Table 1.

Experimental prediction of hemispheric competition and cooperation models assuming either polarity specific or polarity unspecific effects

Hemispheric competition modelHemispheric cooperation model
Polarity-specific: anodal increases, cathodal decreases plasticityBihemispheric < unihemispheric < sham < bihemispheric-RPUnihemispheric < bihemispheric ≤ bihemispheric-RP ≤ sham
Polarity-unspecific: both anodal and cathodal increase plasticityUnihemispheric < bihemispheric = bihemispheric-RP < shamBihemispheric = bihemispheric-RP < unihemispheric < sham
  • Conditions are listed in order of predicted behavioral performance (< means lower movement time, i.e. better performance). Predictions for the hemispheric competition model assuming polarity-specific effects on plasticity and for the hemispheric cooperation model assuming polarity-unspecific effects are presented in the Introduction. Under the hemispheric competition model with polarity-unspecific tDCS effects, stimulating contralateral M1 only would be expected to be more effective than stimulating both (because both M1s are competing). However, both bihemispheric montages should still be more effective than sham as contralateral M1 is being stimulated. Under the hemispheric cooperation model with polarity-specific tDCS effects, unihemispheric tDCS is expected to have the greatest facilitatory effect because contralateral M1 is being stimulated and ipsilateral M1 is unaffected. The exact prediction for the remaining three conditions depends on the relative importance for each hemisphere in developing the skill.