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Shigeru Kitazawa

Publications and source records attributed to Shigeru Kitazawa.

17 recordsLinked to original sources
PubMed2007

Effects of visual stimuli on temporal order judgments of unimanual finger stimuli.

Successive tactile stimuli, delivered one to each hand, are referred to spatial representation before they are ordered in time (Yamamoto and Kitazawa in Nat Neurosci 4:759-765 2001a). In the present study, we examined if this applies even when they are delivered unilaterally to fingers of a single hand. Tactile stimuli were delivered left-to-rightward relative to the body (2nd-3rd-4th) or in reverse with stimulus onset asynchrony of 100 ms. Simultaneously with the delivery of tactile stimuli, three of nine small squares arranged in a matrix of 3 x 3 were turned on as if they appeared near the tips of the fingers. Although subjects were instructed to ignore the visual stimuli and make a forced choice between the two orders of tactile stimuli, the correct-judgment probability depended on the direction of visual stimuli. It was greater than 95% when the direction of visual stimuli matched that of the tactile stimuli, but less than 50% when they were opposite to each other. When the right hand was rotated counterclockwise on the horizontal plane (90 degrees ) so that the fingers were pointing to the left, the preferred direction of visual stimuli that yielded the peak correct judgment was also rotated, although not to the full extent. These results show that subjects cannot be basing their tactile temporal order judgment solely on a somatotopic map, but rather on a spatial map on which both visual and tactile signals converge.

Adult↗
PubMed2006

Encoding of movement dynamics by Purkinje cell simple spike activity during fast arm movements under resistive and assistive force fields.

It is controversial whether simple-spike activity of cerebellar Purkinje cells during arm movements encodes movement kinematics like velocity or dynamics like muscle activities. To examine this issue, we trained monkeys to flex or extend the elbow by 45 degrees in 400 ms under resistive and assistive force fields but without altering kinematics. During the task movements after training, simple-spike discharges were recorded in the intermediate part of the cerebellum in lobules V-VI, and electromyographic activity was recorded from arm muscles. Velocity profiles (kinematics) in the two force fields were almost identical to each other, whereas not only the electromyographic activities (dynamics) but also simple-spike activities in many Purkinje cells differed distinctly depending on the type of force field. Simple-spike activities encoded much larger mutual information with the type of force field than that with the residual small difference in the height of peak velocity. The difference in simple-spike activities averaged over the recorded Purkinje-cells increased approximately 40 ms before the appearance of the difference in electromyographic activities between the two force fields, suggesting that the difference of simple-spike activities could be the origin of the difference of muscle activities. Simple-spike activity of many Purkinje cells correlated with electromyographic activity with a lead of approximately 80 ms, and these neurons had little overlap with another group of neurons the simple-spike activity of which correlated with velocity profiles. These results show that simple-spike activity of at least a group of Purkinje cells in the intermediate part of cerebellar lobules V-VI encodes movement dynamics.

Animals↗
PubMed2006

Statistical parametric mapping of immunopositive cell density.

We developed a new method for comparing immunopositive cell densities across groups of animals and creating statistical parametric maps on standardized sections. As an example, we compared Iba-1 (microglial marker) positive cell densities in rats with (n=6) and without (n=6) unilateral injection of 1-methyl-4-phenylpyridinium salt (MPP+). Immunopositive cells were automatically counted in each animal over a coronal section in the midbrain (bregma -5.9 mm) and a positive cell density map was created for each animal. After the positive cell density map was normalized to a template section from an atlas, positive cell densities of the two groups were compared in each pixel over the section and a statistical parameter (p-value from t-test) was mapped on each pixel. We were able to detect significant increases of microglias in the side of MPP+ injection not only in the substantia nigra pars compacta but also in adjacent white matter. We also applied the same analysis to tyrosine hydroxylase stained sections and detected significant decreases of dopamine neurons in the side of MPP+ injection. The new method was proven to be useful for detecting significant changes of cell densities over the entire area of immunostained sections.

1-Methyl-4-phenylpyridinium↗
PubMed2006

Bayesian calibration of simultaneity in tactile temporal order judgment.

Human judgment of the temporal order of two sensory signals is liable to change depending on our prior experiences. Previous studies have reported that signals presented at short intervals but in the same order as the most frequently repeated signal are perceived as occurring simultaneously. Here we report opposite perceptual changes that conform to a Bayesian integration theory in judging the order of two stimuli delivered one to each hand.

Adult↗
PubMed2005

Rhythmicity, randomness and synchrony in climbing fiber signals.

The role of the climbing fiber input to the cerebellum has been enigmatic, with recent studies focusing on its temporal and spatial firing patterns. Debate remains as to whether climbing fibers provide a periodic clock for coordinating movements or lead to long-term modification of Purkinje cell activity as the basis of motor learning. Rhythmic and synchronous activity of climbing fibers can cause movements at the same frequency in some preparations, suggesting a role in motor timing. However, in awake monkeys climbing fiber signals have been reported to occur at random, presenting a problem for clock theories. Yet synchronous patterns of discharge are consistently observed among several Purkinje cells within a narrow parasagittal longitudinal band. Here, we review recent experimental and theoretical studies and attempt to provide a coherent account of the interplay between rhythmicity, randomness and synchrony in climbing fiber activity, with a particular reference to studies in chaos.

Animals↗
PubMed2005

Cortical activity in multiple motor areas during sequential finger movements: an application of independent component analysis.

Multiple cortical regions such as the supplementary motor area (SMA), premotor cortex (PM), and primary motor cortex (M1) are involved in the sequential execution of hand movements, but it is unclear how these areas collaborate in the preparation and execution of ipsilateral and contralateral hand movements. In this study, we used right-handed subjects to examine the spatial distribution and temporal profiles of motor-related activity during visually cued sequential finger movements by applying independent component analysis (ICA) to event-related functional magnetic resonance imaging (fMRI) signals. The particular merit of the ICA method is that it allows brain activity in individual subjects to be elucidated without making a priori assumptions about the anatomical areas that are activated or the temporal profile of activity. By applying ICA, we found that (1) the SMA contributed to both the preparation and execution of movements of the right and left hand; (2) the left M1 and dorsal premotor cortex (PMd) contributed to both the preparation and execution of movements of the right and left hand, whereas the right M1 and PMd contributed mainly to the execution of movements of the left hand; (3) pre-SMA areas were activated in some subjects in concert with the posterior parietal and prefrontal cortex; and (4) fMRI signals over superficial cortical draining veins could be distinguished from cortical activation. We suggest that ICA is useful for categorizing distributed task-related activities in individual subjects into several spatially independent activities that represent functional units in motor control.

Adult↗
PubMed2005

Temporal order judgment in mice.

A temporal order judgment task was developed for mice. After training male mice (C57BL6NCrj, n=15) to poke their noses into a hole, two stimuli (brief puffs of air) were delivered to the whiskers with a fixed interval of 750 ms in one of four orders: right (R)-left (L), L-R, L-L, and R-R. The mice were rewarded when they oriented their heads toward the first (n=5) or second (n=10) stimulus after a visual go signal. The mice were trained for up to 50 days. All mice met the criterion for task achievement (daily correct response rate >70% on 3 consecutive days) in response to unilateral stimuli (L-L and R-R), and 9 of the 15 mice met the criterion for task achievement in response to bilateral stimuli (L-R and R-L). The median periods for task achievement were 15 and 34 days for unilateral and bilateral stimuli, respectively. The correct response rate dropped to approximately the chance level after all whiskers had been removed. The nine successful mice were trained further and tested with smaller interstimulus intervals. The probability of right-first judgment plotted against the stimulation interval was fitted with a sigmoid function (r2=0.92) with asymptotes of 0.29 and 0.73 and a temporal resolution of 160 ms. The sigmoid curve was biased horizontally by 133 ms, reflecting the fact that stimuli delivered simultaneously were judged as left-first rather than right-first. The results show that mice can be trained to judge the temporal order of tactile stimuli delivered to whiskers and that such judgment might be lateralized to the right hemisphere.

Animals↗
PubMed2005

Referral of tactile sensation to the tips of L-shaped sticks.

When we touch something with a tool, we feel the touch at the tip of the tool rather than at the hand that holds the tool. We reported previously that judging the temporal order of two successive stimuli delivered to the tips of straight sticks held in each hand was dramatically altered by crossing the sticks without changing hand position. The results suggested that tactile signals are referred to the tip of a tool held in the hand. Here we examined temporal order judgement using L-shaped sticks instead of straight ones to determine whether the shape of a tool affects the way tactile signals are referred. Subjects reported the order of stimuli correctly in most trials when the tip of each L-shaped stick occupied the hemispace ipsilateral to the anatomical laterality of the hand holding the L-shaped stick. The subjects, however, misreported the order of stimuli presented at moderately short intervals (<300 ms) when the tip of the stick occupied the hemispace contralateral to the anatomical laterality of the hand holding it. The judgment reversal occurred irrespective of the number of physical crossings between the sticks and the arms (0, 1, and 3), as long as the tips of L-shaped tools were placed in the contralateral hemispace. Our results suggest that our brain refers tactile signals from the hand directly to the location of the tip without much accounting for the route that connects hand and tip.

Adolescent↗
PubMed2004

Accelerated recognition of left oblique views of faces.

Because faces in portraits are depicted more frequently in a left rather than a right oblique (half-profile or 3/4) view, we addressed the question of whether people find it easier to recognize the left or right 3/4 view of a familiar person's face. We examined the ability of 13 subjects to match familiar faces that were presented in either the left or right 3/4 view, with names that were presented either before or after the faces (face-name and name-face matching tasks, respectively). In both tasks, the subjects responded more rapidly to a left than to a right 3/4 view of the same face. This suggests that during face recognition the processing of information from faces that are presented in the left 3/4 view is dominant over the processing of right 3/4 views of familiar faces.

Adult↗
PubMed2004

Dominance of the left oblique view in activating the cortical network for face recognition.

Faces in portraits are often depicted from the left 3/4 view (an oblique view of the face that is intermediate between the frontal view and left profile). Here, we used functional magnetic resonance imaging (fMRI) to show that, compared with photographs of right 3/4 views of familiar faces, photographs of left 3/4 views of the same faces elicited stronger neural responses in the right middle occipital/inferior parietal cortex, and right inferior frontal gyrus; which are known to be involved in face recognition. By contrast, there was no differential activation in the temporal cortex including the superior temporal sulcus and fusiform gyrus, which are thought to process face-related visual stimuli at a stage that precedes recognition. We suggest that the preference for the left 3/4 view of faces was produced at a later stage of facial information processing that involves attention or memory retrieval.

Adult↗
PubMed2004

Effects of handedness on tactile temporal order judgment.

We examined effects of handedness on the judgment of temporal order of successive taps delivered to both hands. When the subjects' arms were uncrossed, the temporal resolution (84% correct responses) of right-handed subjects (52 +/- 4 ms, n = 16) was significantly better than that of left-handed subjects (83 +/- 9 ms, n = 16). When their arms were crossed, both groups tended to invert their judgment to a similar extent at intervals as long as 200-300 ms. In the arms crossed condition, right handed subjects inverted their judgment more often in response to left-hand-first stimuli than to right-hand-first stimuli, whereas left-handed subjects did not show the same asymmetry. We infer that hemispheric lateralization, which is generally stronger in right- than in left-handed subjects, contributes to the relatively better temporal resolution of right-handed subjects in the uncrossed condition, as well as to the asymmetric effect of stimulation order in the crossed condition.

Adolescent↗
PubMed2003

Acquisition and contextual switching of multiple internal models for different viscous force fields.

Humans can learn an enormous number of motor behaviors in different environments. To explain this, the MOSAIC model proposes that multiple internal models are acquired in the brain, which can be switched. However, previous behavioral studies that examined arm-movement adaptations to multiple environments reported a rather limited learning capability. Hitherto, humans have been believed incapable of learning two opposite viscous force fields, which are both dynamic transformations and depend on the same state variable, presented in a random order with only a visual cue. In contrast, this study found that humans are capable of this. Elbow joint movements to specified targets were perturbed by either resistive or assistive viscous force fields generated by a single degree-of-freedom manipulandum. The resistive or assistive viscous force fields were cued by a blue or red color on a CRT screen, respectively. The squared distance between the end point and the target, and the variance of the joint angular velocities were used as kinematic performance indices. These movement errors decreased significantly as a function of the training days. Aftereffects and learning consolidation were demonstrated in the random presentation of the two force fields. Consequently, humans were able to learn the multiple and distinct internal models of the two force fields and appropriately switch them even for a random presentation cued only by color after several days of training. This study suggests that none of the previously proposed conditions for multiple internal model learning are necessary prerequisites, and indicates that the difficulty in learning is determined by the balance between the effectiveness of contextual information and the similarity of force fields.

Adaptation, Psychological↗
PubMed2002

Prism adaptation with delayed visual error signals in the monkey.

Errors in reaching produced by displacing the visual field with wedge prisms decrease with trials, even when the error is not revealed until the completion of the movement. To examine how much additional delay in visual feed-back the monkey can compensate for, the effects of delaying the visual error signals were studied by presenting the terminal visual images after one of five delays, ranging from 0 to 500 ms. Adaptation was fastest when the delay was 0 or 10 ms, decreased significantly with a delay as small as 50 ms and approached zero when the delay was 500 ms. The size of the after-effect decreased with the delay accordingly. The results indicate that prism adaptation in the monkey critically depends on the availability of visual information within 50 ms of completion of the movement. Comparing the results with those for humans, we suggest that monkey and human share a mechanism of adaptation with a short time window of 50 ms, but the monkey lacks another mechanism of adaptation that allows a visual delay of 500 ms or more in humans.

Adaptation, Ocular↗
PubMed2002

Optimization of goal-directed movements in the cerebellum: a random walk hypothesis.

Voluntary goal-directed movements, such as arm reaching, are nearly optimized in terms of smoothness over the entire movement. Such smoothness is lost with cerebellar dysfunction, suggesting the essential role of the cerebellum in optimizing movement. However, it is still not clear how the cerebellum contributes to achieving smoothness over an entire movement. A recent study has shown that such smoothness of movement can be achieved by reducing the variance of errors at the end of the movement. Here, I hypothesize that the terminal errors conveyed by climbing fibers in the cerebellum serve to reduce not only the mean error, but also the variance of the error, through a process analogous to the random walk through movement control candidates. In the random walk, the direction of each step is randomly determined, but the size of each step is determined by the error at the end of each trial.

Cerebellum↗
PubMed2002

Where conscious sensation takes place.

has drawn an alternative conclusion from the data of, and suggested that it takes 80 ms, rather than 500 ms, for the sensation evoked by a stimulus to enter awareness. Here, I suggest that our conscious sensation evolves over time, during the period from 80 to 500 ms after a stimulus, until the sensation is stably localized in space.

Awareness↗