Introduction
The Alzheimer’s Association has announced that every 3 seconds, one person in the world is diagnosed with dementia [1]. Globally, 70% of people who suffer from dementia have Alzheimer’s disease (AD) [2].This disease starts with short-term memory disorder and as the disease progresses, it also affects other cognitive functions [5]. For the treatment of AD, various non-invasive brain stimulation techniques are used. One of these methods is the transcranial direct current stimulation (tDCS) [17]. Another method is the cognitive intervention of the brain, which is called cognitive rehabilitation [27]. The purpose of this study is to compare the effectiveness of short-term cognitive rehabilitation program and tDCS on language skills and attention in the elderly with mild AD.

Methods
This is a quasi-experimental study with a pre-test/posttest/follow-up design. Participants were 60 Iranian older adults over 65 years of age with mild AD visited the neurology clinics in 2022. They were selected using a convenience sampling method, and were randomly (using a lottery method) divided into two experimental groups of cognitive rehabilitation and tDCS and one control group (20 in each group). The tDCS was applied at 10 sessions of 20 minutes, once a week. The short-term cognitive rehabilitation program was provided at 9 sessions of 90 minutes, once a week. One week after (post-test) and one month after (follow-up) the end of the intervention, the assessments were conducted in all groups using Addenbrooke’s cognitive examination-revised (ACE-R). To assess the effectiveness of the two methods, repeated measures analysis of variance was used.

Results
Regarding the attention variable, there was a significant difference between the three evaluation times except for the component of attention/concentration. The effect sizes for the two components of orientation and memory were 0.288 and 0.200, respectively. Although the means of orientation and memory changed with time, but the interaction effect of time and group was not significant. This means that there was no significant difference in the means between three different times or between three different groups at each time. 
Regarding the variable of language skills, the results of showed that except for the two components of writing and naming, there was no significant difference between the three evaluation times. The effect sizes for the two components of writing and naming were 0.291 and 0.306, respectively. The interaction effect of time and group was significant only for the two components of writing and naming. The result of post hoc test showed that both short-term cognitive rehabilitation and tDCS had a similar significant effect on the writing domain at the post-test phase. Contrary to the tDCS method, which had significant effect in the follow-up phase, the short-term cognitive rehabilitation had no sustained effect after one month. Regarding the naming domain, only the tDCS method had a significant effect at the post-phase. 
In the treatment group, there was a significant difference in writing scores between the pre-test and post-test stages (P<0.01); however, no significant difference was observed between the post-test and follow-up phases (P>0.01). Regarding the naming scores, there was a significant difference between the pre-test and post-test stages and between the pre-test and follow-up phases (P<0.01); however, no significant difference was observed in the mean score between the post-test and follow-up phases (P>0.01).

Conclusion
Both methods of tDCS and short-term cognitive rehabilitation can improve writing and naming domains of language skills in the elderly with mild AD. The short-term cognitive rehabilitation does not have sustained effect on writing ability of older adults after one month, but it has sustained effect on their naming ability. Regarding the attention variable, except for the attention/concentration domain, there was a significant difference between the three evaluation times.

Ethical Considerations
Compliance with ethical guidelines
This study was approved by the Ethics Committee of University of Mohaghegh Ardabili (Code: IR.UMA.REC.1401.008). Prior to the study, the study objectives and methods were explained to the participants and signed a written informed consent from.

Funding
This article was extracted from the PhD dissertation of Arezoo Mojarrad, approved by the Department of Counseling, Faculty of Educational Sciences and Psychology, University of Mohaghegh Ardabili.

Authors' contributions
Conceptualization: Arezoo Mojarrad, and Esmaeil Sadri Damirchi; Methodology: Ali Shi Khalaslami, Ali Rezaii Sharif, and Arezoo Mojarrad; Validation: Ali Rezaei Sharif; Analysis: Ali Sheikhal-Eslami; Investigations: Arezoo Mojarrad; Resource: Arezoo Mojarrad, and Vahid Abbasi; Initial draft preparation: Arezoo Mojarrad; Review, editing and final approval: Esmaeil Sadri Damirchi; Visualization: Vahid Abbasi; Supervision: 
 Esmaeil Sadri Damirchi, and Vahid Abbasi; Project administration: Ismail Sadri Demirchi.

Conflicts of interest
The authors declared no conflict of interest.


References

1. Alzheimr’e Disease International. World Alzheimer Report: Attitudes to dementia. London: Alzheimr’e Disease International; 2019. [Link]
2. Sosa-Ortiz AL, Acosta-Castillo I, Prince MJ. Epidemiology of dementias and Alzheimer’s disease. Archives of Medical Research. 2012; 43(8):600-8. [DOI:10.1016/j.arcmed.2012.11.003] [PMID]
3. Jafarjalal E, Haghani H, Carpenter B, Sajady M, Farahaninia M. Knowledge about Alzheimer’s disease among individuals going to neighborhood houses in northern regions of Tehran, Iran. Arvand Journal of Health & Medical Sciences. 2017; 2(2):59-69. [Link]
4. Association AS. Alzheimer’s disease facts and figures. Alzheimer’s & Dementia. 2017; 13(4):325-73. [DOI:10.1016/j.jalz.2017.02.001]
5. Falcão DV, Teodoro ML, Bucher-Maluschke JS. Family cohesion: A study on caregiving daughters of parents with Alzheimer’s disease. Interpersona: An International Journal on Personal Relationships. 2016; 10:61-74. [DOI:10.5964/ijpr.v10isupp1.244]
6. Fisher GG, Chacon M, Chaffee DS. Theories of cognitive aging and work. In: Baltes BB, Rudolph CW, Zacher H, editors. Work across the lifespan. Massachusetts: Academic Press; 2019. [DOI:10.1016/B978-0-12-812756-8.00002-5]
7. Qavamifar A, Hassanpour H. [Identifying functions affecting the cognitive performance of strategic managers (Persian)]. Journal of Human Resource Studies. 2021; 11(2):50-70. [Link]
8. Penner IK, Kappos L. Retraining attention in MS. Journal of The Neurological Sciences. 2006; 245(1-2):147-51. [DOI:10.1016/j.jns.2005.07.015] [PMID]
9. Seidman LJ, Biederman J, Monuteaux MC, Doyle AE, Faraone SV. Learning disabilities and executive dysfunction in boys with attention-deficit/hyperactivity disorder. Neuropsychology. 2001; 15(4):544-56. [DOI:10.1037/0894-4105.15.4.544] [PMID]
10. Nezakat-Alhosseini M. [The effect of mild dehydration on selective and sustained attention (Persian)]. Sport Psychology Studies. 2017; 6(19):1-17. [DOI:10.22089/spsyj.2017.2309.1246]
11. Faizi A. [The effectiveness of the combination of computerized cognitive rehabilitation and motor skill training on working memory, sustained attention and planning ability in the elderly (Persian)][MA thesis). Unpublished. Semnan: Semnan University; 2018.
12. Anushko AE. Multi-domain predictors of trajectories of language development in early childhood [PhD dissertation]. New York: University of Fordham ; 2008. [Link]
13. Steinmetz JN. Cognitional arguments the immateriality of mind[ PhD dissertation]. Washington: Catholic University of America; 2008. [Link]
14. Schirmer CR, Fontoura DR, Nunes ML. Distúrbios da aquisição da linguagem e da aprendizagem. Jornal de Pediatria. 2004; 80:95-103. [DOI:10.1590/S0021-75572004000300012]
15. Flöel A, Suttorp W, Kohl O, Kürten J, Lohmann H, Breitenstein C, et al. Non-invasive brain stimulation improves object-location learning in the elderly. Neurobiology of Aging. 2012; 33(8):1682-9. [DOI:10.1016/j.neurobiolaging.2011.05.007] [PMID]
16. Kuo MF, Paulus W, Nitsche MA. Therapeutic effects of non-invasive brain stimulation with direct currents (tDCS) in neuropsychiatric diseases. Neuroimage. 2014, 85 Pt 3:948-60. [DOI:10.1016/j.neuroimage.2013.05.117] [PMID]
17. Nitsche MA, Liebetanz D, Antal A, Lang N, Tergau F, Paulus W. Modulation of cortical excitability by weak direct current stimulation-technical, safety and functional aspects. Supplements to Clinical Neurophysiology. 2003, 56:255-76. [DOI:10.1016/S1567-424X(09)70230-2] [PMID]
18. Nitsche MA, Paulus W. Sustained excitability elevations induced by transcranial DC motor cortex stimulation in humans. Neurology. 2001, 57(10):1899-901. [DOI:10.1212/WNL.57.10.1899] [PMID]
19. Reti IM, Chang AD. Introduction to brain stimulation. In: Reti IM, editor. Brain stimulation: Methodologies and interventions. New Jersey: Wiley-Blackwell; 2015. [DOI:10.1002/9781118568323.ch1]
20. Akbari F. [The effectiveness of transcranial Direct Current Stimulation of the brain (tDCS) on reducing depressive symptoms among people with Depressive Disorder (Persian)]. International Journal of Behavioral Sciences. 2015; 9(1):95-101. [Link]
21. Lai HY. Application of Transcranial Direct Current Stimulation (tDCS) to enhance attention, visuo-motor coordination and executive function in older adults with mild cognitive impairment. Alzheimer's & Dementia. 2020; 16(6):e036427. [DOI:10.1002/alz.036427]
22. Wang CS, Cheng KS, Tang CH, Hou NT, Chien PF, Huang YC. 314-Effects of Transcranial Direct Current Stimulation (tDCS) on cognitive function in Alzheimer’s Dementia. International Psychogeriatrics. 2020; 32(S1):72. [DOI:10.1017/S1041610220002148]
23. Pancholi U, Vijay D. Quantification of electric field strength of tDCS in alzheimer’s and mild cognitive impairment patients. International Journal of Advanced Technology and Engineering Exploration. 2021; 8(82):1168-82. [DOI:10.19101/IJATEE.2021.874444]
24. Inagawa T, Yokoi Y, Yamada Y, Miyagawa N, Otsuka T, Yasuma N, et al. Effects of multisession transcranial direct current stimulation as an augmentation to cognitive tasks in patients with neurocognitive disorders in Japan: A study protocol for a randomised controlled trial. BMJ Open. 2020, 10(12):e037654. [DOI:10.1136/bmjopen-2020-037654] [PMID] [PMCID]
25. Cruz Gonzalez P, Fong KNK, Chung RCK, Ting KH, Law LLF, Brown T. Can transcranial direct-current stimulation alone or combined with cognitive training be used as a clinical intervention to improve cognitive functioning in persons with mild cognitive impairment and dementia? A systematic review and meta-analysis. Frontiers in Human Neuroscience. 2018; 12:416. [DOI:10.3389/fnhum.2018.00416] [PMID] [PMCID]
26. Dedoncker J, Brunoni AR, Baeken C, Vanderhasselt MA. A systematic review and meta-analysis of the effects of transcranial direct current stimulation (tDCS) over the dorsolateral prefrontal cortex in healthy and neuropsychiatric samples: Influence of stimulation parameters. Brain Stimulation. 2016; 9(4):501-17. [DOI:10.1016/j.brs.2016.04.006] [PMID]
27. Bergo E, Lombardi G, Pambuku A, Della Puppa A, Bellu L, D'Avella D, et al. Cognitive rehabilitation in patients with gliomas and other brain tumors: State of the art. BioMed Research International. 2016; 2016:3041824. [DOI:10.1155/2016/3041824] [PMID] [PMCID]
28. Mattioli F, Stampatori C, Scarpazza C, Parrinello G, Capra R. Persistence of the effects of attention and executive functions intensive rehabilitation in relapsing remitting multiple sclerosis. Multiple Sclerosis and Related Disorders. 2012, 1(4):168-73. [DOI:10.1016/j.msard.2012.06.004] [PMID]
29. Mirzaei M, Hasani Abharian P, Meschi F, Sabet M. [Effectiveness of combination therapy of computerized cognitive rehabilitation and transcranial direct current stimulation on the cognitive function in elderlies (Persian)]. EBNESINA. 2020; 22(4):47-59. [DOI:10.22034/22.4.47]
30. Kurth S, Wojtasik V, Lekeu F, Quittre A, Olivier C, Godichard V, et al. Efficacy of cognitive rehabilitation versus usual treatment at home in patients with early stages of alzheimer disease. Journal of Geriatric Psychiatry and Neurology. 2021; 34(3):209-15. [DOI:10.1177/0891988720924721] [PMID]
31. Irazoki E, Contreras-Somoza LM, Toribio-Guzmán JM, Jenaro-Río C, van der Roest H, Franco-Martín MA. Technologies for cognitive training and cognitive rehabilitation for people with mild cognitive impairment and dementia. A systematic review. Frontiers in Psychology. 2020; 11:648. [DOI:10.3389/fpsyg.2020.00648] [PMID] [PMCID]
32. Huntley JD, Hampshire A, Bor D, Owen A, Howard RJ. Adaptive working memory strategy training in early Alzheimer’s disease: Randomised controlled trial. The British Journal of Psychiatry. 2017; 210(1):61-6. [DOI:10.1192/bjp.bp.116.182048] [PMID] [PMCID]
33. Lambert MA, Bickel H, Prince M, Fratiglioni L, Von Strauss E, Frydecka D, et al. Estimating the burden of early onset dementia; systematic review of disease prevalence. European Journal of Neurology. 2014; 21(4):563-9. [DOI:10.1111/ene.12325] [PMID]
34. Abdollahimohammad A, Firouzkouhi M. [Sample size estimation in randomized clinical trials (RCTs) (Persian)]. Journal of Diabetes Nursing. 2019; 7 (1):737-9. [Link]
35. Luria AR. Restoration of function after brain injury. New York: Macmillan; 1963. [Link]
36. Mathuranath PS, Nestor PJ, Berrios GE, Rakowicz W, Hodges JR. A brief cognitive test battery to differentiate Alzheimer’s disease and frontotemporal dementia. Neurology. 2000; 55(11):1613-20. [DOI:10.1212/01.wnl.0000434309.85312.19] [PMID]
37. Mioshi E, Dawson K, Mitchell J, Arnold R, Hodges JR. The Addenbrooke’s Cognitive Examination Revised (ACE‐R): A brief cognitive test battery for dementia screening. International Journal of Geriatric Psychiatry. 2006; 21(11):1078-85. [DOI:10.1002/gps.1610] [PMID]
38. Hsieh S, Schubert S, Hoon C, Mioshi E, Hodges JR. Validation of the addenbrooke’s cognitive examination III in frontotemporal dementia and Alzheimer’s disease. Dementia and Geriatric Cognitive Disorders. 2013; 36(3-4):242-50. [DOI:10.1159/000351671] [PMID]
39. Pouretemad HR, Khatibi A, Ganjavi A, Shams J, Zarei M. Validation of Addenbrooke’s cognitive examination (ACE) in a Persian-speaking population. Dementia and Geriatric Cognitive Disorders. 2009; 28(4):343-7. [DOI:10.1159/000252772] [PMID]
40. Abdi H. The greenhouse-geisser correction. Encyclopedia of Research Design. 2010; 1(1):544-8. [Link]
41. Rezapour Jaghargh M, Mandegari Najafabadi M, Kavousipour. S. [The effect of computer games on level of attention in children with attention deficit hyperactivity disorder (Persian)]. Journal of Research in Rehabilitation Sciences. 2014; 10(4):528-38. [Link]
42. Siahjani L, Zare H, Oraki M, Sharifolhoseyni M. [Compiling a cognitive rehabilitation program and its effects on cognitive functions and life satisfaction in the Iranian elderly with mild Alzheimer’s (Persian)]. Neuropsychology. 2021, 6(23):70-98. [DOI:10.30473/clpsy.2020.51920.1524]
43. Sohlberg MM, Mateer CA. Cognitive rehabilitation: An integrative neuropsychological approach. New York: Guilford Press; 2001. [Link]
44. Das N, Spence JS, Aslan S, Vanneste S, Mudar R, Rackley A, et al. Cognitive training and transcranial direct current stimulation in mild cognitive impairment: A randomized pilot trial. Frontiers in Neuroscience. 2019; 13:307. [DOI:10.3389/fnins.2019.00307] [PMID] [PMCID]
45. Fregni F, El-Hagrassy MM, Pacheco-Barrios K, Carvalho S, Leite J, Simis M, et al. Evidence-based guidelines and secondary meta-analysis for the use of transcranial direct current stimulation in neurological and psychiatric disorders. International Journal of Neuropsychopharmacology. 2021; 24(4):256-313. [DOI:10.1093/ijnp/pyaa051] [PMID] [PMCID]
46. Benussi A, Dell'Era V, Cosseddu M, Cantoni V, Cotelli MS, Cotelli M, et al. Transcranial stimulation in frontotemporal dementia: a randomized, double‐blind, sham‐controlled trial. Alzheimer’s & Dementia: Translational Research & Clinical Interventions. 2020; 6(1):e12033. [DOI:10.1002/trc2.12033] [PMID] [PMCID]
47. Pellicciari MC, Miniussi C. Transcranial direct current stimulation in neurodegenerative disorders. The Journal of ECT. 2018; 34(3):193-202. [DOI:10.1097/YCT.0000000000000539] [PMID]
48. Amini M, Dowlatshahi B, Dadkhah A, Lotfi M. [The effect of memory and attention rehabilitation to decrease of memory deficits in older adults with alzheimer disease (Persian)]. Salmand: Iranian Journal of Ageing. 2013; 8(3):53-62. [Link]