Naoyuki Osaka

Functional roles of the cingulo-frontal network in performance on working memory

We examined the relationship between brain activities and task performance on working memory. A large-scale study was initially administered to identify good and poor performers using the operation span and reading span tasks. On the basis of those span scores, we divided 20 consenting participants into high- and low-span groups. In an fMRI study, the participants performed verification of arithmetic problems and retention of target words either concurrently or separately. The behavioral results showed that performance was better in the high-span group than in the low-span group under a dual-task condition, but not under two single-task conditions. The anterior cingulate cortex (ACC), left prefrontal cortex (PFC), left inferior frontal cortex, and bilateral parietal cortex were primarily activated for both span groups. We found that signal changes in the ACC were greater in the high-span group than in the low-span group under the dual-task condition, but not under the single-task conditions. Structural equation modeling indicated that an estimate of effective connectivity from the ACC to the left PFC was positive for the high-span group and negative for the-low span group, suggesting that closer cooperation between the two brain regions was strongly related to working memory performance. We conclude that central executive functioning for attention shifting is modulated by the cingulo-frontal network.

The neural basis of executive function in working memory: an fMRI study based on individual differences.

Using fMRI, neural substrates of the executive system were investigated with respect to differences in working memory capacity. To explore the executive control processes, reading span test (RST) and read conditions were performed. Two subject groups were selected: those with large working memory capacities, labeled high-span subjects (HSS) according to the reading span test, and those with small working memory capacities, labeled low-span subjects (LSS). Significant activation was found mainly in three regions in comparison with the control: anterior cingulate cortex (ACC), left inferior frontal gyrus (IFG), visual association cortex (VAC) and superior parietal lobule (SPL). For both groups, the fMRI signal intensity increased in ACC and IFG during the RST condition compared to that under the read condition. A group difference was also found in the ACC and IFG region, specifically a significant increase in signal intensity was observed only for the HSS group but not for the LSS group. Behavioral data also showed that the performance was better in HSS than in LSS. Moreover, the cross correlation of signal change between ACC and IFG was higher in HSS than in LSS, indicating that the network system between ACC and IFG was more activated in HSS compared to that of LSS. These results suggest that executive function, that is, working attention controlling system is more active in HSS than in LSS. Moreover, the results confirmed our hypothesis that there is a general neural basis for the central executive function in both RST and previous LST (listening span test) tasks despite differences in modality-specific buffers.

The neural basis of individual differences in working memory capacity: an fMRI study.

Using fMRI, neural substrates of verbal working memory were investigated with respect to differences in working memory capacity. Listening-span test (LST), Listen, and Remember conditions were performed. Two subjects groups were selected: those who had large working memory capacities, labeled high-span subjects (HSS) according to the working memory span test, and those who had small working memory capacities, labeled low-span subjects (LSS). Significant activation was found mainly in three regions in comparison with resting control: left prefrontal cortex (PFC), anterior cingulate cortex (ACC) and temporal language area. For both groups, fMRI signal intensity increased in PFC during the LST condition compared to the Listen condition. A group difference was found in the ACC region; specifically, a significant increase in signal intensity was observed in ACC only for the HSS group and not for the LSS group. Behavioral data also showed that the performance was better in HSS than in LSS. These results indicate that the attention controlling system, supported by ACC, is more effective in HSS compared to that of LSS.

Cooperation of the anterior cingulate cortex and dorsolateral prefrontal cortex for attention shifting

Attention shifting in the working memory system plays an important role in goal-oriented behavior, such as reading, reasoning, and driving, because it involves several cognitive processes. This study identified brain activity leading to individual differences in attention shifting for dual-task performance by using the group comparison approach. A large-scale pilot study was initially conducted to select suitable good and poor performers. The fMRI experiment consisted of a dual-task condition and two single-task conditions. Under the dual-task condition, participants verified the status of letters while concurrently retaining arrow orientations. The behavioral results indicated that accuracy in arrow recognition was better in the good performers than in the poor performers under the dual-task condition but not under the single-task condition. Dual-task performance showed a positive correlation with mean signal change in the right anterior cingulate cortex (ACC) and right dorsolateral prefrontal cortex (DLPFC). Structural equation modeling indicated that effective connectivity between the right ACC and right DLPFC was present in the good performers but not in the poor performers, although activations of the task-dependent posterior regions were modulated by the right ACC and right DLPFC. We conclude that individual differences in attention shifting heavily depend on the functional efficiency of the cingulo-prefrontal network.

Language-independent working memory as measured by Japanese and English reading span tests

The efficiency of working memory capacity was measured with the use of a reading span test (RST) written in Japanese and in English. The Japanese version of the RST was based on the RST developed by Daneman and Carpenter (1980) in English (CMU version). An English-as-a-second-language version (ESL version) was also developed for native Japanese college students. The correlation between the Japanese and ESL versions was found to be highly significant (0.84). Moreover, the correlation between the Japanese and CMU versions was found to be high (0.72). The results indicate that the efficiency of working memory for reading appears to be independent of language structure. Thus, the presently developed Japanese version of the RST is likely to predict reading efficiency in the same way that the CMU version does.

A word expressing affective pain activates the anterior cingulate cortex in the human brain: an fMRI study

We present an fMRI study demonstrating that an onomatopoeia word highly suggestive of subjective pain, heard by the ear, significantly activates the anterior cingulate cortex (ACC) while hearing non-sense words that did not imply affective pain under the same task does not activate this area in humans. We concluded that the ACC would be a pivotal locus for perceiving affective pain evoked by an onomatopoeia word that implied affective pain closely associated with the unpleasantness of pain. We suggest that the pain affect sustained by pain unpleasantness may depend on ACC-prefrontal cortical interactions that modify cognitive evaluation of emotions associated with word-induced pain.

Neural bases of focusing attention in working memory: an fMRI study based on group differences.

Using fMRI, we investigated neural substrates for focusing attention in working memory. To explore this focusing effect, two kinds of reading span test (RST), focused and nonfocused, were performed. In the focused RST (F-RST), the target word to be maintained was the focus word in the sentence. In the nonfocused RST (NF-RST), the target word was not the focus word in the sentence. In both RST conditions, significant activations were found in three main regions: left dorsolateral prefrontal cortex (DLPFC), anterior cingulate cortex (ACC), and left superior parietal lobule (SPL). In addition, fMRI signal changes increased in the left SPL in the NF-RST condition. These findings suggest that the neural substrates of focusing attention are based on SPL and ACC-DLPFC networks. Furthermore, there were group differences in the focusing effect between high-span and low-span subjects: High-span subjects showed focusing effects (supported by SPL control) greater than those of low-span subjects.

Language-independent working memory: Evidence from German and French reading span tests

The efficiency of working memory was measured with two versions of reading span tests, written in German and in French, using German/French bilingual subjects. The correlation between German and French versions was found to be highly significant (r = 0.85). Our results indicate that the efficiency of working memory for reading is independent of language, reconfirming the results obtained by Osaka and Osaka (1992).

Size of saccade and fixation duration of eye movements during reading: psychophysics of Japanese text processing

The size of saccadic eye movements and eye fixations during Japanese text reading (written in both hirakana phonograms and kanji ideograms) were analyzed. Hirakana is sound based, i.e., it consists of symbols for syllables, but such text was processed differently from English text in terms of saccadic eye movements and fixations. In experiment 1 the reader was asked to read three types of text (hirakana only, kanji-hirakana mixed, and English) in a natural reading manner. The results show that kanji-hirakana-mixed text, which has picturelike symbols, requires shorter eye fixations and longer saccades than those required by hirakana text. The findings show that kanji and hirakana are processed differently. Logographlike kanji text greatly facilitated text processing and understanding during reading. In experiment 2 we found that kanji-based text had a wider perceptual span of reading than did hirakana text. The wider span is consistent with the longer saccade length for kanji-based text found in experiment 1. In experiment 3 we studied the convenient viewing position, i.e., the position within a word where the eye should fixate first for the isolated word to be recognized most quickly. A convenient viewing position was confirmed to exist both for hirakana- and kanji-based words, but for hirakana words the position changed as word length changed, as was expected from the results of experiment 2. In experiment 4 we measured lexical access time for hirakana- and kanji-based words and found that the reaction time to kanji-based words was faster than the reaction time to words written with hirakana.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of focus on verbal working memory: Critical role of the focus word in reading

The effect of focus on working memory was investigated with the reading span test (RST). In two experiments, the span scores and the number of intrusion errors were compared between the focused RST the and the nonfocused RST.Focus word was defined as the most important word for comprehending a sentence. For the focused RST, the target word to be maintained was the focus word for the sentence. In the nonfocused RST, however, the target word was not the focus word for the sentence. The results of both experiments showed that RST span scores were higher for the focused RST than for the nonfocused RST, and intrusion errors were found to increase for the nonfocused RST. In Experiment 2, the effect of focus was compared between high-span and low-span subjects. An effect of sentence length was also investigated. The result showed that low-span subjects were more affected than were high-span subjects by whether the word to be remembered was the focus word. The effect of sentence length was not confirmed. These findings suggest that the low-span subjects had deficits in their ability to establish and/or inhibit mental focus when faced with conflict situations in reading.