Functional connections within the human inferior frontal gyrus

Abstract

The highly convoluted and cytoarchitectonically diverse inferior frontal gyrus (IFG) of humans is known to be critically involved in a wide range of complex operations including speech and language processing. The neural circuitry that underlies these operations is not fully understood. We hypothesized that this neural circuitry includes functional connections within and between the three major IFG subgyri: the pars orbitalis, pars triangularis, and pars opercularis. To test this hypothesis we employed electrical stimulation tract-tracing techniques in 10 human patients undergoing surgical treatment for intractable epilepsy. The approach involved delivering repeated bipolar electrical stimuli to one site on the IFG while recording the electrical response evoked by that stimulus from a 64-contact grid overlying more distant IFG sites. In all subjects, stimulation of a site on one subgyrus evoked polyphasic potentials at distant sites, either on the same subgyrus or on an adjacent subgyrus. This provided prima facie evidence for a functional connection between the site of stimulation and the sites of the evoked response. The averaged evoked potentials tended to aggregate as response fields. The spatial spread of a response field indicated a divergent projection from the site of stimulation. When two or more sites were stimulated, the resulting evoked potentials exhibited different waveforms while the respective response fields could overlap substantially, suggesting that input from multiple sites converged but by engaging different neural circuits. The earliest deflection in the evoked potential ranged from 2 to 10 msec. No differences were noted between language-dominant and language-nondominant hemispheres.

Brain-Wide Analysis of Functional Connectivity in First-Episode and Chronic Stages of Schizophrenia

“…We further note The inferior frontal gyrus, which includes Broca's area, is critically involved in speech production and language processing. 46 It is functionally connected with the temporal lobe to form a language network. Our findings of increased functional connectivity of the inferior frontal gyrus including Broca's area with temporal cortex and cingulate areas, and the correlation of increased functional connectivity with the positive/negative symptoms, implicate language-related frontal areas as key regions related to the onset of schizophrenia.…”

Structural abnormalities in benign childhood epilepsy with centrotemporal spikes (BCECTS)

“…The anterior and posterior cingulate gyri are mainly involved in supporting internally directed cognition, in modulation of emotional responses, and in attentional processing [31,32]. The pars opercularis is critical for speech and language functions [30,33].…”

fMRI of syntactic processing in typically developing children: Structural correlates in the inferior frontal gyrus

“…Recent studies have shown that electrical stimulation in one region of the IFG results in activity in other regions, and a high degree of connectivity between the different regions of the IFG has been demonstrated although the functional significance is unknown (Greenlee et al, 2007). It is unclear from the current study why thickness in the pars triangularis had the strongest relationships with neural activity in other parts of the IFG.…”