Facilitation of picture naming by focal transcranial magnetic stimulation of Wernicke's area.

On the basis of an evolutionary concept of language it was postulated that activation of the motor systems for arm movements, which are phylogenetically older, should facilitate language processes. In aphasic subjects picture naming can be improved by a concomitant movement of the dominant arm. In the present study it was investigated whether a similar facilitation can be observed in normal subjects by studying the effects of transcranial magnetic stimulation (TMS) on picture naming latencies. Suprathreshold focal TMS was applied to the left motor cortex for proximal arm muscles in right-handed subjects. The effects were compared with TMS of Wernicke's area. While TMS of the motor cortex and the non-dominant temporal lobe had no facilitatory effects, TMS of Wernicke's area decreased picture naming latencies significantly when TMS preceded picture presentation by 500 or 1000 ms. The observed effects depended on the intensity of the stimulus used. While clearly present with intensities of 35% and 55% of maximum output the facilitation disappeared with higher stimulation intensities. It is concluded that focal magnetic stimulation is able to facilitate lexical processes due to a general preactivation of language-related neuronal networks when delivered over Wernicke's area.