard Juno will
be active during the Io flyby. The Jovian Infrared Auroral Mapper (JIRAM),
which takes images in infrared, will be collecting the heat signatures emitted
by volcanoes and calderas covering the moon’s surface. The mission’s Stellar
Reference Unit (a navigational star camera that has also provided valuable
science) will obtain the highest-resolution image of the surface to date. And
the JunoCam imager will take visible-light color images.
JunoCam was included on the
spacecraft for the public’s engagement and was designed to operate for up to
eight flybys of Jupiter. The upcoming flyby of Io will be Juno’s 57th orbit
around Jupiter, where the spacecraft and cameras have endured one of the solar
system’s most punishing radiation environments.
“The cumulative effects of all that
radiation has begun to show on JunoCam over the last few orbits,” said Ed
Hirst, project manager of Juno at NASA’s Jet Propulsion Laboratory in Southern
California. “Pictures from the last flyby show a reduction in the imager’s
dynamic range and the appearance of ‘striping’ noise. Our engineering team has
been working on solutions to alleviate the radiation damage and to keep the
imager going.”
More Io,
Please
After several months of study and
assessment, the Juno team adjusted the spacecraft’s planned future trajectory
to add seven new distant Io flybys (for a total of 18) to the extended mission
plan. After the close Io pass on Feb. 3, the spacecraft will fly by Io every
other orbit, with each orbit growing progressively more distant: The first will
be at an altitude of about 10,250 miles (16,500 kilometers) above Io, and the
last will be at about 71,450 miles (115,000 kilometers).
The gravitational pull of Io on
Juno during the Dec. 30 flyby will reduce the spacecraft’s orbit around Jupiter
from 38 days to 35 days. Juno’s orbit will drop to 33 days after the Feb. 3
flyby.
After that, Juno’s new trajectory
will result in Jupiter blocking the Sun from the spacecraft for about five
minutes at the time when the orbiter is at its closest to the planet, a period
called perijove. Although this will be the first time the solar-powered
spacecraft has encountered darkness since its flyby of Earth in October 2013,
the duration will be too short to affect its overall operation. With the
exception of the Feb. 3 perijove, the spacecraft will encounter solar eclipses
like this during every close flyby of Jupiter from now on through the remainder
of its extended mission, which ends in late 2025.
Starting in April 2024, the
spacecraft will carry out a series of occultation experiments that use
Juno’s Gravity
Science experiment to probe Jupiter’s upper atmospheric makeup, which provides key
information on the planet’s shape and interior structure.
More About the
Mission
JPL, a division of Caltech in
Pasadena, California, manages the Juno mission for the principal investigator,
Scott J. Bolton, of the Southwest Research Institute in San Antonio. Juno is
part of NASA’s New Frontiers Program, which is managed at NASA’s Marshall Space
Flight Center in Huntsville, Alabama, for the agency’s Science Mission
Directorate in Washington. Lockheed Martin Space in Denver built and operates
the spacecraft.
More information about Juno is available at: https://www.nasa.gov/juno
Source: NASA’s Juno to Get Close Look at Jupiter’s Volcanic Moon Io on Dec. 30 - NASA
What Happens in the Brain While Daydreaming?
You are sitting quietly, and suddenly your brain tunes out the world and
wanders to something else entirely — perhaps a recent experience, or an old
memory. You just had a daydream.
Yet despite the ubiquity of this experience, what is happening in the brain
while daydreaming is a question that has largely eluded neuroscientists.
Now, a study
in mice, published Dec. 13 in Nature, has
brought a team led by researchers at Harvard Medical School one step closer to
figuring it out.
The researchers tracked the activity of neurons in the visual cortex of the
brains of mice while the animals remained in a quiet waking state. They found
that occasionally these neurons fired in a pattern similar to one that occurred
when a mouse looked at an actual image, suggesting that the mouse was thinking
— or daydreaming — about the image. Moreover, the patterns of activity during a
mouse’s first few daydreams of the day predicted how the brain’s response to
the image would change over time.
The research provides tantalizing, if preliminary, evidence that daydreams
can shape the brain’s future response to what it sees. This causal relationship
needs to be confirmed in further research, the team cautioned, but the results
offer an intriguing clue that daydreams during quiet waking may play a role in
brain plasticity — the brain’s ability to remodel itself in response to new
experiences.
“We wanted to know how this daydreaming process occurred on a neurobiological level, and whether these moments of quiet reflection could be important for learning and memory,” said lead author Nghia Nguyen, a PhD student in neurobiology in the Blavatnik Institute at HMS.
An overlooked brain region
Scientists
have spent considerable time studying how neurons replay past events to form
memories and map the physical environment in the hippocampus, a seahorse-shaped
brain region that plays a key role in memory and spatial navigation.
By contrast, there has been little research on the replay of neurons in other
brain regions, including the visual cortex. Such efforts would provide valuable
insights about how visual memories are formed.
“My lab became
interested in whether we could record from enough neurons in the visual cortex
to understand what exactly the mouse is remembering — and then connect that
information to brain plasticity,” said senior author Mark
Andermann, professor of medicine at Beth Israel Deaconess
Medical Center, and professor of neurobiology at HMS.
During
the experiments, mice repeatedly looked at one of two images, shown here, with
one-minute breaks in between. The images were selected based on their ability
to elicit a strong response from neurons in the visual cortex. Video: Andermann
lab
In the new study, the
researchers repeatedly showed mice one of two images, each consisting of a
different checkerboard pattern of gray and dappled black and white squares.
Between images, the mice spent a minute looking at a gray screen. The team
simultaneously recorded activity from around 7,000 neurons in the visual
cortex.
The researchers found that when a mouse
looked at an image, the neurons fired in a specific pattern, and the patterns
were different enough to discern image one from image two. More important, when
a mouse looked at the gray screen between images, the neurons sometimes fired
in a similar, but not identical, pattern, as when the mouse looked at the
image, a sign that it was daydreaming about the image. These daydreams occurred
only when mice were relaxed, characterized by calm behavior and small pupils.
Unsurprisingly, mice daydreamed more about the most recent image — and they had more daydreams at the beginning of the day than at the end, when they had already seen each image dozens of times.
Between
images, mice spent a minute looking at a gray screen. During this time, neurons
in the visual cortex of the brain, shown here, occasionally fired in a pattern
similar to one seen when the mice were looking at an image, suggesting that
mice were daydreaming about the image. Video: Andermann lab
But what the researchers found next was completely unexpected.
Throughout the day, and across days, the activity patterns seen when the
mice looked at the images changed — what neuroscientists call “representational
drift.” Yet this drift wasn’t random. Over time, the patterns associated with
the images became even more different from each other, until each involved an
almost entirely separate set of neurons. Notably, the pattern seen during a
mouse’s first few daydreams about an image predicted what the pattern would
become when the mouse looked at the image later.
“There’s drift in how the brain responds to the same image over time, and
these early daydreams can predict where the drift is going,” Andermann said.
Finally, the researchers found that the visual cortex daydreams occurred at the same time as replay activity occurred in the hippocampus, suggesting that the two brain regions were communicating during these daydreams.
To sit, perchance to daydream
Based on the results of the study, the researches suspect that these
daydreams may be actively involved in brain plasticity.
“When you see two different images many times, it becomes important to
discriminate between them. Our findings suggest that daydreaming may guide this
process by steering the neural patterns associated with the two images away
from each other,” Nguyen said, while noting that this relationship needs to be
confirmed.
Nguyen added that learning to differentiate between the images should help
the mouse respond to each image with more specificity in the future.
These
observations align with a growing body of evidence in rodents
and humans that entering a state of quiet wakefulness after
an experience can improve learning and memory.
Next, the researchers plan to use their imaging tools to visualize the
connections between individual neurons in the visual cortex and to examine how
these connections change when the brain “sees” an image.
“We were chasing this 99 percent of unexplored brain activity and
discovered that there’s so much richness in the visual cortex that nobody knew
anything about,” Andermann said.
Whether daydreams in people involve similar activity patterns in the visual
cortex is an open question, and the answer will require additional experiments.
However, there is preliminary evidence that an analogous process occurs in
humans when they recall visual imagery.
Randy Buckner, the Sosland Family Professor of
Psychology and of Neuroscience at Harvard University, has shown that brain activity in the visual
cortex increases when people are asked to recall an image in
detail. Other studies have recorded flurries of electrical activity in the
visual cortex and the hippocampus during such recall.
For the researchers, the results of their study and others suggest that it
may be important to make space for moments of quiet waking that lead to
daydreams. For a mouse, this may mean taking a pause from looking at a series
of images and, for a human, this could mean taking a break from scrolling on a
smartphone.
“We feel pretty confident that if you never give yourself any awake
downtime, you’re not going to have as many of these daydream events, which may
be important for brain plasticity,” Andermann said.
Source: https://hms.harvard.edu/news/what-happens-brain-while-daydreaming
Source: What Happens in the Brain While Daydreaming? – Scents of Science (myfusimotors.com)
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