Developmental dyslexia in Chinese and English populations: dissociating the effect of dyslexia from language differences

Previous neuroimaging studies have suggested that developmental dyslexia has a different neural basis in Chinese and English populations because of known differences in the processing demands of the Chinese and English writing systems. Here, using functional magnetic resonance imaging, we provide the first direct statistically based investigation into how the effect of dyslexia on brain activation is influenced by the Chinese and English writing systems. Brain activation for semantic decisions on written words was compared in English dyslexics, Chinese dyslexics, English normal readers and Chinese normal readers, while controlling for all other experimental parameters. By investigating the effects of dyslexia and language in one study, we show common activation in Chinese and English dyslexics despite different activation in Chinese versus English normal readers. The effect of dyslexia in both languages was observed as less than normal activation in the left angular gyrus and in left middle frontal, posterior temporal and occipitotemporal regions. Differences in Chinese and English normal reading were observed as increased activation for Chinese relative to English in the left inferior frontal sulcus; and increased activation for English relative to Chinese in the left posterior superior temporal sulcus. These cultural differences were not observed in dyslexics who activated both left inferior frontal sulcus and left posterior superior temporal sulcus, consistent with the use of culturally independent strategies when reading is less efficient. By dissociating the effect of dyslexia from differences in Chinese and English normal reading, our results reconcile brain activation results with a substantial body of behavioural studies showing commonalities in the cognitive manifestation of dyslexia in Chinese and English populations. They also demonstrate the influence of cognitive ability and learning environment on a common neural system for reading

Top-down modulation of ventral occipito-temporal responses during visual word recognition

Although interactivity is considered a fundamental principle of cognitive (and computational) models of reading, it has received far less attention in neural models of reading that instead focus on serial stages of feed-forward processing from visual input to orthographic processing to accessing the corresponding phonological and semantic information. In particular, the left ventral occipito-temporal (vOT) cortex is proposed to be the first stage where visual word recognition occurs prior to accessing nonvisual information such as semantics and phonology. We used functional magnetic resonance imaging (fMRI) to investigate whether there is evidence that activation in vOT is influenced top-down by the interaction of visual and nonvisual properties of the stimuli during visual word recognition tasks. Participants performed two different types of lexical decision tasks that focused on either visual or nonvisual properties of the word or word-like stimuli. The design allowed us to investigate how vOT activation during visual word recognition was influenced by a task change to the same stimuli and by a stimulus change during the same task. We found both stimulus- and task-driven modulation of vOT activation that can only be explained by top-down processing of nonvisual aspects of the task and stimuli. Our results are consistent with the hypothesis that vOT acts as an interface linking visual form with nonvisual processing in both bottom up and top down directions. Such interactive processing at the neural level is in agreement with cognitive and computational models of reading but challenges some of the assumptions made by current neuro-anatomical models of reading

The Effects of Anatomic Variations on Stereotactic Laser Amygdalohippocampectomy and a Proposed Protocol for Trajectory Planning

BACKGROUND: Stereotactic laser amygdalohippocampectomy (SLAH) is a promising minimally invasive alternative for mesial temporal lobe epilepsy. As seizure outcome has been associated with the extent of amygdalar and hippocampal ablation, it is important to select a safe trajectory optimizing involvement of both structures; however, variations in temporal anatomy significantly affect the overall complexity of planning. OBJECTIVE: To quantify anatomic variables of SLAH and facilitate stereotactic planning by developing a protocol for optimally targeting the amygdalohippocampal complex (AHC). METHODS: We performed a retrospective analysis of 19 SLAHs. Anatomic measurements from preoperative magnetic resonance imaging and laser trajectory measurements from coregistered postoperative magnetic resonance imaging were taken in 11 patients. Simple linear regression analysis was performed to identify significant predictor variables determining ablation extent. Based on these data, a protocol for optimal trajectory planning was developed and subsequently implemented in 8 patients. RESULTS: The medial angle of the laser trajectory correlated with the medial angle of the AHC. The length of amygdalar cannulation was predictive of its ablation volume. All trajectories passed through a posteroinferior corridor formed by the lateral ventricle superiorly and collateral sulcus inferiorly. Our protocol facilitated planning and increased the volume of AHC ablation. CONCLUSION: The medial AHC angle dictates the medial trajectory angle and a path from the posteroinferior corridor through the hippocampus and the center of the amygdala dictates the caudal angle. These observations led to a protocol for long-axis AHC cannulation that maintains an extraventricular trajectory to minimize hemorrhage risk and targets the center of the amygdala to optimize ablation volumes