Koichi Yokosawa

Does the Human Dorsal Stream Really Process a Category for Tools

Previously, Almeida et al. (2008) used a technique called Continuous Flash Suppression to show that human dorsal stream cortical areas specifically responded to a “tool category.” Here, we used the same technique to clarify what attributes of tools are processed in the dorsal stream. We examined surface attributes and shape. A significant priming effect was found when we removed surface attributes by using line drawings instead of photographs. In a second experiment, we manipulated shape and we found that there were no significant priming effects when we used nonelongated tool pictures as tool prime stimuli. To better clarify the effect of shape attributes on priming effects, we conducted a further experiment using elongated stick-like rectangles as prime stimuli and found that elongated shapes significantly shortened the reaction time to the tool pictures as target stimuli. Additionally, when elongated vegetables were used as prime stimuli, the reaction time to the tool pictures as target stimuli was also significantly shortened, but there was no effect when stubby vegetables were used. Finally, when we controlled for orientation by presenting rotated elongated stick-like rectangles, diamond shapes, and cut circles as prime stimuli, we found that rectangles replicated the same significant priming effect as previous experiments, but the others did not. These results suggest that the dorsal stream processes elongated shapes but does not process the tool category specifically.

Functional modulations in brain activity for the first and second music: A comparison of high- and low-proficiency bimusicals

Bilingual studies have shown that brain activities for first (L1) and second (L2) languages are influenced by L2 proficiency. Does proficiency with a second musical system (M2) influence bimusical brains in a manner similar to that of bilingual brains? Our magnetoencephalography study assessed the influence of M2 proficiency on the spatial, strength, and temporal properties of brain activity in a musical syntactic-processing task (i.e., tonal processing) involving first (M1) and second (M2) music systems. Two bimusical groups, differing in M2 proficiency (high, low), listened to melodies from both their M1 and M2 musical cultures. All melodies ended with a tonally consistent or inconsistent tone. In both groups, tonal deviations in both M1 and M2 elicited magnetic early right anterior negativities (mERANs) that were generated from brain areas around the inferior frontal gyrus (IFG). We also analyzed the dipole locations, dipole strengths, and peak latencies of mERAN. Results revealed: (a) the distances between dipole locations for M1 and M2 were shorter in the M2 high-proficiency group than in the M2 low-proficiency group; (b) the dipole strengths were greater in the high than the low group; (c) the peak latencies of M2 were shorter in the high than low group. The dipole location results were consistent with those from bilingual studies in that the distances between the (left) IFG peak activations for L1 and L2 syntactic processing shortened as L2 proficiency increased. The parallel results for bimusicals and bilinguals suggest that the functional changes induced by proficiency in a second (linguistic or musical) system are defined by domain-general neural constraints.

Alpha-band rhythm modulation under the condition of subliminal face presentation: MEG study

The human brain has two streams to process visual information: a dorsal stream and a ventral stream. Negative potential N170 or its magnetic counterpart M170 is known as the face-specific signal originating from the ventral stream. It is possible to present a visual image unconsciously by using continuous flash suppression (CFS), which is a visual masking technique adopting binocular rivalry. In this work, magnetoencephalograms were recorded during presentation of the three invisible images: face images, which are processed by the ventral stream; tool images, which could be processed by the dorsal stream, and a blank image. Alpha-band activities detected by sensors that are sensitive to M170 were compared. The alpha-band rhythm was suppressed more during presentation of face images than during presentation of the blank image (p=.028). The suppression remained for about 1 s after ending presentations. However, no significant difference was observed between tool and other images. These results suggest that alpha-band rhythm can be modulated also by unconscious visual images.

Activation of Auditory Cortex by Anticipating and Hearing Emotional Sounds: An MEG Study

To study how auditory cortical processing is affected by anticipating and hearing of long emotional sounds, we recorded auditory evoked magnetic fields with a whole-scalp MEG device from 15 healthy adults who were listening to emotional or neutral sounds. Pleasant, unpleasant, or neutral sounds, each lasting for 6 s, were played in a random order, preceded by 100-ms cue tones (0.5, 1, or 2 kHz) 2 s before the onset of the sound. The cue tones, indicating the valence of the upcoming emotional sounds, evoked typical transient N100m responses in the auditory cortex. During the rest of the anticipation period (until the beginning of the emotional sound), auditory cortices of both hemispheres generated slow shifts of the same polarity as N100m. During anticipation, the relative strengths of the auditory-cortex signals depended on the upcoming sound: towards the end of the anticipation period the activity became stronger when the subject was anticipating emotional rather than neutral sounds. During the actual emotional and neutral sounds, sustained fields were predominant in the left hemisphere for all sounds. The measured DC MEG signals during both anticipation and hearing of emotional sounds implied that following the cue that indicates the valence of the upcoming sound, the auditory-cortex activity is modulated by the upcoming sound category during the anticipation period.

Neural Representation of Scale Illusion: Magnetoencephalographic Study on the Auditory Illusion Induced by Distinctive Tone Sequences in the Two Ears

The auditory illusory perception “scale illusion” occurs when a tone of ascending scale is presented in one ear, a tone of descending scale is presented simultaneously in the other ear, and vice versa. Most listeners hear illusory percepts of smooth pitch contours of the higher half of the scale in the right ear and the lower half in the left ear. Little is known about neural processes underlying the scale illusion. In this magnetoencephalographic study, we recorded steady-state responses to amplitude-modulated short tones having illusion-inducing pitch sequences, where the sound level of the modulated tones was manipulated to decrease monotonically with increase in pitch. The steady-state responses were decomposed into right- and left-sound components by means of separate modulation frequencies. It was found that the time course of the magnitude of response components of illusion-perceiving listeners was significantly correlated with smooth pitch contour of illusory percepts and that the time course of response components of stimulus-perceiving listeners was significantly correlated with discontinuous pitch contour of stimulus percepts in addition to the contour of illusory percepts. The results suggest that the percept of illusory pitch sequence was represented in the neural activity in or near the primary auditory cortex, i.e., the site of generation of auditory steady-state response, and that perception of scale illusion is maintained by automatic low-level processing.

Alpha-band rhythm suppression during memory recall reflecting memory performance

Alpha-band rhythm is thought to be involved in memory processes, similarly to other spontaneous brain rhythms. Ten right-handed healthy volunteers participated in our proposed sequential short-term memory task that provides a serial position effect in accuracy rate. We recorded alpha-band rhythms by magnetoencephalography during performance of the task and observed that the amplitude of the rhythm was suppressed dramatically in the memory recall period. The suppressed region was estimated to be in the occipital lobe, suggesting that alpha-band rhythm is suppressed by activation of the occipital attentional network. Additionally, the alpha-band suppression reflected accuracy rate, that is, the amplitude was suppressed more when recalling items with higher accuracy rate. The sensors with a significant correlation between alpha-band amplitude and accuracy rate were located widely from the frontal to occipital regions mainly in the right hemisphere. The results suggests that alpha-band rhythm is involved in memory recall and can be index of memory performance.

Magnetic displacement force and torque on dental keepers in the static magnetic field of an MR scanner

To evaluate the effect of the static magnetic field of magnetic resonance (MR) scanners on keepers (ie, ferromagnetic stainless steel plate adhered to the abutment tooth of dental magnetic attachments).

A cross-cultural comparison of tonality perception in Japanese, Chinese, Vietnamese, Indonesian, and American listeners.

We investigated tonal perception of melodies from 2 cultures (Western and traditional Japanese) by 5 different cultural groups (44 Japanese, 25 Chinese, 16 Vietnamese, 18 Indonesians, and 25 U.S. citizens). Listeners rated the degree of “melodic completeness” of the final tone (a tonic vs. a nontonic) and “happiness–sadness” in the mode (major vs. minor, YOH vs. IN) of each melody. When Western melodies were presented, American and Japanese listeners responded similarly, such that they reflected implicit tonal knowledge of Western music. By contrast, the responses of Chinese, Vietnamese, and Indonesian listeners were different from those of American and Japanese listeners. When traditional Japanese melodies were presented, Japanese listeners exhibited responses that reflected implicit tonal knowledge of traditional Japanese music. American listeners also showed responses that were like the Japanese; however, the pattern of responses differed between the 2 groups. Alternatively, Chinese, Vietnamese, and Indonesian listeners exhibited different responses from the Japanese. These results show large differences between the Chinese/Vietnamese/Indonesian group and the American/Japanese group. Furthermore, the differences in responses to Western melodies between Americans and Japanese were less pronounced than that between Chinese, Vietnamese, and Indonesians. These findings imply that cultural differences in tonal perception are more diverse and distinctive than previously believed.

Speech Disfluency-dependent Amygdala Activity in Adults Who Stutter: Neuroimaging of Interpersonal Communication in MRI Scanner Environment

Affective states, such as anticipatory anxiety, critically influence speech communication behavior in adults who stutter. However, there is currently little evidence regarding the involvement of the limbic system in speech disfluency during interpersonal communication. We designed this neuroimaging study and experimental procedure to sample neural activity during interpersonal communication between human participants, and to investigate the relationship between the amygdala activity and speech disfluency. Participants were required to engage in live communication with a stranger of the opposite sex in the MRI scanner environment. In the gaze condition, the stranger gazed at the participant without speaking, while in the live conversation condition, the stranger asked questions that the participant was required to answer. The stranger continued to gaze silently at the participant while the participant answered. Adults who stutter reported significantly higher discomfort than fluent controls during the experiment. Activity in the right amygdala, a key anatomical region in the limbic system involved in emotion, was significantly correlated with stuttering occurrences in adults who stutter. Right amygdala activity from pooled data of all participants also showed a significant correlation with discomfort level during the experiment. Activity in the prefrontal cortex, which forms emotion regulation neural circuitry with the amygdala, was decreased in adults who stutter than in fluent controls. This is the first study to demonstrate that amygdala activity during interpersonal communication is involved in disfluent speech in adults who stutter.

Turning a cylindrical treadmill with feet: An MR-compatible device for assessment of the neural correlates of lower-limb movement

BACKGROUND Locomotion, which is one of the most basic motor functions, is critical for performing various daily-life activities. Despite its essential function, assessment of brain activity during lower-limb movement is still limited because of the constraints of existing brain imaging methods. NEW METHOD Here, we describe an MR-compatible, cylindrical treadmill device that allows participants to perform stepping movements on an MRI scanner table. The device was constructed from wood and all of the parts were handmade by the authors. RESULTS We confirmed the MR-compatibility of the device by evaluating the temporal signal-to-noise ratio of 64 voxels of a phantom during scanning. Brain activity was measured while twenty participants turned the treadmill with feet in sync with metronome sounds. The rotary speed of the cylinder was encoded by optical fibers. The post/pre-central gyrus and cerebellum showed significant activity during the movements, which was comparable to the activity patterns reported in previous studies. Head movement on the y- and z-axes was influenced more by lower-limb movement than was head movement on the x-axis. Among the 60 runs (3 runs × 20 participants), head movement during two of the runs (3.3%) was excessive due to the lower-limb movement. COMPARISON WITH EXISTING METHODS Compared to MR-compatible devices proposed in the previous studies, the advantage of this device may be simple structure and replicability to realize stepping movement with a supine position. CONCLUSIONS Collectively, our results suggest that the treadmill device is useful for evaluating lower-limb-related neural activity.