The hippocampus plays a critical role in learning, memory, and spatial representation, processes that depend on the NMDA receptor (NMDAR).

Despite explosive expansion of artificial intelligence based on artificial neural networks (ANNs), these are employed as "black boxes'', as it is unclear how, during learning, they form memories or develop unwanted features, including spurious memories and catastrophic forgetting. Much research is available on isolated aspects of learning ANNs, but due to their high dimensionality and non-linearity, their comprehensive analysis remains a challenge. In ANNs, knowledge is thought to reside in connection weights or in attractor basins, but these two paradigms are not linked explicitly. Here we comprehensively analyse mechanisms of memory formation in an 81-neuron Hopfield network undergoing Hebbian learning by revealing bifurcations leading to formation and destruction of attractors and their basin boundaries. We show that, by affecting evolution of connection weights, the applied stimuli induce a pitchfork and then a cascade of saddle-node bifurcations creating new attractors with their basins that can code true or spurious memories, and an abrupt disappearance of old memories (catastrophic forgetting). With successful learning, new categories are represented by the basins of newly born point attractors, and their boundaries by the stable manifolds of new saddles. With this, memorisation and forgetting represent two manifestations of the same mechanism. Our strategy to analyse high-dimensional learning ANNs is universal and applicable to recurrent ANNs of any form. The demonstrated mechanisms of memory formation and of catastrophic forgetting shed light on the operation of a wider class of recurrent ANNs and could aid the development of approaches to mitigate their flaws.

It's no hidden health secret that sleep is really good for us. It helps our immune systems and supports almost every organ system in the body. We've also known for almost two decades that the slow, synchronous electrical waves in the brain during deep sleep supports memory formation. However, we did not know exactly how the brain does this until now. These slow waves make the neocortex–where long-term memory is stored in the brain–particularly receptive to new information.

Brains consume metabolic energy to process information, but also to store memories. The energy required for memory formation can be substantial, for instance in fruit flies memory formation leads to a shorter lifespan upon subsequent starvation (Mery and Kawecki, 2005). Here we estimate that the energy required corresponds to about 10mJ/bit and compare this to biophysical estimates as well as energy requirements in computer hardware. The cost for computation and information transmission, mostly for synaptic transmission and spike generation, is well documented, and the brain's design is now widely believed to be constrained by energy needs (Attwell and Laughlin, 2001; Lennie, 2003; Harris et al., 2012; Karbowski, 2012). More recently the metabolic cost of learning has been added to the brain's energy budget.

Neuroscience Beyond down-regulating cortical activity, sleep also promotes long-term memory formation and the strengthening of synaptic connections. It is possible that both core sleep stages, slow-wave sleep (SWS) and rapid eye movement (REM) sleep, contribute to these processes. Niethard et al. used in vivo two-photon calcium imaging in mice to assess the activity of large populations of cortical layer 2/3 cells during SWS and REM sleep. Most pyramidal neurons substantially decreased their activity during SWS and REM sleep episodes. The decrease during SWS sleep, but not during REM sleep, was accompanied by increased inhibitory interneuron activity. However, a subpopulation of pyramidal cells exhibited upregulated activity during SWS. These neurons are possibly involved in memory formation, and also underwent profound down-regulation during subsequent REM sleep. J. Neurosci. , 41 , 4212 (2021).

Forgetful people who struggle to remember something should wait till later in the day, according to results from a new study. Research by the University of Tokyo has found memory is worse in the morning or just after waking up. Their study pinpointed a gene in mice that seems to influence memory recall at different times of day and tracked how it causes mice to be more forgetful just before they normally wake up. Study leader Professor Satoshi Kida, of the University of Tokyo, said: 'We may have identified the first gene in mice specific to memory retrieval.' The team believes the internal clock in mammals that is responsible for regulating sleep-wake cycles also affects learning and memory formation.

Zapping older people's brains could sharpen their memories to be as good as those of people decades younger. Scientists found stimulating a certain part of the brain boosted the memory of over-64s who had normal age-related memory loss. It worked so well the researchers saw no difference in the test results of volunteers who'd had the therapy and younger, healthier adults. The findings are the latest in a long line of medical trials to delve into the benefits of electrical stimulation on the brain. Just two weeks ago a similar study found zapping the brains of over-60s can restore their memory power to that of people in their twenties.

Our memories leave a clear and unique genetic mark on our brains. That's the remarkable discovery of scientists in Israel who say these genetic markers could be used to unlock memories after people die. The technology opens the door to strange scenarios, similar to those portrayed in the series'Black Mirror', where investigators can record and playback the memories of suspected criminals. It could even lead to a future in which police are able to read and replay memories of murder victims to help them piece together the events leading up to their death. Our memories leave a clear and unique genetic mark on our brains.

The memory mechanisms of great pond snails could one day help develop drugs for trauma and dementia patients. If you think of a snail, and then think of a human, there are some obvious differences. But decades of studies say our memories might have more in common than some might guess. Memory, and its formation, has been the subject of neuroscientific research for quite some time, yet science has only made incremental steps in this extremely complicated field. One of the recent advances is the discovery that memory is likely similar across organisms, at least at a molecular level.