How many times have you wondered where did I leave my keys? Activity in your hippocampus and medial temporal lobes encodes the answer.

A new study using high resolution brain imaging has shown that the encoding of memories involves the precise pattern of activity of a very large number of neurons in the human hippocampus. The hippocampus and surround medial temporal lobes are important parts of the brain for our ability to navigate, form and recall memories, and imagine future experience. This study found that the pattern of activity can be read like a map to accurately “predict” what environment you are in and your location within the environment.

A group of Neuroscientists at the Welcome Trust Centre for Neuroimaging at University College London led by Dr. Eleanor Maguire have imaged the pattern of activity in the hippocampus and surrounding medial temporal lobe of human subjects while they navigated around a virtual environment. The researchers asked if there is a reliable pattern of activity in the hippocampus, like a map, that can be read to predict where the subject is in the environment. The results of this study are “yes” — there is a functional structure to the pattern of activity in the human hippocampus that encodes your location in an environment.



This study used high resolution brain imaging fMRI and a new analysis that looked at the pattern of active voxels in the human hippocampus and medial temporal lobes. A voxel is like a pixel, but the voxel is 3D and in brain imaging it represents a small volume of the brain. The subjects’ brains were imaged as they moved around a virtual environment that had a green and blue room. Remarkably, the scientists were able to predict which room and where it the room the subject was just by the pattern of active voxels. Activity in the medial temporal lobe predicted whether the subject was in the green or blue room. And the pattern of active voxels in the hippocampus predicted their location in that room.

These are exciting findings, especially when you stop to think about how many neurons are imaged in a single voxel. Even with high resolution imaging there are about 10,000 neurons in each voxel. This means that navigating around an environment and remembering your location depends on the coordinated firing of tens of thousands of neurons in our hippocampus and medial temporal lobes. But perhaps even more amazing is that this team of neuroscientists has shown that they can accurately decode this pattern of brain activity.

So the next time you lose your keys it will be the activity of many thousands of neurons in your medial temporal lobe that will help you remember which room you left them in. And it will be the precise pattern of activity among tens of thousand of neurons in your hippocampus that will help you to recall the exact location of your keys in that room.

For more information about Dr. Maguire’s research you can go to her webpage.

For more information about this study you can read the paper published in the journal Current Biology.

Current Biology, Volume 19, Issue 7, 546-554, 12 March 2009

Decoding Neuronal Ensembles in the Human Hippocampus

Demis Hassabis1, Carlton Chu1, Geraint Rees1,2, Nikolaus Weiskopf1, Peter D. Molyneux3 and Eleanor A. Maguire1,

1 Wellcome Trust Centre for Neuroimaging, Institute of Neurology, University College London, 12 Queen Square, London WC1N 3BG, UK

2 Institute of Cognitive Neuroscience, University College London, 17 Queen Square, London WC1N 3AR, UK

3 Lionhead Studios, 1 Occam Court, Surrey Research Park, Guildford, Surrey GU2 7YQ, UK