Functional Magnetic Resonance Imaging Assessment of the Human Brain Auditory Cortex Response to Increasing Word Presentation Rates

Abstract

In an investigation of the auditory cortex response to speech, six subjects were studied using echo-planar functional magnetic resonance imaging (fMRI) at 2.1T. The subjects were asked to listen to English nouns presented at various rates ranging from 0 words per minute (wpm) to 130 wpm while fMRI images encompassing their primary and posterior superior secondary auditory cortices were acquired. An asymmetric spin echo imaging sequence was used with an induced T2 weighting of 50 ms to allow for transverse relaxation effects. Images were acquired in two or four axial-oblique slices with a repetition time of 3.75 or 7.5 s, in plane resolution of 6 x 3 mm, and a slice thickness of 5 mm. Localized activation centered over grey matter was consistently observed in all subjects in the transverse temporal gyrus (TTG), the transverse temporal sulcus (TTS), and the posterior superior aspect of the superior temporal gyrus (STG). The total activate volume and the integrated signal response in bilateral primary and posterior superior secondary auditory cortices increased with increasing rate of word presentation, peaking at 90 wpm (with some intersubject variability) with a subsequent fall at 130 wpm. There were no significant differences in the rate dependence of the signal response in bilateral primary and bilateral posterior superior secondary auditory cortices (P < 0.05).

A Temporal Bottleneck in the Language Comprehension Network

“…Previous publications (Binder et al, 1994;Dhankhar et al, 1997;Buchel et al, 1998;Poldrack et al, 2001;Peelle et al, 2004) and pilot analyses indicated that distinct fMRI profiles could be identified: a linear activation with sentence duration (increasing or decreasing); a step function, i.e., a constant activation collapsing suddenly at the shortest duration (similar to behavioral reports of intelligibility); and a quadratic function, i.e., showing a peak of activation at intermediate durations. One difficulty is that these profiles are nonorthogonal (e.g., there are strong correlations between the linear and step functions and between the step and quadratic functions).…”

“…By varying word rate, several studies observed that activation amplitude in regions surrounding the primary sensory cortices varies linearly with stimulus duration (Binder et al, 1994;Dhankhar et al, 1997;Buchel et al, 1998;Poldrack et al, 2001), while other regions show a quadratic variation (Binder et al, 1994;Buchel et al, 1998;Poldrack et al, 2001) or a peak of activation at the fastest presentation rate (Peelle et al, 2004). However, previous studies used block designs, which prevents identification of the temporal response profile and drastically complicates modeling and interpretation.…”

Assessment and discrimination of odor stimuli in rat olfactory bulb by dynamic functional MRI

“…With higher SNR, as in these experiments, recruitment is not observed. As we have discussed before, in conjunction with fMRI of the auditory response in humans, the concept of ''recruitment'' is coupled to SNR and can only be unambiguously claimed to exist if the experiment had infinite SNR (38).…”

Functional Differentiation in the Human Auditory and Language Areas Revealed by a Dichotic Listening Task

“…However, higher presentation rate of nonsense syllables (nontarget stimuli that the subject neglected) may not cause enhanced cortical activity under the DIC condition in regions that are distant from A1; PT, ST, and IF, for example. Recent fMRI studies reported that signal changes in the posterior periauditory regions exhibited a nonlinear (inverted U) relationship to word rate, reaching a peak at about 60 words per minute (wpm) (Bü chel et al, 1998) or at 90 wpm in the primary auditory cortex as well (Dhankhar et al, 1997). Furthermore, frontal regions showed a response to words irrespective of their presentation rate (Bü chel et al, 1998).…”