Decoding the Halle Berry cell

About 2 years ago, researchers reported the discovery of the so-called “Halle Berry cell” in the human brain. This, and similar cells which respond selectively to other well-known celebrities, famous landmarks or categories of objects are located on the medial surface of the temporal lobe.

The same group of researchers now report that they can decode the activity of these cells to predict what people are seeing. The ability to decode this neural activity will prove to be very useful in the development of brain-computer interfaces for amputees and paralyzed patients.

The cells in question were identified in epileptic patients who did not respond to drugs and  were therefore treated surgically. Prior to the operation, clinicians electrically stimulate the brain of the conscious patient in order to determine the focus of the abnormal electrical activity causing the seizures.

The cells are located in the anterior hippocampus, and are likely to be involved in the formation of long-term memories. They carry out higher order processing of visual stimuli; some fire in response to several different images, while others are highly selective.

The Halle Berry cell, for example, becomes active only when different photographs of that actress was shown. The cell fired when the patient saw a photograph of the actress dressed as Catwoman, and even when just her name was presented. This cell therefore appears to encode the abstract concept of “Halle Berry”, rather than visual features which might be common to other images.

Using electrodes which recorded the activity of 100 neurons simultaneously,  the researchers recorded the activity of 1,500 individual cells in 11 different epileptic patients. Confirming their previous study, the researchers found that 265 of those cells fired only in response to specific images.

One was found to fire when the patient was shown images of spiders; others fired in response to images of the leaning tower of Pisa, the Eiffel Tower, or the twin towers of the World Trade Center; yet others fired in response to pictures of Pamela Anderson, Jennifer Aniston, Denzel Washington or Saddam Hussein.

It was found that the cells responded in a typical way in response to the appropriate stimulus, by generating a train of 4 action potentials between 300-600 milliseconds after presentation of the stimulus. 

The researchers developed a decoding algorithm based on the knowledge of  which cells fire in response to which stimuli, and the pattern of neural activity that occurs in response to those stimuli. Using that algorithm, they were able to predict accurately which images the patients were seeing from the activity of the cells. 

As before, the responses of some of the cells were very specific. For example, those that fired in resposne to a particular individual also responded to previously unseen images of the same person.

The presence of these cells supports the cardinal cell theory proposed in 1972 by the British neurophysiologist Horace Barlow, which states that complex percepts such faces and objects are encoded explicitly by small numbers neurons (up to 1,000), rather than than by a more generalized implicit code distributed throughout a larger population of cells.

Reference:

Quian Quiroga, R., et al. (2007) Decoding vidual inputs from multiple neurons in the human temporal lobe J. Neurophysiol. 98: 1997-2007. [Abstract]

6 thoughts on “Decoding the Halle Berry cell

  1. My boss did a phd on modeling individual neuron behavior. his research direction is to find out if there is some sort of state held internally inside single neurons, based on the memory rna work i understand (i’m a big iron jocky but i’ve always loved molecular biology since it began). He got seduced into govt consulting and hasn’t done any more work AFAIK; do you know of any studies in this direction given the “small cell” concept?

  2. It’s hardly surprising, if I understand the study, that the researchers were able to interpret the neuraral firings like this: if a neuron responds preferentially to a stimulus then when we see it responding we know that that stimulus has been presented (right?)
    But given that the researchers were able to find just the right stimuli in the relatively short time the patients’ brains were exposed, isn’t it likely that the neurons involved don’t respond only to the stimulus presented, but to multiple stimuli? Obviously they can’t respond to very many, otherwise they wouldn’t have found the pattern of preferential firing. But if they only responded to Halle and absolutely nothing else, then what is the chance of them having hit on just the right picture (out of the entire class of objects)?

  3. This proposal of a single or a small number of cells that specifically code each individual exemplar in memory is sometimes referred to as the “grandmother cell” hypothesis – see this wikipedia article:
    http://en.wikipedia.org/wiki/Grandmother_cell
    Neil hits on the fundamental problem – how do we know that a seemingly selective cell wouldn’t respond to something else as well? Granted, you have the same problem with any single cell recording study, but the problem is particularly evident here due to the problem of replication; finding that same Halle Berry cell in another patient for further testing would be very much a needle in a haystack scenario.

  4. Following up on Johan’s point that we don’t know if a cell would respond to a different stimuli, my question is: how do we know that other cells aren’t also responding in almost the same way?
    In other words, maybe the mental image is formed when a particular ‘sparse cluster’ of 3 cells spread out through the brain respond simultaneously.
    However, I still find this discovery very exciting.

  5. I think this research is great! And it is going to proceed at a rapid pace to the great benefit of computer amputee, etc., interfaces, but also for more cool toys, like the Firefox interface mentioned above! LOL!
    Dave Briggs :~)

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