treating cognitive impairment , along with motor recovery and improving performance in daily activities , is one of the key focus areas of stroke rehabilitation . as cognition is closely related to patient motivation and motor function improvement , implementing cognitive function treatment in a timely and effective manner is crucial for the overall success of poststroke rehabilitation . previous reports showed 25%-40% of patients suffer from dementia by three months after stroke , and the number increased to 50%-75% when patients with minor symptoms of cognitive impairment are included [ 2 - 4 ] . among patients with brain lesions , memory disturbance is commonly a critical challenge in rehabilitating patients to enable them to return to active participation in society and the workforce . research has suggested that rehabilitation programs designed to maximize neuroplasticity are effective for improving memory functions in these patients . recently , transcranial direct - current stimulation ( tdcs ) and repetitive transcranial magnetic stimulation ( rtms ) , noninvasive methods for stimulating the cerebral cortex , have been intensively studied as a treatment for brain injury . while both modalities are used to treat brain injury , tdcs is the preferred method , as it allows simultaneous application of brain stimulation and conventional rehabilitation . concluded that applying tdcs to the brain region improved motor functions and increased motor cortex excitability . recent studies also suggested that tdcs was useful in treating cognitive dysfunction , and improving attention , memory , and executive function [ 7 - 9 ] . however , there are still insufficient data to confirm its effect on the cognitive functions of stroke patients . thus , in this study , we determined the effectiveness of tdcs in cognitive recovery in acute and subacute stroke patients . we selected stroke patients with cognitive impairment and a score of  27 on the korean version of mini mental state exam ( k - mmse ) from patients treated at the department of rehabilitation medicine , asan medical center , from october 1 , 2010 to march 30 , 2012 . the guardians of the patients indicated that the patients had experienced their first stroke , and had no previous history of abnormal cognitive functions . patients who were classified as acute or subacute , within 6 months from their stroke , and who showed no damage to their temporal lobe on magnetic resonance imaging , were selected . subjects were then included when they were willing and available for five treatment sessions per week . patients with apraxia , aphasia , and neglect were excluded , given that these factors may have an impact on the outcome of cognitive function tests . for the safety of patients , we excluded those who had a history of craniectomy or seizure . we used the double - blind method to randomly divide the subjects into three test groups : ( 1 ) the left fronto - temporal anode stimulation ( left - ftas ) group , ( 2 ) the right fronto - temporal anode stimulation ( right - ftas ) group , and ( 3 ) the sham group . patients in each group received tdcs treatment for 30 min , five times a week , for 3 weeks . the treatments were performed using a phoresor ii auto model pm850 ( iomed , salt lake city , ut , usa ) , an fda - approved device , with 5  5 cm sponge electrodes attached to the patient s scalp . the intensity of the current was set at 2 ma , which was confirmed as safe by iyer et al . tdcs anodal electrodes were placed according to the 10 - 20 international eeg system , at t3 for the left - ftas group and at t4 for the right - ftas group . for the sham group , sponge electrodes were attached using the same method as for the left - ftas group , but without any current running . the cognitive rehabilitation program used in the study was comcog ( maxmedica inc . , seoul , korea ) , with the focus on attention and memory improvement for cognitive disorder patients . the subjects were evaluated before the treatment and after completing the 3-week program , using the k - mmse and computerized neurocognitive function tests ( cnt , maxmedica , seoul , korea ) to assess cognitive function , and the korean version of the modified barthel index ( k - mbi ) to assess activities of daily living . the cnt included visual and auditory continuous performance tests ( cpts ) to evaluate continuous concentration on visual and auditory stimuli . the kruskal - wallis test was used to test the homogeneity among the three groups , and the wilcoxon signed - rank test was used to analyze the preand post - treatment data for each test group . the kruskal - wallis test was used to compare the three test groups , and the mann - whitney test was used as the follow - up test . we selected stroke patients with cognitive impairment and a score of  27 on the korean version of mini mental state exam ( k - mmse ) from patients treated at the department of rehabilitation medicine , asan medical center , from october 1 , 2010 to march 30 , 2012 . the guardians of the patients indicated that the patients had experienced their first stroke , and had no previous history of abnormal cognitive functions . patients who were classified as acute or subacute , within 6 months from their stroke , and who showed no damage to their temporal lobe on magnetic resonance imaging , were selected . subjects were then included when they were willing and available for five treatment sessions per week . patients with apraxia , aphasia , and neglect were excluded , given that these factors may have an impact on the outcome of cognitive function tests . for the safety of patients we used the double - blind method to randomly divide the subjects into three test groups : ( 1 ) the left fronto - temporal anode stimulation ( left - ftas ) group , ( 2 ) the right fronto - temporal anode stimulation ( right - ftas ) group , and ( 3 ) the sham group . patients in each group received tdcs treatment for 30 min , five times a week , for 3 weeks . the treatments were performed using a phoresor ii auto model pm850 ( iomed , salt lake city , ut , usa ) , an fda - approved device , with 5  5 cm sponge electrodes attached to the patient s scalp . the intensity of the current was set at 2 ma , which was confirmed as safe by iyer et al . tdcs anodal electrodes were placed according to the 10 - 20 international eeg system , at t3 for the left - ftas group and at t4 for the right - ftas group . for the sham group , sponge electrodes were attached using the same method as for the left - ftas group , but without any current running . the cognitive rehabilitation program used in the study was comcog ( maxmedica inc . , seoul , korea ) , with the focus on attention and memory improvement for cognitive disorder patients . the subjects were evaluated before the treatment and after completing the 3-week program , using the k - mmse and computerized neurocognitive function tests ( cnt , maxmedica , seoul , korea ) to assess cognitive function , and the korean version of the modified barthel index ( k - mbi ) to assess activities of daily living . the cnt included visual and auditory continuous performance tests ( cpts ) to evaluate continuous concentration on visual and auditory stimuli . the kruskal - wallis test was used to test the homogeneity among the three groups , and the wilcoxon signed - rank test was used to analyze the preand post - treatment data for each test group . the kruskal - wallis test was used to compare the three test groups , and the mann - whitney test was used as the follow - up test . the subjects for this study included : ( 1 ) six male and nine female patients in the left - ftas group , ( 2 ) seven male and eight female patients in the right - ftas group , and ( 3 ) seven male and eight female patients in the sham group . the mean age of patients in each group was as follows : ( 1 ) 60.9 12.9 years for the left - ftas group , ( 2 ) 58.915.0 years for the right - ftas group , and ( 3 ) 68.514.6 years for the control group , with no significant differences between the groups . the mean time elapsed from the onset of stroke to the start of the treatment program was : ( 1 ) 42.231.9 days for the left - ftas group , ( 2 ) 38.127.0 days for the right - ftas group , and ( 3 ) 39.529.6 days for the sham group , with no significant differences between the groups ( table 1 ) . the results from post - treatment cnt suggested that the left - ftas group showed significant improvement in the backward digit span test , the verbal learning test - delayed recall , a visual span test , and the k - mmse . all three groups showed significant improvement in k - mbi scores ( table 2 ) . comparison of pre- and post - treatment data for each group suggests that the left - ftas group showed significant improvement in auditory memory , compared to the other groups . however , there were no significant differences between the groups in terms of visual memory and attention . there were no differences between the groups in terms of k - bmi ( table 3 ) . the subjects for this study included : ( 1 ) six male and nine female patients in the left - ftas group , ( 2 ) seven male and eight female patients in the right - ftas group , and ( 3 ) seven male and eight female patients in the sham group . the mean age of patients in each group was as follows : ( 1 ) 60.9 12.9 years for the left - ftas group , ( 2 ) 58.915.0 years for the right - ftas group , and ( 3 ) 68.514.6 years for the control group , with no significant differences between the groups . the mean time elapsed from the onset of stroke to the start of the treatment program was : ( 1 ) 42.231.9 days for the left - ftas group , ( 2 ) 38.127.0 days for the right - ftas group , and ( 3 ) 39.529.6 days for the sham group , with no significant differences between the groups ( table 1 ) . the results from post - treatment cnt suggested that the left - ftas group showed significant improvement in the backward digit span test , the verbal learning test - delayed recall , a visual span test , and the k - mmse . all three groups showed significant improvement in k - mbi scores ( table 2 ) . comparison of pre- and post - treatment data for each group suggests that the left - ftas group showed significant improvement in auditory memory , compared to the other groups . however , there were no significant differences between the groups in terms of visual memory and attention . there were no differences between the groups in terms of k - bmi ( table 3 ) . the objective of this study was to determine the effect of tdcs treatment on the temporal lobe in terms of cognitive recovery of poststroke patients . to date , only a small number of studies have been done on tdcs as a treatment method for cognitive impairment . while montie et al . suggested that cathode stimulation to the left fronto - temporal lobe resulted in improvement in naming in aphasia , other studies concluded that anode stimulation to the left perisylvian region resulted improvement in word memory in healthy patients . boggio et al . also concluded that anode stimulation to the left fronto - temporal lobe helped to improve memory performance in alzheimer disease . the results of our study suggested that anodal stimulation to the left fronto - temporal lobe improved auditory memory , confirming the conclusion of earlier studies , although the treatment did not affect visual memory . cnt test showed that the treatment had been positively effective in all areas , but other three groups , excluding auditory memory , showed no statistical difference . only few studies have been done on the effect of tdcs on cognitive function in stroke patients . while kang et al . suggested that anode stimulation at the dorso - lateral prefrontal cortex improved attention , kim et al .   concluded that rtms on the same region was only effective in treating depression , and there have been two reports on patients with stroke who experienced linguistic improvement , but these studies only involved 10 and 13 patients , respectively . no studies have clearly defined the effects of noninvasive brain stimulation on the cognitive function of stroke patients . studies have discovered that tdcs affects the brain by activating n - methyl - d - aspartic acid ( nmda ) receptors and suppressing the cerebral cortex via gamma - aminobutyric acid ( gaba ) receptors . the effect of tdcs is known to last for approximately 90 minutes , during which the cerebral cortex remains excited , but there are too few studies to be able to draw conclusions on the accumulated effect . this report showed that marked improvements are noted after 3 weeks of tdcs treatment , but the accumulated effect could not be determined because serial cognitive function was not assessed . the findings from this study may have been limited by the small number of patients in each test group . cerebral infarction and hemorrhage were both included and lesions varied largely , so that spontaneous recovery could not be fully excluded . as well as excluding cathode stimulation from the treatment . additionally , the subjects were not tested for depression , which may have affected the outcome . as it has been suggested that depression is prominent among stroke patients and as depression may affect attention and memory , the possibility remains that the study may have included patients with depression , whose depression symptoms were affected by tdcs , which then subsequently resulted in improved cognitive function . furthermore , poststroke apathy can affect cognitive function , but this could not be addressed in this study . since the subjects were evaluated for cognitive performance at 24 hours after completion of the 3-week treatment program , the long - term effect of tdcs treatment remains undetermined . moreover , we excluded patients with abnormal cognitive function based on the guardian s statement , but we had not tested the cognitive function of patients before they suffered their stroke , which may have an impact on the study result . nevertheless , this study confirmed that tdcs is effective in treating poststroke cognitive impairment . we were also able to conclude that stimulation on the temporal lobe , as well as on the prefrontal lobe , as suggested by earlier studies , is helpful in cognitive recovery . the results from this study confirmed that applying tdcs to the left temporal lobe effectively improved auditory memory of patients with poststroke cognitive impairment . we concluded that tdcs can be employed as a treatment sub - protocol in a cognitive treatment program . however , further studies with a larger subject pool and various stimulation methods should be conducted to confirm these findings .