Manipulating the neural network responsible for temporal selective attention using brain stimulation

2236 

Abstract Submission 

Monday, June 27 & Tuesday, June 28 

Matthew Tang¹, David Badcock², James Enns³, Troy Visser⁴

¹University of Queensland, St Lucia, Australia, ²School of Psychology, The University of Western Australia,, Crawley, Australia, ³Department of Psychology, University of British Columbia, West Mall, Canada, ⁴School of Psychology, The University of Western Australia, Crawley, Australia

There is more incoming information than the sensory systems can process. Mechanisms of attention are therefore needed to select the most behaviorally relevant inputs, while filtering or suppressing irrelevant information. A pertinent issue for input selection is how long attention needs to be allocated to each object before the next item can be processed and what neural mechanisms support this process. Temporal attention can be measured using dual-target rapid serial visual presentation (RSVP) tasks. These tasks result in a ubiquitous failure to detect the second item when it appears within 500 ms of the first, known as the attentional blink (AB). The fronto-partial cognitive control network has been implicated in such temporal attention tasks (Gross, et al. 2004, Husain and Rorden, 2003). Two main regions of this network are thought to support separate aspects of successful target detection. The posterior parietal cortex (PPC) is theorized to select relevant targets from distractors and is guided by bottom-up saliency (Buschman and Miller, 2007), whereas the dorsolateral pre-frontal cortex (DLPFC) controls the top-down allocation of attentional resources (Botvinick, et al., 2001). We used transcranial direct current stimulation (tDCS) to experimentally alter the functioning of each of these areas in turn, to determine their role in different aspects of temporal selective attention.

tDCS differently modulates cortical excitability depending on the polarity, with anodal increasing, and cathodal decreasing, excitability (Nitsche and Paulus, 2001). Four separate groups of participants (20 in each group) received either anodal or cathodal tDCS stimulation at 2 mA over PPC or DLPFC and another group (n = 20) received sham (null) stimulation. Temporal selective attention was quantified using a standard dual-target RSVP task. To measure participants' ability to select targets from distractors, the distractors were made to have high or low structural similarity to the targets. Each participant first completed one block of trials before stimulation to provide a baseline level for the task. Stimulation was then applied for 30 mins while participants completed another four blocks of trials. The difference in performance between pre- and during stimulation blocks was used to quantify the effect of tDCS on the AB.

Anodal stimulation over PPC impaired detection during the AB window in trials where the targets and distractors were highly similar, with no corresponding effect of cathodal stimulation over this area. However, both anodal and cathodal stimulation over DLPFC improved target detection under both low and high target-distractor similarity.

Our results provide one of the first causal tests of the proposal temporal selection network, and show how nodes within this network support successful target detection during rapid visual presentations. The results suggest that increasing the excitability of PPC severely impairs the ability to ignore similar, but task-irrelevant, items. This is consistent with results showing this area is involved in attention guided by stimulus' saliency (Buschman and Miller, 2007). Increased excitability likely caused attention to be allocated to the highly similar distractors, interfering with target selection, whereas the ability to ignore highly dissimilar distractors was maintained. Conversely, applying either stimulation polarity over DLPFC reduced the magnitude of the AB, possibly because it alleviated some of the negative effects of excessive cognitive control on the AB. Excessive control exacerbates the AB because attention is allocated to both targets and distractors causing these items to be selected for extended processing (Olivers and Nieuwenhuis, 2006, Biggs, et al., 2006). Applying either polarity of tDCS over DLPFC may reduce excessive cognitive control, which, in turn, reduces the AB.

Non-invasive Electrical/tDCS/tACS/tRNS ²

Attention: Visual ¹

Cognition

Consciousness

Vision

Other - Transcranial direct current stimulation (tDCS)