Single Neuron Recordings Help Explore How Human Brain Responds to Visual Stimuli

Although functional brain imaging techniques (such as PET and fMRI) have told us a great deal about the workings of the human brain, they do not permit direct analysis of the responses of individual nerve cells, the fundamental units of brain processing. Techniques that allow a direct measure of single neuron activity have been around for over 50 years, but practical and ethical issues generally prevent their use in humans. In this issue of NATURE NEUROSCIENCE [September 2000 Volume 3 Number 9 pp 845 - 959], Fried and colleagues report on a rare study in which they inserted electrodes into the brains of humans and were able to record from single neurons that are involved in processing complex visual scenes.

The subjects in this study were epilepsy patients who had not responded to drug treatment, and who were therefore being evaluated for possible surgical intervention. Part of the evaluation process involves implanting electrodes within the brain to search for abnormal patterns of electrical activity, and while the electrodes were in place, the researchers were able to use them to explore how the human brain responds to visual stimuli. The patients were shown sets of pictures of various visual categories, including faces,
natural scenes, famous people and animals. The researchers found that some neurons responded selectively to particular visual categories. For example, a neuron might respond to pictures of famous people (and not to other visual categories); moreover, its response was not specific to a particular person, in that it would respond similarly to any famous person. The results are not unexpected based on previous microelectrode recordings in monkeys, and of course it remains to be determined exactly how these neural responses may participate in human perception. Nevertheless, it is important to confirm that results obtained in monkey brains can be extrapolated to humans, and the results also accord well with observations of brain-damaged patients who report deficits in recognizing specific visual categories (such as faces).

This work is discussed in an accompanying News and Views by Charles Gross.

CONTACTS:

Dr. Itzhak Fried
UCLA School of Medicine
Neurosurgery and Psychiatry & Biobehavioral Sciences, Box 957039
Box 957039
740 Westwood Plaza
Los Angeles, California 90095-7039
USA
tel: 310-825-8409
fax: 310-794-2147
email: ifried@mednet.ucla.edu

Dr. Charles Gross
Princeton University
Department of Psychology
Green Hall
Princeton, New Jersey 08540
USA
tel: 609-258-4430
fax : 609-258-1113
email: cggross@princeton.edu

(C) NATURE NEUROSCIENCE press release.

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