13 January 1989
Vol 243, Issue 4888

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Visualization of brain activity during mental rotation. The neuronal population vector (green) rotated gradually from 2 to 10 o'clock as a monkey was thinking (time upward, white line). The population vector was calculated from an ensemble of neurons recorded in the motor cortex. See page 234. [A. P. Georgopoulos, Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD 21205]