Mar 12 2010

Memory and the Hippocampus

Neuroscientists are making steady progress in mapping the brain using fMRI and other new techniques. Researchers at the Wellcome Trust Centre for Neuroimaging at UCL (University College London) have been publishing a steady stream of interesting results.

It has been known for some time that the hippocampus, a small structure in the medial temporal lobe, is important for learning and memory. The structure gets its name from the seahorse, because it looks curled up like the tail of a seahorse. Many details of the anatomy and function of the hippocampus remain to be explored, and the new technology is providing a useful window.

Recently it was discovered that the hippocampus contains what are called place cells – neurons that are activated according to our location in three-dimensional space. These neurons, in essence, process information relating to our location. However, it was not known whether or not these cells are laid out in the hippocampus in a predictable pattern, or if they are essentially random from person to person.

Demis Hassabis and Professor Eleanor Maguire at the Wellcome Trust Centre published a study about a year ago looking at human volunteers while walking around a virtual space. By analyzing the activity of their hippocampus with a computer algorithm they developed, they were able to predict greater than chance where the subjects had been. This strongly implies that there is a regular pattern to the layout of place cells in the hippocampus. Like most anatomical structures, there is almost certainly a great deal of individual variation around a basic layout. This means that greater success rates might be achieved if the algorithm were first calibrated to an individual – perhaps a subject of future research.

Now the same team has published follow up research involving subjects looking at three films, all involving women on a city street performing some task, like mailing a letter. Afterwards they were placed in an fMRI and asked to recall each of the films in turn. The computer algorithm was then able to analyze the pattern of activity in their hippocampuses (there is one on each side) and predict greater than chance which of the three films they were watching. This supports the hypothesis that there is some regularity to the layout of neurons in the hippocampus.

Of course these preliminary results led to extrapolation of this technology to the potential of “reading minds”. This may be theoretically possible, but don’t hold your breath. We are a long way away from the Matrix, where an almost flawless reality can be jacked directly into, and read from, the brain.

What is certainly true is that we are in the middle of an exciting time in neuroscience where new tools have accelerated the research, allowing us to map and understand the brain better than ever before. It seems likely that we will continue to make incremental improvements in our ability to model the brain, and even interpret brain activity. There are researchers mapping out the visual cortex, and able to use fMRI to see what a person is reading. And these researchers are able to see where a person has been or what location they are thinking of (from a limited set of choices).

However, these applications represent the low-hanging-fruit of this research – areas of the brain that are visuo-spatial where the brain has some degree of topical mapping. In other words, the neurons in the brain are laid out physically in a way that maps to the visual or spatial data they represent. The same is true of the motor and sensory cortex – there is, in fact, a homunculus – a representation of the body laid out along the motor cortex and  the sensory cortex.

As we get to other areas of the brain, however, it remains to be seen how much this somatotopic mapping will hold up. Abstract areas of the brain involved with math, language, emotion, and similar functions may not be so conveniently organized. I also imagine that the level of complexity will increase not linearly but geometrically or even exponentially. Further, the amount of variation will likely also increase significantly. Systems used to read brain activity may require exhausting calibration.

But there is nothing inherently impossible about such mind-reading technology, it is just likely to become increasingly difficult and complex. I liken it to the problem of artificial intelligence. Fifty years ago computer scientists were starting to see Moore’s Law in action, with steady and stunning increasing in computer power. They optimistically extrapolated that increase and predicted that human level computer intelligence would be reached in 20-30 years. We thought nothing in 1969 about the HAL computer in the movie 2001 – sure, in 32 years we will have AI. How cool.

But the AI problem turned out to be much more difficult than anticipated, not just a matter of simple extrapolation from existing advances, and now we still seem to be 30-50 years away from true AI approaching human level intelligence. Maybe there will be unanticipated hurdles still.

Mind reading computers will likely follow the same pattern. We will make incremental advances, but the real futuristic applications may be more challenging than we think. It is difficult to impossible to predict such things, however. While everyone overestimated our ability to develop AI, everyone also underestimated the true power of computers to revolutionize communication.

As an aside, there is some other recent research involving the hippocampus. As I stated, the hippocampus is involved in both memory and learning. Recent research, however, suggests it may be involved more in processing information than just storing it. These researchers ran rats through a maze and then looked at their hippocampus function with fMRI. They found that the pattern of activation in the rats following learning the maze did not match the routes they learned, but rather correlated to other parts of the maze they explored, and even to parts of the maze they never ventured into.

The researchers interpret this study as possibly meaning that the hippocampus was processing the visuo-spatial information of the maze – going over possible routes and reconstructing the maze, even the parts the rats did not directly explore. They conclude that the hippocampus may be more important for information processing than memory.

It is difficult to make too much out of a single study, but the research does suggest the role and function of the hippocampus may be more complex than existing models suggest (which I think we can assume is probably true of all our current brain models). It also reinforces what I have seen from other research – that memory and information processing are closely linked.

One thing is certain – it is an exciting time for neuroscience.

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