Mapping brain asymmetry in health and disease through the ENIGMA consortium

Relations between hemispheric asymmetries of grey matter and auditory processing of spoken syllables in 281 healthy adults

Most people have a right-ear advantage for the perception of spoken syllables, consistent with left hemisphere dominance for speech processing. However, there is considerable variation, with some people showing left-ear advantage. The extent to which this variation is reflected in brain structure remains unclear. We tested for relations between hemispheric asymmetries of auditory processing and of grey matter in 281 adults, using dichotic listening and voxel-based morphometry. This was the largest study of this issue to date. Per-voxel asymmetry indexes were derived for each participant following registration of brain magnetic resonance images to a template that was symmetrized. The asymmetry index derived from dichotic listening was related to grey matter asymmetry in clusters of voxels corresponding to the amygdala and cerebellum lobule VI. There was also a smaller, non-significant cluster in the posterior superior temporal gyrus, a region of auditory cortex. These findings contribute to the mapping of asymmetrical structure–function links in the human brain and suggest that subcortical structures should be investigated in relation to hemispheric dominance for speech processing, in addition to auditory cortex.

Chimpanzee brain morphometry utilizing standardized MRI preprocessing and macroanatomical annotations

Chimpanzees are among the closest living relatives to humans and, as such, provide a crucial comparative model for investigating primate brain evolution. In recent years, human brain mapping has strongly benefited from enhanced computational models and image processing pipelines that could also improve data analyses in animals by using species-specific templates. In this study, we use structural MRI data from the National Chimpanzee Brain Resource (NCBR) to develop the chimpanzee brain reference template Juna.Chimp for spatial registration and the macro-anatomical brain parcellation Davi130 for standardized whole-brain analysis. Additionally, we introduce a ready-to-use image processing pipeline built upon the CAT12 toolbox in SPM12, implementing a standard human image preprocessing framework in chimpanzees. Applying this approach to data from 194 subjects, we find strong evidence for human-like age-related gray matter atrophy in multiple regions of the chimpanzee brain, as well as, a general rightward asymmetry in brain regions.

Assessing within-task verbal fluency performance: the utility of individual time intervals in predicting incident mild cognitive impairment

The current study aimed to determine whether word generation performance on individual within-task 20-second time intervals predicted conversion to Mild Cognitive Impairment (MCI) status. Longitudinal data (Mean follow-up=2.95±1.64 years) was collected from cognitively-healthy community-dwelling older adults (N=344; %female=56.1). Performance on letter and semantic fluency tasks was divided into three consecutive within-task 20-second intervals. Incident MCI status (n=50) was determined via established diagnostic case conference. Fully adjusted Cox proportional-hazards regression models revealed that greater word production on semantic fluency across all time intervals significantly predicted a reduced risk of incident MCI [0-20 seconds (HR=0.906, p=0.002), 21-40 seconds (HR=0.904, p=0.02), and 41-60 seconds (HR=0.892, p=0.017)]. Conversely, on letter fluency, greater word production within the 41-60 second time interval only was significantly associated with reduced risk of incident MCI (HR=0.886, p=0.002). Overall, the clinical use of within-interval performance is supported given evidence of predictive sensitivity and ease of administration.