Brain Response to Aversive Taste for Investigating Taste Preference

To clarify the intrinsic food preference mechanism, we investigated brain neurophysiological responses to unpleasant gustatory stimuli using electroencephalogram (EEG) and near-infrared hemoencepalogram (NIR-HEG) simultaneously. A conventional delayed response task based on Go/Nogo paradigm was adopted to extract real brain response components from spontaneous background signals. We found excessive evoked EEG potential responses to both bitter and sour stimuli, while we didn’t find excessive changes in purified water condition. These potentials appeared before P3, hence, they potentially predicted unconscious attention to the gustatory stimuli. We also identified a late contingent negative variation (CNV) and corresponding P3 for sour stimulus. In addition, NIR-HEG responses showed relative changes for every stimulus and we considered that these NIR-HEG signal changes were attributed to the prefrontal cortex activity for regulating negative emotional valence against aversive tastes typically including sour and bitter. In spite of limitation to timing accuracy of taste presentations, the early markers found in this study could be fundamentals for investigating individual food preference.

Prior Somatic Stimulation Improves Performance of Acquired Motor Skill by Facilitating Functional Connectivity in Cortico-Subcortical Motor Circuits

Once people have a well-trained motor skill, their performance becomes stabilized and achieving substantial improvement is difficult. Recently, we have shown that even a plateaued hand motor skill can be upgraded with short-period electrical stimulation to the hand prior to the task. Here, we identify the neuronal substrates underlying the improvement of the plateaued skill by examining the enhanced functional connectivity in the sensory-motor regions that are associated with motor learning. We measured brain activity using functional magnetic resonance imaging and performed psychophysiological interaction analysis. We recruited seven right-handed very-well trained participants, whose motor performance of continuously rotating two balls with their right hands became stabilized at higher performance levels. We prepared two experiments, in each of which they repeated an experimental run 16 times. In each run, they performed this cyclic rotation as many times as possible in 16 s. In the thenar-stimulation experiment, we applied 60-s stimulation to the thenar muscle before each of the 5th - 12th runs, and the others were preceded by ineffective sham stimulation. In the control experiment, the sham was always provided. Thenar stimulation enabled the participants to perform the movements at higher cycles. In association with this performance improvement, we found enhanced activity couplings between the primary motor cortex and the sensorimotor territory of the putamen and between the cerebellum and the primary sensorimotor cortices, without any quantitative activity increase. Neither behavioral change nor these increased activity couplings were observed in the control.Thus, in contrast to the stable neuronal states in the cortico-subcortical motor circuits when the well-learned task is repeated at the later stages of motor skill learning, plastic changes in the motor circuits seem to be required when the plateaued skill is upgraded, and the stimulation may entail a state of readiness for the plastic change that allows subsequent performance improvement.

Human-Related Emotional Stimuli Can Cause a Hippocampal and Thalamic Over-Response in People with Unstable Personalities

Hippocampus is crucial for the formation of emotional memory. We found the relationship between hippocampal responses to emotional stimuli and the mental stabilities of people in our preliminary study. In this study, we have also evaluated how the emotional stimuli would affect amygdala and thalamus in the brain, and how the personality stabilities could relate to the responses in the brain using functional magnetic resonance imaging (fMRI). We evaluated the subjects’ personality features with the Yatabe-Guilford Personality Test (Y-G test) and psychosomatic symptoms with the Cornell Medical Index (CMI). The subjects were categorized into the mentally stable group and the mentally unstable group according to the total scores of the Y-G test and the CMI. The brain functional responses under emotional stimuli were measured using fMRI. The region of interest (ROI) analysis was performed to abstract significant changes in order to compare responses among the different emotional stimuli. We conducted the regression analysis to abstract the relationship between the mean % signal change from fMRI and the personality stability. The fMRI results showed that the hippocampus, thalamus, and right amygdala activities under the human relationship stimuli increased with ascending value of mental instability. Our findings suggest that the memory process in the hippocampus and the threat alarm system in the thalamus under the human-related stimuli crucially influence the emotional reaction of mentally unstable people. These processes in the brain would affect the event that stresses on human relationships that often cause people to suffer from mental disorders.

Combining Motor Imagery and Action Observation with Vibratory Stimulation Increases Corticomotor Excitability in Healthy Young Adults

Vibratory stimulation but also motor imagery and action observation can induce corticomotor modulation, as a bottom-up stimulus and top-down stimuli, respectively. However, it remains unknown whether the combination of motor imagery, action observation, and vibratory stimulation can effectively increase corticomotor excitability. This study aimed to investigate the effect of motor imagery and/or action observation, in the presence or absence of vibratory stimulation, on the corticomotor excitability of healthy young adults. Vibratory stimulation was provided to the palm of the right hand. Action observation consisted in viewing a movie of someone else’s finger flexion and extension movements. The imagery condition required the participants to imagine they were moving their fingers while viewing the movie and attempting to move their fingers in accordance with the movie. Eleven right-handed healthy young adults were asked to perform six conditions randomly: 1) vibratory stimulation, imagery, and action observation, 2) vibratory stimulation and action observation, 3) vibratory stimulation and viewing of a blank screen, 4) imagery and action observation, 5) action observation, and 6) viewing of a blank screen. Single-pulse transcranial magnetic stimulation was conducted to assess corticomotor excitability and the peak-to-peak amplitude of the motor evoked potentials. The results showed that vibratory stimulation increases corticospinal excitability. The findings further revealed that performing motor imagery while viewing finger movement is more effective at inducing an augmentation of corticomotor excitability compared to action observation alone. Thus, the combination of motor imagery, action observation, and vibratory stimulation can effectively augment corticomotor excitability.

Feasibility of Improved Attenuation Correction for SPECT Reconstruction in the Presence of Dense Materials Using Dual-Energy Virtual Monochromatic CT: A Phantom Study

Objective: Computed tomography (CT)-based attenuation correction (CTAC) offers the clear benefit of reliable reconstruction of single-photon emission computed tomography (SPECT) images through its ability to achieve object-specific attenuation maps, but artifacts from dense materials often deteriorate CTAC performance. Therefore, we investigate the feasibility of CTAC in the presence of dense materials using dual-energy virtual monochromatic CT data. Methods: A sodium pertechnetate-filled cylindrical uniform phantom, with a pair of undiluted iodine syringes attached, is scanned with a dual-source CT scanner to obtain both single-energy (120 kVp) polychromatic and dual-energy (80 kVp/140 kVp with tin filtering) virtual monochromatic CT images. The single-energy and the dual-energy CT images are then converted to attenuation maps at 141 keV. SPECT images are reconstructed from 99mTc emission data of the phantom using each single-energy and dual-energy attenuation map and incorporating CTAC procedure. A region-of-in- terest analysis is performed to quantitatively compare the attenuation maps between the single-energy and the dual-energy techniques, each at an iodine-free position and a position adjacent to the iodine solutions. Results: At the iodine-free position, the phantom provides a uniform distribution of attenuation maps in both the single-energy and the dual-energy techniques. In the presence of adjacent iodine solutions, however, severe artifacts appeare in the single-energy CT images. These artifacts make attenuation values fluctuate, resulting in erroneous pixel values in the CTAC SPECT images. In contrast, dual-energy CT strongly suppresses the artifacts and hence improves the uniformity of the attenuation maps and the resultant SPECT images. Conclusions: Dual-energy CT with virtual monochromatic reconstruction has the potential to substantially reduce artifacts arising from dense materials. It has the potential to improve the accuracy of attenuation maps and the resultant CTAC SPECT images.

Quantitative evaluation of perceived depth of transparently-visualized medical 3D data presented with a multi-view 3D display

Transparent visualization is used in many fields because it can visualize not only the frontal object but also other important objects behind it.Although in many situations,it would be very important for the 3D structures of the visualized transparent images to be perceived as they are simulated,little is known quantitatively as to how such transparent 3D structures are perceived.To address this question,in the present study,we conducted a psychophysical experiment in which the observers reported the perceived depth magnitude of a transparent object in medical images,presented with a multiview 3D display.For the visualization,we employed a stochastic point-based rendering(SPBR)method,which was developed recently as a technique for efficient transparentrendering.Perceived depth of the transparent object was smaller than the simulated depth.We found,however,that such depth underestimation can be alleviated to some extent by(1)applying luminance gradient inherent in the SPBR method,(2)employing high opacities,and(3)introducing binocular disparity and motion parallax produced by a multi-view 3D display.