The relationship between the superior frontal cortex and alpha oscillation in a flanker task: Simultaneous recording of electroencephalogram (EEG) and near infrared spectroscopy (NIRS).

Activity in the alpha band of the electroencephalogram (EEG) reflects functional inhibition of the cerebral cortex. The superior frontal cortex (SFC) is known to control alpha activity. Based on this relationship between SFC and alpha, we hypothesized that SFC controlled alpha mediates proactive control over interference. In this study, we examined the relationship between SFC and alpha in the flanker task by simultaneously recording EEG and near infrared spectroscopy (NIRS). Forty participants performed a flanker task with occasional (compatible 75%, incompatible 25%) and successive (incompatible 100%) conditions. In the occasional condition, larger SFC activity was related to pre-stimulus alpha enhancement under occipital electrodes. This is consistent with a model in which SFC enhances pre-stimulus alpha activity, leading to proactive control over interference. However, we could not detect a correlation between SFC activity and alpha activity in the successive condition. Active inhibition may have been reduced by a need to continuously inhibit brain regions associated with the irrelevant information. This may have reduced the role of the SFC in controlling alpha activity. Based on these findings, we postulate that there are two cerebral mechanisms of proactive control over interference.

Topographical Subcomponents of Electrical Brain Activity Allow to Identify Semantic Learning.

We investigated the change of event-related brain activity elicited by reading meaningful or meaningless Japanese symbols in 20 healthy German adults. In a learning phase of about 20 min, subjects acquired the meaning of 20 Kanji characters. As control stimuli 20 different Kanji characters were presented. Electrical brain activity was obtained before and after learning, The mean learning performance of all subjects was 92.5% correct responses. EEG was measured simultaneously from 30 channels, artifacts were removed offline, and the data before and after learning were compared. We found five spatial principal components that accounted for 83.8% of the variance. A significant interaction between training time (before/after learning) and stimulus (learning/control) illustrates a significant relation between successful learning and topographical changes of brain activity elicited by Kanji characters. Effects that were induced by learning were seen at short latencies in the order of 100 ms. In addition, we present evidence that differences in the weighted combination of spatial components allow to identify experimental conditions successfully by linear discriminant analysis using topographical ERP data of a single time point. In conclusion, semantic meaning can be aquired rapidly and it is associated with specific changes of ERP components.

Spatial working memory encoding type modulates prefrontal cortical activity.

Spatial working memory (SWM) involves both simultaneous and sequential encoding, but the differences in their neural correlates are unclear. We investigated the differences in prefrontal cortex activity related to these SWM encoding types. We also examined the patterns of brain activity influencing individual visuospatial abilities (VSA). We conducted SWM tasks with two different conditions, sequential and simultaneous encoding, and examined hemodynamic activity in 39 healthy adults using near-infrared spectroscopy. The bilateral dorsolateral prefrontal cortex was activated more strongly in the sequential condition compared with the simultaneous condition. This suggests that prefrontal cortex activity underlying SWM is modulated by the type of encoding. We also found that individuals with high VSA showed weaker activation in the right-dorsolateral prefrontal cortex compared with those with lower VSA during the simultaneous condition. This hypoactivation is thought to reflect neural efficiency in the individuals with high ability. These findings are expected to lead to a better understanding of neural substrates for SWM.

Transition from reactive control to proactive control across conflict adaptation: An sLORETA study.

In a flanker task, behavioral performance is modulated by previous trial compatibility (i.e., conflict adaptation); a longer response time (RT) is found for a compatible stimulus preceded by an incompatible stimulus than by a compatible stimulus, whereas a shorter RT is found for an incompatible stimulus preceded by an incompatible stimulus than by a compatible stimulus. We examined the temporal characteristics of cognitive control across conflict adaptation using prestimulus electroencephalogram oscillatory activity and an event-related potential component, N1. Prestimulus frontal (Fz) and posterior (O1 and O2) alpha1 (7-9 Hz) and alpha2 (10-13 Hz) activities were enhanced in trials preceded by incompatible stimuli more than those preceded by compatible stimuli. Furthermore, there were significant differences of alpha2 current densities between previous trial compatibilities in the superior/medial frontal cortex. We suggested that the modulation of alpha activity by previous trial compatibility was associated with proactive attentional control. N1 amplitude was decreased in trials preceded by incompatible stimuli more than in those preceded by compatible stimuli. N1 current densities in the right inferior frontal cortex were smaller for an incompatible stimulus preceded by an incompatible stimulus than those preceded by a compatible stimulus, suggesting that demands of transient cognitive control induced by an incompatible stimulus were decreased by the proactive control. Moreover, correlational analysis showed that participants with a larger increase in alpha2 activity tended to have a larger decrease in N1 in trials preceded by incompatible stimulus. These findings revealed that the manner of cognitive control for the incompatible stimulus was transited from reactive control to proactive control across conflict adaptation.

Topographic changes in event-related potentials because of learning of meaningful Kanji characters.

Japanese Kanji constitutes meaningful logograms, and its processing shows interhemispheric features. In the present study, human semantic learning of Kanji characters in 18 healthy native German adults was examined. Twenty Kanji characters were presented before and after a learning phase of about 20 min, and the electroencephalographic activity was recorded from 30 electrodes and averaged for each condition. Twenty different Kanji characters served as control stimuli. Successful learning was observed in all participants. The evoked potential maps showed the largest component occurring over occipital areas at latencies between 100 and 130 ms. Significant differences in the field strength (global field power) were observed for this component before and after learning. After learning, the distribution between the left and the right hemispheres significantly changed the negative centroid location from the left to the right hemisphere and from the posterior to the anterior area in each hemisphere. These effects were observed only after successful learning, and our findings suggest that the acquisition of meaning of Kanji characters following intensive short-term learning is related to neurophysiological changes at an early stage of processing. The topographical changes in electrical brain activity reflect plasticity presumably in primary sensory areas during learning of meaningful materials that is related to top-down information processing.

Cross-cultural comparison of ADHD symptoms among Japanese and US university students.

Problems related to attention, hyperactivity, and impulsiveness are known to impact social, academic, and vocational success. When the problems begin in childhood and lead to impaired functioning, the syndrome is identified as attention-deficit/hyperactivity disorder (ADHD). Symptoms of the syndrome persist into adolescence and adulthood for many individuals, but less is known about characteristics of adults compared to children, especially adults attending university. Furthermore, there is little cross-national and cross-cultural research. This study compared DSM-IV-TR ADHD symptoms of US university students (N=271) to Japanese peers (N=712). Comparison of group means on a DSM-IV-TR-based checklist indicated that Japanese students reported more problems with inattention (and overall ADHD symptoms) but not hyperactive-impulsive symptoms. Although differences were statistically significant, effect sizes were small, indicating that for practical purposes, the students reported similar levels of symptoms. Japanese students reported higher rates of meeting or exceeding symptom counts that comprise diagnostic criteria for ADHD, but differences were quite small. Using DSM-IV-TR thresholds, 5.70% of US students and 6.27% of Japanese students reported enough symptoms to meet the cut-off for inattentive, hyperactive/impulsive, or combined type during childhood. With regard to recent problems, 2.66% of US students and 4.52% of Japanese students reported enough symptoms to meet the cut-off for one of the three subtypes. Comparisons using other methods of calculating rates are also provided. This research adds to the limited knowledge of ADHD symptoms in university students across countries and it supports the view that ADHD is not merely a cultural construct. This study is among the first to identify potential attention problems in Japanese university students.

Reduced prefrontal hemodynamic response in children with ADHD during the Go/NoGo task: a NIRS study.

The current study examined the hemodynamic response during the Go/NoGo task in children with/without attention deficit/hyperactivity disorder (ADHD). Using near-infrared spectroscopy, oxy-Hb and deoxy-Hb concentration changes in the frontal areas were compared during the conditions with/without inhibitory demand. Compared with typically developing children, children with ADHD showed significantly reduced activation during the conditions with inhibitory demand (NoGo-condition) in the frontal areas. However, no significant differences in activation during the conditions without inhibitory demand (Go-condition) were found between the two groups. The current findings revealed that children with ADHD exhibit an altered hemodynamic response specifically during response inhibition, but not during response execution, and suggested the clinical usefulness of near-infrared spectroscopy for the evaluation of response inhibition deficits in children with ADHD.

Probability effects of response and stimulus on error-related negativity.

Recent theories suggest that error is detected based on the process generating an appropriate response from the presented stimulus, including stimulus processing (e.g. encoding and evaluation) and activation of the appropriate response. This study examines the effects of stimulus processing (related to stimulus deviance) and activation of the appropriate response on error-related negativity (ERN/Ne). We administered a three-choice-response task, in which participants were asked to respond with a finger corresponding to the presented stimulus. The stimuli consisted of three letters, one of those was presented with low probability (20%) and the others were presented with high probability (40%) each. Using error-correcting responses, we estimated the degree to which the appropriate response is activated. The error-correcting response was faster on the high-probability rather than the low-probability trials, suggesting that the appropriate response was more active immediately after an error on the high-probability trials. However, the ERN/Ne amplitude was not larger on the high-probability as compared with the low-probability trials. Moreover, we found an increase in ERN/Ne amplitude on the low-probability trials, in which N1 was enhanced with regard to stimulus deviance. These results suggested that ERN/Ne is associated with stimulus processing rather than activation of the appropriate response.

Cross-national invariance of Attention-Deficit/Hyperactivity Disorder factors in Japanese and U.S. university students.

Prior research with children generally supports the two-dimensional structure of Attention-Deficit/Hyperactivity Disorder (ADHD; inattentive and hyperactive/impulsive factors) of the DSM-IV-TR as well as invariance of the two-factor structure across nations and cultures. Research with adults supports either a two-factor or three-factor structure depending on reporting source and breadth of symptoms assessed. However, research with adults is limited and there are few studies addressing cross-national invariance in adults. The purposes of this study were to (1) assess relative fit of two- versus three-factor solutions for self-report of childhood and recent ADHD symptoms in adults; and (2) further establish cross-national invariance of factors. Participants included 271 U.S. and 712 Japanese university students who completed a rating scale assessing the 18 DSM-IV-TR ADHD symptoms. Confirmatory factor analysis using Mplus (Version 6) and the mean and variance-adjusted weighted least squares (WLSMV) procedure showed invariance of two- and three-factor models across U.S. and Japanese samples. The two- and three-factor models showed similar fit indices. Neither a two-factor or three-factor model was clearly superior. The two-factor model was favored, however, because it is more parsimonious and consistent with current theory, and because of high correlations between hyperactive and impulsive factors in the three-factor models. Invariance across nations is consistent with previous studies and supports ADHD as a universally valid syndrome rather than a cultural construct. These results add to the limited knowledge of assessment of ADHD symptoms in Japan.