In 17 ET-patients with thalamic-DBS , Tremor-Rating-Scale ( TRS ) , standardized phonemic and semantic verbal fluency ( VF ) , Stroop-Color-Word-Test and Digit-span-test were investigated in three randomized stimulation-settings : i ) high-frequency stimulation ( HFS ) , ii ) low-frequency stimulation ( LFS ) and iii ) OFF-stimulation ( DBS-OFF ) .