Yusuke Uchida

Neuronal Activity Related to Reward Size and Rewarded Target Position in Primate Supplementary Eye Field

Several areas of the macaque brain are known to be related to the reward during the performance of saccadic eye-movement tasks. Neurons in the supplementary eye field (SEF) have been reported to be involved in the prediction and detection of a reward. We describe a group of neurons in the SEF that became active during the period of reward delivery after saccades toward a specific direction, but showed weaker activity in other directions, although the same amount of reward was given in each direction. Moreover, this directional reward activity was modulated by the reward size. Our results demonstrate that the SEF cells may reflect both reward amount and target positions toward which a movement was rewarded, and suggest that they may play an important role in providing information about the value of each saccade according to the spatial target location.

Origins of Superior Dynamic Visual Acuity in Baseball Players: Superior Eye Movements or Superior Image Processing

Dynamic visual acuity (DVA) is defined as the ability to discriminate the fine parts of a moving object. DVA is generally better in athletes than in non-athletes, and the better DVA of athletes has been attributed to a better ability to track moving objects. In the present study, we hypothesized that the better DVA of athletes is partly derived from better perception of moving images on the retina through some kind of perceptual learning. To test this hypothesis, we quantitatively measured DVA in baseball players and non-athletes using moving Landolt rings in two conditions. In the first experiment, the participants were allowed to move their eyes (free-eye-movement conditions), whereas in the second they were required to fixate on a fixation target (fixation conditions). The athletes displayed significantly better DVA than the non-athletes in the free-eye-movement conditions. However, there was no significant difference between the groups in the fixation conditions. These results suggest that the better DVA of athletes is primarily due to an improved ability to track moving targets with their eyes, rather than to improved perception of moving images on the retina.

Neuronal activity related to anticipated and elapsed time in macaque supplementary eye field

It is essential to sense anticipated and elapsed time in our daily life. Several areas of the brain including parietal cortex, prefrontal cortex, basal ganglia and olivo-cerebellar system are known to be related to this temporal processing. We now describe a number of cells in the supplementary eye field (SEF) with phasic, delay activity and postdelay activity modulation that varied with the length of the delay period. This variation occurred in two manners. First, cells became active with the shorter delay periods (GO signal presented earlier). We call these cells “short-delay cells”. Second, cells became active with the longer delay periods (GO signal presented later). We call these cells “long-delay cells”. However, such changed neuronal activity did not correlate with reaction time. These results suggest that the delay-dependent activity may reflect anticipated and elapsed time during performance of a delayed saccadic eye movement.

Dynamic visual acuity in baseball players is due to superior tracking abilities.

PURPOSE Dynamic visual acuity (DVA) is defined as the ability to discriminate the fine parts of a moving object. DVA is generally better in baseball players than that in nonplayers. Although the better DVA of baseball players has been attributed to a better ability to track moving objects, it might be derived from the ability to perceive an object even in the presence of a great distance between the image on the retina and the fovea (retinal error). However, the ability to perceive moving visual stimuli has not been compared between baseball players and nonplayers. METHODS To clarify this, we quantitatively measured abilities of eye movement and visual perception using moving Landolt C rings in baseball players and nonplayers. RESULTS Baseball players could achieve high DVA with significantly faster eye movement at shorter latencies than nonplayers. There was no difference in the ability to perceive moving objects images projected onto the retina between baseball players and nonplayers. CONCLUSIONS These results suggest that the better DVA of baseball players is primarily due to a better ability to track moving objects with their eyes rather than to improved perception of moving images on the retina. This skill is probably obtained through baseball training.

Effects of mechanical repetitive load on bone quality around implants in rat maxillae

Greater understanding and acceptance of the new concept “bone quality”, which was proposed by the National Institutes of Health and is based on bone cells and collagen fibers, are required. The novel protein Semaphorin3A (Sema3A) is associated with osteoprotection by regulating bone cells. The aims of this study were to investigate the effects of mechanical loads on Sema3A production and bone quality based on bone cells and collagen fibers around implants in rat maxillae. Grade IV-titanium threaded implants were placed at 4 weeks post-extraction in maxillary first molars. Implants received mechanical loads (10 N, 3 Hz for 1800 cycles, 2 days/week) for 5 weeks from 3 weeks post-implant placement to minimize the effects of wound healing processes by implant placement. Bone structures, bone mineral density (BMD), Sema3A production and bone quality based on bone cells and collagen fibers were analyzed using microcomputed tomography, histomorphometry, immunohistomorphometry, polarized light microscopy and birefringence measurement system inside of the first and second thread (designated as thread A and B, respectively), as mechanical stresses are concentrated and differently distributed on the first two threads from the implant neck. Mechanical load significantly increased BMD, but not bone volume around implants. Inside thread B, but not thread A, mechanical load significantly accelerated Sema3A production with increased number of osteoblasts and osteocytes, and enhanced production of both type I and III collagen. Moreover, mechanical load also significantly induced preferential alignment of collagen fibers in the lower flank of thread B. These data demonstrate that mechanical load has different effects on Sema3A production and bone quality based on bone cells and collagen fibers between the inside threads of A and B. Mechanical load-induced Sema3A production may be differentially regulated by the type of bone structure or distinct stress distribution, resulting in control of bone quality around implants in jaw bones.

Factors determining performance of two limb coordinated movements in the sagittal plane

When humans perform rhythmic movement of two limbs in the sagittal plane, the “directional principle” appears: that is, the movement in the same direction is easier than the opposite direction. The purpose of this study is to examine the basis of this principle. In the first experiment, we tested the hypothesis that sending separate motor commands to two limbs is important. We compared the difficulty of movement in two conditions: (1) coordination of voluntary movements of ipsilateral hand and foot, and (2) coordination of voluntary movement of the hand and passive movement of the foot. Each condition composed of the “same direction” task and “opposite direction” task. In both conditions the difficulty of movement obeyed the directional principle. In the second experiment, we investigated the influence of kinesthetic afferent from the foot on the stability of the relationships between the positions of hand and foot. Subjects performed voluntary movement of hand with guidance of auditory pace signal, while ignoring the passive movement of ipsilateral foot that was moved by the experimenter in the same or opposite direction to the hand. No difference of the stability appeared depending on the direction of the foot movement. The results of the first and second experiments suggest that the directional principle is not based on sending separate motor commands to two limbs, nor interference of afferent signals from two limbs. Instead, comparing kinesthetic afferent from two limbs seems to be crucial for the stability of movements of two limbs.