This review of 12 RCTs in 467 participants finds a statistically-significant medium effect of ABMT on anxiety with a relatively large fail-safe calculation. Thus, a significant beneficial effect still would be present even if 54 unpublished studies had produced null results. Given the early stage of research on ABMT, no head-to-head trials compare ABMT with established interventions. Indeed, the effect of ABMT on anxiety appears smaller than for SSRIs and CBT, which typically produce large effects (6
In one sense, a difference in effect-size magnitude between ABMT and SSRIs or CBT may seem unsurprising. ABMT is a limited, focused intervention, in terms of clinician involvement. As a result, contributions to efficacy from staff contact, other non-specific factors, and expectancy are likely to be small in ABMT. In addition, SSRIs or CBT trials exclusively focused on clinical populations whereas the ABMT RCTs analyzed in the present report are mostly of nonclinical or subclinical populations. When isolating the ABMT RCTs conducted in clinical settings and with clinical samples (20
), the effect sizes are comparable to those observed for CBT and SSRIs. Moreover, CBT often has been compared to conditions, such as wait-list control, which are poorly matched to the active treatment, in terms of non-specific treatment factors and expectancy (9
). The studies of ABMT typically involve tight experimental control in which all participants are exposed to the exact same cue stimuli, number of training/placebo trials, number of treatment sessions, and overall procedures. As a result, while the current data suggest that ABMT is probably inferior to SSRIs and CBT, they also suggest a possible applicability of ABMT to the overall management of anxiety.
The current analysis also showed a large effect size of ABMT in reducing threat-related attention bias, indicating that overall, the attention training protocols are effective. The correlation between effect sizes on attention bias change scores and on anxiety change scores was also large, suggesting that ABMT reduces anxiety via effects on attention bias. However, more studies are needed to reveal the mechanism underlying the effects of ABMT on anxiety.
Benefits of ABMT appear to emerge under various experimental conditions, in diverse samples, assessed with a variety of clinical response measures. This conclusion is supported by the analyses of heterogeneity in response (see ). ABMT produced a greater effect on trait than state anxiety measures. This suggests that ABMT may target the more enduring aspects of anxiety. Similarly, procedural factors also predicted response: the nature of stimuli and their location moderated outcome. Specifically, studies that used a Top-Bottom stimulus presentation achieved better effects than those using a Side-by-Side presentation, as did studies that used words relative to pictures. Interestingly, extent of training moderated effects on attention bias but not anxiety symptoms. More work is needed to characterize the nature and robustness of these influences. In particular, given the relatively small number of studies, negative findings should be viewed particularly cautiously. However, research on ABMT as an evidence-based therapy remains immature, and well-controlled clinical RCTs are costly. As a result, future research may be shaped by results from these moderator analyses.
These data may shape therapeutics. If future RCTs yield positive results, ABMT and similar computer-based training regimens may be viable stand-alone treatments in patients who do not have access to CBT or SSRI treatment, or who are either are unwilling or incapable of undergoing such treatment. ABMT may also serve as a viable alternative for treatment of children with anxiety disorders. However, only three of the reviewed studies of ABMT were conducted in anxiety-disorder patients, and none examined children. While biased allocation of attention represents an important correlate of anxiety, it is only one of many cognitive biases (44
); differences in attention bias between healthy and anxious subjects are only moderate in size (11
); and a significant group of anxiety-disorder patients exhibit no biasing of attention. Adopting a personalized medicine approach, future ABMT studies might consider the magnitude and nature of patients’ biases before prescribing training protocols [see also (34
Future studies could also test the utility of ABMT as an adjunct to SSRIs or CBT, both of which show strong effects but fail to produce remission in many patients. While SSRIs or CBT target a broad array of biases, ABMT provides a more focused, targeted approach that might augment the impact of the other treatments on attention bias. Similarly, the finding in the current meta-analysis that verbal stimuli appear more powerful than pictures when attempting alter anxiety may implicate personalized information as a target for training. This, in turn, may provide targets for other computerized approaches, focused on various other biases to be altered by novel treatments in anxiety. Taken together, such views resonate with those emerging from neuroscience, emphasizing delineation of the unique substrates that underlie distinct forms of learning (45
). In fact, beyond the clinical relevance of the findings reported in the current meta-analysis, the findings reported here also may usefully shape theoretical views on anxiety disorder pathophysiology and treatment.
In anxious patients, therapeutic goal-based learning may be achieved through deliberative teaching, verbal instruction, and guided experiences with threats. Each of these learning tasks is targeted by CBT. ABMT, on the other hand, represents a focused attempt to teach patients one specific skill, attention control. Available neuroscience literature suggests that attention control abilities reflect competencies in specific, dedicated neural architecture. Thus, brain imaging studies on individual differences in anxiety implicate perturbed subcortical engagement to threats presented relatively rapidly or outside the focus of attention (12
). Prior work on other forms of learning, such as motor skill development, suggest that abilities moderated by subcortical pathways, such as habitual responses, may be most efficiently shaped through repeated exposures to specific, focused tasks, as occurs in ABMT, even without verbal instruction or deliberative teaching (8
). On the other hand, much like in motor learning (46
), attention control also is likely to be shaped by multiple, convergent neural pathways. In the case of ABMT, available research implicates lateral expanses of prefrontal cortex in the control of attention (8
). Consistent with these observational data, the only imaging study to examine the effect of ABMT found that training altered lateral frontal regions in healthy individuals, in tandem with attention biases (35
). This suggests that both frontal-cortical and subcortical circuitry may be targeted by ABMT.
For various reasons, the review generates only tentative conclusions. Perhaps most importantly, the review is based in a relatively small number of studies, containing relatively few patients with anxiety disorders, performed by a limited number of research groups. Moreover, the available data, as illustrated by an asymmetrical funnel plot and variable effect sizes across the 12 experiments, suggest heterogeneity in treatment response and possibly some degree of outliers, though findings remained significant, albeit weakened, when the three findings with the strongest results were removed. Such patterns are not unusual in early research on promising novel treatments. Given the promising nature of these early results, the next few years may herald a growing series of RCTs evaluating ABMT as a treatment for anxiety disorders.
In closing, this meta-analysis indicates that ABMT shows promise as a novel treatment for anxiety disorders. These results emerge from an initial, small series of RCTs demonstrating greater benefits on anxiety from ABMT, relative to control-training regimens. Reflecting a translational approach, the ideas for ABMT emerge from a melding of cognitive and neuroscience theory over the past 20 years. These ideas generate novel procedures that may enhance currently available treatments focused on perturbed cognition. Given the role for perturbed cognition in many common, impairing psychiatric disorders, such an approach in the anxiety disorders may serve as a guide for developing other novel, learning based therapies in a range of conditions.