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Background: Rumination, a tendency to focus on negative self-related thoughts, is a central symptom of depression. Studying the self-related aspect of such symptoms is challenging because of the need to distinguish self effects from the emotional content of task stimuli. This study employed an emotionally neutral self-related paradigm to investigate possible altered self-processing in depression and its link to rumination. Methods: People with major depressive disorder (n = 25) and controls (n = 25) underwent task-based electro-encephalogram recording. We studied late event-related potentials, along with low-frequency oscillatory power. We compared electroencephalogram metrics between groups and correlated them with depressive symptoms and reported rumination. Results: Participants with major depressive disorder displayed a difference in late positive potentials across frontocentral electrodes between self-related and non-self-related conditions. We found no such difference in controls. The magnitude of this difference was positively correlated with depressive symptoms and reported rumination. Participants with major depressive disorder also had elevated theta oscillation power at central electrodes in self-related conditions, a finding that we did not see in controls. Limitations: Patients with major depressive disorder were medicated at the time of the study. The group studied was primarily female, so the observed effects may have been sex-specific. Conclusion: Rumination appears to be linked to altered self-related processing in depression, independent of stimuli-related emotional confounds. This connection between self-related processing and depression may point to a self disorder as a core component of depression.

Despite increasing growth of interest in transcranial direct current stimulation (tDCS), its underlying mechanisms are still unclear. With many claims based on the anodal-excitation and cathodal-inhibition dichotomy originally observed in the motor cortex, surprisingly few studies have examined these fundamental polarity-specific effects beyond the motor cortex. The after-effects of tDCS on the visual cortex are of particular interest because of their potential application to vision restoration and migraine treatment. Yet the limited studies revealed conflicting results. Here we investigated whether polarity-specific tDCS effects exist in the visual cortex. In a counterbalanced within-subject crossover design, 20 healthy subjects each completed three sessions of anodal, cathodal and sham tDCS (2 mA for 20 min) applied over the visual cortex. Pattern-reversal visual evoked potentials (VEP) and their habituation slopes were measured at five time-points immediately before, after and every 15 min following the end of tDCS. Compared to sham, we found no significant tDCS induced after-effects on VEP amplitudes or habituation slopes, supported by strong evidence from Bayesian statistics. Neither were there any after-effects of tDCS on EEG power of the frequency of stimulus presentation, theta or alpha band. In conclusion, our results challenge previous findings of robust polarity-dependent after-effects of tDCS over the visual cortex.

The limits of human visual short-term memory (VSTM) have been well documented, and recent neuroscientific studies suggest that VSTM performance is associated with activity in the posterior parietal cortex. Here we show that artificially elevating parietal activity via positively charged electric current through the skull can rapidly and effortlessly improve people's VSTM performance. This artificial improvement, however, comes with an interesting twist: it interacts with people's natural VSTM capability such that low performers who tend to remember less information benefitted from the stimulation, whereas high performers did not. This behavioral dichotomy is explained by event-related potentials around the parietal regions: low performers showed increased waveforms in N2pc and contralateral delay activity (CDA), which implies improvement in attention deployment and memory access in the current paradigm, respectively. Interestingly, these components are found during the presentation of the test array instead of the retention interval, from the parietal sites ipsilateral to the target location, thus suggesting that transcranial direct current stimulation (tDCS) was mainly improving one's ability to suppress no-change distractors located on the irrelevant side of the display during the comparison stage. The high performers, however, did not benefit from tDCS as they showed equally large waveforms in N2pc and CDA, or SPCN (sustained parietal contralateral negativity), before and after the stimulation such that electrical stimulation could not help any further, which also accurately accounts for our behavioral observations. Together, these results suggest that there is indeed a fixed upper limit in VSTM, but the low performers can benefit from neurostimulation to reach that maximum via enhanced comparison processes, and such behavioral improvement can be directly quantified and visualized by the magnitude of its associated electrophysiological waveforms.

The executive control of voluntary action involves not only choosing from a range of possible actions but also the inhibition of responses as circumstances demand. Recent studies have demonstrated that many clinical populations, such as people with attention-deficit hyperactivity disorder, exhibit difficulties in inhibitory control. One prefrontal area that has been particularly associated with inhibitory control is the pre-supplementary motor area (Pre-SMA). Here we applied non-invasive transcranial direct current stimulation (tDCS) over Pre-SMA to test its role in this behavior. tDCS allows for current to be applied in two directions to selectively excite or suppress the neural activity of Pre-SMA. Our results showed that anodal tDCS improved efficiency of inhibitory control. Conversely, cathodal tDCS showed a tendency towards impaired inhibitory control. To our knowledge, this is the first demonstration of non-invasive intervention tDCS altering subjects' inhibitory control. These results further our understanding of the neural bases of inhibitory control and suggest a possible therapeutic intervention method for clinical populations.

Predictability in the visual environment provides a powerful cue for efficient processing of scenes and objects. Recently, studies have suggested that the directionality and magnitude of saccade curvature can be informative as to how the visual system processes predictive information. The present study investigated the role of the right posterior parietal cortex (rPPC) in shaping saccade curvatures in the context of predictive and non‐predictive visual cues. We used an orienting paradigm that incorporated manipulation of target location predictability and delivered transcranial magnetic stimulation (TMS) over rPPC. Participants were presented with either an informative or uninformative cue to upcoming target locations. Our results showed that rPPC TMS generally increased saccade latency and saccade error rates. Intriguingly, rPPC TMS increased curvatures away from the distractor only when the target location was unpredictable and decreased saccadic errors towards the distractor. These effects on curvature and accuracy were not present when the target location was predictable. These results dissociate the strong contingency between saccade latency and saccade curvature and also indicate that rPPC plays an important role in allocating and suppressing attention to distractors when the target demands visual disambiguation. Furthermore, the present study suggests that, like the frontal eye fields, rPPC is critically involved in determining saccade curvature and the generation of saccadic behaviors under conditions of differing target predictability. Hum Brain Mapp, 2011. © 2011 Wiley‐Liss, Inc.

Although both the presupplementary motor area (pre-SMA) and the right inferior frontal gyrus (rIFG) have been demonstrated to be critical for response inhibition, there is still considerable disagreement over the roles they play in the process. In the present study, we investigated the causal relations of the pre-SMA and the rIFG in a conditional stop-signal task by applying offline theta-burst transcranial magnetic stimulation. The task introduced a continue condition, which requires the same motor response as in a go trial but captures attention as in a stop trial. We found great individual differences in the amount of slowing on continue trials. Temporary suppression of pre-SMA activity prolonged the continue RT in participants who slowed little in response to continue trials, whereas disruption of the rIFG did not lead to significant changes in performance irrespective of the degree of slowing. Our results contribute to the understanding of the role of the pre-SMA by providing causal evidence that it is involved in response slowing on continue trials during conditional stopping, and it is likely that its efficiency in updating motor planning and reinitiating an inhibited response was associated with the amount of slowing.

Alpha band activity changes accompanied with the level attentional state, and recent studies suggest that such oscillation is associated with activities in the posterior parietal cortex. Here we show that artificially elevating parietal activity via positively-charged electric current through the skull can rapidly and effortlessly change people's prestimulus alpha power and improve subsequent performance on a visual short-term memory (VSTM) task. This modulation of alpha power and behavioral performance, however, is dependent on people's natural VSTM capability such that only the low performers benefitted from the stimulation, whereas high performers did not. This behavioral dichotomy is accounted by prestimulus alpha powers around the parieto-occipital regions: low performers showed decreased prestimulus alpha power, suggesting improvement in attention deployment in the current paradigm, whereas the high performers did not benefit from tDCS as they showed equally-low prestimulus alpha power before and after the stimulation. Together, these results suggest that prestimulus alpha power, especially in low performers, can be modulated by anodal stimulation and alter subsequent VSTM performance/capacity. Thus, measuring alpha before stimulus onset may be as important as measuring other VSTM-related electrophysiological components such as attentional allocation and memory capacity related components (i.e. N2 posterior-contralateral, N2pc, or contralateral delay activity, CDA). In addition, low VSTM performers perhaps do not suffer not only from poor VSTM capacity, but also from broad attentional mechanisms, and prestimulus alpha may be an useful tool in understanding the nature of individual differences in VSTM.

The interaction between goal‐directed and stimulus‐driven attentional control allows humans to rapidly reorient to relevant objects outside the focus of attention—a phenomenon termed contingent reorienting. Neuroimaging studies have observed activation of the ventral and dorsal attentional networks, but specific involvement of each network remains unclear. The present study aimed to determine whether both networks are critical to the processes of top‐down contingent reorienting. To this end, we combined the contingent attentional capture paradigm with the use of transcranial magnetic stimulation (TMS) to interfere with temporoparietal junction (TPJ; ventral network) and frontal eye field (dorsal network) activity. The results showed that only right TPJ (rTPJ) TMS modulated contingent orienting. Furthermore, this modulation was highly dependent on visual fields: rTPJ TMS increased contingent capture in the left visual field and decreased the effect in the right visual field. These results demonstrate a critical involvement of the ventral network in attentional reorienting and reveal the spatial selectivity within such network. Hum Brain Mapp, 2013. © 2012 Wiley Periodicals, Inc.

The visual system possesses a remarkable ability in learning regularities from the environment. In the case of contextual cuing, predictive visual contexts such as spatial configurations are implicitly learned, retained, and used to facilitate visual search—all without one's subjective awareness and conscious effort. Here we investigated whether implicit learning and its facilitatory effects are sensitive to the statistical property of such implicit knowledge. In other words, are highly probable events learned better than less probable ones even when such learning is implicit? We systematically varied the frequencies of context repetition to alter the degrees of learning. Our results showed that search efficiency increased consistently as contextual probabilities increased. Thus, the visual contexts, along with their probability of occurrences, were both picked up by the visual system. Furthermore, even when the total number of exposures was held constant between each probability, the highest probability still enjoyed a greater cuing effect, suggesting that the temporal aspect of implicit learning is also an important factor to consider in addition to the effect of mere frequency. Together, these findings suggest that implicit learning, although bypassing observers' conscious encoding and retrieval effort, behaves much like explicit learning in the sense that its facilitatory effect also varies as a function of its associative strengths.

In a number comparison task, it is easier to respond faster when the two numbers are further apart than when they are close. This inverse relationship between the size difference and the time to judge such difference is called the numerical distance effect (NDE). In this study we investigated whether attention plays a critical role in the surfacing of NDE and the way we process Arabic numbers. In experiments 1 and 2, with an attentional blink paradigm that was designed to modulate attention, we tested whether a limited or unlimited pool of attentional resources would have an impact on the performance and trend of NDE. The results showed a dissociable effect of attention that changed the overall accuracy but not the trend of NDE. In experiment 3 we examined whether the number priming effect, another phenomenon associated with the distance-related effect, would be affected during the attentional blink period. We found the pattern of number priming effect was not affected by attentional blink. An explanation of the role of attention in number distance processing, as well as how it interacts with Arabic number representation, is discussed.

It is commonly accepted that right posterior parietal cortex (PPC) plays an important role in updating spatial representations, directing visuospatial attention, and planning actions. However, recent studies suggest that right PPC may also be involved in processes that are more closely associated with our visual awareness as its activation level positively correlates with successful conscious change detection (Beck, D.M., Rees, G., Frith, C.D., & Lavie, N. (2001). Neural correlates of change detection and change blindness. Nature Neuroscience, 4, 645–650.). Furthermore, disruption of its activity increases the occurrences of change blindness, thus suggesting a causal role for right PPC in change detection (Beck, D.M., Muggleton, N., Walsh, V., & Lavie, N. (2006). Right parietal cortex plays a critical role in change blindness. Cerebral Cortex, 16, 712–717.). In the context of a 1-shot change detection paradigm, we applied transcranial magnetic stimulation (TMS) during different time intervals to elucidate the temporally precise involvement of PPC in change detection. While subjects attempted to detect changes between two image sets separated by a brief time interval, TMS was applied either during the presentation of picture 1 when subjects were encoding and maintaining information into visual short-term memory, or picture 2 when subjects were retrieving information relating to picture 1 and comparing it to picture 2. Our results show that change blindness occurred more often when TMS was applied during the viewing of picture 1, which implies that right PPC plays a crucial role in the processes of encoding and maintaining information in visual short-term memory. In addition, since our stimuli did not involve changes in spatial locations, our findings also support previous studies suggesting that PPC may be involved in the processes of encoding non-spatial visual information (Todd, J.J. & Marois, R. (2004). Capacity limit of visual short-term memory in human posterior parietal cortex. Nature, 428, 751–754.).