Psychology ETDs

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Transcranial direct current stimulation (tDCS) has been shown to enhance many cognitive and motor functions, and has been used in many areas, including rehabilitation of speech after stroke, cognitive enhancement, and treatment of mental illness. Our lab has demonstrated that, paired with training, anodal tDCS over electrode site F10 as well as cathodal tDCS over site T5 both increased the ability to detect hidden objects in a complex visual environment in a discovery learning paradigm. Stimulation of F10 has further been shown to enhance perceptual sensitivity selectively, without a change to response bias, and this effect was further enhanced when images presented during training were repeated in a post-training, post-stimulation test (Clark et al., 2012; Coffman et al., 2012; Falcone et al., 2012). Furthermore, this increased ability to detect hidden objects persisted for at least 24 hours Falcone et al., 2012). It has also been shown to increase measures of attention, using the Attention Network Task (ANT; Fan, 2002). Specifically, alerting network scores were increased in participants receiving active anode F10 stimulation compared to sham. Since both F10 anode as well as T5 cathode stimulation both resulted in increased learning the object detection task, potential additive effects were inferred, and an F10 anode/T5 cathode electrode montage was investigated. Surprisingly, this montage had an effect of about half of the other two montages (F10 anode/shoulder, T5 cathode/shoulder). Finite element current modeling studies were conducted to investigate more precisely where in the brain the electricity is traveling during these different stimulation protocols. Results suggested that both cephalic/extra-cephalic electrode placements exhibited far-field effects in subcortical areas, bilateral temporal poles, as well as in the cerebellum, albeit with opposite polarities. During F10 anode/shoulder cathode stimulation, a negative electrical field effect was seen in the cerebellum. During T5 cathode/shoulder anode stimulation, the opposite was true: there was a positive field effect in the cerebellum. However, the montage with a bi-cephalic placement showed no such effect in the cerebellum. Based on these modeling data, the difficulty of reaching subcortical areas with tDCS, and the evidence that the cerebellum is not only involved in motor behavior, but cognition as well, the cerebellum was chosen for direct stimulation with tDCS and was hypothesized to be contributing to the learning and attention effects reported in previous studies. Thirty-six participants received either anodal, cathodal, or sham stimulation of the medial posterior cerebellum during training to detect hidden objects in a complex visual environment. Measures of learning, signal detection, and interactions with stimulus type were investigated. Regression models were also built to investigate the contribution of each electrode placement in the two different montages. Measures of attention assessed with the ANT were also investigated. To our surprise, neither anodal nor cathodal stimulation of the cerebellum led to an increase in learning compared to sham stimulation. Furthermore, no effects were observed between groups on signal detection measures, nor was there an effect of group on stimulus type, all of which had previously been reported with F10 stimulation. Likewise, neither anode nor cathode stimulation led to an improvement on measures of attention compared to sham. The conclusion is that the cerebellum does not appear to be involved in the network contributing to learning and performing the object detection task. Although there were no direct effects of anodal or cathodal tDCS of the cerebellum on learning or attention, this study is an important step in elucidating the network involved in the robust finding of increased ability to detect hidden objects after administration of tDCS paired with training, as it rules out one potential contributor.

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First Advisor

Clark, Vincent P.

First Committee Member (Chair)

Witkiewitz, Katie

Second Committee Member

Ruthruff, Eric




Cerebellum, Transcranial Direct Current Stimulation, Learning, Signal Detection, Neuromodulation

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