Hirohito M. Kondo

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.

Involvement of the Thalamocortical Loop in the Spontaneous Switching of Percepts in Auditory Streaming

Perceptual grouping of successive frequency components, namely, auditory streaming, is essential for auditory scene analysis. Prolonged listening to an unchanging triplet-tone sequence produces a series of illusory switches between a single coherent stream (S1) and two distinct streams (S2). The predominant percept depends on the frequency difference (Δf) between high and low tones. Here, we combined the use of different Δfs with an event-related fMRI design to identify whether the temporal dynamics of brain activity differs depending on the direction of perceptual switches. The results demonstrated that the activity of the medial geniculate body (MGB) in the thalamus occurred earlier during switching from nonpredominant to predominant percepts, whereas that of the auditory cortex (AC) occurred earlier during switching from predominant to nonpredominant percepts, regardless of Δf. The asymmetry of temporal precedence indicates that the MGB and AC activations play different roles in perceptual switching and depend on perceptual predominance rather than on S1 and S2 percepts per se. Our results suggest that feedforward and feedback processes in the thalamocortical loop are involved in the formation of percepts in auditory streaming.

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.

Functional brain networks underlying perceptual switching: auditory streaming and verbal transformations

Recent studies have shown that auditory scene analysis involves distributed neural sites below, in, and beyond the auditory cortex (AC). However, it remains unclear what role each site plays and how they interact in the formation and selection of auditory percepts. We addressed this issue through perceptual multistability phenomena, namely, spontaneous perceptual switching in auditory streaming (AS) for a sequence of repeated triplet tones, and perceptual changes for a repeated word, known as verbal transformations (VTs). An event-related fMRI analysis revealed brain activity timelocked to perceptual switching in the cerebellum for AS, in frontal areas for VT, and the AC and thalamus for both. The results suggest that motor-based prediction, produced by neural networks outside the auditory system, plays essential roles in the segmentation of acoustic sequences both in AS and VT. The frequency of perceptual switching was determined by a balance between the activation of two sites, which are proposed to be involved in exploring novel perceptual organization and stabilizing current perceptual organization. The effect of the gene polymorphism of catechol-O-methyltransferase (COMT) on individual variations in switching frequency suggests that the balance of exploration and stabilization is modulated by catecholamines such as dopamine and noradrenalin. These mechanisms would support the noteworthy flexibility of auditory scene analysis.

Neural mechanisms of auditory awareness underlying verbal transformations

Prolonged listening to a repeated word without a pause produces a series of illusory transitions of the physically unchanging word, which is called verbal transformation. Verbal transformations provide a rare opportunity to examine how auditory percepts are formed in the brain. We found that verbal forms are affected by phonetic reorganization of a word, rather than by auditory adaptation and lexical distortion of it. We identified brain activity leading to individual differences between perceptual transitions and tone detection. An event-related fMRI analysis revealed that the left inferior frontal cortex (IFC), anterior cingulate cortex (ACC), and the left prefrontal cortex were activated when perceptual transitions from one verbal form to another occurred, but not when tone pips were detected. The number of perceptual transitions showed positive and negative correlations with signal intensity in the left IFC and the left ACC, respectively. The results suggest that active generation of verbal forms is linked with articulatory gestures for speech production and that the frequency of perceptual transitions is determined by a balance of the activations between the two brain regions. Structural equation modeling demonstrated that individual differences in the number of perceptual transitions rely on negative feedback from the ACC to the IFC via the posterior insula. These findings suggest that distributed frontal areas are involved in auditory awareness underlying verbal transformations.

An emotion-based facial expression word activates laughter module in the human brain: a functional magnetic resonance imaging study.

We report an fMRI experiment demonstrating that visualization of onomatopoeia, an emotion-based facial expression word, highly suggestive of laughter, heard by the ear, significantly activates both the extrastriate visual cortex near the inferior occipital gyrus and the premotor (PM)/supplementary motor area (SMA) in the superior frontal gyrus while non-onomatopoeic words under the same task that did not imply laughter do not activate these areas in humans. We tested the specific hypothesis that an activation in extrastriate visual cortex and PM/SMA would be modulated by image formation of onomatopoeia implying laughter and found the hypothesis to be true.

Effects of self-motion on auditory scene analysis

Auditory scene analysis requires the listener to parse the incoming flow of acoustic information into perceptual “streams,” such as sentences from a single talker in the midst of background noise. Behavioral and neural data show that the formation of streams is not instantaneous; rather, streaming builds up over time and can be reset by sudden changes in the acoustics of the scene. Here, we investigated the effect of changes induced by voluntary head motion on streaming. We used a telepresence robot in a virtual reality setup to disentangle all potential consequences of head motion: changes in acoustic cues at the ears, changes in apparent source location, and changes in motor or attentional processes. The results showed that self-motion influenced streaming in at least two ways. Right after the onset of movement, self-motion always induced some resetting of perceptual organization to one stream, even when the acoustic scene itself had not changed. Then, after the motion, the prevalent organization was rapidly biased by the binaural cues discovered through motion. Auditory scene analysis thus appears to be a dynamic process that is affected by the active sensing of the environment.