Brain waves are part of memory

Spatial navigation and spatial memory play a central role in our lives. Without these abilities, we would hardly be able to find our way around our surroundings and would find it difficult to remember past events. However, the neuronal basis of spatial memory is far from being fully understood.

A research group has gained new insights into this gap in knowledge. They discovered that different types of nerve cells become active together during spatial memory and are coordinated by brain waves ("ripples"). The results have now been published in the journal Nature Neuroscience.

Associative memory allows that different pieces of information are linked together. "In the context of spatial memory, associative memory enables us to remember the locations of certain objects in the spatial environment," explains the senior author. "For example, we can remember where in the house we put our keys". At older age or in certain diseases such as Alzheimer's, however, this ability is limited. "It is therefore important to investigate the neuronal basis of different forms of human memory," says the author. In the long term, this could help develop new therapies for memory impairments.

Nerve cells are active while information is retrieved from memory. To further investigate this phenomenon, the researchers recorded the activity of individual nerve cells in epilepsy patients performing a memory task. "In a virtual world, the participants were asked to remember the locations of different objects," explains the senior author.

The recordings showed that different types of nerve cells became active during this memory task. Some nerve cells responded to certain objects, while other nerve cells activated in response to certain locations. The scientists observed that interactions between the different types of nerve cells became stronger over time when participants remembered the right object in the right place.

In addition to place and object neurons, the researchers observed hippocampal brain waves ("ripples") that also occurred during the memory task, presumably playing a crucial role in the formation and retrieval of associative memories. "Ripples could be important for the connection of different types of nerve cells and the formation of complex memories. It will be exciting to further investigate this idea in future studies," explains the author. It will also be interesting to study how memory performance is modulated when ripples are suppressed or triggered, providing insights into the causal relevance of ripples.