Jn-00609-2003.r1 1 a Functional Connection between Inferior Frontal Gyrus and Orofacial Motor Cortex in Human

The inferior frontal gyrus (IFG) of humans is known to play a critical role in speech production. The IFG is a highly convoluted and cytoarchitectonically diverse structure, classically forming three sub-gyri. It is reasonable to speculate that during speaking the IFG, or some portion of it, influences via cortico-cortical connections the oro-facial representational area of primary motor cortex. To test the hypothesis that such cortico-cortical connections exist, electrical-stimulation tract tracing experiments were performed intra-operatively on fourteen human subjects undergoing surgical treatment of medically intractable epilepsy. Bipolar electrical stimulation was applied to sites on the IFG, while the resulting evoked potentials were recorded from oro-facial motor cortex, using a multi-channel recording array. Stimulation of the IFG evoked polyphasic waveforms on motor cortex of both languagedominant and non-dominant hemispheres. The evoked waveforms had consistent features across subjects. The responses were seen in discrete regions on precentral cortex. Stimulation of motor cortex also evoked responses on portions of IFG. The data provide evidence for a functional connection between the human IFG and orofacial motor cortex.