Most of us have had to function with less sleep than we wanted. When at home, we can usually find ways to function and get things done. If we need to put some things off, or take a nap, we have some options. But what about at work? In a recent article Dr. Michael Breus takes a look at some of the insidious aspects of sleep loss. He states: “It’s difficult to identify a cognitive skill that isn’t affected by sleep and compromised by sleep deprivation. That’s how pervasive the effects of insufficient sleep are on the brain”
For aviators, this is critical information. We are very aware of the loss of alertness when we are fatigued, but are we aware of the cognitive loss as well. The danger lives in the lack of visibility and awareness of cognitive decrements developing due to sleep loss fatigue.
UCLA’s Dr. Itzhak Fried and his team have revealed, through studies, that sleep deprivation disrupts brain cells’ ability to communicate with each other. “This leads to cognitive lapses in how we perceive and react to the world around us,” said Fried. The result is delays in translating what we see into conscious thought. Fried noted that when fatigued, “It takes longer for the brain to register what it is perceiving.” His team also discovered that portions of the brain will shut down or “doze” while the rest of the brain is up and running. “Severe fatigue exerts a similar influence on the brain to drinking too much,” Fried said.
Breus points out, “Sleep deprivation leaves key areas of the brain in an “always on” state of activation.”
In an unrelated study, Mizuno, K, et al say; “During the fatigue-inducing mental tasks…, the prefrontal cortex, which is associated with the processing of executive functions such asvisuospatial workingmemory and divided attention,… may have been continuously activated. Therefore, although further neuroimaging studies are necessary, prolonged cognitive load may induce decreases in prefrontal cortex activity and inhibitory capacity for sympathoexcitatory response.
Breus and Mizuno have identified that both sleep induced fatigue as well as task loaded mental fatigue, can produce the same cognitive loss and lack of ability to respond appropriately to sudden stimulus.
In his study “Effects of mental fatigue on attention,” Boksem states,” …when an unexpected and potentially dangerous situation arises, fatigued people lack the flexibility that is needed to handle the new and unexpected situation in an adequate way…” 
Much has been said about “startle events” and the impact thereof. What we are learning now, is that our perception of events and ability to process information may be degraded by fatigue, to the point where we don’t recognize the events developing until they become startle like events. Then, due to degraded cognitive abilities, we may not respond appropriately. It is likely that there will never be a way to train for these events if they occur during periods of sleep loss or mental fatigue. We must not compromise safety. Data, now available, argues that fatigue rules and operating procedures can be science based and safety oriented. All industries look to aviation as the leader in High Reliability Organizations. It is through understanding the neuroscience impact of fatigue, on cognition and performance safety, that we will retain and expand that leadership role.
 Michael J Breus, Ph.D. psychologytoday.com, Nov 01,2018
 UCLA Newsroom online, Elaine Schmidt, Nov 06, 2017
  Mizuno, K., Tanaka, M., Yamaguti, K., Kajimoto, O., Kuratsune, H., & Watanabe, Y. (2011). Mental fatigue caused by prolonged cognitive load associated with sympathetic hyperactivity. Behavioral and Brain Functions : BBF, 7, 17. http://doi.org/10.1186/1744-9081-7-17
 Effects of mental fatigue on attention: An ERP study
Maarten A.S. Boksem*, Theo F. Meijman, Monicque M. Lorist
Cognitive Brain Research 25 (2005) 107 – 116