Alzheimer＇s disease （AD） is the most common type of dementia, comprising an estimated 60-80% of all dementia cases. It is clinically characterized by impairments of memory and other cognitive functions. Previous studies have demonstrated that these impairments are associated with abnormal structural and functional connections among brain regions, leading to a disconnection concept of AD. With the advent of a combination of non-invasive neuroimaging （structural magnetic resonance imaging （MRI）, diffusion MRI, and functional MRI） and neurophysiological techniques （electroencephalography and magnetoencephaJography） with graph theoretical analysis, recent studies have shown that patients with AD and mild cognitive impairment （MCI）, the prodromal stage of AD, exhibit disrupted topological organization in large-scale brain networks （i.e., connectomics） and that this disruption is significantly correlated with the decline of cognitive functions. In this review, we summarize the recent progress of brain connectomics in AD and MCI, focusing on the changes in the topological organization of large-scale structural and functional brain networks using graph theoretical approaches. Based on the two different perspectives of information segregation and integration, the literature reviewed here suggests that AD and MCI are associated with disrupted segregation and integration in brain networks. Thus, these connectomics studies open up a new window for understanding the pathophysiological mechanisms of AD and demonstrate the potential to uncover imaging biomarkers for clinical diagnosis and treatment evaluation for this disease.
Integrating letters and sounds are essential for successful reading in alphabetic languages. It remains unclear if native speakers of non-alphabetic languages integrate letters and sounds in reading an alphabetic lan- guage in the same way as native alphabetic readers do. Chinese is a morpho-syllabic system （each character cor- responds to one syllable） and contrasts sharply with alphabetic languages such as English. Several fMRI studies have shown that native Chinese speakers apply their native language system to read English words. By using the cross- modal mismatch negativity （MMN） paradigm, we directly investigated letter-sound integration for reading in English among native Chinese speakers. To investigate the effect of native language background on letter-sound integration in second language reading, a group of native Korean English learners served as a comparison group. We compared MMN responses between an auditory only condition （only vowels presented） and two audiovisual conditions （AV0, vowel presented synchronously with the corresponding letter; AV200, the letter presented 200 ms before the corresponding vowel） for both native Chinese and native Korean speakers. Native Chinese speakers demonstrated significantly attenuated MMN amplitudes in audiovisual conditions compared with the auditory only condition, regardless of their phonological decoding speed. In con- trast, native Korean speakers showed amplified amplitude MMN in AV200 compared with that in the auditory only condition. The results suggest that native language may shape the brain responses of second language learners to reading a second language in the early stages. Native non- alphabetic language speakers may be unable to use visual information to facilitate their phonological processing in the early stage while naT：lye alphabetic language speakers are capable of integrating letter sounds automatically.
