Fluency-dependent cortical activation associated with speech production and comprehension in second language learners.

This functional magnetic resonance imaging (fMRI) study investigated the brain regions underlying language task performance in adult second language (L2) learners. Specifically, we identified brain regions where the level of activation was associated with L2 fluency levels. Thirty Japanese-speaking adults participated in the study. All participants were L2 learners of English and had achieved varying levels of fluency, as determined by a standardized L2 English proficiency test, the Versant English Test (Pearson Education Inc., 2011). When participants performed the oral sentence building task from the production tasks administered, the dorsal part of the left inferior frontal gyrus (dIFG) showed activation patterns that differed depending on the L2 fluency levels: The more fluent the participants were, the more dIFG activation decreased. This decreased activation of the dIFG might reflect the increased automaticity of a syntactic building process. In contrast, when participants performed an oral story comprehension task, the left posterior superior temporal gyrus (pSTG) showed increased activation with higher fluency levels. This suggests that the learners with higher L2 fluency were actively engaged in post-syntactic integration processing supported by the left pSTG. These data imply that L2 fluency predicts neural resource allocation during language comprehension tasks as well as in production tasks. This study sheds light on the neural underpinnings of L2 learning by identifying the brain regions recruited during different language tasks across different modalities (production vs. comprehension).

Neural representation of animacy in the early visual areas: a functional MRI study.

Animacy helps to identify objects as living entities. To test the hypothesis that the perception of animacy via visual motion cues is represented in the same ventral visual pathways associated with living object identification through static visual information processing, 28 normal volunteers underwent functional MRI whilst tracking the movements of a self-propelling object. The target movement was held constant between conditions, whilst the animacy was externally manipulated by the presence of "chasers", from which the target was perceived to be escaping, and by "obstacles", which were static geometric objects with which the target avoided collision. The perception of target animacy was most powerfully induced by chasers, and a proximity effect was more prominently produced by obstacles. Animacy as induced by a chaser was associated with effects in the bilateral occipital poles (OPs) and the left inferior temporal gyrus to the lateral occipital complex (LOC). The LOC showed a stronger animacy effect, relative to the proximity effect, than the OPs. The effective connectivity between the LOC and the OPs was bi-directionally enhanced by the chasers. These findings suggest that both the LOC and the OPs play important roles in the identification of animated entities through the integration of information about the relationships between objects encoded in retinotopic coordinates.

Ventrolateral prefrontal cortex activity associated with individual differences in arbitrary delayed paired-association learning performance: a functional magnetic resonance imaging study.

To describe the neural substrates of successful episodic long-term memory encoding, we collected functional magnetic-resonance imaging data as participants completed an arbitrary delayed auditory paired-association learning task. During the task, subjects learned predefined but hidden stimulus pairs by trial and error based on visual feedback. Delay period activity represents the retrieval of the relationship between the cue item and its candidate for associates, that is, working memory. Our hypothesis was that the neural substrates of working memory would be related to long-term memory encoding in a performance-dependent manner. Thus, inter-individual variance in performance following a fixed learning set would be associated with differing neural activations during the delay period. The number of learning trials was adjusted such that performance following completion of the learning set varied across subjects. Each trial consisted of the successive presentation of two stimuli (first stimulus and second stimulus [S2]) with a fixed delay interval, allowing extraction of sustained activity during the delay period. Sustained activities during the delay period were found in the bilateral dorsolateral prefrontal cortex, intraparietal sulcus, and left ventrolateral prefrontal cortex, as well as the premotor and pre-supplementary motor areas. The activities did not change in strength across learning, suggesting that these effects represent working memory components. The sustained activity in the ventrolateral prefrontal region was correlated with task performance. Task performance was also positively correlated with the decrement in S2/feedback-related activity during learning in the superior temporal sulcus, a region previously shown to be involved in association learning. These findings are consistent with lesion and neuroimaging studies showing that the ventrolateral prefrontal cortex plays an important role in long-term memory encoding, and raise the possibility that working memory processes interact with long-term memory formation as represented by the covariation of activity in the superior temporal sulcus and the ventrolateral prefrontal cortex.

Neural substrates of intermanual transfer of a newly acquired motor skill.

In healthy humans, the two cerebral hemispheres show functional specialization to a degree unmatched in other animals, and such strong hemispheric specialization contributes to unimanual skill acquisition [1, 2]. When most humans learn a new motor skill with one hand, this process results in performance improvements in the opposite hand as well [3-6]. Despite the obvious adaptive advantage of such intermanual transfer, there is no direct evidence identifying the neural substrates of this form of skill acquisition [7-9]. Here, we used functional magnetic resonance imaging (fMRI) to study brain regions activated during intermanual transfer of a learned sequence of finger movements. First, we found that the supplementary motor area (SMA) has more activity when a skill has transferred well than when it has transferred poorly. Second, we found that fMRI activity in the ventrolateral posterior thalamic nucleus correlated with successful future intermanual transfer, whereas activity in the ventrolateral anterior thalamic nucleus correlated with past intermanual transfer. Third, we found that repetitive transcranial magnetic stimulation applied over the SMA blocked intermanual transfer without affecting skill acquisition. These findings provide direct evidence for an SMA-based mechanism that supports intermanual transfer of motor-skill learning.

Cortical mapping of gait in humans: a near-infrared spectroscopic topography study.

While we have a fair understanding of how and where forelimb-hand manipulative movements are controlled by the neocortex, due to functional imaging studies, we know little about the control of bipedal movements such as walking because of technical difficulties. We succeeded in visualizing cortical activation patterns of human gait by measuring relative changes in local hemoglobin oxygenation using a recently developed near-infrared spectroscopic (NIRS) topography technique. Walking activities were bilaterally associated with increased levels of oxygenated and total hemoglobin in the medial primary sensorimotor cortices and the supplementary motor areas. Alternating foot movements activated similar but less broad regions. Gait imagery increased activities caudally located in the supplementary motor areas. These findings provide new insight into cortical control of human locomotion. NIRS topography might be also useful for evaluating cerebral activation patterns during pathological gait and rehabilitative intervention.