Language selection (or control) refers to the cognitive mechanism that controls which language to use at a given moment and context. It allows bilinguals to selectively communicate in one target language while minimizing the interferences from the nontarget language. Previous studies have suggested the participation in language control of different brain areas. However, the question remains whether the selection of one language among others relies on a language-specific neural module or general executive regions that also allow switching between different competing behavioral responses including the switching between various linguistic registers. In this functional magnetic resonance imaging study, we investigated the neural correlates of language selection processes in German-French bilingual subjects during picture naming in different monolingual and bilingual selection contexts. We show that naming in the first language in the bilingual context (compared with monolingual contexts) increased activation in the left caudate and anterior cingulate cortex. Furthermore, the activation of these areas is even more extended when the subjects are using a second weaker language. These findings show that language control processes engaged in contexts during which both languages must remain active recruit the left caudate and the anterior cingulate cortex (ACC) in a manner that can be distinguished from areas engaged in intralanguage task switching.

The non-invasive nature of arterial spin labelling (ASL) has opened a unique window into human brain function and perfusion physiology. High spatial and temporal resolution makes the technique very appealing not only for the diagnosis of vascular diseases, but also in basic neuroscience where the aim is to develop a more comprehensive picture of the physiological events accompanying neuronal activation. However, low signal-to-noise ratio and the complexity of flow quantification make ASL one of the more demanding disciplines within MRI. In this review, the theoretical background and main implementations of ASL are revisited. In particular, the perfusion quantification methods, including the problems and pitfalls involved, are thoroughly discussed in this article. Finally, a brief summary of applications is provided.

Assessing inter-individual variability of functional activations is of practical importance in the use of functional magnetic resonance imaging (fMRI) in a clinical context. In this fMRI study we addressed this issue in 30 right-handed, healthy subjects using rhyme detection (phonologic) and semantic categorization tasks. Significant activations, found mainly in the left hemisphere, concerned the inferior frontal gyrus, the superior/middle temporal gyri, the prefrontal cortex, the inferior parietal lobe, the superior parietal lobule/superior occipital gyrus, the pre-central gyrus, and the supplementary motor area. Intensity/spatial analysis comparing activations in both tasks revealed an increased involvement of frontal regions in the semantic task and of temporo-parietal regions in the phonologic task. The frequency of activation analyzed in nine regional subdivisions revealed a high inter-subject variability but showed that the most frequently activated regions were the inferior frontal gyrus and the prefrontal cortex. Laterality indices, strongly lateralizing in both tasks, were slightly higher in the semantic (0.76 +/- 0.19) than the phonologic task (0.66 +/- 0.27). Frontal dominance indices (a measure of frontal vs. posterior left hemisphere dominance) indicated more robust frontal activations in the semantic than the phonologic task. Our study allowed the characterization of the most frequently involved foci in two language tasks and showed that the combination of these tasks constitutes a suitable tool for determining language lateralization and for mapping major language areas.

Background and Purpose-Collateral circulation plays a vital role in patients with steno-occlusive disease, in particular for predicting stroke outcome. Digital subtraction angiography (DSA) is the gold standard for the assessment of collateral circulation, despite its invasive nature. Recently, the development of a new class of arterial spin labeling (ASL) methods allowed independent measurement of territorial flow information without the need for contrast media injection. Here, we compared combined territorial ASL (TASL) and MR angiography (MRA) against DSA in the assessment of collateral circulation. Methods-Eighteen patients presenting with extra-or intracranial arterial steno-occlusive disease were recruited. All DSA studies were performed using a biplane angiography unit. MR imaging consisted of time-of-flight MRA and TASL, performed at 3T. Collateral circulation on both modalities was evaluated in consensus in a double-blinded manner by 3 neuroradiologists. Results-Good agreement was found between DSA and TASL in the assessment of collateral flow: Cramer coefficient, Vϭ0.53 (PϽ0.0001) and Contingency coefficient, Cϭ0.67, with kappaϭ0.70 and kappaϭ0.72 in the assessment of flow and collaterals, respectively. TASL and DSA successfully evaluated 89% and 98% of the vessels, respectfully. Failure was linked to motion-related artifacts in TASL, and highly tortuous vessels in DSA. Generally, combined MRA-TASL was comparable to DSA in diagnostic quality. Conclusions-TASL provided radiological information comparable to DSA on collateral flow, with the advantage that it could be performed during routine MRI studies. TASL may provide insight on collateral perfusion in patients who may not otherwise be candidates for DSA, and may potentially replace it. (Stroke. 2008;39:3248-3254.)