Working Memory Training Combined With Transcranial Magnetic Stimulation in Smokers: 2x2 Factorial Study
Working Memory Training Combined With Transcranial Magnetic Stimulation in Smokers: 2x2 Factorial Study
Smoking remains the leading cause of preventable death in the United States, and current first-line treatments leave the majority of tobacco dependent individuals unable to quit. The inability to quit despite motivation to do so, is thought to result in part, from self-control failure. Working memory (WM) deficits contribute to imbalanced self-control and allow automatic impulses to drive behavior. Thus, WM plays a critical role in addictive behavior, and is particularly relevant to smoking. Indeed, a strong link between WM and smoking has been established in the literature; most notably, degree of WM impairment and deficits in activation in associated brain regions predict time to relapse, and WM moderates the relationship between craving and relapse. Given these insights, researchers have been examining interventions that may target WM including WM training (WMT) and repetitive Transcranial Magnetic Stimulation (rTMS). WMT involves taxing this executive function repeatedly over time and has shown positive preliminary results in improving measures of self-control and reducing consumption of addictive substances. Similarly, rTMS, a non-invasive brain stimulation procedure that stimulates neuronal tissues and increases cortical excitability, has been shown to increase WM capacity and reduce craving and consumption of several addictive substances including nicotine. While these interventions have demonstrated initial promise in affecting addictive behaviors, the magnitude and durability of their effects may be limited. Recently, researchers have posited - but not yet empirically tested - that WMT administered in combination with rTMS may result in an additive or supra-additive effect in treating addictive processes. This is highly significant; the clinical utility of rTMS over current first line treatments may be limited if factors with potential to enhance its effectiveness are not examined. Given these recent advances in the literature, the primary objective of the proposed study is to evaluate the individual and combined effects of Working Memory (WM) training and repetitive Transcranial Magnetic Stimulation (rTMS) on WM performance and smoking behaviors as well as critical mediators of these effects. These aims will be examined in a sample of tobacco dependent adults (N=130) utilizing a 2x2 factorial experimental design including four groups (WMT+rTMS, sham WMT+rTMS, WMT+sham TMS, and sham WMT+sham rTMS) capable of isolating independent and combined effects of WMT and rTMS.
SPECIFIC AIMS Smoking remains the leading cause of preventable death in the U.S. Current first line treatments leave approximately 70% of tobacco dependent individuals unsuccessful in their attempt to quit. Specifically, only 5-30% of those who initiate treatment, including intensive first-line interventions, are able to maintain abstinence for one or more years. The inability to quit despite motivation to do so is thought to result, in part, from self-control failure and can be understood within the framework of dual process models of addiction. Dual process models view vulnerability to tobacco dependence as the relative balance between automatic impulses and control processes orchestrated through the interplay of multiple executive function. Working memory (WM) is an executive function associated with updating information to solve immediate problems, and achieve current goals. WM is a key cognitive process underlying the regulatory control component of dual process models and is involved in the initiation, maintenance, and relapse stages of tobacco dependence. Most notably, deficits in WM performance and activation in associated brain regions predict time to relapse and strong WM has been shown to reduce the effect of craving on the ability to resist smoking. Given this relationship, individuals with tobacco dependence are likely to benefit from interventions that strengthen WM. Recently, several studies have demonstrated that increasing WM capacity through WM training (WMT) is associated with positive outcomes in several populations with substance use or impulse control disorders. Specifically, studies have demonstrated that WMT is associated with decreased: delay discounting in substance users, weight re-gain after a weight loss program, and alcohol use in heavy drinkers.
A second emerging innovation in the treatment of addictions is repetitive Transcranial Magnetic Stimulation (rTMS), a procedure which sends magnetic pulses through the scalp to stimulate neuronal tissue resulting in observed changes in neuronal plasticity and striatal dopamine. rTMS has now demonstrated positive effects in several substance use disorders including nicotine, alcohol, and stimulant dependence. This procedure has been shown to be effective in reducing smoking urges in abstinent as well as satiated smokers and to reduce cigarette consumption. While promising results for this treatment have been demonstrated, the size and durability of the therapeutic effect may be limited. Additionally, the mechanism by which rTMS exerts positive effects on smoking outcomes is unknown. Recently it has been posited that changes in WM performance resulting from rTMS may be the key pathway to its observed effects on smoking related outcomes, and furthermore that WMT administered in close temporal precedence to rTMS may result in an additive or supra-additive effect in treating addictive processes. However, these hypotheses have not been tested to date despite their importance for understanding and improving the clinical impact of these emerging therapeutic modalities for treating addictive behaviors. Interventions with the ability to effectively target self-control processes fill in a critical gap in currently available treatment options.
The primary objective of the proposed study is to evaluate the potential for improved effects and examine mediating pathways of WMT in combination with rTMS on a laboratory based smoking task and neuropsychological measures of WM performance. These aims will be examined in a sample of tobacco dependent adults (N=130) utilizing a 2x2 factorial design including four groups (WMT+rTMS, sham WMT+rTMS, WMT+sham TMS, and sham WMT+sham rTMS) capable of isolating independent and combined effects of WMT and rTMS. The study will include a baseline laboratory assessment, 10 WMT sessions over two weeks, followed by 10 days of WMT immediately preceding and following brain stimulation sessions (10 Hz rTMS, 2000 pulses per session, applied to left DLPFC). Neurocognitive and psychological mediators will be assessed between baseline and final laboratory assessment. Lastly, a follow-up assessment will occur one-month after the final laboratory visit. The proposed study will test the following Specific Aims:
Aim 1: To test the potential for improved effects of combining WMT with rTMS on smoking behaviors as compared to the independent effects of either condition alone. Hypothesis: Single active conditions (WMT+sham rTMS and sham WMT+rTMS) will result in significant increases in time to lapse on an analogue task as compared to the double sham condition (sham WMT+sham rTMS), and the WMT+rTMS condition will result in significant increases in time to lapse as compared to the single active conditions.
Aim 2: To test the potential for improved effects of combining WMT with rTMS on WM performance.
Hypothesis: WMT + rTMS will result in significant increases in WM performance as compared to all other conditions, including the additive increases in conditions outlined in Aim 1.
Aim 3: To test mediating pathways of the effects rTMS on smoking behaviors including changes in craving, mood, and WM performance. Hypothesis: The direct effect of rTMS on smoking outcomes will be mediated by gains in WM performance, and this effect will be largest in the WMT+rTMS condition.
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