Swiss cheese model

Network fatigue

Swiss cheese model of homeostatic fatigue is a metaphoric way to understand the functioning of the brain in conditions of cognitive "tiredness".

As richly evidenced by the research on the two-process model of sleep regulation, the brain gradually loses its cognitive capacity during a waking day. This results in cognitive fatigue that was originally named Process S, or homeostatic component of sleep propensity.

High fatigue will result in portions of cortex losing its function (see: Local sleep in portions of the awake cortex). This can produce bouts of microsleep that affect human productivity. When portions of a neural network are disabled, normal function becomes impaired. Fatigued networks may resemble a Swiss cheese in that their disabled subcomponents may be visualized as holes in the cheese.

In a Swiss cheese network, error rate increases. This results in false associations, increased interference, increased forgetting, recall failure (transient forgetting), etc. Gradually, less fatigued portions of the cortex can compensate for more fatigue portions. As a result, we observe tangible changes in behavior.

Amnesia and creativity

In network terms, the shortage of active neurons may have similar effects as a shortage in recruitment of new cells in the hippocampus (e.g. overgeneralization).

Paradoxically, on rare occasions, mildly fatigued state may be beneficial in a stalled creative process. Due to the stochastic nature of creativity, processing errors may serve creative disruption (see: How to solve any problem).

Learning

Sleep deprivation has a major impact on learning. Not only does the recall and consolidation drop. The chances of forming wrong memories also increase. When the concept network displays erratic activations, we may end up with erratic connections (memories). As a result, learning in a sleep deprived or fatigued state will increase interference.

While cramming on a sleepy head, learning may be outweighed by unlearning

A graph showing the average recall of a teenager who often needs to get up early for school, far ahead of his natural waking time

Figure: Early school time has a dramatic impact on recall as evidenced by grades in SuperMemo. This is one of many disastrous side effects of sleep deprivation. The problem can be resolved by free running sleep, however, this would require the possibility of being late for school or later starting times. For more see: Sleep loss, learning capacity and academic performance

Further reading

• Sleep deprivation amplifies the harm of schooling
• Local sleep in portions of the awake cortex
• Bad learning contributes to Alzheimer's

This glossary entry is used to explain "Good sleep, good learning, good life" (2017) by Piotr Wozniak