Transcranial direct current stimulation modulates activation and effective connectivity during spatial navigation.
BACKGROUND
Allocentric navigation declines with age and neurologic disease whereas egocentric navigation does not; differences that likely arise from maladaptive changes in brain regions mediating spatial (parietal cortex; hippocampus) but not procedural processing (caudate nucleus). Transcranial direct current stimulation (tDCS) holds promise for treating such decline given its ability to modulate neuronal excitability, but its effects have yet to be examined on spatial navigation.


OBJECTIVE
Using healthy young adults as a model, Study 1 intended to validate a novel spatial navigation paradigm using functional magnetic resonance imaging (fMRI). Using these data to determine targets for tDCS, Study 2 aimed to determine if 1) stimulation modulates activation in a polarity-specific manner; 2) stimulation results in global and/or task-specific activation changes; 3) activation changes are accompanied by changes in effective connectivity.


METHODS
All participants underwent fMRI while learning allocentric and egocentric environments. Twelve participants completed Study 1. In Study 2, 16 participants were randomized to 20 min of tDCS (2 mA) using a montage with the anode over PZ and cathode over AF4 (P+F-) or the reverse montage (P-F+).


RESULTS
Study 1 revealed that distinct networks preferentially mediate allocentric and egocentric navigation. Study 2 revealed polarity-dependent changes in activation and connectivity. The P+F- montage increased these measures in spatial regions, especially during allocentric navigation, and the caudate nucleus. Conversely, the P-F+ montage increased activation and connectivity in lateral prefrontal cortices and posterior hippocampus.


CONCLUSIONS
These findings support the neuromodulatory effects of tDCS in non-motor areas and demonstrate proof-of-principle for ameliorating age- and disease-related decline in navigational abilities.
Rehabilitation R&D Center of Excellence, Atlanta VAMC, Decatur, GA, USA; Department of Rehabilitation Medicine, Emory University, Atlanta, GA, USA. Electronic address: bhampst@emory.edu.
Benjamin M
BM
Hampstead
Department of Rehabilitation Medicine, Emory University, Atlanta, GA, USA.
Gregory S
GS
Brown
Rehabilitation R&D Center of Excellence, Atlanta VAMC, Decatur, GA, USA.
Justin F
JF
Hartley
D000328:Adult; D001931:Brain Mapping; D004777:Environment; D005260:Female; D006801:Humans; D007858:Learning / Q000502:physiology*; D008279:Magnetic Resonance Imaging; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D065854:Spatial Navigation / Q000502:physiology*; D065908:Transcranial Direct Current Stimulation; D055815:Young Adult
Allocentric; Granger causality analysis; Hippocampus; Learning; Memory; fMRI; tDCS