Horizontal portion of arcuate fasciculus fibers track to pars opercularis, not pars triangularis, in right and left hemispheres: A DTI study

Abstract

The arcuate fasciculus (AF) is a white matter pathway traditionally considered to connect left Broca's area with posterior language zones. We utilized diffusion tensor imaging (DTI) in eight healthy subjects (5M) to track pathways in the horizontal mid-portion of the AF (hAF) to subregions of Broca's area -pars triangularis (PTr) and pars opercularis (POp); and to ventral premotor cortex (vPMC) in the right and left hemispheres (RH, LH). These pathways have previously been studied in the LH, but not in the RH. Only 1/8 subjects showed fiber tracts between PTr and hAF in the RH (also, only 1/8 in the LH). In contrast to PTr, 5/8 subjects showed fiber tracts between POp and hAF in the RH (8/8 in the LH). Fiber tracts for vPMC were similar to those of POp, where 7/8 subjects showed fiber tracts between vPMC and hAF in the RH (8/8 in the LH). Our designated hAF could have included some of the superior longitudinal fasciculus (SLF) III, because it is difficult to separate the two fiber bundles. The SLF III has been previously reported to connect supramarginal gyrus with POp and vPMC in the LH. Thus, although the present DTI study showed almost no pathways between PTr and hAF in the RH (and in the LH), robust pathways were observed between POp and/or vPMC with hAF in the RH (and in LH). These results replicate previous studies for the LH, but are new, for the RH. They could contribute to better understanding of recovery in aphasia.

Pathways to lexical ambiguity: fMRI evidence for bilateral fronto-parietal involvement in language processing

“…These direct contrasts Overall, the comparisons employed in the present study yielded very similar patterns of cerebral activity. In all comparisons against the baseline, increased activity was found in the frontal operculum in IFG area 44 bilaterally as well as in the IPL area 40 bilaterally (except for the contrast HD minus CR for which the IPL activation was observed only in the left hemisphere) consistent with studies that have shown strong connections between these two areas (Frey et al, 2005;Frey et al, 2008;Kaplan et al, 2010). Furthermore, direct contrasts between the subordinate and dominant meanings revealed increased activity only in the right IPL (area 40) 21 implicating that area especially in the computation of alternative interpretations (see Table 1 for the complete list of peaks of increased activity).…”

“…Based on evidence from diffusion tractography studies (Frey et al, 2008) and resting state connectivity studies (Kelly et al, 2010) that suggested that the region of the pars opercularis has distinct connections with the supramarginal region of the IPL (area 40; area PF/PFG) through the third branch of the superior longitudinal fasciculus, while area 45 (pars triangularis) connects with the superior temporal gyrus and sulcus via the extreme capsule fiber system (see also Dick & Tremblay, 2012;Kaplan et al, 2010), it was hypothesised that if the IFG activations were localised in area 44, then co-modulations should be observed in IPL area 40. Indeed, the results of the present study revealed that the IPL area 40 bilaterally was involved in the computation of meaning of linguistic items with multiple interpretations.…”

“…In particular, Frey et al (2008), using diffusion fiber tractography demonstrated that area 44 (pars opercularis) has distinct connections with rostral inferior parietal lobule, namely the supramarginal gyrus, through the third branch of the superior longitudinal fasciculus (SLF III), while area 45 (pars triangularis) connects with the superior temporal gyrus via the extreme capsule fiber system (see also Dick & Tremblay, 2012;Kaplan et al, 2010). These results which replicated previous findings from experimental anatomical tracer studies in the macaque monkey (Petrides & Pandya, 1984) highlight the differences in connectivity between areas 44…”

Fiber tracts of the dorsal language stream in the human brain

“…5,12,21,33,37,56,64 The semantic region is located anterosuperiorly in the inferior frontal gyrus, pars orbitalis (BA 47) and triangularis (BA 45), and dorsolateral prefrontal cortex (middle part of the middle frontal gyrus) (BA 46/9). 4,18,25,35,46,47 Similarly, we found 4 frontal cortical areas included in the AF segments: the pars opercularis, pars triangularis, ventral premotor cortex, and the posterior part of the middle frontal gyrus. The ventral AF terminated in 3 areas: the pars opercularis (96%), pars triangularis (40%), and ventral premotor cortex (84%).…”

Neuroimagen funcional y lenguaje

“…La capacidad de repetición, con y sin sentido semántico, puede depender de una activación bilateral 16 o principalmente izquierda del FA 17 , que, a su vez, es estructuralmente asimétrico entre ambos hemisferios con un mayor grosor en el hemisferio izquierdo, tanto para diestros como para zurdos, y con un grosor similar para ambos hemisferios en los ambidiestros 17 . Sin embargo, el FA muestra una mayor conexión estructural con el BA47 de ambos hemisferios 15 . En relación con la capacidad de denominación, se ha demostrado un clá-sico postulado de un posible circuito neural diferente para la denominación de acciones y de objetos.…”