Noninvasive stimulation increases fMRI connectivity during autobiographical memory retrieval more so than during rest
Kristen Warren1, Molly S Hermiller1, Steven VanHaerents1, Joel L Voss1; 1Northwestern University
Episodic memory is supported by the hippocampus and a distributed network of cortical regions. We have previously shown that noninvasive brain stimulation targeting this hippocampal-cortical network (HCN) increases resting-state fMRI correlations among network regions and improves episodic memory. However, the relevance of resting-state fMRI connectivity to cognitive processing is uncertain. Therefore, we investigated the effects of network-targeted brain stimulation on fMRI connectivity measured during a specific memory demand: autobiographical retrieval. Furthermore, we compared these effects of stimulation on memory-related fMRI connectivity to those observed via resting-state fMRI in the same subjects. Subjects (N=16) underwent resting-state and autobiographical-retrieval fMRI scans followed by five consecutive days of high-frequency (20 Hz) repetitive transcranial magnetic stimulation to left lateral parietal cortex. Follow-up fMRI occurred 24 hours after the last day of stimulation. There were significant changes in fMRI connectivity with the hippocampus in a variety of distributed brain regions during both resting-state and autobiographical-retrieval scans. Changes in connectivity were more robust during autobiographical retrieval compared to resting state. Regions with significantly different stimulation-induced changes in autobiographical-retrieval versus resting-state scans were analyzed using hierarchical clustering of connectivity graphs, which identified three distributed networks. One comprised predominately frontal regions that increased interconnectivity, one comprised frontal regions that decreased interconnectivity, and the third comprised the HCN and additional parietal regions that showed increased interconnectivity. These findings suggest that the effects of noninvasive stimulation on fMRI connectivity are assessment-specific, with greater effects when targeted brain networks are involved in relevant cognitive processing.
Topic Area: LONG-TERM MEMORY: Episodic