Klosterneuburg (Austria) – Neurologists have been able to use brain activity patterns to read, as it were, the thoughts of experimental rats and to predict from the observations, in which direction the animal will move within a labyrinth in a next step and when the rat will make a mistake.
As reported by the team headed by Jozsef Csicsvari and the Institute of Science and Technology Austria (IST Austria) in the journal “Neuron” (DOI: 10.1016 / j.neuron.2018.11.015), they first observed that certain brain activities contributed to the directional decision Animals precede.
As early as 2014, John O’Keefe, May-Britt Moser, and Edvard Moser observed that so-called “space cells” send signals when we are in a particular position-a discovery that earned the scientists the Nobel Prize for Medicine at the time. Based on which square cell fires, scientists can determine where a rat is.
When the researchers then exposed the animals to an eight-armed laboratory labyrinth known to animals from previous tests, three of which contained food rewards, these observations not only enabled them to determine the position of the rats but also to predict which way to go The rats would each decide next – depending on which neuron fires while the rat solves a task that tests their so-called reference memory.
According to the researchers, this task separates two different forms of spatial memory: reference and working memory. “Reference memory is the memory that allows a rat to remember which arms contain rewards and which do not. Working memory is the memory that keeps track of which arms the rat has not yet visited and which it has already visited. ”
The researchers thus tested the pure working memory by modifying the experiment so that only labyrinth arms containing the rewards were open. Alternatively, they tested pure reference memory by closing already visited arms.
The researchers then asked how the cells fire when rats navigate through a maze, and how firing differs between the reference and working memory tasks.
“In the middle of the labyrinth, before the rat enters the next arm, the sequence of cells firing corresponds to either the route taken in the last arm visited or the arm through which the rat will run next,” Csicsvari and colleagues explain, “In the reference memory tests, the sequence corresponds to the next labyrinth arm the rat will visit. This gives the researchers an insight into the immediate plans of the rat. “So the experimental animal thinks of a place other than the one it is located in, which allows the researchers to predict which arm of the labyrinth the rat will enter next.
In fact, researchers can not only predict where the rat will go next, but they also know when the rat will make a mistake: “If the rat makes a mistake, it remembers a random path. Based on the space cells, we can predict that the rat will make a mistake before committing it, “explains Csicsvari. However, the prediction does not work for tasks that test the memory: “In these, the firing of the square cells corresponds to the arm that the animal has recently visited.”
Scientists believe that the brain employs different strategies for solving homing and working memory problems. “With the reference memory, the brain navigates and remembers ‘this is a place I have to visit’. It uses the hippocampus, which is important for spatial tasks. The memory is more abstract, every place is a point on the list of places to visit. The hippocampus probably signals the prefrontal cortex where the rat was, and the prefrontal cortex keeps track of which objects it can ‘peel off’, “concludes Csicsvari.