TIME - GLUING CROSS-MODAL MEMORIES VIA SYNCHRONISATION

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When we remember past events we often find that these events are multisensory. For instance, when you think about your favourite camping holiday, you might recall the flickering light of the campfire and the crackle of the wood as it burned. This proposal addresses the fundamental question of what the mechanism is that holds all these different elements together so that we can have these integrated memories. This question is not trivial given that decades of brain research has taught us that different aspects of a multisensory stimulus are processed in different brain regions. A possible mechanism that our brains might use to link the different elements that make up a memory has to do with the abundant rhythmicity of human brain activity. Specifically, groups of neurons discharge synchronously, rather than chaotically. These rhythms allow neurons to engage in collaborative processing of incoming information, processed in different parts of the brain. Furthermore, neuroscience studies in animals showed that such synchronised activity is more likely to result in modifications of connections between neurons, which is the "hardware" underlying all memories. It therefore appears only logical that synchronisation is the key mechanism that turns a transient experience into a memory. Surprisingly, however, evidence for this fundamental role of synchronisation in building memories is scarce. This project capitalises on a recent discovery that was made by the applicants shedding a first light onto the critical role of neural synchronisation for multisensory memories. Using a novel way of controlling the synchronisation between auditory and visual brain regions via rhythmic sensory stimulation (i.e. a flickering video/sound) the applicants demonstrated that a multisensory stimulus is more likely to be remembered when the two modalities were synchronised compared to when they were not synchronised. We refer to this effect as the Timing Induced Memory Effect (TIME). The aim of this research is to build on these initial exciting findings and to provide a range of empirical behavioural and neural data on how TIME impacts on human memory under different conditions. To this end, five work packages are proposed which will use variants of an experiment where the volume of a 3-s sound clip and the luminance of a 3-s video clip are modulated at different frequencies. Animal studies predict that TIME should only work at particular brain rhythms, i.e. a slower 4 Hz rhythm and a faster 40 Hz rhythm. A prediction that will be tested in the first work package. The second work package addresses the exciting question of whether synchronised presentation of stimuli increases memory performance beyond its natural limits. This result could have strong implications for improving memory in healthy and non-healthy populations. A third work package tests an important boundary condition, namely whether attention is required to obtain TIME. In a fourth work package we will unravel the brain regions at which TIME exerts its effects on memory. In a final fifth work package we will test whether it is possible to boost the capacity for audio-visual memory associations by delivering rhythmic stimulation to the right index finger. This experiment, has a strong translational potential as it could spark the development of cheap stimulation devices to improve memory in healthy students, older adults, or patients.Together, this proposal tests the relatively simple but elegant idea that the ability to form memories for events which contain different elements depends on the synchronisation of the brain regions processing these elements in the first place. Using an innovative newly developed approach this project could therefore illuminate the critical component that holds our memories together, i.e. synchronisation.