Sometimes life is just too stressful. Whether you're a freshwater snail struggling to breathe in a dwindling puddle or a student facing an assessment that could change your future, it can be hard to form memories when the pressure is on; even the smartest can struggle. ‘We have been exploring how stress alters both memory formation and the ability to recall memory for a number of years’, says Ken Lukowiak from the University of Calgary, Canada, who is intrigued by how the humble pond snail (Lymnaea stagnalis) forms memories. Having recently discovered a ‘smart’ colony of pond snails at White Sand Lake in Saskatchewan that learn quickly (after just one training session) to keep their breathing tubes closed when immersed in deoxygenated water – compared with ‘average’ snails, which require multiple training sessions before they get the point – Lukowiak wondered how resilient the ‘smart’ Saskatchewan snails’ memories would be when they experienced a snail-scale shock.
Lukowiak and a large team of assistants trained ‘smart’ and ‘average’ snails to keep their breathing tubes closed when immersed in deoxygenated water by gently tapping the snails on the breathing tube whenever they tried to extend it above the surface to breathe. While the unstressed ‘smart’ snails got to grips with the idea of keeping their breathing tubes closed after a single training session, the ‘average’ unstressed snails – which had been found in a pond outside Calgary – required two training sessions, 1 h apart to catch on. Then, considering a range of scenarios that are stressful for pond snails – including experiencing a heat wave, starvation, an approaching predator and incurring damage to the shell – the team wondered how the memories of the ‘smart’ snails would fare after experiencing the stress and whether the ‘average’ snails might receive a memory boost and recall the tube-tapping lesson after just one training session.
Impressively, the stressful sensations seemed to sharpen the ‘average’ Calgary snails’ memories, allowing them to recall that they must keep their breathing tubes closed after the reduced training regime. However, the A-grade snails seemed to be struggling. While a sniff of the scary odour of the aggressive crayfish that share their Saskatchewan home did not affect the snails’ memories, a heat wave, the smell of food when hungry and receiving a small amount of damage to their shells all impaired the ‘smart’ snails’ ability to form memories.
‘Being smart made them less resilient and thus they could not handle stress as well as the more average individuals’, says Lukowiak, who admits that he was surprised that the Saskatchewan snails were so badly affected. ‘Even though both the ‘smart’ and ‘average’ snails were freshly collected from ponds that experience temperature spikes in the summer, the ‘smart’ snails have their ability to form memory obstructed by a thermal shock’, he says. Adding that many of the snails that he encountered in the wild had also incurred damage to their shells – which should affect their memories – Lukowiak says, ‘How that alters their ability to survive in the wild is not clear to us’.
In short, the ‘smart’ snails’ superior intellect is a clear disadvantage for their memories in stressful situations and Lukowiak is now eager to understand why the snails are so impaired. ‘One idea is that maybe the ‘smart’ snails do in fact make memory, but they can't retrieve it because of the stress, much like a smart student taking an exam’, he suggests. Maybe exam-brain-freeze has a longer history than any of us knew.