Aberrant resting-state brain activity in Huntington's disease: A voxel-based meta-analysis

Thalamo-insular cortex connections in the rat and human

The insular cortex (ICx) has a role in large a variety of functions. Thalamus plays an important role in modulating cortical functions. The present study aims to show thalamic-ICx connections using the fluoro-gold (FG) tracing method in rats and diffusion tensoring-based tractography (DTI) in humans. Wistar albino rats were pressure injected with the FG tracer into the anterior and posterior ICx. The DTI data were obtained from the Human Connectome Project database. Our findings showed that the thalamic-ICx connections were strictly ipsilateral in the rat, however, bilateral connections were present in humans. The anterior ICx was connected to the paraventricular, centromedial, paracentral, centrolateral, ventral posteromedial, and medial geniculate thalamic nuclei. The posterior ICx was connected to the centromedian, parafasicular, renuence, lateral, posterior, ventral posteromedial, and medial geniculate thalamic nuclei. The DTI in humans corresponded with the results of the experimental study on rats. The results of the current study may provide an understanding of how thalamic nuclei may contribute to higher-order ICx functions. The ipsilateral connections in the rat and bilateral in humans may provide insights into anatomical evolution and functional differences of the ICx circuit in humans and rats. Further, stimulation of the thalamus can be a potential target for treating or modulating ICx functions such as anxiety, depression, and certain chronic pain conditions.

Neurophysiological hallmarks of Huntington's disease progression: an EEG and fMRI connectivity study

Electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) can provide corroborative data on neurophysiological alterations in Huntington's disease (HD). However, the alterations in EEG and fMRI resting-state functional connectivity (rsFC), as well as their interrelations, at different stages of HD remain insufficiently investigated. This study aimed to identify neurophysiological alterations in individuals with preclinical HD (preHD) and early manifest HD (EMHD) by analyzing EEG and fMRI rsFC and examining their interrelationships. We found significant differences in EEG power between preHD individuals and healthy controls (HC), with a decrease in power in a specific frequency range at the theta-alpha border and slow alpha activity. In EMHD patients, in addition to the decrease in power in the 7-9 Hz range, a reduction in power within the classic alpha band compared to HC was observed. The fMRI analysis revealed disrupted functional connectivity in various brain networks, particularly within frontal lobe, putamen-cortical, and cortico-cerebellar networks, in individuals with the HD mutation compared to HC. The analysis of the relationship between EEG and fMRI rsFC revealed an association between decreased alpha power, observed in individuals with EMHD, and increased connectivity in large-scale brain networks. These networks include putamen-cortical, DMN-related and cortico-hippocampal circuits. Overall, the findings suggest that EEG and fMRI provide valuable information for monitoring pathological processes during the development of HD. A decrease in inhibitory control within the putamen-cortical, DMN-related and cortico-hippocampal circuits, accompanied by a reduction in alpha and theta-alpha border oscillatory activity, could potentially contribute to cognitive decline in HD.