Monday, 19 December 2011

Happiest days of 2011: Tweeting reveals our daily mood swings

If you wanted to measure daily rhythms in activity of mice, you could record wheel running behaviour. If you wanted to measure daily changes in hormone levels, you could take regular samples throughout the day and night. And these days apparently, if you want to measure daily mood swings in humans, you can look at what words they are tweeting.

Twitter is a 5-year-old social networking website, claiming over 100 million users who are tweeting an average of 230 million tweets a day. Scientists this year have taken advantage of this free public access to our real time moods and have used tweets to analyse our daily, weekly, and seasonal mood swings.

Cornell researchers Scott Golder and Michael Macy analysed 509 million messages tweeted between 2008-10 from 84 countries [1]. These tweets were published online by 2.4 million English speakers that had written between 25-400 messages.

They measured positive words (agree, fantastic, super) which showed tweeters delight/enthusiasm/activeness/alertness as well as negative associated words (afraid, mad, panic) which reflected writers' distress/fear/anger/guilt/disgust. Then they looked for changes in the amount of positive or negative words over the day and across seasons.

Their first finding was that positive words and negative words have different rhythms, showing that these moods are not different ends of the same spectrum, but more complex.

They found daily mood changes: people are more positive early in the morning. This happiness dips during the day and then rises again in the evening. This daily mood swing also happens at the weekend, albeit 2 hours later (after a lie-in?) suggesting that work isn't entirely to be blamed for our daily dip in enthusiasm. However, overall people are happier at weekends when they don't have to work and can sleep when they like.

Our daily mood swings as analysed from 509 million "tweets" from 2008-10. Adapted from Golder & Macy 2011
One of the real strengths in this analysis is they also looked at tweets from those living in the United Arab Emirates, where the weekend is on Friday and Saturday. They observed the same weekend trend as we have in the West, where the weekend is Saturday and Sunday.

Larks (morning risers) and owls (evening types) who tweet at different times of the day also have different rhythms in positive and negative tweets [1.1].

Golder & Macy's final findings show that when the days are getting longer, we get happier, but when the days are getting shorter our positivity decreases. However, there are no seasonal affects of negative words, so the "winter blues" seem to be a net result of less positive thoughts rather than more negative ones.

A more recently published study of the happiness of tweets over 3 years, has produced an incredibly detailed picture of rhythms of tweets [2].  The daily peak for 'coffee' tweets occurs between 8 and 9 am. Outliers of our daily happiness can also be picked up: these occur on holidays, such as Christmas, and during global tragedies, such as the tsunami.
"Coffee" is most frequently tweeted between 8 and 9am
Twitter and social media sites are becoming an invaluable resource to scientists studying our social rhythms. The data is generated real-time with no reliance on memory. They provide a larger data set, representing the general public better than small groups of American undergraduates. However, like any questionnaire, they do rely on the emotions that people publicly share, rather than what might be their innermost emotions.

Overall twitter is helping to reveal humanity's mood swings, and the universal effect sleep and the body clock have on our mood.

[1] “Diurnal and Seasonal Mood Vary with Work, Sleep, and Daylength Across Diverse Cultures.” Scott A. Golder and Michael W. Macy. Science, Vol. 333, Sept. 30, 2011

[2] "Temporal patterns of happiness and information in a global social network: Hedonometrics and Twitter" Dodds et al., PLoS ONE, Vol 6, e26752, 2011

Monday, 12 December 2011

How a Poinsettia knows it's Christmas Time

Today, Monday 12th December, is National Poinsettia Day, yup there really is a day for everything in the US. Poinsettia, or Euphorbia Pulcherrima, flowers red during the winter season. It's star-like shape, representing the Star of Bethlehem, and it's blood-red colour, symbolic of Christ's blood, has made it a popular Christmas plant.

However, if you've kept a poinsettia throughout the year, you would notice that during the summer it is a white plant, and it's only when the days become shorter that it develops it's redness.

The Poinsettia flowers red at Christmastime (C) bourgeoisbee
How does the poinsettia know when to flower red? Is it counting the number of days throughout the year? Or does it count the number of hours of daylight each day? In fact, it's neither of these, but down to it's internal clock...

The poinsettia is a short-day plant, requiring a long period of darkness to flower. A lot of the experiments to understand when plants flower have been done on long day plants such as Arabidopsis. These plants need a long period of light in the day to flower (usually >12 hours) and a short night.

The chemical that absorbs light is called phytochrome, this can exist in two forms. The "red" form, PR, which absorbs light during the day, and the "far-red" form, PFR, that is converted from PR during the night when there is no daylight.
Phytochrome is the chemical in the plant that absorbs light which converts it from the Red to the Far Red form

During the day PR is produced by daylight. During the night all the PR is converted into PFR, this only takes 2 hours to complete. If you expose a long-day plant to pulses of light during the night, it can trick it to thinking the day is long and it's time to flower. If the plant were merely counting the number of hours in the day, this wouldn't work.

The longer hours of light allow for the accumulation of PR alongside the protein Constans (CO), which initiates flowering. CO is controlled by the plants internal clock, so it has low levels during the day, and only rise during the late afternoon if there is enough light and PR. In order to flower the Arabidopsis requires both daylight to be detected by phytochrome, and the circadian rhythm of CO.

Understanding how short day plants work was a bit more tricky. But genetic studies on the short day plant rice are beginning to reveal that the clock in short day plants effect the same genes, but they have opposite effects on the plant [1]. So in a long day plant genes that activate flowering in a short day plant inhibit flowering.

Other short day plants include the tobacco plant, strawberries, and chrysanthemums.

I hope you enjoy celebrating National Poinsettia Day with a greater appreciation of the seasonal colouring in these short day flowering plants.

[1] "Genetic Control of Flowering Time in Rice, a Short-Day Plant" Yano, M et al., Plant Physiology, vol. 127 no. 4 1425-1429, 2001

Monday, 5 December 2011

Double summertime: Double trouble? Part 3

In this third blog post about single double summertime (SDST) I will respond to some of the supposed health benefits advocated by supporters of the lighter later campaign.

Dr Mayer Hillman, an active advocate of SDST, has predicted health benefits including, lighter afternoons might encourage more outdoor leisure pursuits leading to a reduction of obesity and related disorders[1]. 

However, these are assumptions on behavioural habits and there is currently no scientific evidence to support that an extra hour of light in the afternoon will be sufficient to increase outdoor exercise in the UK population. For those in London during winter the sun will set before 5pm, not significantly lengthening the daylight leisure time (map showing changes).

Will an extra hour of daylight encourage more outdoor exercise?  (c) Jon Candy
Hillman also suggests people will be exposed to more hours of daylight and are therefore likely to have improved mental wellbeing, more energy and lower rates of sickness. However, SDST will not increase the number of hours of daylight: it will only shift the timing of daylight hours to later in the day. In fact, deprivation of morning daylight is likely to cause the opposite effects: depression, sluggishness and higher rates of Seasonal Affective Disorder, SAD.

SAD, sometimes called the "winter blues", is thought to affect 2 million people in the UK. SAD in its most severe form can be debilitating, rendering sufferers unable to function during winter without treatment. It is often treated successfully with light therapy alone. The most successful treatment is morning light exposure from daylight imitating lamps, and is effective with over half of patients not requiring any other type of treatment[2]. This highlights how important quality, quantity and, crucially, timing of light is to our biology.

Lamps that simulate dawn are effective at combating SAD (C)  Susannah
In 2011 medical professionals at the British Medical Association annual conference rejected a bid to support SDST. There was a lack of categorical evidence for the supposed health benefits.

To achieve a healthier society, with increased productivity and performance, we need to encourage better synchronised body clocks. The health consequences of exposing ourselves to unnatural lighting conditions are being unravelled. Unnatural daylight hours are likely to intensify these detrimental consequences. 

Giving the proven importance of light in the morning on health, a policy that reduces morning daylight should not be supported on health purposes.

2.          Terman, M. & Terman, J.S. Lighttherapy for seasonal and nonseasonal depression: efficacy, protocol, safety,and side effects. CNS spectrums 10, 647-63; quiz 672 (2005).