High rates of stress block the processes associated with memory.
This was shown by experiments with snails. As established by scientists, after effects of a large number of irritants that provoke stress, snails forget everything they have learned previously.
Stress also affects the human ability to remember information. A few stressful events occurring at the same time produce a cumulative effect. So, a little stressful time reduces the quality of memory, but a few things do not provide information to stay in the memory at all.
During the experiment, the snails have been learned to breathe with some frequency, when they were out of water (usually they breathe under water, absorbing oxygen with skin). Snail cannot breathe in water with low oxygen level that makes them surface and inhale through the breathing hole.
Scientists have tried to wean the snails to breathe normally out of the water. Every time a snail tries to take a breath, respiratory specialists touched the hole. Memory of the snails was tested by the number of attempts to take a breath after exercise. Numerous irritants knocked out waterless breath regime.