Assessing language dominance with functional MRI: The role of control tasks and statistical analysis

Abstract

There is a discrepancy between the brain regions revealed by functional neuroimaging techniques and those brain regions where a loss of function, either by lesion or by electrocortical stimulation, induces language disorders. To differentiate between essential and non-essential language-related processes, we investigated the effects of linguistic control tasks and different analysis methods for functional MRI data. Twelve subjects solved two linguistic generation tasks: (1) a verb generation task and (2) an antonym generation task (each with a linguistic control task on the phonological level) as well as two decision tasks of semantic congruency (each with a cognitive high-level control task). Differential contrasts and conjunction analyses were carried out on the single-subject level and an individual lateralization index (LI) was computed. On the group level we determined the percent signal change in the left inferior frontal gyrus (IFG: BA 44 and BA 45). The conjunction analysis of multiple language tasks led to significantly greater absolute LIs than the LIs based on the single task versus fixation contrasts. A further significant increase of the magnitude of the LIs could be achieved by using the phonological control conditions. Although the decision tasks appear to be more robust to changes in the statistical threshold, the combined generation tasks had an advantage over the decision tasks both for assessing language dominance and locating Broca's area. These results underline the need for conjunction analysis based on several language tasks to suppress highly task-specific processes. They also point to the need for high-level cognitive control tasks to partial out general, language supporting but not language critical processes. Higher absolute LIs, which reflect unambiguously hemispheric language dominance, can be thus obtained.

American Society of Functional Neuroradiology–Recommended fMRI Paradigm Algorithms for Presurgical Language Assessment

“…The Antonym Generation task is reported to provide a higher percentage BOLD signal change in the Broca area (versus baseline) compared with the Antonym Decision task (versus baseline). 41 It is reported that activation of the speech areas and speech lateralization in the various Word Generation tasks (letter, category, antonym word generation) is comparable. 42 However, in our experience with pediatric patients, the Antonym Generation paradigm does much better in terms of the extent of activation in the speech areas and patient compliance versus letter Word Generation tasks; thus, SWG was not included in the pediatric algorithm.…”

CANDICE A1: Measuring language lateralisation with different language tasks: A systematic review

“…Across the papers reviewed here, verbal fluency tasks are consistently reported as yielding the strongest laterality when compared to other receptive and expressive tasks within studies (Baciu et al, 2005;Deblaere et al, 2002;Van der Haegen, Cai & Brysbaert, 2012;Dodoo-Schittko et al, 2012;Harrington, Buonocore & Farias, 2006;Jensen-Kondering et al, 2012;Niskanen et al, 2012;Ocklenburg, Hugdahl & Westerhausen, 2013;Ramsey et al, 2001;Vikingstad et al, 2000;Zaca, Jarso & Pillai, 2013). Studies included in the forest plots produced here report a wide spread of LI values for verbal fluency tasks, ranging from 0.05 to 0.94 (see Fig.…”

“…region of interest). Interestingly, multiple studies report that LIs from generation tasks can vary substantially depending on methodological choices made when calculating laterality, such as the threshold chosen (Dodoo-Schittko et al, 2012), the use of normalisation, smoothing and clustering techniques (Baciu et al, 2005), and the activity measure used (Harrington, Buonocore & Farias, 2006).…”

“…2 and Table 2). Dodoo- Schittko et al (2012) reported that an active baseline task which required subvocal manipulation of the order of syllables within a pseudoword yielded significantly stronger laterality for a verb generation task compared to the use of a passive resting baseline. This is consistent with the idea of subtraction of bilateral activity related to speech-motor planning (Poeppel, 2014;Price, 2012b).…”

“…In this way, CTA can represent a theoretical alternative to baseline tasks to subtract domain-general activity, assuming that different tasks involve different patterns of non-linguistically relevant activity. Indeed, there is evidence that CTA results in higher and more reliable and robust estimates of laterality for language (Dodoo-Schittko et al, 2012;Harrington, Buonocore & Farias, 2006;Jansen et al, 2006;Niskanen et al, 2012;Ramsey et al, 2001;Rutten et al, 2002;Sommer et al, 2003;Van Rijn et al, 2008). Nevertheless, the theoretical assumptions which motivate CTA can be questioned.…”