Brain structure & function
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Recent research on Alzheimer's disease (AD) has shown that the altered structure and function of the inferior parietal lobule (IPL) provides a promising indicator of AD. However, little is known about the functional connectivity of the IPL subregions in AD subjects. In this study, we collected resting-state functional magnetic resonance imaging data from 32 AD patients and 38 healthy controls. ⋯ Finally, these abnormal IPL functional connectivity changes were closely associated with cognitive performance. Collectively, we show that the subregions of the IPL present distinct functional connectivity patterns with various functional networks that are differentially impaired in AD patients. Our results also suggest that functional disconnection and compensation in the IPL may coexist in AD.
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Episodic memory is typically affected during the course of Alzheimer's disease (AD). Due to the pronounced heterogeneity of functional neuroimaging studies on episodic memory impairments in mild cognitive impairment (MCI) and AD regarding their methodology and findings, we aimed to delineate consistent episodic memory-related brain activation patterns. We performed a systematic, quantitative, coordinate-based whole-brain activation likelihood estimation meta-analysis of 28 functional magnetic resonance imaging (fMRI) studies comprising 292 MCI and 102 AD patients contrasted to 409 age-matched control subjects. ⋯ In AD patients, however, stronger activation within the precuneus during encoding tasks was accompanied by attenuated right hippocampal activation during retrieval tasks. Low cognitive performance (MMSE scores) was associated with stronger activation of the precuneus and reduced activation of the right (para)hippocampus and anterior insula/inferior frontal gyrus. This meta-analysis provides evidence for a specific and probably disease stage-dependent brain activation pattern related to the pathognomonic AD characteristic of episodic memory loss.
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Reduced hippocampal GABAergic inhibition is acknowledged to be associated with epilepsy. However, there are no studies that had quantitatively compared the loss of various interneuron populations in different models of epilepsy. We tested a hypothesis that the more severe the loss of hippocampal interneurons, the more severe was the epilepsy. ⋯ Taken together, interneuron loss was substantially more severe, widespread, progressive, and included more interneuron subclasses after TBI than after SE. Interneurons responsible for perisomatic inhibition were more vulnerable to TBI than those providing dendritic inhibition. Unlike expected, we could not demonstrate any etiology-independent link between the severity of hippocampal interneuron loss and the overall risk of spontaneous seizures.
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Recent results from diffusion tensor imaging (DTI) studies provide evidence of a ventral-lexical stream and a dorsal-sublexical stream associated with reading processing. We investigated the relationship between behavioural reading speed for stimuli thought to rely on either the ventral-lexical, dorsal-sublexical, or both streams and white matter via fractional anisotropy (FA) and mean diffusivity (MD) using DTI tractography. Participants (N = 32) overtly named exception words (e.g., 'one', ventral-lexical), regular words (e.g., 'won', both streams), nonwords ('wum', dorsal-sublexical) and pseudohomophones ('wun', dorsal-sublexical) in a behavioural lab. ⋯ Multiple regression analyses revealed that exception word RT accounted for unique variability in FA of the uncinate over and above regular words. There were no robust relationships found between pseudohomophones, or nonwords, and tracts thought to underlie the dorsal processing stream. These results support the notion that word recognition, in general, and exception word reading in particular, rely on ventral-lexical brain regions.
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Auditory verbal hallucinations (AVH) in schizophrenia have previously been associated with functional deficiencies in language networks, specifically with functional disconnectivity in fronto-temporal connections in the left hemisphere and in interhemispheric connections between frontal regions. Here, we investigate whether AVH are accompanied by white matter abnormalities in tracts connecting the frontal, parietal and temporal lobes, also engaged during language tasks. We combined diffusion tensor imaging with tract-based spatial statistics and found white matter abnormalities in patients with schizophrenia as compared with healthy controls. ⋯ Compared to patients without current hallucinations, patients with hallucinations revealed decreased fractional anisotropy in the left IFOF, uncinate fasciculus, arcuate fasciculus with SLF, corpus callosum (posterior parts-forceps major), cingulate, corticospinal tract and ATR. The severity of hallucinations correlated negatively with white matter integrity in tracts connecting the left frontal lobe with temporal regions (uncinate fasciculus, IFOF, cingulum, arcuate fasciculus anterior and long part and superior long fasciculus frontal part) and in interhemispheric connections (anterior corona radiata). These findings support the hypothesis that hallucinations in schizophrenia are accompanied by a complex pattern of white matter alterations that negatively affect the language, emotion and attention/perception networks.