A comparison of dual gradient‐echo and spin‐echo fMRI of the inferior temporal lobe

Abstract

Magnetic susceptibility differences at tissue interfaces lead to signal loss in conventional gradient-echo (GE) EPI. This poses a problem for fMRI in language and memory paradigms, which activate the most affected regions. Two methods proposed to overcome this are spin-echo EPI and dual GE EPI, where two EPI read-outs are serially collected at a short and longer echo time. The spin-echo method applies a refocusing pulse to recover dephased MR signal due to static field inhomogeneities, but is known to have a relatively low blood oxygenation level dependant (BOLD) sensitivity. In comparison, GE has superior BOLD sensitivity, and by employing an additional shorter echo, in a dual GE sequence, it can reduce signal loss due to spin dephasing. We directly compared dual GE and spin-echo fMRI during a semantic categorization task, which has been shown to activate the inferior temporal region-a region known to be affected by magnetic susceptibility. A whole brain analysis showed that the dual GE resulted in significantly higher activation within the left inferior temporal fusiform (ITF) cortex, compared to spin-echo. The inferior frontal gyrus (IFG) was activated for dual GE, but not spin-echo. Regions of interest analysis was carried out on the anterior and posterior ITF, left and right IFG, and part of the cerebellum. Dual GE outperformed spin-echo in the anterior and posterior ITF and bilateral IFG regions, whilst being equal in the cerebellum. Hence, dual GE should be the method of choice for fMRI studies of inferior temporal regions.

Overlapping Networks Engaged during Spoken Language Production and Its Cognitive Control

“…It also engages motor-sensory systems (Bohland and Guenther, 2006;Guenther et al, 2006), controlled access to semantic representations Whitney et al, 2012;Noonan et al, 2013), and domain-general cognitive systems (Raboyeau et al, 2008;Eckert et al, 2009;Brownsett et al, 2014;Vaden et al, 2013). In addition to these "task-positive" systems, a network normally considered to be "task negative," known as the default mode network (DMN), is engaged in the absence of externally driven tasks and may be involved in accessing episodic and semantic memories, without which speech is nonpropositional (Raichle et al, 2001;McKiernan et al, 2006;Binder et al, 2009). Some of these brain networks spatially overlap and interact with each other (de Pasquale et al, 2012;Seghier and Price, 2012;Braga et al, 2013;Simmonds et al, 2014).…”

“…In addition to these "task-positive" systems, a network normally considered to be "task negative," known as the default mode network (DMN), is engaged in the absence of externally driven tasks and may be involved in accessing episodic and semantic memories, without which speech is nonpropositional (Raichle et al, 2001;McKiernan et al, 2006;Binder et al, 2009). Some of these brain networks spatially overlap and interact with each other (de Pasquale et al, 2012;Seghier and Price, 2012;Braga et al, 2013;Simmonds et al, 2014).…”

“…For example, the involvement of the parietal lobe in spoken language has not been apparent in many neuroimaging studies of language (Brownsett and Wise, 2010). Equally, nonlinguistic tasks can activate accepted language-specific regions (Fedorenko et al, 2012). Similarly, domain-general systems can activate bilateral frontal-temporalparietal (FTP) cortices that overlap with putative language networks (Dosenbach et al, 2008;Vincent et al, 2008;Duncan, 2010;Fedorenko et al, 2013).…”

“…Equally, nonlinguistic tasks can activate accepted language-specific regions (Fedorenko et al, 2012). Similarly, domain-general systems can activate bilateral frontal-temporalparietal (FTP) cortices that overlap with putative language networks (Dosenbach et al, 2008;Vincent et al, 2008;Duncan, 2010;Fedorenko et al, 2013). This ambiguity in the neuroimaging studies of spoken language may arise from the interplay between domain-specific and domain-general networks and the spatial overlap of these networks within the left hemisphere.…”

“…Multivariate techniques may better reveal activity in networks that are spatially overlapping than univariate subtractive techniques (Leech et al, 2011;Geranmayeh et al, 2012;. We have shown previously, using independent component analysis, that a left-lateralized FTP network is involved in speech production (Geranmayeh et al, 2012).…”