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It happens to us all. You’re introduced to someone at a party. You then ‘forget’ their name, only to find it comes back to you hours later.

Scientists have observed that, in all animals, memories that can be recalled several hours after learning may paradoxically become inaccessible for brief periods after their formation.

Although it’s not understood fully why these lapses occur, it’s believed that they are a necessary part of the brain’s process to consolidate memories.

Now University of Sussex neuroscientists have discovered that causing a disturbance during these memory lapses disrupts the process and appears to prevent the memories being formed.

Dr Ildiko Kemenes and colleagues from Sussex Neuroscience introduced snails to an unfamiliar substance during feeding so that the snails would learn to recognise it as food. During subsequent feeding they found that the snails responded to the stimulus, with memory lapses (i.e. not responding) after 30 minutes and two hours, before the memory became consolidated at about four hours.

However, if the snail received another different stimulus during the memory-lapse periods, the memory consolidation, as identified by examining neural pathways in the brain, became disrupted.

Dr Kemenes says: “Scientists have long wondered why the brain shows these memory lapses.

“Here we showed that lapses in memory coincide with periods when consolidation of memory is susceptible to disturbances from outside the memory network. Changes in the molecular pathways underlying consolidation are responsible for these periods of vulnerability.”

Dr Kemenes suggests these lapses are decision-making points, during which the brain decides whether to proceed with the process of consolidation into long-term memory. “From an evolutionary perspective, this would be an advantage,” she adds.

“Memory formation is an energy-consuming process. The brain would need to decide if it was worth expending energy for the consolidation of that particular memory. The brain has a restricted capacity to learn things and preventing some memory formation would be a way to avoid overload.”

For the next stage of the study, which is funded by the Biotechnology and Biological Sciences Research Council (BBSRC), the scientists will be investigating what happens to the brain during the memory disruption.

Co-investigator Professor Paul Benjamin says: “We hadn’t realised quite how complicated the process would be. It could be that, rather than just disrupting the original stimulus, the brain is creating a new memory from the second stimulus.”

‘Susceptibility of memory consolidation during lapse in recall’, by Vincenzo Marra, Michael O’Shea, Paul R. Benjamin and Ildiko Kemenes, is published in Nature Communications.