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Updated: Nov 20, 2025

Transcranial Direct Current Stimulation tDCS for Memory Enhancement
Published on: September 18, 2021
Brain structures and networks responsible for stimulation-induced memory flashbacks during forniceal deep brain
Jürgen Germann1, Gavin J B Elias1, Alexandre Boutet1,2
1Division of Neurosurgery, Toronto Western Hospital, University Health Network, University of Toronto, Toronto, Canada.
Introduction:
Fornix deep brain stimulation (fx-DBS) is under investigation for treatment of Alzheimer's disease (AD). We investigated the anatomic correlates of flashback phenomena that were reported previously during acute diencephalic stimulation.
Methods:
Thirty-nine patients with mild AD who took part in a prior fx-DBS trial (NCT01608061) were studied. After localizing patients' implanted electrodes and modeling the volume of tissue activated (VTA) by DBS during systematic stimulation testing, we performed (1) voxel-wise VTA mapping to identify flashback-associated zones; (2) machine learning-based prediction of flashback occurrence given VTA overlap with specific structures; (3) normative functional connectomics to define flashback-associated brain-wide networks.
Results:
A distinct diencephalic region was associated with greater flashback likelihood. Fornix, bed nucleus of stria terminalis, and anterior commissure involvement predicted memory events with 72% accuracy. Flashback-inducing stimulation exhibited greater functional connectivity to a network of memory-evoking and autobiographical memory-related sites.
Discussion:
These results clarify the neuroanatomical substrates of stimulation-evoked flashbacks.
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