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, 117 (3), 103-9

Sub-centimeter Language Organization in the Human Temporal Lobe

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Sub-centimeter Language Organization in the Human Temporal Lobe

A Flinker et al. Brain Lang.

Abstract

The human temporal lobe is well known to be critical for language comprehension. Previous physiological research has focused mainly on non-invasive neuroimaging and electrophysiological techniques with each approach requiring averaging across many trials and subjects. The results of these studies have implicated extended anatomical regions in peri-sylvian cortex in speech perception. These non-invasive studies typically report a spatially homogenous functional pattern of activity across several centimeters of cortex. We examined the spatiotemporal dynamics of word processing using electrophysiological signals acquired from high-density electrode arrays (4mm spacing) placed directly on the human temporal lobe. Electrocorticographic (ECoG) activity revealed a rich mosaic of language activity, which was functionally distinct at four mm separation. Cortical sites responding specifically to word and not phoneme stimuli were surrounded by sites that responded to both words and phonemes. Other sub-regions of the temporal lobe responded robustly to self-produced speech and minimally to external stimuli while surrounding sites at 4mm distance exhibited an inverse pattern of activation. These data provide evidence for temporal lobe specificity to words as well as self-produced speech. Furthermore, the results provide evidence that cortical processing in the temporal lobe is not spatially homogenous over centimeters of cortex. Rather, language processing is supported by independent and spatially distinct functional sub-regions of cortex at a resolution of at least 4mm.

Figures

Figure 1
Figure 1
Spatiotemporal responses to phonemes (top) and words (bottoms) across a 64 contact 8×8 electrode grid in subject S1. Event related spectral perturbations are shown for each electrode locked to the onset of stimuli. Color scale represents statistically significant changes in power compared to a bootstrapped surrogate distribution (only significant data is shown, p<0.05 after FDR multiple comparison correction). Electrodes with no contact or abnormal signal are not shown.
Figure 2
Figure 2
Event related spectral perturbations of two adjacent electrodes in three subjects locked to phonemes and words. Electrode A (top row) responds selectively to word stimuli while Electrode B (bottom row) 4 mm away responds to both stimuli types. Vertical line marks stimuli onset, horizontal line marks 100 Hz, the color scale represents statistical significant changes in power compared to a bootstrapped surrogate distribution. Only statistically significant values are shown (p<0.05, after FDR multiple comparison correction). See Supplemental Figure 1 for electrode anatomical positions.
Figure 3
Figure 3
Spatiotemporal responses to hearing and then producing phonemes across a 64 contact 8×8 electrode grid in subject S4. Event related spectral perturbations are shown for each electrode locked to the onset of phonemes. Color scale represents statistically significant changes in power compared to a bootstrapped surrogate distribution (only significant data is shown, p<0.05 after FDR correction). Blue box marks an area of approximately 1 cm2 of cortex; blue arrowhead marks an electrode exhibiting self-speech specificity. Electrodes with no contact or abnormal signal are not shown. See Supplemental Figure 3 for a direct comparison of spectral yHigh responses locked to hearing and speaking.
Figure 4
Figure 4
Single trial γHigh power traces vertically stacked for two adjacent electrodes in subjects S2 and S4. Zero ms marks phoneme onset and black lines mark production onset (trials are sorted for display purposes). Color-scale represents percent change from the pre-stimulus baseline in each trial. See Supplemental Figure 1 for electrode anatomical positions.

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