Targeting neuropsychological mechanisms in anxiety - an evaluation of transcranial direct current stimulation and attention training in the 7.5% carbon dioxide experimental model of anxiety

Abstract

Neuropsychological models of anxiety suggest that deficits in prefrontal mechanisms underlie maladaptive biases in attention control and hypervigilance to threat. Current first line treatments do not target those mechanisms (e.g. Bar-Haim, 2010). Transcranial direct current stimulation (tDCS) - a non-invasive brain stimulation modality which alters cortical tissue excitability - and Attentional Bias Modification Training (AMBT) - a novel computer-based attention training protocol which implicitly modifies biased attentional patterns - both offer a way to target those mechanisms, and may represent alternative treatment options for patients with mood and anxiety disorders. Numerous studies suggest beneficial effects of tDCS in the treatment of depression (e.g. Brunoni et al, 2012; Fregni et al, 2006; Fregni et al, 2006b; Boggio et al, 2008a) but despite high comorbidity and shared neurocognitive mechanisms between depression and anxiety (e.g. Hirschfeld et al, 2001; Lamers et al, 2011) no studies to date have evaluated potential beneficial effects of tDCS in anxiety.

Experimental models of anxiety (for example the 7.5% CO? model), which temporarily mimic anxiety symptoms in healthy samples, can provide a useful way of investigating the effectiveness of such novel treatments. This thesis presents a series of experiments that use the 7.5% CO? model to evaluate the therapeutic potential of treatments that target attentional mechanisms. Study One (Chapter 2) investigates the effects of tDCS on attention network function in healthy (unchallenged) humans and provides evidence that 20 minutes of left anodal tDCS of the DLPFC results in superior executive function as compared to sham stimulation, in the absence of mood changes. Study Two (Chapter 3) investigates the effects of tDCS on the response to the CO? challenge and attention control in an emotional antisaccade task. Results suggest that tDCS administered immediately prior to 20 mins of a 7.5% CO? inhalation reduces erroneous eye-movements towards threat images relative to neutral images relative to sham. Study Three (Chapter 4) similarly investigates the effects of ABMT on the response to the CO? challenge and antisaccade performance: contrary to predictions and previous evidence, the ABMT protocol did not train an attentional bias, did not alter response to CO? challenge, nor affect antisaccade performance.

The goal of the thesis extended beyond evaluation of potential treatments for anxiety, and for the first time, in a within-participants design examined changes in cortical brain activation during the 7.5% CO? challenge vs. inhalation of air (Study Four, Chapter 5). A different activation pattern between the CO? and air inhalations was observed, characterised by significantly lower alpha activity in parietal and occipital regions, paired with significantly higher gamma and theta activity across all sites, suggesting that the CO? model induces brain activation changes broadly consistent with those observed in clinical anxiety. The thesis ends with a general discussion, and considers implications of the findings for future research.

More information

Identifiers

ORCID for Matthew Garner: orcid.org/0000-0001-9481-2226

Catalogue record

Export record