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Cracking the spatial memory code
March 12, 2009Researchers have shown that they can tell where a person is "standing" within a virtual reality room on the basis of the pattern of activity in the brain alone. The findings, published online on March 12th in Current Biology, a Cell Press publication, offer compelling evidence that the hippocampus, a region of the brain critical to navigation, memory, and imagining future experiences, works in a structured and predictable way. That discovery is contrary to what many experts had previously suspected, according to the researchers.
"You can predict where someone is standing by reading the patterns in their brain activity," said Demis Hassabis of University College London. "You can track what is purely an internal thought."
"With this kind of research, we are approaching the realm of mindreading," added Eleanor Maguire, also of University College London.
In the new study, Hassabis, Maguire, and their colleagues asked four participants to navigate to target locations within a virtual reality room while their brains were scanned with a functional magnetic resonance imager (fMRI). fMRI measures blood flow related to neural activity in the brain. They then applied a sophisticated analytical procedure known as multivariate pattern classification to see if they could relate the pattern of brain activity to each individual's location in virtual space.
And it worked. The pattern they uncovered reflected the participants' memory for where they were, the researchers explained, since once they had reached their final destination, there were no visual cues to discern one target spot from another. The activity they examined spanned some two to five million of the 40 million or so cells in the hippocampus, Hassabis noted.
Earlier studies done primarily in rats had suggested that spatial memories stored in the hippocampus had neuronal representations that were uniform and randomly distributed. But if that were the whole story, the predictions made in the new study would not have been possible.
Now that they have shown that such a predictable functional structure exists in the hippocampus, additional studies will seek to crack that neural code for other memories. Indeed, spatial representations of the type investigated in the study are thought to form the scaffold upon which memories of our personal experiences, known as episodic memories, are built.
"By showing it is possible to detect and discriminate between memories of adjacent spatial positions, our combination of non-invasive in vivo high-resolution fMRI and multivariate analyses opens up a new avenue for exploring episodic memory at the population level," the researchers wrote. "In the future it may be feasible to decode individual episodic memory traces from the activity of neuronal ensembles in the human hippocampus."
"We know that the hippocampus is critical for remembering our life experiences," Maguire said. This discovery "opens a whole world of possibility previously thought inaccessible to human brain imaging."
Cell Press
In the new study, Hassabis, Maguire, and their colleagues asked four participants to navigate to target locations within a virtual reality room while their brains were scanned with a functional magnetic resonance imager (fMRI). fMRI measures blood flow related to neural activity in the brain. They then applied a sophisticated analytical procedure known as multivariate pattern classification to see if they could relate the pattern of brain activity to each individual's location in virtual space.
And it worked. The pattern they uncovered reflected the participants' memory for where they were, the researchers explained, since once they had reached their final destination, there were no visual cues to discern one target spot from another. The activity they examined spanned some two to five million of the 40 million or so cells in the hippocampus, Hassabis noted.
Earlier studies done primarily in rats had suggested that spatial memories stored in the hippocampus had neuronal representations that were uniform and randomly distributed. But if that were the whole story, the predictions made in the new study would not have been possible.
Now that they have shown that such a predictable functional structure exists in the hippocampus, additional studies will seek to crack that neural code for other memories. Indeed, spatial representations of the type investigated in the study are thought to form the scaffold upon which memories of our personal experiences, known as episodic memories, are built.
"By showing it is possible to detect and discriminate between memories of adjacent spatial positions, our combination of non-invasive in vivo high-resolution fMRI and multivariate analyses opens up a new avenue for exploring episodic memory at the population level," the researchers wrote. "In the future it may be feasible to decode individual episodic memory traces from the activity of neuronal ensembles in the human hippocampus."
"We know that the hippocampus is critical for remembering our life experiences," Maguire said. This discovery "opens a whole world of possibility previously thought inaccessible to human brain imaging."
Cell Press
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The Hippocampus Book (Oxford Neuroscience Series) by Per Andersen (Editor), Richard Morris (Editor), David Amaral (Editor), Tim Bliss (Editor), John O'Keefe (Editor) The hippocampus is one of a group of remarkable structures embedded within the brain's medial temporal lobe. Long known to be important for memory, it has been a prime focus of neuroscience research for many years. The Hippocampus Book promises to facilitate developments in the field in a major way by bringing together, for the first time, contributions by leading international scientists knowledgeable about hippocampal anatomy, physiology, and function. This authoritative volume offers the most comprehensive, up-to-date account of what the hippocampus does, how it does it, and what happens when things go wrong. At the same time, it illustrates how research focusing on this single brain structure has revealed principles of wider generality for the whole brain in relation to anatomical... |
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Neuronal Networks of the Hippocampus by Roger D. Traub (Author), Richard Miles (Author) The questions of how a large population of neurons in the brain functions, how synchronized firing of neurons is achieved, and what factors regulate how many and which neurons fire under different conditions form the central theme of this book. Using a combined experimental-theoretical approach unique in neuroscience, the authors present important new techniques for the physiological reconstruction of a large biological neuronal network. They begin by discussing experimental studies of the CA3 hippocampal region in vitro, focusing on single-cell and synaptic electrophysiology, particularly the effects a single neuron exerts on its neighbors. This is followed by a description of a computer model of the system, first for individual cells then for the entire detailed network, and the model... | |
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Hippocampus: Anatomy, Functions and Neurobiology (Neuroanatomy Research at the Leading Edge) by Ambroise Gartner (Editor), Dener Frantz (Editor) A peculiar feature of the mammalian hippocampus is that it maintains the ability to generate new neurons throughout adult life while most other areas of the brain do not. In this book, we outline evidence for the functional consequences of adult neurogenesis in the dentate gyrus highlighting a possible role in learning and memory and depression. Presynaptic modulation at the MF synapse is also described with respect to its involvement in the activity-dependent nature of the MF synapse and contribution to physiological functions of MFs. In addition, the hippocampus is one of the first and most affected brain regions impacted by both Alzheimer's disease and mild cognitive impairment. This book discusses such negative consequences of aging and diseases which may be prevented or reversed by... |
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Gateway to Memory: An Introduction to Neural Network Modeling of the Hippocampus and Learning (Issues in Clinical and Cognitive Neuropsychology) by Mark A. Gluck (Author), Catherine E. Myers (Author) "Gateway to Memory is an exciting and badly needed text that integrates computational and neurobiological approaches to memory. Authoritative and clearly written, this book will be valuable for students and researchers alike." -- Daniel L. Schacter, Professor and Chair of Psychology, Harvard University, and author of Searching for Memory This book is for students and researchers who have a specific interest in learning and memory and want to understand how computational models can be integrated into experimental research on the hippocampus and learning. It emphasizes the function of brain structures as they give rise to behavior, rather than the molecular or neuronal details. It also emphasizes the process of modeling, rather than the mathematical details of the models... |
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