Oct 31 2008

Single Neuron Neuroscience

Published by under Uncategorized
Comments: 21

During some of my skeptical lectures I flash a picture of a familiar movie star on the screen for a fraction of a second to demonstrate that most people can recognize the person, out of the millions they have ever seen, even after such a brief exposure. It’s a quick way to demonstrate the power of our face-recognition ability, which still outstrips that of supercomputers. I use it to make the point that our brains are exceptional at pattern recognition, which also helps us understand one of our major cognitive weaknesses – hyperactive pattern recognition, or seeing patterns where they do not really exist.

Neuroscientists are also interested in face-recognition, and other pattern-recognition, that occurs in the human brain. R. Quian Quiroga from the University of Leicester has published a number of studies exploring this ability. His latest research reveals what the press has dubbed “The Jennifer Aniston neuron.” Quiroga recorded the activity in the visual cortex of using micro-electrodes of subjects viewing the faces of familiar stars, like Aniston, Tom Cruise or Halle Berry. He found that each familiar face seems to be encoded in a single neuron.

This finding is a bit surprising as it was previously thought that visual memories such as this would be stored in a network of neurons. Rather, our brains assign a single neuron to remember a single familiar face, and that neuron will fire whenever that face is viewed – in any condition and from any angle. Previous research from Quiroga looking at medial temporal lobe responses to familiar faces and object found that the response of the memory neuron is an all-or-none response, and that it can be fired even by stimulation as brief as 33 miliseconds (thousandths of a second).

This all-or-nothing finding is not surprising at all – the nervous system generally functions that way. You cannot partially fire a neuron (although the rate at which a neuron fires can alter). It also matches our common subjective experience, when trying to recognize someone the answer may seem to just click into place – recognition comes suddenly with all the attendant information in tow.

How does a single neuron store so much information? Well, those single neurons do not exist in isolation – on average they make over a thousand synapses (connections) with other neurons. Those synapses can be excitatory or inhibitory, and they can vary in strength. So while a single neuron may be the location where the memory of a specific face, for example, is stored, the abstract information about that face is likely stored in the pattern of synapses made by that neuron. Individual neurons may be part of many such groupings, reflecting the brain’s massively parrallel structure. This also explains the brain’s pattern recognition ability, as overlapping networks of neurons will allow one image to remind us of another image because they share neurons.

Understanding the role of these single master neurons, acting like the “address” of a memory, is an important incremental step in our progressive understanding of how the brain works. This research also shows that our technology is starting to get down to the resolution, both in time and space, at which the brain is functioning. At least we are getting down to the single neuron level. There is still a finer level of detail in all the synapses being made by those neurons.

21 responses so far