Functional organization of human auditory cortex: Investigation of response latencies through direct recordings

Abstract

The model for functional organization of human auditory cortex is in part based on findings in non-human primates, where the auditory cortex is hierarchically delineated into core, belt and parabelt fields. This model envisions that core cortex directly projects to belt, but not to parabelt, whereas belt regions are a major source of direct input for auditory parabelt. In humans, the posteromedial portion of Heschl’s gyrus (HG) represents core auditory cortex, whereas the anterolateral portion of HG and the posterolateral superior temporal gyrus (PLST) are generally interpreted as belt and parabelt, respectively. In this scheme, response latencies can be hypothesized to progress in serial fashion from posteromedial to anterolateral HG to PLST. We examined this hypothesis by comparing response latencies to multiple stimuli, measured across these regions using simultaneous intracranial recordings in neurosurgical patients. Stimuli were 100 Hz click trains and the speech syllable /da/. Response latencies were determined by examining event-related band power in the high gamma frequency range. The earliest responses in auditory cortex occurred in posteromedial HG. Responses elicited from sites in anterolateral HG were neither earlier in latency from sites on PLST, nor more robust. Anterolateral HG and PLST exhibited some preference for speech syllable stimuli compared to click trains. These findings are not supportive of a strict serial model envisioning principal flow of information along HG to PLST. In contrast, data suggest that a portion of PLST may represent a relatively early stage in the auditory cortical hierarchy.

Sound identification in human auditory cortex: Differential contribution of local field potentials and high gamma power as revealed by direct intracranial recordings

“…On average, peak activity occurred on the falling phase of the N α peak of the AEP, consistent with earlier findings (Steinschneider et al, 2011). Sources of variability likely include differences in sensitivity of different cortical sites to specific acoustic attributes of speech sounds and tones, state of arousal of the subject during the passive-listening paradigm, differences in electrode coverage and response timings within PLST (Nourski et al, 2014a). In the latter study, high gamma activity was shown to have the shortest onset latency in the middle portion of PLST, increasing in both anterior and posterior directions along the gyrus.…”

Can you hear me yet? An intracranial investigation of speech and non-speech audiovisual interactions in human cortex

“…Sites on HG were subdivided into core (posteromedial) and non-core (anterolateral) areas based on the morphology and latency of evoked responses and frequency following responses to click train stimuli (Brugge et al, 2008; Nourski et al, 2014). While separate statistical analysis of core and non-core areas of HG was not possible due to the small number of recording sites, we do present an exploratory analysis comparing these two subdivisions.…”

“…We used this approach rather than an individual site-by-site analyses or area-wide ANOVAs for several reasons (see also Nourski et al, 2014). First, site-by-site analyses offer no way to account for the fact that the sites only come from a small number of participants (instead, each site is treated as an independent measure [analogous to an independent subject]).…”

“…The anterolateral portion of HG exhibits markedly different physiological response properties and has been interpreted as non-core (belt and/or parabelt) cortex (Brugge et al, 2008, 2009; Nourski, Steinschneider, McMurray, et al, 2014). …”

“…It generally responds more robustly to speech than non-speech, and the pattern of activity across STG reflects the phonological content of the speech input with some specificity (Mesgarani, Cheung, Johnson, & Chang, 2014; Nourski, Steinschneider, Oya, et al, 2014; Steinschneider, 2011), though it is also involved in other complex auditory domains (e.g. Liégeois-Chauvel, Peretz, Babaï, Laguitton, & Chauvel, 1998; Price, 2000).…”