Recent therapeutic human studies testing transcranial direct current stimulation
(tDCS) have shown promising results, although many questions remain unanswered.
Translational research with experimental animals is an appropriate framework for
investigating its mechanisms of action that are still undetermined.
Nevertheless, animal and human studies are often discordant. Our aim was to
review tDCS animal studies, examining and comparing their main findings with
human studies. We performed a systematic review in Medline and other databases,
screening for animal studies in vivo that delivered tDCS.
Studies in vitro and using other neuromodulatory techniques
were excluded. We extracted data according to Animal Research: Reporting
In Vivo Experiments (ARRIVE) guidelines for reporting
in vivo animal research. Thus, we collected data on sample
characteristics (size, gender, weight and specimen) and methodology
(experimental procedures, experimental animals, housing and husbandry, as well
as analysis). We also collected data on methods for delivering tDCS (location,
size, current and current density of electrodes and electrode montage),
experimental effects (polarity-, intensity- and after-effects) and safety. Only
12 of 48 potentially eligible studies met our inclusion criteria and were
reviewed. Quality assessment reporting was only moderate and studies were
heterogeneous regarding tDCS montage methodology, position of active and
reference electrodes, and current density used. Nonetheless, almost all studies
demonstrated that tDCS had positive immediate and long-lasting effects.
Vis-à-vis human trials, animal studies applied
higher current densities (34.2 vs. 0.4 A/m2, respectively), preferred
extra-cephalic positions for reference electrodes (60% vs. 10%,
respectively) and used electrodes with different sizes more often. Potential
implications for translational tDCS research are discussed.
Reviews in the Neurosciences provides a forum for reviews, critical evaluations and theoretical treatment of selective topics in the neurosciences. The journal provides an authoritative reference work for those interested in the structure and functions of the nervous system at all levels of analysis, including the genetic, molecular, cellular, behavioral, cognitive and clinical neurosciences.