Atsushi Takemoto

Phased processing of facial emotion: an ERP study.

We examined the temporal characteristics of facial-emotion processing. The stimuli were several morphed images containing seven facial emotions (neutral, anger, happiness, disgust, sadness, surprise, and fear) and ten-graded intensity levels to parametrically control these aspects of facial emotions. Brain activity was recorded with electroencephalography as the subjects detected the facial emotion and assessed its intensity. We found that the temporal profile of detection was quite different from the assessment of intensity. A positive component 100 ms after stimulus onset (P100) was significantly correlated with the correct detection of facial emotion, whereas a negative component 170 ms after stimulus onset (N170) was significantly correlated with the assessment of intensity level. The source of both the P100 and N170 signals was consistently localized to the right occipito-parietal region. We propose phased processing of facial emotion, in which rapid detection of any facial emotion occurs within 100 ms and detailed processing, including the assessment of the intensity, occurs shortly afterwards.

Development of a compact and general-purpose experimental apparatus with a touch-sensitive screen for use in evaluating cognitive functions in common marmosets

Common marmosets have been used extensively in biomedical research and the recent advent of techniques to generate transgenic marmosets has accelerated the use of this model. New methods that efficiently assess the degree of cognitive function in common marmosets are needed in order to establish their suitability as non-human primate models of higher brain function disorders. Here, we have developed a new apparatus suitable for testing the cognitive functions of common marmosets. Utilizing a mini laptop PC with a touch-sensitive screen as the main component, the apparatus is small and lightweight and can be easily attached to the home cages. The ease of designing and testing new paradigms with the flexible software is another advantage of this system. We have tested visual discrimination and its reversal tasks using this apparatus and confirmed its efficacy.

Information processing of geometrical features of a surface based on binocular disparity cues: an fMRI study

Cortical areas related to the information processing of binocular disparity-defined geometrical features of a surface, such as depth, orientation and shape are examined by functional magnetic resonance imaging while subjects discriminated these three types of geometrical feature in random dot stereograms. Results indicate that disparity-defined information of depth and that of orientation are processed in the parietal area. Furthermore, the visual system for 3D vision in the parietal area may be organized in a hierarchical manner and the posterior part of the right intraparietal sulcus may be involved in cognitive process of 3D vision. On the other hand, disparity-defined shape information seems to be processed in the occipital visual areas and the crucial involvement of human LOS for this process is suggested.

Individual variability in visual discrimination and reversal learning performance in common marmosets

Detailed information about the characteristics of learning behavior in marmosets is useful for future marmoset research. We trained 42 marmosets in visual discrimination and reversal learning. All marmosets could learn visual discrimination, and all but one could complete reversal learning, though some marmosets failed to touch the visual stimuli and were screened out. In 87% of measurements, the final percentage of correct responses was over 95%. We quantified performance with two measures: onset trial and dynamic interval. Onset trial represents the number of trials that elapsed before the marmoset started to learn. Dynamic interval represents the number of trials from the start before reaching the final percentage of correct responses. Both measures decreased drastically as a result of the formation of discrimination learning sets. In reversal learning, both measures worsened, but the effect on onset trial was far greater. The effects of age and sex were not significant as far as we used adolescent or young adult marmosets. Unexpectedly, experimental circumstance (in the colony or isolator) had only a subtle effect on performance. However, we found that marmosets from different families exhibited different learning process characteristics, suggesting some family effect on learning.

Single-trial EEG data to classify type and intensity of facial emotion from P100 and N170

Two aspects of facial emotions are type and intensity level. This study is an attempt to find the relation of electrode location and latencies of EEG data with specific aspects of facial emotions. A neural network was applied to single trial EEG data for classifying the type and intensity level of facial emotions. Images of two types of facial emotions (happiness and disgust) with two intensity levels (high and low) were parametrically controlled and presented as main stimuli to evoke brain signals. Results of this study indicated that data from electrodes over the right-posterior area in the time-range window 80 to 200 ms post stimulus presentation contains P100 and N170 components strongly related to the process of recognition of facial emotions. Relative to other components, N170 was strongly related to the intensity levels of facial emotion, where it could be used for classifying low and high intensity levels of facial emotion. P100 and N170 can be used for classifying the type of facial emotions, with the accuracy when using P100 being slightly higher. Time-range window 200 to 280 ms contains N2, which can also be used for classifying the intensity level of facial emotion, but its accuracy is less than that of N170. Data from time-range window 300 to 360 ms, which contains the P300 component, was not significant for classifying type and intensity level of facial emotion relative to that of other components. This study is the first to show the possibility of using other components besides P300 for EEG-based BCIs. The results also suggest the mechanism of recognition of facial emotion, started by recognizing the type of facial emotion followed by how intense the facial emotion is expressed.

Visual discrimination and reversal learning in aged common marmosets (Callithrix jacchus)

Common marmosets (Callithrix jacchus) have been suggested as a new model for analysis of age-related changes and neurodegenerative diseases. However, the effects of age on learning and memory processes are not well defined within this species. Therefore, we employed visual discrimination and reversal learning tasks to evaluate learning and memory in four aged common marmosets relative to a younger cohort. We found that aged marmosets commit significantly more errors in initial stages of visual discrimination and more perseverative errors in reversal learning, indicating prefrontal dysfunction. However, they showed comparable performance with younger marmosets in the later stages of both tasks.

Distinct roles for primate caudate dopamine D1 and D2 receptors in visual discrimination learning revealed using shRNA knockdown

The striatum plays important motor, associative and cognitive roles in brain functions. However, the rodent dorsolateral (the primate putamen) and dorsomedial (the primate caudate nucleus) striatum are not anatomically separated, making it difficult to distinguish their functions. By contrast, anatomical separation exists between the caudate nucleus and putamen in primates. Here, we successfully decreased dopamine D1 receptor (D1R) or D2R mRNA expression levels selectively in the marmoset caudate using shRNA knockdown techniques, as determined using positron emission tomography imaging with specific D1R and D2R ligands and postmortem in situ hybridization analysis. We then conducted a voxel-based correlation analysis between binding potential values of PET imaging and visual discrimination learning task performance in these genetically modified marmosets to find a critical role for the caudate D2R but no apparent role for the caudate D1R. This latter finding challenges the current understanding of the mechanisms underlying D1R activation in the caudate.

Characteristics of Serial Order Learning in Common Marmosets (Callithrix jacchus)

We investigated the characteristics of serial order learning in common marmosets (Callithrix jacchus). Five marmosets were trained in a sequential responding task in which they were required to touch four graphic patterns in a given order (A→B→C→D) to obtain a reward. All five marmosets learned the task with over 65% accuracy. Shuffling the positions of B, C, and D immediately after the marmoset had correctly identified and selected the first stimulus (A) either decreased accuracy or lengthened response latency for the second stimulus (B). These results suggest that the marmosets planned the response to the second stimulus before they touched the first stimulus. In addition, when we presented a pair of stimuli (AB, AC, AD, BC, BD, and CD pairs), the marmosets responded to the stimuli in the pair in the appropriate order, according to the learned order (A→B→C→D). The analyses of first and second response latencies clearly demonstrated both the first-item and missing-item effects in task performance. Our data provide direct evidence that marmosets can learn the relative order of the four stimuli in a sequential responding task.

Serial Processing of Emotional Type and Intensity: Evidence from an ERP Study

ERP responses were examined while subjects were identifying type of facial emotion as well as assessing intensity of facial emotion. We found a significant correlation between the magnitude of P100 response and the correct identification of type of facial emotion over the right posterior region and that between the magnitude of N170 response and the assessment of intensity of facial emotion over the right posterior and left frontal regions. Finding of these significant correlations from the same right occipital region suggested that the human brain processes information about facial emotion serially; type of facial emotion is processed first and thereafter its saliency or intensity level.

A Method to Train Marmosets in Visual Working Memory Task and Their Performance

Learning and memory processes are similarly organized in humans and monkeys; therefore, monkeys can be ideal models for analyzing human aging processes and neurodegenerative diseases such as Alzheimer’s disease. With the development of novel gene modification methods, common marmosets (Callithrix jacchus) have been suggested as an animal model for neurodegenerative diseases. Furthermore, the common marmoset’s lifespan is relatively short, which makes it a practical animal model for aging. Working memory deficits are a prominent symptom of both dementia and aging, but no data are currently available for visual working memory in common marmosets. The delayed matching-to-sample task is a powerful tool for evaluating visual working memory in humans and monkeys; therefore, we developed a novel procedure for training common marmosets in such a task. Using visual discrimination and reversal tasks to direct the marmosets’ attention to the physical properties of visual stimuli, we successfully trained 11 out of 13 marmosets in the initial stage of the delayed matching-to-sample task and provided the first available data on visual working memory in common marmosets. We found that the marmosets required many trials to initially learn the task (median: 1316 trials), but once the task was learned, the animals needed fewer trials to learn the task with novel stimuli (476 trials or fewer, with the exception of one marmoset). The marmosets could retain visual information for up to 16 s. Our novel training procedure could enable us to use the common marmoset as a useful non-human primate model for studying visual working memory deficits in neurodegenerative diseases and aging.