Have you ever noticed that you get snippy when you haven’t slept well? Not you, right? Ok, what about a shift-worker you might be close to…ever notice how snippy they get when they are fatigued?
I am here to defend the cranky ones. Their often exaggerated reactions, to what you might think are tiny little annoyances, are justified. They can’t help it. A lack of sleep impairs two parts of the brain that are integral to controlling emotional reactions.
1-The amygdala is an area deep in the brain’s medial temporal lobe and part of the limbic system.
It plays a key role in forming our reactions to emotionally charged information.
2-The medial prefrontal cortex (MPFC), part of the frontal lobe, is like our censor, it can inhibit the emotional reactions of our amygdala when they are out of proportion from the emotionally charged information.
A functional magnetic resonance imaging (fMRI) study showed that the amygdala’s reaction to negative emotional stimuli is greater in magnitude/intensity and volume in people who miss a night of sleep when compared to a control group. This study also showed that the connections between the amygdala and the MPFC were weaker in the sleep deprived group. This means that the amygdala’s reactions can’t be inhibited as well by the MPFC in people who lack sleep and it can lead to the emotional outbursts in your shift-worker.
The next time your shift-worker flies off the handle or breaks into tears, cut them a little slack, it’s their amygdala running wild without the controlling influence of their medial prefrontal cortex. If you are the snippy one, then it might be a good idea to get some sleep to restore your brain to its less reactive state.
 Yoo, S., Gujar, N., Hu, P., Ferenc, A.J., & Walker, M. (2007). The human emotional brain without sleep – A prefrontal amygdala disconnect. Current Biology, 17(20), R877-R878.