Environmental light triggers production of memory proteins in fruit flies
January 13, 2020
Science Daily/Society for Neuroscience
Maintaining long-term memories requires environmental light, according to research in fruit flies recently published in JNeurosci.
Memories begin in a temporary form, which are converted into long term memories as protein expression and brain circuits change. But, long term memories require active maintenance in order to survive the changing molecular landscape of the brain. Previous research indicates exposure to different colors of light alters memory function in humans and animals, but the role of natural lighting conditions in memory maintenance remains unknown.
Inami et al. explored this question by testing the ability of male fruit flies to learn that their proposal is not accepted by females through their courtship toward unreceptive females. After the learning period, the male fruit flies were either exposed to constant darkness, constant light, or a 12-hour light/dark cycle. The flies experiencing a light/dark cycle recognized the ready-to-mate females for five days, whereas flies in constant darkness couldn't maintain the memory. The researchers found environmental light exposure activates light-sensitive neurons, triggering the production of memory maintenance proteins. Darkness during the learning period did not affect memory formation, indicating that light is required for the maintenance, but not creation, of long-term memories.
https://www.sciencedaily.com/releases/2020/01/200113131644.htm
Human daily rhythms: Clocks vs light/dark cycle
April 3, 2018
Science Daily/University of Seville
A new study analyses daily primary activities of European laborers and the sources of social synchronization.
Should people living along a meridian be doing their basic activities (sleep/wake, working, eating, leaving home/coming home) at the same time? A 'yes' is an intuitive answer since solar noon happens simultaneously along the meridian. This phenomenon helps setting clock time. Therefore, a 'yes' is also pointing to clock synchronization, irrespective of latitude.
On a second thought we may understand that nobody gets to work at, say, 8am because it is four hours before noon, the bare meaning of clock ticking 8am. Instead the decision making process (whether 8am is fine, late or early) is driven by light conditions: did the Sun already rise? The answer to this question varies with latitude and season following the natural cycle of light and dark. Therefore, if this question influences human behaviour then people living along a meridian would not be doing their basic activities at the same time.
José María Martín Olalla, professor at University of Seville, addresses this issue in a paper entitled "Latitudinal trends in human primary activities: characterizing the winter day as a synchronizer" published in Scientific Reports, the Springer Nature open access megajournal. From time use surveys in 17 European countries and 2 American countries (located from 35º to 61º latitude) he characterizes laborer's primary activities and get them positioned along the daily and yearly cycle of light and dark.
Results show up latitudinal patterns tied to the light/dark cycle with the winter terminator as a source of synchronization for daily activities of laborers. Societies memorize the shortest photoperiod (daytime) of the year, the most challenging condition in one year. Winter photoperiod decreases by two hours from 40 to 54 degree latitude.
Winter sunrise (the later sunrise of the year and increasingly later with increasing latitude) triggers human activity in the morning year round and dominates morning trends. Its fingerprint can be traced on rising times, leaving home and working start times, all of them occur earlier with decreasing latitude. From 40 to 54 degree latitude, winter sunrise delays by one whole hour, the size of a standard time zone.
Winter sunset (the earliest sunset of the year, increasingly earlier with increasing latitude, it delays another whole hour from 54 to 40 degree latitude) triggers the reverse, shutdown process and dominates evening activities like stop working, coming home or dinning.
Two overturning sequences can also be identified. The first one occur at noon where lunch times exhibit both a meridional behaviour (tied to noon) and a latitudinal trend tied to the winter sunset. In this case people advance lunch times as latitude increases foreseeing the incoming dusk while people delay lunch times with decreasing latitude as light conditions do not worsen comparatively too much.
The second overturning sequence occurs at night and indoors: TV prime time marks and bedtimes are not tied to the winter sunset. Instead, they exhibit meridional behavior or trends weakly coupled to the winter sunrise. Societies are foreseeing the uprise in the following day.
The magnitude of the latitudinal gradient which dominates human activity can be comparatively traced out by observing how the terminator sweeps Europe in winter, when morning times are relatively similar as the sunrise terminator efficiently sweeps the continent, while evening times goes step by step following the sunset terminator.
Indirectly this study also inspects the role of time zone and time advance in human behaviour. The case of France, Belgium and Spain illustrates this issue. There, clocks are set one hour ahead of their physical time zone: that is an advanced clock, not an uncommon option for local time on Earth. Despite this time marks make perfect sense when properly tested against the LD cycle. That means people offset clock advancing by delaying time schedules apparently. In so doing they kept in phase with the LD cycle. This poses no harm to population. It only jeopardizes time comparisons, most notably in Spain due to its Southwestern most location. A rule of thumb valid for comparisons (both academic and non-academic) is subtracting one whole hour. That would convert "advanced clock" reading into standard time values.
https://www.sciencedaily.com/releases/2018/04/180403090052.htm