There are two types of people at Christmas: those who delight at playing Mariah Carey's All I Want for Christmas is You on repeat, and those who spend the festivities muttering "Bah, humbug" under their breath.
It seems some of us have more holiday cheer than others, which raises the question about whether Christmas spirit actually exists - and if so, where would we store it?
New research published in this month's British Medical Journal suggests Christmas spirit is actually stored in our mind. The finding came after studying the brain scans of people who have different experiences of Christmas.
Volunteers were surveyed to see if they had ever celebrated Christmas and if their associations with the holiday were positive or negative. From their answers, 20 participants were found to be suitable, 10 of whom were classed as Christmas celebrators and 10 as a non-Christmas group.
The volunteers were placed in a functional magnetic resonance imaging (fMRI) scanner and their resting brains scanned, which showed the same normal cerebral perfusion blood flow for both groups. A slideshow of 84 images were then played to them through a pair of video goggles, with some of the images containing Christmas themes.
During the viewing, the scientist used the scanner to see if any specific images caused measurable changes in blood flow and blood oxygenation to parts of the brain, and if so, if they were similar for the two groups.
Because there is a tight coupling between neural activity and blood flow, fMRI scans are often used to measure blood-flow changes which can then be used as a surrogate for increased brain activity showing which parts of the brain are active at the time of the scan.
From the results they found that volunteers who had never celebrated Christmas showed no change in the blood flow for any images viewed. However, the Christmas-loving volunteers produced scans where several neural networks lit up across regions of the brain including the parietal lobules, premotor cortex, and the somatosensory cortex whenever a Christmas image was shown, implying that their Christmas spirit resided in the areas of the brain associated with recollection of joyful emotions, pleasant food experience memories and retrieving relevant social information from faces.
This fun study does seem to locate cerebral regions which are more active in people who celebrate Christmas.
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You may be wondering why scientists would spend so much time and money searching for something so trivial, but like many scientific discoveries, this Christmas-themed study came about partly by accident and partly for fun when they were looking at how blood flow in the brain changes in migraine-prone patients.
As they tried to catch the physiology of the migraine process inside an fMRI scanner, they discovered that they needed to find something to do for the patients lying in a very boring scanner waiting for a migraine to happen, and for the control non-migraine suffering volunteers being scanned for baseline brain measurements.
Science, like the invention of post-it notes, sometimes goes this way where you are looking for one thing, and happen to stumble on another.
Although the definition of Christmas spirit is not yet scientifically agreed upon, this fun study does seem to locate cerebral regions which are more active in people who celebrate Christmas. The evidence shows it is activated by images of Christmas themes, but with my experience of several overly happy people this season, I think it can also be brought on by overplayed Christmas music, fake pine-scented oils and bad cracker jokes.
• Dr Michelle Dickinson, also known as Nanogirl, is an Auckland University nanotechnologist who is passionate about getting Kiwis hooked on science.