Introduction
Smoking is one of the most important causes of death worldwide, and at the same time, it is challenging to avoid smoking [1]. Executive functioning is a psychological construct that refers to higher-order cognitive processes and self-regulatory processes that coordinate thought and action [2]. A person addicted to tobacco may have a defect in inhibition, one of the executive functions contributing to temptation and relapse [3, 4]. Another higher-order cognitive process is decision-making, where finding and choosing options relies on the decision-makers’ values and preferences [5, 6]. Decision-making problems form the core of impulsivity, a diagnostic criterion for many disorders, including mania, personality disorders, substance use disorders, and attention-deficit/hyperactivity disorder [7, 8]. There are various interventions to promote cognitive processes, including transcranial stimulation. Transcranial alternating electrical stimulation (tACS) is a method that could be effective in improving and promoting inhibition and impulsivity [9, 10]. In alpha-tACS, the frequency of the input current is between 8 and 12 Hz, creating an active mechanism to modulate the descending activities of the cerebral cortex [12, 13]. In the prefrontal region, alpha oscillations are associated with inhibitory processes and goal-directed behavior in healthy individuals and adults with substance abuse problems [14, 15]. This study investigated the effectiveness of alpha-tACS in the dorsolateral prefrontal cortex (DLPFC) on nicotine dependents’ inhibitory control and impulsivity.

Methods
This semi-experimental research design had a pre-test, post-test, and a two-month follow-up design with control and sham groups. All right-handed men between 18 and 40 years in Mashhad with a strong nicotine addiction were included in this study, of whom 30 people were randomly assigned to three groups. Fagerström questionnaire, Barrett impulsivity questionnaire, and go-no-go task were used for the measurements.
The DLPFC region was stimulated with a stimulation current of 2 mA using a double-channel transcranial electrical stimulation device called NEUROSTIM2. The subjects received eight stimulation sessions of 20 minutes at 10 Hz, according to the alpha-tACS protocol.

Results
In this study, the mean and standard deviation of the age of the experimental group were 28.8 and 4.46, respectively, those of the sham group were 30.2 and 4.81, and those of the control group were 27.9 and 5.89 years. According to the statistical analysis, it can be concluded that by controlling the effect of the pre-test, based on group membership, there was a significant relationship in inhibition accuracy (post-test) (P<0.004) and inhibition accuracy (follow-up) (P<0/003). Also, the effect size related to the inhibition accuracy in the post-test and follow-up was 0.368 and 0.378, respectively. Also, post-test impulsivity with a significance level of 0.6 showed that the interventions did not significantly affect changes in this variable.

Discussion 
To examine the effectiveness of alternating electrical current stimulation in the dorsolateral prefrontal region on cognitive components of inhibition and impulsivity in people with severe nicotine dependence, alpha frequency (10 Hz) was used in this study. Similar to previous findings [15, 16], this study revealed that nicotine-dependent people’s inhibition accuracy could be significantly affected by 10 Hz alternating current stimulation. Despite this, it does not significantly affect the speed of inhibition or reduce impulsivity in these people. According to the results, the effectiveness of electrical stimulation on impulsivity was not confirmed. As Bell et al. pointed out, the effects of electrical stimulation may depend on people’s individual and personality characteristics [17]. Thus, the results of this study on the effectiveness of electrical stimulation on impulsivity are doubtful, and we need more studies in this field.

Ethical Considerations
Compliance with ethical guidelines
This study was approved by the Ethics Committee of the Ferdowsi University of Mashhad (Code: IR.UM.REC.1400.366)

Funding
There was no funding from any governmental, private, or non-profit organization.

Authors' contributions
The authors contributed equally to designing, writing, and conducting the research.

Conflicts of interest
The authors declared no conflict of interest.

Acknowledgements
The authors would like to thank the managers and all staff of Astan Mehr Clinic in Mashhad, for their cooperation and  Shakiba Mahmoodi for her guidance on the research findings.

References

1. Fagerström K. The epidemiology of smoking. Drugs. 2002; 62(2):1-9. [Link]
2. Harmsen H, Bischof G, Brooks A, Hohagen F, Rumpf HJ. The relationship between impaired decision-making, sensation seeking and readiness to change in cigarette smokers. Addictive Behaviors. 2006; 31(4):581-92. [DOI:10.1016/j.addbeh.2005.05.038] [PMID]
3. Kim SJ, Chae W, Park WH, Park MH, Park EC, Jang SI. The impact of smoking cessation attempts on stress levels. BMC Public Health. 2019; 19(1):267. [DOI:10.1186/s12889-019-6592-9] [PMID] [PMCID]
4. Kelly ME, Guillot CR, Quinn EN, Lucke HR, Bello MS, Pang RD, et al. Anxiety sensitivity in relation to cigarette smoking and other substance use in African American smokers. Psychology of Addictive Behaviors. 2020; 34(6):669-79. [DOI:10.1037/adb0000573] [PMID] [PMCID]
5. Stubbs B, Vancampfort D, Firth J, Solmi M, Siddiqi N, Smith L, et al. Association between depression and smoking: A global perspective from 48 low-and middle-income countries. Journal of Psychiatric Research. 2018; 103:142-9. [DOI:10.1016/j.jpsychires.2018.05.018] [PMID]
6. Amini R, Sahli M, Ganai S. Cigarette smoking and cognitive function among older adults living in the community. Aging, Neuropsychology and Cognition. 2021; 28(4):616-31. [DOI:10.1080/13825585.2020.1806199] [PMID]
7. Carlson SM, Mandell DJ, Williams L. Executive function and theory of mind: Stability and prediction from ages 2 to 3. Developmental Psychology. 2004; 40(6):1105-22. [DOI:10.1037/0012-1649.40.6.1105] [PMID]
8. Volkow ND, Fowler JS, Wang GJ, Telang F, Logan J, Jayne M, et al. Cognitive control of drug craving inhibits brain reward regions in cocaine abusers. Neuroimage. 2010; 49(3):2536-43. [DOI:10.1016/j.neuroimage.2009.10.088] [PMID] [PMCID]
9. MacLeod CM. The concept of inhibition in cognition. In: Gorfein DS, MacLeod CM, editors. Inhibition in cognition. Washington, D.C: American Psychological Association; 2007. [Link]
10. Schroeder PA, Schwippel T, Wolz I, Svaldi J. Meta-analysis of the effects of transcranial direct current stimulation on inhibitory control. Brain stimulation. 2020; 13(5):1159-67 [DOI:10.1016/j.brs.2020.05.006] [PMID]
11. Fülöp, J. Introduction to decision making methods. Paper presented at: BDEI-3 workshop. November 2005; Washington, USA. [Link]
12. Ekhtiari H, Behzadi A. [Prefrontal cortex, decision making deficits, and assessment instruments (Persian)] Advances in Cognitive Science. 2002; 3(3):64-86. [Link]
13. Ekhtiari H, Rezvanfard M, Mokri A. [Impulsivity and its different assessment tools: A review of view points and conducted researches (Persian)]. Iranian Journal of Psychiatry and Clinical Psychology. 2008; 14(3):247-57. [Link]

14. Ekhtiari H, Behzadi A, Jannati A, Moghimi A. [Delayed discounting procedure and impulsive behaviors: A preliminary study (Persian)]. Advances in Cognitive Sciences. 2003; 5 (2):46-55. [Link]
15. Stahl C, Voss A, Schmitz F, Nuszbaum M, Tüscher O, Lieb K, et al. Behavioral components of impulsivity. Journal of Experimental Psychology: General. 2014; 143(2):850-86. [DOI:10.1037/a0033981] [PMID]
16. Evenden JL. Varieties of impulsivity. Psychopharmacology. 1999; 146(4):348-61. [DOI:10.1007/PL00005481] [PMID]
17. Herrmann CS, Rach S, Neuling T, Strüber D. Transcranial alternating current stimulation: A review of the underlying mechanisms and modulation of cognitive processes. Frontiers in Human Neuroscience. 2013; 7:279. [DOI:10.3389/fnhum.2013.00279] [PMID] [PMCID]
18. Vossen A, Gross J, Thut G. Alpha power increase after transcranial alternating current stimulation at alpha frequency (α-tACS) reflects plastic changes rather than entrainment. Brain Stimulation. 2015; 8(3):499-508. [DOI:10.1016/j.brs.2014.12.004] [PMID] [PMCID]
19. Jensen O, Mazaheri A. Shaping functional architecture by oscillatory alpha activity: Gating by inhibition. Frontiers in Human Neuroscience. 2010; 4:186. [DOI:10.3389/fnhum.2010.00186]
20. Borghini G, Candini M, Filannino C, Hussain M, Walsh V, Romei V, et al. Alpha oscillations are causally linked to inhibitory abilities in ageing. Journal of Neuroscience. 2018; 38(18):4418-29. [DOI:10.1523/JNEUROSCI.1285-17.2018] [PMID] [PMCID]
21. Klimesch W. Alpha-band oscillations, attention, and controlled access to stored information. Trends in Cognitive Sciences. 2012; 16(12):606-17. [DOI:10.1016/j.tics.2012.10.007] [PMID] [PMCID]
22. Knyazev GG. Motivation, emotion, and their inhibitory control mirrored in brain oscillations. Neuroscience & Biobehavioral Reviews. 2007; 31(3):377-95. [DOI:10.1016/j.neubiorev.2006.10.004] [PMID]
23. Pandey AK, Kamarajan C, Manz N, Chorlian DB, Stimus A, Porjesz B. Delta, theta, and alpha event-related oscillations in alcoholics during Go/NoGo task: Neurocognitive deficits in execution, inhibition, and attention processing. Progress in Neuro-Psychopharmacology and Biological Psychiatry. 2016; 65:158-71. [DOI:10.1016/j.pnpbp.2015.10.002] [PMID] [PMCID]
24. Feil J, Sheppard D, Fitzgerald PB, Yücel M, Lubman DI, Bradshaw JL. Addiction, compulsive drug seeking, and the role of frontostriatal mechanisms in regulating inhibitory control. Neuroscience & Biobehavioral Reviews. 2010; 35(2):248-75. [DOI:10.1016/j.neubiorev.2010.03.001] [PMID]
25. Daughters SB, Jennifer YY, Phillips RD, Carelli RM, Fröhlich F. Alpha-tACS effect on inhibitory control and feasibility of administration in community outpatient substance use treatment. Drug and Alcohol Dependence. 2020; 213:108132. [DOI:10.1016/j.drugalcdep.2020.108132] [PMID] [PMCID]
26. Vaghef L, Zahedi M. [The effect of transcranial alternating current stimulation (tACS) on Alpha wave Absolute power of the frontal region in methamphetamine users (Persian)]. Neuropsychology. 2019; 5(17):43-58. [Link]
27. Gilmore CS, Dickmann PJ, Nelson BG, Lamberty GJ, Lim KO. Transcranial Direct Current Stimulation (tDCS) paired with a decision-making task reduces risk-taking in a clinically impulsive sample. Brain Stimulation. 2018; 11(2):302-9. [DOI:10.1016/j.brs.2017.11.011] [PMID]
28. Farokhzadi F, Mohamadi MR, Khosli AK, Akbarfahim M, Beigi NA, Torabi P. Comparing the Effectiveness of the Transcranial Alternating Current Stimulation (TACS) and ritalin on symptoms of attention deficit hyperactivity disorder in 7-14-year-old children. Acta Medica Iranica. 2020. [DOI:10.18502/acta.v58i12.5156]
29. Mauer L, Yang CC, Khalifa N. The use of noninvasive brain stimulation techniques to modulate impulsivity. Health Sciences. 2018; 28(4):51-6. [DOI:10.5200/sm-hs.2018.050]
30. VanVoorhis CW, Morgan BL. Understanding power and rules of thumb for determining sample sizes. Tutorials in Quantitative Methods for Psychology. 2007; 3(2):43-50. [Link]
31. Fagerstrom KO, Schneider NG. Measuring nicotine dependence: A review of the Fagerstrom Tolerance Questionnaire. Journal of Behavioral Medicine. 1989; 12(2):159-82. [Link]
32. Lefaucheur JP, Antal A, Ayache SS, Benninger DH, Brunelin J, Cogiamanian F, et al. Evidence-based guidelines on the therapeutic use of transcranial direct current stimulation (tDCS). Clinical Neurophysiology. 2017; 128(1):56-92. [DOI:10.1016/j.clinph.2016.10.087] [PMID]
33. 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]
34. Heydari GR, Arianpour M, Sharif KB, Ramezan KA, Falah TS, Hosseini M, et al. Tobacco dependency evaluation with fagerstrom test among the entrants of smoking cessation clinic. Tanaffos .2007; 6(4):47-52. [Link]
35. Patton JH, Stanford MS, Barratt ES. Factor structure of the Barratt impulsiveness scale. Journal of Clinical Psychology. 1995; 51(6):768-74. [DOI:10.1002/1097-4679(199511)51:63.0.CO;2-1] [PMID]
36. Javid M, Mohammadi N, Rahimi C. [Psychometric properties of an Iranian version of the Barratt Impulsiveness Scale-11 (BIS-11) (Persian)]. Psychological Methods and Models. 2012; 2(8):23-34. [Link]
37. Georgiou G, Essau CA. Go/No-Go Task. In: Goldstein S, Naglieri JA, editors. Encyclopedia of child behavior and development. Boston: Springer. [DOI:10.1007/978-0-387-79061-9_1267]
38. Gordon B, Caramazza A. Lexical decision for open-and closed-class words: Failure to replicate differential frequency sensitivity. Brain and Language. 1982; 15(1):143-60. [DOI:10.1016/0093-934X(82)90053-0] [PMID]
39. Ghadiri F, Jazayeri A, Ashaeri H, Ghazi Tabatabaei M. [Deficit in executive functioning in patients with schizo-obsessive disorder (Persian)]. Advances in Cognitive Science. 2006; 8(3):11-24. [Link]
40. Antal A, Boros K, Poreisz C, Chaieb L, Terney D, Paulus W. Comparatively weak after-effects of transcranial alternating current stimulation (tACS) on cortical excitability in humans. Brain Stimulation. 2008; 1(2):97-105. [DOI:10.1016/j.brs.2007.10.001] [PMID]
41. Paulus W. Transcranial electrical stimulation (tES-tDCS; tRNS, tACS) methods. Neuropsychological Rehabilitation. 2011; 21(5):602-17. [DOI:10.1080/09602011.2011.557292] [PMID]
42. Bu L, Yu D, Su S, Ma Y, von Deneen KM, Luo L, et al. Functional connectivity abnormalities of brain regions with structural deficits in young adult male smokers. Frontiers in Human Neuroscience. 2016; 10:494. [DOI:10.3389/fnhum.2016.00494]
43. Brody AL, Mandelkern MA, Olmstead RE, Scheibal D, Hahn E, Shiraga S, et al. Gene variants of brain dopamine pathways and smoking-induced dopamine release in the ventral caudate/nucleus accumbens. Archives of General Psychiatry. 2006; 63(7):808-16. [DOI:10.1001/archpsyc.63.7.808] [PMID] [PMCID]
44. Yuan K, Yu D, Cai C, Feng D, Li Y, Bi Y, et al. Frontostriatal circuits, resting state functional connectivity and cognitive control in internet gaming disorder. Addiction Biology. 2017; 22(3):813-22. [DOI:10.1111/adb.12348] [PMID]
45. Tomasi D, Volkow ND. Striatocortical pathway dysfunction in addiction and obesity: Differences and similarities. Critical Reviews in Biochemistry and Molecular Biology. 2013; 48(1):1-19. [DOI:10.3109/10409238.2012.735642] [PMID] [PMCID]
46. Li Y, Yuan K, Bi Y, Guan Y, Cheng J, Zhang Y, et al. Neural correlates of 12-h abstinence-induced craving in young adult smokers: a resting-state study. Brain Imaging and Behavior. 2017; 11(3):677-684. [DOI:10.1007/s11682-016-9544-3] [PMID]
47. Kober H, Mende-Siedlecki P, Kross EF, Weber J, Mischel W, Hart CL, et al. Prefrontal-striatal pathway underlies cognitive regulation of craving. Proceedings of the National Academy of Sciences of the United States of America. 2010; 107(33):14811-6. [DOI:10.1073/pnas.1007779107] [PMID] [PMCID]
48. Engelmann JM, Versace F, Robinson JD, Minnix JA, Lam CY, Cui Y, et al. Neural substrates of smoking cue reactivity: A meta-analysis of fMRI studies. Neuroimage. 2012; 60(1):252-62 [DOI:10.1016/j.neuroimage.2011.12.024] [PMID] [PMCID]
49. Barrett SP, Boileau I, Okker J, Pihl RO, Dagher A. The hedonic response to cigarette smoking is proportional to dopamine release in the human striatum as measured by positron emission tomography and [11C]raclopride. Synapse. 2004; 54(2):65-71. [DOI:10.1002/syn.20066] [PMID]
50. Yuan K, Yu D, Bi Y, Wang R, Li M, Zhang Y, et al. The left dorsolateral prefrontal cortex and caudate pathway: New evidence for cue-induced craving of smokers. Human Brain Mapping. 2017; 38(9):4644-56. [DOI:10.1002/hbm.23690] [PMID] [PMCID]
51. Bindman LJ, Lippold OC, Redfearn JW. The action of brief polarizing currents on the cerebral cortex of the rat (1) during current flow and (2) in the production of long-lasting after-effects. The Journal of physiology. 1964; 172(3):369-82. [DOI:10.1113/jphysiol.1964.sp007425] [PMID] [PMCID]
52. Lapenta OM, Marques LM, Rego GG, Comfort WE, Boggio PS. tDCS in addiction and impulse control disorders. The Journal of ECT. 2018; 34(3):182-92. [DOI:10.1097/YCT.0000000000000541] [PMID]
53. Nitsche MA, Fricke K, Henschke U, Schlitterlau A, Liebetanz D, Lang N, et al. Pharmacological modulation of cortical excitability shifts induced by transcranial direct current stimulation in humans. The Journal of Physiology. 2003; 553(Pt 1):293-301. [DOI:10.1113/jphysiol.2003.049916] [PMID] [PMCID]
54. Stagg CJ, Best JG, Stephenson MC, O'Shea J, Wylezinska M, Kincses ZT, et al. Polarity-sensitive modulation of cortical neurotransmitters by transcranial stimulation. The Journal of Neuroscience. 2009; 29(16):5202-6. [DOI:10.1523/JNEUROSCI.4432-08.2009] [PMID]
55. Mayer JT, Chopard G, Nicolier M, Gabriel D, Masse C, Giustiniani J, et al. Can transcranial direct current stimulation (tDCS) improve impulsivity in healthy and psychiatric adult populations? A systematic review. Progress in Neuro-Psychopharmacology and Biological Psychiatry. 2020; 98:109814. [DOI:10.1016/j.pnpbp.2019.109814] [PMID]