Hiroshi Kadota

Sequential muscle activity and its functional role in the upper extremity and trunk during overarm throwing

The proximal-to-distal segmental sequence has been identified in many sports activities, including baseball pitching and ball kicking. However, proximal-to-distal sequential muscle activity has not been identified. The aims of this study were to establish whether sequential muscle activity does occur and, if it does, to determine its functional role. We recorded surface electromyograms (EMGs) for 17 muscles from the upper extremity and abdomen during overarm throwing and detected the onset and peak times as indices of muscle activity. The following electromyographic properties were commonly identified in the participants. First, sequential muscle activity was observed from the scapular protractors to the shoulder horizontal flexors and from the shoulder horizontal flexors to the elbow extensor, but not from the elbow extensor to the wrist flexor or forearm pronator. Secondly, the external oblique contralateral to the throwing arm became activated before the ipsilateral external oblique. This sequence is considered to be very effective for the generation of high force and energy in the trunk. Thirdly, the ipsilateral external oblique began its activity almost at foot strike. Finally, the main activity of the rectus abdominis appeared just before the point of release.

Neural correlates of attitude change following positive and negative advertisements

Understanding changes in attitudes towards others is critical to understanding human behaviour. Neuropolitical studies have found that the activation of emotion-related areas in the brain is linked to resilient political preferences, and neuroeconomic research has analysed the neural correlates of social preferences that favour or oppose consideration of intrinsic rewards. This study aims to identify the neural correlates in the prefrontal cortices of changes in political attitudes toward others that are linked to social cognition. Functional magnetic resonance imaging (fMRI) experiments have presented videos from previous electoral campaigns and television commercials for major cola brands and then used the subjects self-rated affinity toward political candidates as behavioural indicators. After viewing negative campaign videos, subjects showing stronger fMRI activation in the dorsolateral prefrontal cortex lowered their ratings of the candidate they originally supported more than did those with smaller fMRI signal changes in the same region. Subjects showing stronger activation in the medial prefrontal cortex tended to increase their ratings more than did those with less activation. The same regions were not activated by viewing negative advertisements for cola. Correlations between the self-rated values and the neural signal changes underscore the metric representation of observed decisions (i.e., whether to support or not) in the brain. This indicates that neurometric analysis may contribute to the exploration of the neural correlates of daily social behaviour.

An fMRI study of musicians with focal dystonia during tapping tasks.

Musician’s dystonia is a type of task specific dystonia for which the pathophysiology is not clear. In this study, we performed functional magnetic resonance imaging to investigate the motor-related brain activity associated with musician’s dystonia. We compared brain activities measured from subjects with focal hand dystonia and normal (control) musicians during right-hand, left-hand, and both-hands tapping tasks. We found activations in the thalamus and the basal ganglia during the tapping tasks in the control group but not in the dystonia group. For both groups, we detected significant activations in the contralateral sensorimotor areas, including the premotor area and cerebellum, during each tapping task. Moreover, direct comparison between the dystonia and control groups showed that the dystonia group had greater activity in the ipsilateral premotor area during the right-hand tapping task and less activity in the left cerebellum during the both-hands tapping task. Thus, the dystonic musicians showed irregular activation patterns in the motor-association system. We suggest that irregular neural activity patterns in dystonic subjects reflect dystonic neural malfunction and consequent compensatory activity to maintain appropriate voluntary movements.

The role of the dorsolateral prefrontal cortex in the inhibition of stereotyped responses

Stereotyped behaviors should be inhibited under some circumstances in order to encourage appropriate behavior. Psychiatrists have used the modified rock-paper-scissors (RPS) task to examine the inhibition of stereotyped behavior. When subjects are required to lose in response to a gesture, it is difficult for them to lose, and they have a tendency to win involuntarily. It is thought that the win response is the stereotyped response in the RPS task, and the difficulty in making positive attempts to lose is due to the requirement for inhibition of the stereotyped response. In this study, we investigated the brain regions related to inhibition of the stereotyped response using functional magnetic resonance imaging (fMRI). Subjects were assigned to one of two groups: the “win group” or the “lose group.” The lose group showed higher activation of the left dorsolateral prefrontal cortex (DLFPC) when compared to the win group. We also delivered transcranial magnetic stimulation (TMS) while the subjects performed the modified RPS task to investigate whether the left DLPFC (middle frontal gyrus, Brodmann area, BA 9) was directly involved in the inhibition of the stereotyped response. When TMS was delivered before onset of the visual stimulus, the subjects displayed increased response errors. In particular, the subjects had a tendency to win erroneously in a lose condition even though they were required to lose. These results indicate involvement of the left DLPFC in inhibition of the stereotyped responses, which suggests that this region is associated with inhibition of the preparatory setting for stereotyped responses rather than inhibition of ongoing processing to produce a stereotyped response.

TMS-induced artifacts on EEG can be reduced by rearrangement of the electrode’s lead wire before recording

OBJECTIVEnOur purpose was to establish a technique to reduce residual artifacts after transcranial magnetic stimulation (TMS) from electroencephalographic (EEG) signals.nnnMETHODSnWe investigated the effects of coil direction and stimulus intensity on residual artifacts in an artificial circuit, and tested whether or not the size of the circuit area affects the residual artifact (the model study). Based on the results, the optimization by rearranging the electrodes lead wire was tested on the human scalp (the human study).nnnRESULTSnThe residual artifact after TMS was dependent on the direction of the figure-of-eight coil, and on the artificial circuit area size.nnnCONCLUSIONSnIn accordance with the model study, the scalp EEG shows that TMS-induced artifacts can be reduced dramatically before the amplifier input stages in TMS-EEG experiments by a step-wise procedure rearranging the lead wires relative to the fixed coil orientation.nnnSIGNIFICANCEnOur technique makes it possible to significantly reduce the residual artifacts from recordings of short-latency TMS-evoked potentials.

Selective activation and deactivation of the human brain structures between speeded and precisely timed tapping responses to identical visual stimulus: an fMRI study.

We investigated the difference between brain activities in speeded and precisely timed responses to identical visual stimulus using fMRI. Stimulus used was a row of seven light-emitting diodes (LEDs) lightened up one after another with constant speed within a trial but with various speeds between trials. Subjects were asked to execute finger-thumb tapping with the right hand in response to the onset of the first LED light in the reaction time (RT) task and in anticipation of the onset of the last (i.e., seventh) LED light in the timing task. In control condition, they were asked to passively view the stimulus without motor response. Results showed that various movement-related areas including contralateral cingulate motor cortex were commonly activated for both tasks relative to the control condition, suggesting these structures are involved in general perception and response execution rather than specific function for speeded or precisely timed responses. In the RT task, the presupplementary motor area extending to the cingulate sulcus was activated more strongly than in the timing task probably to focus attention to the onset of the first LED light unpredictably presented after random foreperiods. The lateral occipital area extending to the temporo-parieto-occipital junction was activated more strongly in the timing task than in the RT task; the same area was deactivated in the RT task relative to the control condition. Auditory-related areas were also deactivated in the both tasks. This inter- and intramodal task-specific modification including deactivation underscores significance of the context for perception and action and can have an important role in dexterous or skilled performance.

Time-series pattern changes related to movement rate in synchronized human tapping

We investigated the effect of movement rate on the time-series properties of human synchronization errors by applying power spectrum analysis and detrended fluctuation analysis (DFA). Participants were required to execute a finger-tapping task with their right index finger in synchrony with periodic sounds under seven conditions of movement rates ranging from 1 to 4 Hz and separated by 0.5 Hz. At slow movement rates (1 and 1.5 Hz), the power spectrum of the synchronization errors flattened in the low-frequency portion, resulting in short-range correlation. At fast movement rates (from 2 to 4 Hz), on the other hand, the time series of the timing errors exhibited a 1/fbeta-type long-range correlation. These results indicate that the movement rate has an effect on the temporal coordination pattern in the human timing control mechanism. We inferred that this change in the coordination pattern reflects the transition between different states in human synchronization movements with an external signal.

1/f-type fluctuation in human visuomotor transformation.

In the absence of vision of the limb, movements toward a visual target exhibit substantial errors which are considered to originate mainly in the visuomotor transformation process. To determine the time-dependent property of human visuomotor transformation, we investigated the error sequences in movements toward visual target using scaling analyses. When subjects could see their controlling limb, the error sequences could not be distinguished from a random sequence. On the other hand, when the controlling limb was invisible, the error sequences were not random in order, but exhibited 1/f-type time correlation. This finding that the variation in human visuomotor transformation shows 1/f-type fluctuation provides a significant index for mathematical modeling and system identification in human visuomotor control.

Fractal correlation of initial trajectory dynamics vanishes at the movement end point in human rapid goal-directed movements

Many researchers have investigated the variability of discrete goal-directed movements. However, a possible time-dependent property for them has been ignored. We investigated the time-dependent property of the kinematic variability in human rapid goal-directed movements by using fractal analysis. The variability of the peak acceleration had fractal time correlation characterized by a non-negligible frequency-spectral exponent (beta=0.3). This beta value was reduced at the peak velocity (beta=0.2) and nearly reached zero at the peak movement amplitude, indicating that the variability became white noise with no time correlation. A similar result was observed in the progress of the positional trajectory. The functional significance of this phenomenon for the goal-directed task demand is discussed.

Functional Modulation of Corticospinal Excitability with Adaptation of Wrist Movements to Novel Dynamical Environments

Adaptation of reaching movements to a novel dynamic environment is associated with changes in neuronal activity in the primary motor cortex (M1), suggesting that M1 neurons are part of the internal model. Here, we investigated whether such changes in neuronal activity, resulting from motor adaptation, were also accompanied by changes in human corticospinal excitability, which reflects M1 activity at a macroscopic level. Participants moved a cursor on a display using the right wrist joint from the starting position toward one of eight equally spaced peripheral targets. Motor-evoked potentials (MEPs) were elicited from the wrist muscles by transcranial magnetic stimulation delivered over the left M1 before and after adaptation to a clockwise velocity-dependent force field. We found that the MEP elicited even during the preparatory period exhibited a directional tuning property, and that the preferred direction shifted clockwise after adaptation to the force field. In a subsequent experiment, participants simultaneously adapted an identical wrist movement to two opposing force fields, each of which was associated with unimanual or bimanual contexts, and the MEP during the preparatory period was flexibly modulated, depending on the context. In contrast, such modulation of the MEP was not observed when participants tried to adapt to two opposing force fields that were each associated with a target color. These results suggest that the internal model formed in the M1 is retrieved flexibly even during the preparatory period, and that the MEP could be a very useful probe for evaluating the formation and retrieval of motor memory.