Introduction
The world population is aging, and aging is now considered a global concern [1]. Aging is associated with a decline in cognitive function [2]. Alzheimer’s disease and mild cognitive impairment (MCI) are major challenges in geriatric health care in the 21st century [3]. MCI is an intermediate phase between the cognitive decline expected in the normal aging period and dementia, which can cause problems related to memory, language, thinking, and judgment, and these deficits are more than normal aging-related changes. Problems related to MCI in the elderly can affect mental health and the overall quality of life of affected people. This study aims to investigate the effectiveness of cognitive rehabilitation and transcranial direct current stimulation (tDCS) on the quality of life and subjective vitality of the elderly with MCI.

Methods
This is a quasi-experimental study with a pre-test/post-test/follow-up design. The study population consists of all older adults with MCI referred to Payambaran Hospital in Tehran, Iran in 2020-2021. Using a convenience sampling and based on Cochran’s formula, 40 eligible people were selected. They were randomly divided into two groups of intervention (n=20) and control (n=20). The data collection tools were the subjective vitality scale of Ryan and Fredrick and the LEIPAD quality of life questionnaire.
For the intervention group, 12 sessions of the cognitive rehabilitation protocol and tDCS were provided every other day, 3 times a week. Each session was 50 minutes, first 20 minutes of tDCS and then 30 minutes of cognitive rehabilitation. For cognitive rehabilitation, the Captain’s Log MindPower Builder was used, which is designed to improve cognitive abilities. In this software, both basic and higher cognitive functions are improved and promoted at the same time. In the tDCS protocol, the 4×4 anode electrode was placed over the F3 region and the 6×4 cathode electrode was placed on the right shoulder. Stimulation was performed by the researcher (corresponding author) using the Oasis Pro device made in Canada. 

Results
The mean scores of the quality of life and subjective vitality in the intervention group were changed in the post-test compared to the pre-test scores, but no change was observed in the control group. Levene’s test was used to check the homogeneity of variances between the control and intervention groups. The results for the quality of life in the pre-test (F(1, 38)=0.039, P>0.05), post-test (F(1, 38)=0.101, P>0.05), follow-up (F(1, 38) =0.216, P>0.05) and for subjective vitality variable in pre-test (F(1, 38)=0.088, P>0.05), post-test (F(1, 38)=0.144, P>0.05) and follow-up (F(1, 38)=0.001, P>0.05) was not significant. Therefore, the homogeneity of variances was confirmed. 
Repeated measures analysis of variance was performed to examine the data. The results of the within-subject effects test showed that the F values related to the interaction effects of group and time for all variables were significant (P<0.01). Benferroni’s post hoc test was used to compare the mean scores during the measurement stages. Based on the results, in the intervention group, the difference between the mean scores in the pre-test, post-test, and follow-up phases was significant (P<0.05). The mean scores of quality of life and subjective vitality in the post-test and follow-up phases increased significantly compared to the pre-test phase, which indicates the effectiveness of the intervention. The difference between the post-test and follow-up scores was not significant (P>0.05), which indicates the stability of the treatment effects over time. In the control group, the difference between three time points was not significant (P>0.05).

Conclusion
Based on the findings, the combination of cognitive rehabilitation with tDCS had a significant effect on the quality of life and subjective vitality of the elderly with MCI. However, the effect was stable over time. As a promising strategy, tDCS can affect people’s quality of life by increasing the brain’s functional connectivity [49]. MCI is associated with a continuous decrease in a person’s cognitive abilities. Cognitive rehabilitation is a method based on training specific brain functions such as memory and attention to prevent or slow down cognitive decline. By improving brain function and functional connectivity, and consequently, cognitive abilities, the mental health of people can also be affected and improved. The present study shows convincing evidence that non-pharmacological, non-invasive methods such as cognitive rehabilitation along with tDCS are useful in improving the subjective vitality of the elderly.

Ethical Considerations
Compliance with ethical guidelines
This study was approved by the Ethics Committee of Shahid Beheshti University of Medical Sciences (Code: IR.SBU.REC.1400.261).

Funding
This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors

Authors' contributions
The authors contributed equally to preparing this article.

Conflicts of interest
The authors declared no conflict of interest. 

1. Prince MJ, Wu F, Guo Y, Gutierrez Robledo LM, O'Donnell M, Sullivan R, et al.The burden of disease in older people and implications for health policy and practice. The Lancet. 2015; 385(9967):549-62. [DOI:10.1016/S0140-6736(14)61347-7] [PMID]
2. Rao D, Luo X, Tang M, Shen Y, Huang R, Yu J, et al. Prevalence of mild cognitive impairment and its subtypes in community-dwelling residents aged 65 years or older in Guangzhou, China. Archives of Gerontology and Geriatrics. 2018; 75:70-5. [DOI:10.1016/j.archger.2017.11.003] [PMID]
3. Crimmins EM, Saito Y, Kim JK. Change in cognitively healthy and cognitively impaired life expectancy in the United States: 2000-2010. SSM-Population Health. 2016; 2:793-7. [DOI:10.1016/j.ssmph.2016.10.007] [PMID] [PMCID]
4. Calero M. Effects of environmental enrichment and training across life span in cognition. In: Fernández-Ballesteros R, Benetos  A, Robine J, editors. The Cambridge handbook of successful aging. Cambridge: Cambridge University Press; 2019. [DOI:10.1017/9781316677018.020]
5. Klimova B, Maresova P. Computer-based training programs for older people with mild cognitive impairment and/or dementia. Frontiers in Human Neuroscience. 2017; 11:262. [DOI:10.3389/fnhum.2017.00262] [PMID] [PMCID]
6. Livingston G, Huntley J, Sommerlad A, Ames D, Ballard C, Banerjee S, et al. Dementia prevention, intervention, and care: 2020 report of the Lancet Commission. The Lancet. 2020; 396(10248):413-46. [DOI:10.1016/S0140-6736(20)30367-6] [PMID]
7. Hu C, Yu D, Sun X, Zhang M, Wang L, Qin H. The prevalence and progression of mild cognitive impairment among clinic and community populations: A systematic review and meta-analysis. International Psychogeriatrics. 2017; 29(10):1595-608. [DOI:10.1017/S1041610217000473] [PMID]
8. Lima AP, Castilhos R, Chaves ML. The use of the clinical dementia rating scale sum of boxes scores in detecting and staging cognitive impairment/dementia in Brazilian patients with low educational attainment. Alzheimer Disease & Associated Disorders. 2017; 31(4):322-7. [DOI:10.1097/WAD.0000000000000205] [PMID]
9. Pachana NA, Laidlaw K. The Oxford handbook of clinical geropsychology. Oxford: Oxford Academic; 2015. [DOI:10.1093/oxfordhb/9780199663170.001.0001]
10. Ryan RM, Deci EL. Self-determination theory and the facilitation of intrinsic motivation, social development, and well-being. American Psychologist. 2000, 55(1):68-78. [DOI:10.1037/0003-066X.55.1.68] [PMID]
11. Kawabata M, Yamazaki F, Guo DW, Chatzisarantis NL. Advancement of the Subjective Vitality Scale: Examination of alternative measurement models for Japanese and Singaporeans. Scandinavian Journal of Medicine & Science in Sports. 2017; 27(12):1793-800. [DOI:10.1111/sms.12760] [PMID]
12. Ugur E, Kaya Ç, Özçelik B. Subjective vitality mediates the relationship between respect toward partner and subjective happiness on teachers. Universal Journal of Educational Research. 2019; 7(1):126-32. [DOI:10.13189/ujer.2019.070117]

13. Arslan G, Yıldırım M, Aytaç M. Subjective vitality and loneliness explain how coronavirus anxiety increases rumination among college students. Death Studies. 2022; 46(5):1042-51. [DOI:10.1080/07481187.2020.1824204] [PMID]
14. Windsor TD, Burns RA, Byles JE. Age, physical functioning, and affect in midlife and older adulthood. Journals of Gerontology Series B: Psychological Sciences and Social Sciences. 2013; 68(3):395-9. [DOI:10.1093/geronb/gbs088] [PMID]
15. Daig I, Lehmann A. Verfahren zur Messung der Lebensqualität. Zeitschrift für medizinische Psychologie. 2007; 16(1-2):5-23. [Link]
16. Stites SD, Karlawish J, Harkins K, Rubright JD, Wolk D. Awareness of mild cognitive impairment and mild Alzheimer’s disease dementia diagnoses associated with lower self-ratings of quality of life in older adults. Journals of Gerontology Series B: Psychological Sciences and Social Sciences. 2017; 72(6):974-85. [DOI:10.1093/geronb/gbx100] [PMID] [PMCID]
17. Hussenoeder FS, Conrad I, Roehr S, Fuchs A, Pentzek M, Bickel H, et al. Mild cognitive impairment and quality of life in the oldest old: A closer look. Quality of Life Research. 2020; 29(6):1675-83. [DOI:10.1007/s11136-020-02425-5] [PMID] [PMCID]
18. Song D, Yu DS, Li PW, He G, Sun Q. Correlates of health-related quality of life among Chinese older adults with mild cognitive impairment. Clinical Interventions in Aging. 2019; 14:2205-12.[DOI:10.2147/CIA.S227767] [PMID] [PMCID]
19. Orinstein AJ, Stevens MC. Brain activity in predominantly-inattentive subtype attention-deficit/hyperactivity disorder during an auditory oddball attention task. Psychiatry Research:Neuroimaging. 2014; 223(2):121-8. [DOI:10.1016/j.pscychresns.2014.05.012] [PMID] [PMCID]
20. 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]
21. Bahar-Fuchs A, Webb S, Bartsch L, Clare L, Rebok G, Cherbuin N, et al. Tailored and adaptive computerized cognitive training in older adults at risk for dementia: A randomized controlled trial. Journal of Alzheimer’s Disease. 2017; 60(3):889-911. [DOI:10.3233/JAD-170404] [PMID]
22. Ge S, Zhu Z, Wu B, McConnell ES. Technology-based cognitive training and rehabilitation interventions for individuals with mild cognitive impairment: A systematic review. BMC Geriatrics. 2018; 18(1):213. [DOI:10.1186/s12877-018-0893-1] [PMID] [PMCID]
23. Coffman BA, Trumbo MC, Clark VP. Enhancement of object detection with transcranial direct current stimulation is associated with increased attention. BMC Neuroscience. 2012; 13:108. [DOI:10.1186/1471-2202-13-108] [PMID] [PMCID]
24. Satorres E, Meléndez JC, Pitarque A, Real E, Abella M, Escudero J. Enhancing immediate memory, potential learning, and working memory with transcranial direct current stimulation in healthy older adults. International Journal of Environmental Research and Public Health. 2022; 19(19):12716.‏ [DOI:10.21203/rs.3.rs-1163460/v1] [PMID]
25. Gomes MA, Akiba HT, Gomes JS, Trevizol AP, de Lacerda ALT, Dias ÁM. Transcranial direct current stimulation (tDCS) in elderly with mild cognitive impairment: A pilot study. Dementia & Neuropsychologia. 2019; 13(2):187-95. [DOI:10.1590/1980-57642018dn13-020007] [PMID] [PMCID]
26. Gonzalez PC, Fong KNK, Brown T. Transcranial direct current stimulation as an adjunct to cognitive training for older adults with mild cognitive impairment: A randomized controlled trial. Annals of Physical and Rehabilitation Medicine. 2021; 64(5):101536. ‏ [DOI:10.1016/j.rehab.2021.101536] [PMID]
27. Kirova AM, Bays RB, Lagalwar S. Working memory and executive function decline across normal aging, mild cognitive impairment, and Alzheimer’s disease. BioMed Research International. 2015; 2015:748212. [DOI:10.1155/2015/748212] [PMID] [PMCID]
28. Cosmo C, Ferreira C, Miranda JG, do Rosário RS, Baptista AF, Montoya P, et al. Spreading effect of tDCS in individuals with attention-deficit/hyperactivity disorder as shown by functional cortical networks: A randomized, double-blind, sham-controlled trial. Frontiers in Psychiatry. 2015; 6:111. [DOI:10.3389/fpsyt.2015.00111] [PMID] [PMCID]
29. Biundo R, Weis L, Fiorenzato E, Gentile G, Giglio M, Schifano R, et al. Double-blind randomized trial of t-DCS versus sham in Parkinson patients with mild cognitive impairment receiving cognitive training. Brain Stimulation: Basic, Translational, and Clinical Research in Neuromodulation. 2015; 8(6):1223-5. [DOI:10.1016/j.brs.2015.07.043] [PMID]
30. 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. 2021; 22(4):47-59. [Link]
31. Park SH, Koh EJ, Choi HY, Ko MH. A double-blind, sham-controlled, pilot study to assess the effects of the concomitant use of transcranial direct current stimulation with the computer assisted cognitive rehabilitation to the prefrontal cortex on cognitive functions in patients with stroke. Journal of Korean Neurosurgical Society. 2013; 54(6):484-8. [DOI:10.3340/jkns.2013.54.6.484] [PMID] [PMCID]
32. Miniussi C, Harris JA, Ruzzoli M. Modelling non-invasive brain stimulation in cognitive neuroscience. Neuroscience and Biobehavioral Reviews. 2013; 37(8):1702-12. [DOI:10.1016/j.neubiorev.2013.06.014] [PMID]
33. Birba A, Ibáñez A, Sedeño L, Ferrari J, García AM, Zimerman M. Non-invasive brain stimulation: A new strategy in mild cognitive impairment?. Frontiers in Aging Neuroscience. 2017; 9:16. [DOI:10.3389/fnagi.2017.00016]
34. Cruz Gonzalez P, Fong KNK, Brown T. The effects of transcranial direct current stimulation on the cognitive functions in older adults with mild cognitive impairment: A pilot study. Behavioural Neurology. 2018; 2018:5971385. [DOI:10.1155/2018/5971385] [PMID] [PMCID]
35. Kotradyová K. The psychosocial aspects of the genesis of depression in old age and the possibilities of using group psychotherapy. Kontakt. 2016; 18(3):e194-202. [DOI:10.1016/j.kontakt.2016.07.002]
36. Syaifullah AH, Shiino A, Kitahara H, Ito R, Ishida M, Tanigaki K. Machine learning for diagnosis of AD and prediction of MCI progression from brain MRI using brain anatomical analysis using diffeomorphic deformation. Frontiers in Neurology. 2021; 11:576029. [DOI:10.3389/fneur.2020.576029] [PMID] [PMCID]
37. Mirza SS, Ikram MA, Bos D, Mihaescu R, Hofman A, Tiemeier H. Mild cognitive impairment and risk of depression and anxiety: A population-based study. Alzheimer’s & Dementia. 2017; 13(2):130-9. [DOI:10.1016/j.jalz.2016.06.2361] [PMID]
38. Ryan RM, Frederick C. On energy, personality, and health: Subjective vitality as a dynamic reflection of well‐being. Journal of Personality. 1997; 65(3):529-65. [DOI:10.1111/j.1467-6494.1997.tb00326.x] [PMID]
39. Milyavskaya M, Koestner R. Psychological needs, motivation, and well-being: A test of self-determination theory across multiple domains. Personality and Individual Differences. 2011; 50(3):387-91. ‏ [DOI:10.1016/j.paid.2010.10.029]
40. Tanhaye Reshvanloo F, Keramati R, Kareshki H, Torkamani M. [Factor structure and gender invariance of subjective vitality scale in students (Persian)]. Journal of Applied Psychological Research. 2018; 9(3):1-14. [DOI:10.22059/JAPR.2018.69108]
41. De Leo D, Diekstra RF, Lonnqvist J, Trabucchi M, Cleiren MH, Frisoni GB, et al. LEIPAD, an internationally applicable instrument to assess quality of life in the elderly. Behavioral Medicine. 1998; 24(1):17-27. [DOI:10.1080/08964289809596377] [PMID]
42. Sajadi H, Biglarian A. [Quality of life among elderly women in Kahrizak charity Foundation, Tehran, Iran (Persian)]. Payesh. 2007; 6(2):105-8. [Link]
43. Hosseini SF, Bahramipour Isfahani M. [Effectiveness of Captain’s log cognitive rehabilitation program on visual working memory, attention skills, processing speed and fluid reasoning of students ages 8-12 years in Isfahan (Persian)]. Neuropsychology. 2021; 7(1):37-58.‏ [Link]
44. Adenzato M, Manenti R, Enrici I, Gobbi E, Brambilla M, Alberici A, et al. Transcranial direct current stimulation enhances theory of mind in Parkinson’s disease patients with mild cognitive impairment: A randomized, double-blind, sham-controlled study. Translational Neurodegeneration. 2019; 8:1 [DOI:10.1186/s40035-018-0141-9] [PMID] [PMCID]
45. Lawrence BJ, Gasson N, Johnson AR, Booth L, Loftus AM. Cognitive training and transcranial direct current stimulation for mild cognitive impairment in Parkinson’s disease: A randomized controlled trial. Parkinson’s Disease. 2018; 2018:4318475.[DOI:10.1155/2018/4318475] [PMID] [PMCID]
46. An TG, Kim SH, Kim KU. Effect of transcranial direct current stimulation of stroke patients on depression and quality of life. Journal of Physical Therapy Science. 2017; 29(3):505-7. [DOI:10.1589/jpts.29.505] [PMID] [PMCID]
47. Hyer L, Scott C, Atkinson MM, Mullen CM, Lee A, Johnson A, et al. Cognitive training program to improve working memory in older adults with MCI. Clinical Gerontologist. 2016; 39(5):410-27. [DOI:10.1080/07317115.2015.1120257] [PMID]
48. Zare H, Sharifi AA, Hashamdar S. Effect of computerized cognitive rehabilitation on improvement of mild cognitive impairment and working memory capacity. Journal of Psychology. 2019; 4(92). [Link]
49. Indahlastari A, Hardcastle C, Albizu A, Alvarez-Alvarado S, Boutzoukas EM, Evangelista ND, et al. A systematic review and meta-analysis of transcranial direct current stimulation to remediate age-related cognitive decline in healthy older adults. Neuropsychiatric Disease and Treatment. 2021; 17:971-90.  [DOI:10.2147/NDT.S259499] [PMID] [PMCID]
50. Sanjuán M, Navarro E, Calero MD. Effectiveness of cognitive interventions in older adults: A review. European Journal of Investigation in Health, Psychology and Education. 2020; 10(3):876-98. [DOI:10.3390/ejihpe10030063] [PMID] [PMCID]
51. Chandler MJ, Parks AC, Marsiske M, Rotblatt LJ, Smith GE. Everyday impact of cognitive interventions in mild cognitive impairment: a systematic review and meta-analysis. Neuropsychology Review. 2016; 26(3):225-51. [DOI:10.1007/s11065-016-9330-4] [PMID] [PMCID]
52. Casemiro FG, Rodrigues IA, Dias JC, Alves LC, Inouye K, Gratão AC. Impact of cognitive stimulation on depression, anxiety, cognition and functional capacity among adults and elderly participants of an open university for senior citizens. Revista Brasileira de Geriatria e Gerontologia. 2016; 19:683-94. [DOI:10.1590/1809-98232016019.150214]
53. Gil-González I, Pérez-San-Gregorio MÁ, Conrad R, Martín-Rodríguez A. Predicting improvement of quality of life and mental health over 18-months in multiple sclerosis patients. Multiple Sclerosis and Related Disorders. 2021; 53:103093. [DOI:10.1016/j.msard.2021.103093] [PMID]
54. Montejo P, Montenegro M, Fernandez MA, Maestu F. Memory complaints in the elderly: Quality of life and daily living activities. A population based study. Archives of Gerontology and Geriatrics. 2012; 54(2):298-304. [DOI:10.1016/j.archger.2011.05.021] [PMID]
55. Trigg R, Watts S, Jones R, Tod A. Predictors of quality of life ratings from persons with dementia: The role of insight. International Journal of Geriatric Psychiatry. 2011; 26(1):83-91. [DOI:10.1002/gps.2494] [PMID]
56. Mhaoláin AM, Gallagher D, Crosby L, Ryan D, Lacey L, Coen RF, et al. Frailty and quality of life for people with Alzheimer’s dementia and mild cognitive impairment. American Journal of Alzheimer’s Disease & Other Dementias®. 2012; 27(1):48-54. [DOI:10.1177/1533317511435661] [PMID]
57. Park S, Park K, Hancox J, Castaneda-Gameros D, Koo KC.  Physical activity and subjective vitality in older adults from community-and assisted-living settings. Asian Nursing Research. 2019; 13(5):313-7. [DOI:10.1016/j.anr.2019.11.004] [PMID]
58. Solaimani Khashab A, Ghamari Kivi H, Fathi D. Effectiveness of cognitive-behavioral therapy on spiritual well-being and emotional intelligence of the elderly mourners. Iranian Journal of Psychiatry. 2017; 12(2):93-9. [PMID]
59. Ferreira G, Silva-Filho E, de Oliveira A, de Lucena C, Lopes J, Pegado R. Transcranial direct current stimulation improves quality of life and physical fitness in diabetic polyneuropathy: A pilot double blind randomized controlled trial. Journal of Diabetes & Metabolic Disorders. 2020; 19(1):327-35. [DOI:10.1007/s40200-020-00513-4] [PMID] [PMCID]
60. Belleville S, Gilbert B, Fontaine F, Gagnon L, Ménard E, Gauthier S. Improvement of episodic memory in persons with mild cognitive impairment and healthy older adults: Evidence from a cognitive intervention program. Dementia and Geriatric Cognitive Disorders. 2006; 22(5-6):486-99. [DOI:10.1159/000096316] [PMID]
61. Fernandez E, Bergado Rosado JA, Rodriguez Perez D, Salazar Santana S, Torres Aguilar M, Bringas ML. Effectiveness of a computer-based training program of attention and memory in patients with acquired brain damage. Behavioral Sciences. 2017; 8(1):4. [DOI:10.3390/bs8010004] [PMID] [PMCID]
62. Sharma RK, Singh B, Sharma S. Efficacy of cognitive behaviour therapy and quality of life in the amputees. The International Journal of Indian Psychology. 2016; 3(3):151-66. [DOI:10.25215/0303.130]
63. Langa KM, Levine DA. The diagnosis and management of mild cognitive impairment: A clinical review. JAMA. 2014; 312(23):2551-61. [DOI:10.1001/jama.2014.13806] [PMID] [PMCID] l