Electrocorticographic correlates of overt articulation of 44 English phonemes: Intracranial recording in children with focal epilepsy

Abstract

Objective We determined the temporal-spatial patterns of electrocorticography (ECoG) signal modulation during overt articulation of 44 American English phonemes. Methods We studied two children with focal epilepsy who underwent extraoperative ECoG recording. Using animation movies, we delineated ‘when’ and ‘where’ gamma- (70–110 Hz) and low-frequency-band activities (10–30 Hz) were modulated during self-paced articulation. Results Regardless of the classes of phoneme articulated, gamma-augmentation initially involved a common site within the left inferior Rolandic area. Subsequently, gamma-augmentation and/or attenuation involved distinct sites within the left oral-sensorimotor area with a timing variable across phonemes. Finally, gamma-augmentation in a larynx-sensorimotor area took place uniformly at the onset of sound generation, and effectively distinguished voiced and voiceless phonemes. Gamma-attenuation involved the left inferior-frontal and superior-temporal regions simultaneously during articulation. Low-frequency band attenuation involved widespread regions including the frontal, temporal, and parietal regions. Conclusions Our preliminary results support the notion that articulation of distinct phonemes recruits specific sensori-motor activation and deactivation. Gamma attenuation in the left inferior-frontal and superior-temporal regions may reflect transient functional suppression in these cortical regions during automatic, self-paced vocalization of phonemes containing no semantic or syntactic information. Significance Further studies are warranted to determine if measurement of event-related modulations of gamma-band activity, compared to that of the low-frequency-band, is more useful for decoding the underlying articulatory functions.

Spatio-temporal dynamics of working memory maintenance and scanning of verbal information

“…Reduction of high-gamma activation in the left superior-temporal cortex may have been induced by increased working memory maintenance load in the left pre-central gyrus via the arcuate fasciculus (Brown et al, 2014a); likewise, suppression of the post-central gyrus may have been mediated via U-fibers between pre- and post-central gyri. Such transient suppression of the sensory cortex has been reported in the primary auditory cortex during retrieval of a relevant answer for a question (Towle et al, 2008), in the primary somatosensory cortex during articulation of phonemes (Toyoda et al, 2014), and in the primary visual cortex for the peripheral vision during attention directed to central vision (Uematsu et al, 2013). …”

“…The time-frequency analysis used in the present study was previously described and validated (Brown et al, 2012; Kojima et al, 2013; Nishida et al, 2016; Toyoda et al, 2014). The primary measures of interest were the percent change in amplitude (a measure proportional to the square root of power) of high-gamma activity 70–110 Hz relative to that during the reference period at 600–200 ms prior to stimulus onset (Supplementary Figure S1).…”

Brain network dynamics in the human articulatory loop

“…We measured high-gamma activity during ‘sound-listening alone’ and ‘sound-listening and humming’ (Figure 2), using a method similar to that previously reported (Brown et al, 2008b; Fukuda et al, 2008; Toyoda et al, 2014). Patients were initially instructed to covertly listen to a total of thirty 1,000 ms auditory stimuli.…”

Spatial–temporal patterns of electrocorticographic spectral changes during midazolam sedation

“…At each channel, we measured the percent change in amplitude at a given frequency band, in steps of 0.5 Hz and 100 milliseconds, relative to the mean amplitude in a control period for 20 seconds prior to the administration of midazolam (Nagasawa et al, 2012; Matsuzaki et al, 2015). We subsequently superimposed ECoG amplitude measures to each individual three-dimensional MRI (Brown et al, 2008; Nariai et al, 2011; Toyoda et al, 2014), yielding animation movies of amplitude changes at eight frequency bands (Figures 1 and 2; Video S1 and S2). We provided the detailed methodology in the Supplementary Document.…”