As per a study conducted by researchers from the University of Exeter (U.K.) and the University of Calgary (Canada), high levels of stress can block memory processes.
What was the study?
Researchers performed experiments on pond snails (Lymnaea stagnalis) which have easily observable behaviors linked to memory and large neurons in the brain and they also respond to stressful events in a similar way to mammals, making them a useful model species to study learning and memory.
Pond snails generally breathe underwater through skin and if the water has low oxygen levels the snails emerge and inhale air using a basic lung opened to the air via a breathing hole. In the experiment, the pond snails were trained to reduce how often they breathed outside water. To train the snails not to breathe air they were placed in poorly oxygenated water and their breathing holes were gently poked every time they emerged to breathe. Snail memory was tested by observing how many times the snails attempted to breathe air after they had received their training. Memory was considered to be present if there was a decrease in the number of times they opened their breathing holes. Their memory was also assessed by monitoring neural activity in their brain.
Just before training, the snails were subjected to two different stressful situations, low calcium — which is stressful as calcium is necessary for healthy shells — and overcrowding by other pond snails.
What was found?
It was found that when snails faced with the stressors individually, their ability to form long term memory declined, although they were still able to learn and form short and intermediate term memory. However, when they were exposed to both stressors simultaneously, it made an additive impact on the snails’ ability to form memory and all learning and memory processes were blocked. It was found that when they were exposed to multiple stressful events they were unable to remember what they had learned.