A sham-controlled, phase II trial of transcranial direct current stimulation for the treatment of central pain in traumatic spinal cord injury - Fregni, F; Boggio, PS; Lima, MC; Ferreira, MJ; Wagner, T; Rigonatti, SP; Castro, AW; Souza, DR; Riberto, M; Freedman, SD; Nitsche, MA; Pascual-Leone, A (Pain, 2006)