Thursday, February 9, 2017

Memory and mental maps (time and space)

Kate Jeffrey and a fascinating article in Aeon. It's about mental maps, the neural structures that organize our spatial experience. They're also memory structures. Here's the concluding paragraphs:
Grid cells were discovered in 2005, and more than a decade later we still don’t know exactly what they are for, but they are believed to be the brain’s equivalent of the grid reference on a map. Whatever their function, their existence does prove, however, that these structures in the brain – hippocampus, entorhinal cortex and a host of their neighbours – collaborate in forming a metric representation of space. This is a real map. It might not look like a conventional map because it’s not written on parchment and isn’t labelled with printed text and a compass rose. However, the neurons in these regions respond in a way that shows that they are somehow stimulated, not by bells and food, as the Behaviourists believed, but by abstract properties of the animal’s experience, such as how far it has walked and what place it has reached. The discovery of grid cells confirmed O’Keefe’s cognitive map proposal, and the Mosers and O’Keefe together shared the 2014 Nobel Prize in Physiology or Medicine ‘for their discoveries of cells that constitute a positioning system in the brain’.

But where does this leave memory? This is where research in the hippocampus began: do place cells have anything to do with memory?

Yes, we think they do, and research now aims to uncover precisely what. One of the most important implications for humans, arising from study of the hippocampus, is its involvement in Alzheimer’s disease, which begins in the entorhinal cortex (where the grid cells are) and spreads throughout the hippocampus and thence to the rest of the brain. The first symptom of Alzheimer’s disease is often disorientation (eg, getting lost on the way back from the shops), but this progresses rapidly to a more general amnesia. Scientists now know that the hippocampus is both a map and a memory system. For some reason, nature long ago decided that a map was a handy way to organise life’s experiences. This makes a lot of sense, since knowing where things happened is a critical part of knowing how to act in the world. The quest now is to understand how memories get attached to this map. Armed with this knowledge about memory, we might one day be able to study memories directly, and even, perhaps, manipulate them – to soften traumatic memories, for example, or repair damaged ones such as those affected in Alzheimer’s disease.
H/t Faculty of Language

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