Fig. 1: Suprasylvian speech response characteristics.
From: Parallel encoding of speech in human frontal and temporal lobes
A The classic hierarchical speech pathway from the medical geniculate body (MGB) of the thalamus to the front lobe is shown in the top panel. The orange arrows illustrate the hypothesized long-range parallel pathways from the medial geniculate body (MGB) and primary auditory cortex (PAC) to the frontal lobe. B Acoustic waveform of a single example sentence presented to participants. C Example responses to a single sentence from the right hemisphere participant in (D). D Representative example of two participants showing example responses in suprasylvian cortex and superior temporal gyrus (STG) to the single sentence shown in (B). The brain reconstructions show the spatial locations of responses to this sentence. This shows high similarity in response characteristics in the frontal lobe and STG. E Spatial distribution of significant responses to speech across all participants. This shows three areas of peak response probability in IFG, middle precentral gyrus (mPreCG), and ventral sensorimotor cortex (vSMC) (electrodes collapsed to the left hemisphere). F Spatial clustering using a Gaussian mixture model demonstrates three areas of speech responses in IFG, mPreCG, and vSMC. The number of clusters was determined by Bayesian information criterion and silhouette criterion values (both converged on 3 clusters)13. G Suprasylvian area versus STG responsivity. The proportion of electrodes with significant responses and the mean response amplitude is lower in IFG, mPreCG, and vSMC than in STG (p < 0.005, two-sided Wilcoxon rank-sum test, Bonferroni corrected, n proportion samples for left/right hem. = 9/8 IFG, 8/8 mPreCG, 9/8 vSMC, 9/8 STG, n response amplitudes for left/right hem. = 52/84 IFG, 120/180 mPreCG, 98/91 vSMC, 645/548 STG). Each area has no left-right hemispheric differences regarding the proportion or magnitude of significant responses (p > 0.05, two-sided Wilcoxon rank-sum test). All data are presented as mean values ± SEM. CS central sulcus; Hem hemisphere; IFG inferior frontal gyrus; IPL inferior parietal lobe; ITS inferior temporal sulcus; MGB medial geniculate body; mPreCG middle precentral gyrus; MTG middle temporal gyrus; PostC postcentral gyrus; PreC precentral gyrus; Spt Sylvian fissure at the parieto-temporal boundary; STG superior temporal gyrus; STS superior temporal sulcus; Sulc. sulcus; vSMC ventral sensorimotor cortex. A contains brain illustrations from Kenneth Probst, reproduced with permission, licensed under a Creative Commons Attribution 4.0 https://creativecommons.org/licenses/by/4.0/deed.en.
