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Light and the Brain: more than just sight

The words

The development of a new smartphone app could uncover how light affects human memory and alertness. The app being developed at the University of Manchester will measure human performance and light levels. Here, Marina Gardasevic explores her research on how light affects different people.

Light is all around us, but what most of us don’t appreciate is its richness in information. Obviously we use light to see, but from the colour and intensity of light our bodies can also tell what time of day it is, what time of year it is, what the weather is like and much more.

In humans light is sensed via our eyes, a light sensor in the eye, called melanopsin, detects the light around us and sends this information to the body clock in the brain – the SCN (suprachiasmatic nuclei). The SCN acts as our body clock and regulates our “circadian rhythms”. It uses light, detected by melanopsin, to realign the clock to the day:night cycle.

A human eye

Different people have different natural body clock types, you may notice that elderly relatives naturally wake up much earlier than your average teenager. This isn’t because teenagers are lazy, but because their body clocks are typically more “evening-type”. There are also differences between people of the same age group, known as “natural variation”. Light affects people of different body clocks differently depending on when the person is exposed to it.

In fact, light exposure can have large effects on our bodies, for example, if you present yourself with light at night (such as from your phone screen) this confuses your SCN and causes you to sleep less, and less deeply. Circadian researchers know a vast amount about how light affects circadian rhythms, from the timings of the light, to its duration, to how bright the light is, differences in ages and sexes and much more. But what about other ways light can impact the brain? Like our memory or how alert we are? This is what we are researching. We’d like to know how the amount of light around a person affects their performance at different times of day, and how this is different for morning/evening type people.

So this is our aim, but the challenge now is how do we measure it? A well-studied performance measure is alertness. An easy way to assess this is to look at how alert people feel by asking them to rate their alertness on a scale. This is known as “subjective alertness”. Studies using this agree that more light makes people feel more alert. But what about how alert people are? This can be done with tasks that measure reaction time. Some studies have tried to look at light on objective (actual measured) alertness but have found different results, and it’s the same story when looking at light’s effect on memory.

There is also the problem that these studies are conducted in a lab environment where participants come in and are exposed to controlled lights. These types of studies are beneficial in that they can help answer questions in a controlled environment so we can really pull out little differences that may otherwise be hard to identify. However, the problem with lab studies is that their findings are hard to extend to the real world, where there is a vast amount of variability and we don’t have “controlled” lighting environments. Lab studies are also expensive and difficult to do, meaning they often end up with small sample sizes. The problem with small sample sizes? Not being able to tell what is natural variation and what is the trend you are interested in.

If you present yourself with light at night (such as from your phone screen) this confuses your body clock and causes you to sleep less.

A hand controlling a mobile phone, the phone is switching from day mode to night mode

How can we address this? How can we measure performance and light in the field? How can we get a large sample size with lots of different body clock types? Thankfully the answer lies in our pockets: smartphones!

Smartphones can measure reaction times as good as most computers and they have the ability to measure the level of light through the camera or the light sensor. We have developed an app containing tasks which measure a person’s performance whilst the app measures the amount of light around and sends this data to us. The app also asks people about their age, caffeine and smoking, health problems, level of physical exercise and sleep patterns which allows us to calculate if they are morning- or evening-type people. This powerful tool, which is currently in the testing phase, will enable us to collect data from hundreds of people thus helping us disentangle the facts that other studies have been struggling with.

And what about the real world? What can this information do? Well knowing how this puzzle works could prove super useful; we could change indoor lighting to best support people’s performance, maximising workplaces and schools to be better suited to our biology. Even on an individual level; if you knew that more light in the afternoon improved your memory and attention; you’d be able to give yourself a boost when writing that essay. After all, light is all around us, we may as well harness it.

You can find out more about this research at:

Marina is a science communicator, you can follow her on Twitter @MarinaGNeuro

Melanopsin – the light sensor in the eye that detects how much light is around us and sends this information to the SCN
Suprachiasmatic nuclei (SCN)
– a small region in the brain which is responsible for our circadian rhythms and causes body changes (e.g. hormone release for sleepiness) depending on the time of day. Also known as the “Body Clock”
Circadian rhythm – the natural rhythm inside our brain that predicts the time of day, it gets synchronised to the actual day:night schedule predominantly using light detected by melanopsin
Alertness – a state of high attention
Objective – a quantified (numbers) measure of something without human bias. e.g. measuring alertness as reaction time in milliseconds. As opposed to Subjective
Subjective – a measure of something that varies depending on who is measuring it. e.g. measuring alertness by asking people how alert the feel on a scale of one to ten. As opposed to Objective
Natural variation – the differences in a measure that you naturally see between people (e.g. some people have quicker reaction times than others)
Lab study – a study in a controlled environment where as many variables are controlled as possible (e.g. measuring performance by asking people to come into the same room, with the same lights, same temperature, at the same time of day etc). As opposed to Field Study.
Field study – a study conducted in the natural environment that you are interested in (e.g. schools) including all the uncontrolled variables those environments have (e.g. different schools have different lighting conditions). As opposed to Lab Study.
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Marina Gardasevic
PhD researcher in Neurosicence University of Manchester

Marina Gardasevic

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