Increased fMRI connectivity of the anterior-medial hippocampal-cortical network via noninvasive brain stimulation
Molly S. Hermiller1, Melissa Gunlogson1, Robert Palumbo1, Brennan Durr1, Valerie McDonald1, Stephen VanHaerants1, Joel L. Voss1; 1Northwestern University Feinberg School of Medicine
The hippocampus interacts with distributed brain regions forming a hippocampal-cortical network in support of episodic memory. Anterior-temporal and posterior-medial subdivisions of this network have been linked to distinct memory processes primarily on the basis of fMRI findings. Noninvasive brain stimulation can be used to test the causal role of brain networks in cognitive function, but it is unclear whether distinct subdivisions can be separately influenced by stimulation. We have previously shown that the posterior-medial subdivision can be selectively modulated using transcranial magnetic stimulation. Here, we aimed to determine whether fMRI connectivity of the anterior-temporal subdivision could be selectively influenced. In this sham-controlled, multi-day study (N=16), 20-Hz transcranial magnetic stimulation was delivered for five consecutive days. Subject-specific hippocampal targets and stimulation locations in the dorsal lateral prefrontal cortex were identified using baseline fMRI connectivity. Prior to and 24-hours following the five days of stimulation, resting-state fMRI scans were acquired. Several core regions of the anterior-temporal network critical for memory showed increased fMRI connectivity due to stimulation, including the medial prefrontal/orbitofrontal and anterior cingulate cortex, as well as the left anterior hippocampus and surrounding rhinal cortex, which are also the intended deep-brain targets of stimulation. These findings demonstrate that the anterior-temporal subdivision of the hippocampal-cortical network can be indirectly, yet selectively, modulated by noninvasive stimulation. These findings provide the framework for future studies using stimulation to distinguish the role of distinct hippocampal-cortical network subdivisions in episodic memory.
Topic Area: LONG-TERM MEMORY: Episodic