Uder, M. | bioRxiv Science

bioRxiv2022

Capturing early human memory consolidation utilizing the higher functional specificity of 7T compared to 3T-fMRI

Functional magnetic resonance imaging (fMRI) visualizes brain structures at increasingly higher resolution and better signal-to-noise ratio (SNR) as field strength increases. Yet, mapping the BOLD response to distinct neuronal processes continues to be challenging. Here, we performed 3T and 7T-fMRI analysis of motor-task activation and resting-state connectivity with adjusted SNR. We then applied graph theory to analyze resting-state neuronal networks detected by fMRI after a simple motor task. Despite adjusted SNR, 7T achieved a higher functional specificity of the BOLD response than 3T-fMRI. Following the motor task, 7T-fMRI therefore enabled the detection of an offline replay that was directly linked to brain regions associated with memory consolidation. These findings reveal how memory processing is initiated even after simple motor tasks and begins earlier than previously shown. Thus, the superior capability of 7T-fMRI to detect subtle functional dynamics promises to improve diagnostics and therapeutic assessment of neurological diseases.

neuroscience↗

bioRxiv2017

A new analysis of resting state connectivity and graph theory reveals distinctive short-term modulations due to whisker stimulation in rats.

Resting state (RS) connectivity has been increasingly studied in healthy and diseased brains in humans and animals. This paper presents a new method to analyze RS data from fMRI that combines multiple seed correlation analysis with graph-theory (MSRA). We characterize and evaluate this new method in relation to two other graph-theoretical methods and ICA. The graph-theoretical methods calculate cross-correlations of regional average time-courses, one using seed regions of the same size (SRCC) and the other using whole brain structure regions (RCCA). We evaluated the reproducibility, power, and capacity of these methods to characterize short term RS modulation to unilateral physiological whisker stimulation in rats. Graph-theoretical networks found with the MSRA approach were highly reproducible, and their communities showed large overlaps with ICA components. Additionally, MSRA was the only one of all tested methods that had the power to detect significant RS modulations induced by whisker stimulation that are controlled by family-wise error rate (FWE). Compared to the reduced resting state network connectivity during task performance, these modulations implied decreased connectivity strength in the bilateral sensorimotor and entorhinal cortex. Additionally, the contralateral ventromedial thalamus (part of the barrel field related lemniscal pathway) and the hypothalamus showed reduced connectivity. Enhanced connectivity was observed in the amygdala, especially the contralateral basolateral amygdala (involved in emotional learning processes). In conclusion, MSRA is a powerful analytical approach that can reliably detect tiny modulations of RS connectivity. It shows a great promise as a method for studying RS dynamics in healthy and pathological conditions.

neuroscience↗