...most scientists thought that when light struck the retina, only two kinds of cells responded: rods and cones. But Hattar and Berson thought there were other light-sensitive cells that hadn't been identified.
"People used to laugh at us if we say there are other photoreceptors distinct from rods and cones in the retina," Hattar says.
The skeptics stopped laughing when the team discovered a third kind of photoreceptor that contained a light-sensitive substance called melanopsin not found in rods and cones. (The full name of these cells, if you're interested, is intrinsically photosensitive retinal ganglion cells, or ipRGCs.) These receptors responded to light but weren't part of the visual system.
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In September, Hattar's team published a study about mice suggesting a direct pathway between the third kind of photoreceptor in the retina and brain areas that affect mood.
When these cells were present, an artificially shortened cycle of light and dark caused a version of depression in a mouse. But when the team removed the cells with gene-editing tools, the mouse didn't become depressed.
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Sanes' team put young adults in an MRI machine and measured their brain activity as they were exposed to different levels of light. This allowed the team to identify brain areas that seemed to be receiving signals from the photoreceptors Hattar and Berson had discovered.
Two of these areas were in the front of the brain. "It's interesting because these areas seem to be the areas that have been shown in many studies to be involved in depression and other affective disorders," Sanes says.
As someone who gets a bad case of the SADs in wintertime, this is pretty interesting stuff. I wonder if there is any correlation between this (the pathway, or SAD in general) and whether people...
As someone who gets a bad case of the SADs in wintertime, this is pretty interesting stuff. I wonder if there is any correlation between this (the pathway, or SAD in general) and whether people end up being early birds or night owls.
Early birds or night owls is determined by the intrinsic period of your circadian clock. We all have an internal clock in our brains that ticks with a period of about 24h when left in constant...
Early birds or night owls is determined by the intrinsic period of your circadian clock. We all have an internal clock in our brains that ticks with a period of about 24h when left in constant conditions (i.e. in a cave). When you are exposed to sunlight the clock synchronized itself to it, but if your intrinsic period is longer or shorter that 24 hours this results in a phase delay or advance. Intuitively, if your clock is a bit slower than 24h it means the sun as to pull you to keep you in phase, so you lag behind.
So if you are an night owl it means that if you were to go in a cave for some weeks, you would adopt a 25h or 26h cycle.
Article highlights, tl;dr in bold:
As someone who gets a bad case of the SADs in wintertime, this is pretty interesting stuff. I wonder if there is any correlation between this (the pathway, or SAD in general) and whether people end up being early birds or night owls.
Early birds or night owls is determined by the intrinsic period of your circadian clock. We all have an internal clock in our brains that ticks with a period of about 24h when left in constant conditions (i.e. in a cave). When you are exposed to sunlight the clock synchronized itself to it, but if your intrinsic period is longer or shorter that 24 hours this results in a phase delay or advance. Intuitively, if your clock is a bit slower than 24h it means the sun as to pull you to keep you in phase, so you lag behind.
So if you are an night owl it means that if you were to go in a cave for some weeks, you would adopt a 25h or 26h cycle.