L2-Proficiency-Dependent Laterality Shift in Structural Connectivity of Brain Language Pathways

Diffusion tensor imaging (DTI) and a longitudinal language learning approach were applied to investigate the relationship between the achieved second language (L2) proficiency during L2 learning and the reorganization of structural connectivity between core language areas. Language proficiency tests and DTI scans were obtained from German students before and after they completed an intensive 6-week course of the Dutch language. In the initial learning stage, with increasing L2 proficiency, the hemispheric dominance of the Brodmann area (BA) 6-temporal pathway (mainly along the arcuate fasciculus) shifted from the left to the right hemisphere. With further increased proficiency, however, lateralization dominance was again found in the left BA6-temporal pathway. This result is consistent with reports in the literature that imply a stronger involvement of the right hemisphere in L2 processing especially for less proficient L2 speakers. This is the first time that an L2 proficiency-dependent laterality shift in the structural connectivity of language pathways during L2 acquisition has been observed to shift from left to right and back to left hemisphere dominance with increasing L2 proficiency. The authors additionally find that changes in fractional anisotropy values after the course are related to the time elapsed between the two scans. The results suggest that structural connectivity in (at least part of) the perisylvian language network may be subject to fast dynamic changes following language learning

The Sinusoidal Array: A Theory of Representation for Spatial Vectors

We describe a theoretical model of spatial representation in cortex, including computer simulations, that is compatible with data from single neuron recordings. Our proposed architecture, called a sinusoidal array, encodes a polar vector ~v = (r; OE) as distributed activity across a neuronal population. We demonstrate how sinusoidal arrays might be used for vector computations such as addition, subtraction, and rotation in tasks such as primate reaching and rodent navigation. 1 The Sinusoidal Array Spatial representation in the mammalian brain has been widely studied in hippocampus, parietal cortex, and throughout the motor system. But most of the modeling work to date has focused on place cells in hippocampus and on the transformation of retinal to head centered coordinates in parietal cortex. Our work models spatial representations in the motor system, but it is also applicable to certain navigational tasks. We offer a general computation mechanism, the sinusoidal array, which is ..