A recent study of three epilepsy patients has shed new light on this linguistic phenomenon. Electrodes implanted in the subjects’ brains in preparation for surgery allowed a team from the University of California, San Francisco, to record neural activity from the brain surface. The scans showed that sites in a region called the ventral sensorimotor cortex (vSMC) control different parts of the vocal tract (tongue, lips, etc) to form each syllable. Stringing syllables together appears to require co-ordinating complex sequences of activity across vSMC sites, timed down to tens of milliseconds. Sounds that require similar vocal tract movements, such as ‘Sss’ and ‘Shh’, are especially tricky as their representations in the brain overlap. Tongue-twisters are likely tricky because they require a rapid sequence of overlapping neural patterns that simply overwhelms the brain.
Answered by Tom Harris