Electrode placement on speech motor cortex

Wilder Penfield's famous homonculus map of the brain had a large area on one side capped by a gaping cartoon mouth labeled simply "vocalization."

During the 1930s, Penfield stimulated that same area, but was unable to elicit any recognizable utterances. A group of researchers led by Edward F. Chang of the University of California San Francisco has now had better luck. The team captured brain activity from the sensorimotor cortex of three epilepsy patients undergoing surgery who were asked to pronounce syllables like "bah," "dee," and "goo."

Recording with dozens of electrodes, Chang and colleagues produced a detailed map of the areas in the cortex that activate the anatomical structures involved with speech and also chronicled the synchronized firing of neurons in the various speech centers. "What wasn't known was how these populations of neurons were coordinated," Chang says. "It turns out that this question is a very critical one for understanding how speech works. The vocal tract is sort of like an orchestra where you have individual players like the lips, the tongue the jaw, what we call articulators. Speech arises from the coordination of these players." The research was published in the Feb. 20 Nature.

Neural codes, the electrical signals from the cortex that engage the vocal tract, could, in theory, be used one day as inputs to an artificial speech synthesizer for "locked-in" patients unable to speak—a still elusive goal of brain-machine technology researchers.

Image source: Nature Publishing Group

NOTE: A correction was made to Penfield's first name.