Biomedical subjects

Keiichiro Toma

Publications and source records attributed to Keiichiro Toma.

14 recordsLinked to original sources

PubMed2005

Activation of the precuneus is related to reduced reaction time in serial reaction time tasks.

Multiple brain areas are activated during serial reaction time (RT) tasks (SRTTs), but the part of the brain that facilitates reductions in RT remains unclear. The present study attempted to determine the brain region contributing most to improved RTs during explicit SRTTs. Subjects comprised 18 healthy volunteers who were instructed to press one of four buttons corresponding to visual stimuli as quickly as possible and with minimal errors during functional MRI. Stimuli were presented either in random order (control condition) or in a repeated six-item sequence (learning condition). Conventional analysis contrasting learning and control conditions revealed activation in the prefrontal-parietal area, which shifted to motor area. Subjects with high RT reduction showed more prominent activation in the precuneus than subjects with low RT reduction. Intra-subject correlation analysis revealed that time course of precuneus activation was unrelated to time-course of RT reduction. However, inter-subject correlation analysis revealed that RT changes correlate only with precuneus activation, meaning that subjects showing more prominent RT reduction revealed more prominent activation of the precuneus, which is known to play critical roles in controlling finger movements with reference to buffered memory.

Adult↗

PubMed2004

Short-term high-frequency transcutaneous electrical nerve stimulation decreases human motor cortex excitability.

Several previous studies have shown that periods of changed sensory input can have after effects on the excitability of the corticospinal system. Here we test whether the parameters of peripheral stimulation conventionally used to treat pain with transcutaneous electrical nerve stimulation (TENS: 90 Hz) also have modulatory effects on the motor system. We measured the amplitude of motor evoked potentials (MEPs) elicited by the focal transcranial magnetic stimulation in the right abductor pollicis brevis and first dorsal interosseous muscles before and after 30 min TENS over the right thenar eminence. In addition, we evaluated tactile and 2-point discrimination thresholds at the same site. TENS transiently reduced MEPs and increased sensory thresholds. This suggests that short-term TENS might have an inhibitory effect on both the sensory and motor systems.

Adult↗

PubMed2004

Implicit and explicit processing of kanji and kana words and non-words studied with fMRI.

Using functional magnetic resonance imaging (fMRI), we investigated the implicit language processing of kanji and kana words (i.e., hiragana transcriptions of normally written kanji words) and non-words. Twelve right-handed native Japanese speakers performed size judgments for character stimuli (implicit language task for linguistic stimuli), size judgments for scrambled-character stimuli (implicit language task for non-linguistic stimuli), and lexical decisions (explicit language task). The size judgments for scrambled-kanji stimuli and scrambled-kana stimuli produced activations on the bilateral lingual gyri (BA 18), the bilateral occipitotemporal regions (BA 19/37), and the bilateral superior and inferior parietal cortices (BA 7/40). Interestingly, besides these areas, activations of the left inferior frontal region (Broca's area, BA 44/45) and the left posterior inferior temporal cortex (PITC, BA 37), which have been considered as language areas, were additionally activated during size judgment for kanji character stimuli. Size judgment for kana character stimuli also activated Broca's area, the left PITC, and the left supramarginal gyrus (SMG, BA 40). The activations of these language areas were replicated in the lexical decisions for both kanji and kana. These findings suggest that language processing of both kanji and kana scripts is obligatory to literate Japanese subjects. Moreover, comparison between the scrambled kanji and the scrambled kana showed no activation in the language areas, while greater activation in the bilateral fusiform gyri (left-side predominant) was found in kanji vs. kana comparison during the size judgment and the lexical decision. Kana minus kanji activated the left SMG during the size judgment, and Broca's area and the left middle/superior temporal junction during the lexical decision. These results probably reflect that in implicit or explicit reading of kanji words and kana words (i.e., hiragana transcriptions of kanji words), although using largely overlapping cortical regions, there are still some differences. Kanji reading may involve more heavily visual orthographic retrieval and lexical-semantic system through the ventral route, while kana transcriptions of kanji words require phonological recoding to gain semantic access through the dorsal route.

Adult↗

PubMed2003

Cortical motor areas in plantar response: an event-related functional magnetic resonance imaging study in normal subjects.

The role of the cerebral cortices in normal plantar response was investigated with event-related functional magnetic resonance imaging (fMRI) at 3 Tesla in 12 right-handed normal subjects. During fMRI acquisition, the lateral (LS) and medial (MS) side of the left sole was mechanically stimulated every 16 s to evoke the plantar response under monitoring of the surface electromyogram. LS activated the contralateral supplementary motor area (SMA) more intensively than MS. In contrast, no difference was found in the commonly activated areas including the contralateral primary sensorimotor area, bilateral secondary sensory areas and the thalamus. The results support the hypothesis that the normal plantar response is influenced by the cerebral cortices, and that the SMA likely participates in the regulation of the plantar reflex arc at the spinal level.

Adult↗

PubMed2003

The role of the human supplementary motor area in reactive motor operation.

The role of the supplementary motor area (SMA) in reactive motor operation was investigated with functional magnetic resonance imaging in 13 normal subjects. A visual cue was presented at a regular (1 Hz) or irregular (mean, 1 Hz) rate, and the subject pressed a button with the right index finger in a predictive or reactive manner. Brain regions associated with reactive movement were detected by comparing reactive with predictive movement tasks, and those with irregular movement by comparing irregular and regular cueing tasks. During regular cueing, the SMA showed greater activation for reactive than predictive movement. However, the SMA was equally activated between regular and irregular cueing once the subject reacted to the cue. The SMA is likely involved in reactive adjustment of movement to the external cue.

Adult↗

PubMed2003

A functional magnetic resonance imaging study of internal modulation of an external visual cue for motor execution.

The strategy to perform a task differs according to how a cue is interpreted. In order to investigate the basic mechanisms of temporal regulation in the higher motor areas, the interaction between two different types of internal modulations of an external visual cue was evaluated using functional magnetic resonance imaging (fMRI). An opposing finger movement task guided by dot prompting was employed. In the intermittent tapping experiment, two taps per second and a rest for one second were alternatively repeated in the task blocks. In the constant tapping experiments, the volunteers performed finger movements at 0.5, 1 or 2 Hz. The activation in the primary sensory motor area correlated with the amount of movement. Activities in the supplementary motor area, left dorsal pre-motor area, left superior parietal lobule and right cerebellum depended on the demand for internal modulation. Activation in these areas was maximum for the intermittent task which was a combination of two different internal modulations, and minimum for the 1 Hz movement that did not require internal modulation. It was suggested that these four areas are directly involved in the generation of a complex movement sequence driven by a visual cue, and they are organized for performance. The translation of external pacing and initiation for self-pacing may share the same neuronal basis. Activation in the left supramarginal gyrus, bilateral frontal operticula and basal ganglia did not depend on the combination of the two internal modulations.

Adult↗

PubMed2003

Discrimination of Exner's area and the frontal eye field in humans--functional magnetic resonance imaging during language and saccade tasks.

In the left frontal lobe, Exner's area (EXA), which is responsible for writing and reading, is located close to the frontal eye field (FEF), which is responsible for eye movements. To discriminate EXA from FEF anatomically and functionally, functional magnetic resonance imaging was conducted in 12 healthy volunteers. The saccadic eye movement experiment activated a region defined as the FEF, whereas three language experiments that included translation between grapheme and phoneme activated another region defined as EXA. EXA was found to be located only 1.5 cm apart from the FEF in the Talairach brain template. By conducting the saccade and language experiments in the same individuals, this study was able to successfully separate EXA from FEF.

Adult↗

PubMed2003

Transcranial magnetic stimulation (TMS) of the sensorimotor cortex and medial frontal cortex modifies human pain perception.

OBJECTIVE: Although recent neuroimaging studies have shown that painful stimuli can produce activity in multiple cortical areas, the question remains as to the role of each area in particular aspects of human pain perception. To solve this problem we used transcranial magnetic stimulation (TMS) as an 'interference approach' tool to test the consequence on pain perception of disrupting activity in several areas of cortex known to be activated by painful input. METHODS: Weak CO(2) laser stimuli at an intensity around the threshold for pain were given to the dorsum of the left hand in 9 normal subjects. At variable delays (50, 150, 250, 350 ms) after the onset of the laser stimulus, pairs of TMS pulses (dTMS: interpulse interval of 50 ms, and stimulus intensity of 120% resting motor threshold) were applied in separate blocks of trials over either the right sensorimotor cortex (SMI), midline occipital cortex (OCC), second somatosensory cortex (SII), or medial frontal cortex (MFC). Subjects were instructed to judge whether or not the stimulus was painful and to point to the stimulated spot on a drawing of subject's hand. RESULTS: Subjects judged that the stimulus was painful on more trials than control when dTMS was delivered over SMI at 150-200 ms after the laser stimulus; the opposite occurred when dTMS was delivered over MFC at 50-100 ms. dTMS over the SII or OCC failed to alter the pain threshold. CONCLUSIONS: These results suggest that TMS to SMI can facilitate whereas stimulation over MFC suppresses central processing of pain perception. Since there was no effect of dTMS at any of the scalp sites on the localization task, the cortical locus for point localization of pain may be different from that for perception of pain intensity or may involve a more complex mechanism than the latter. SIGNIFICANCE: This is the first report that TMS of SMI facilitates while that of MFC suppresses the central processing of pain perception. This raises the possibility of using TMS as a therapeutic device to control pain.

Adult↗

PubMed2003

Neural correlates of cross-modal binding.

Little is known about how the brain binds together signals from multiple sensory modalities to produce unified percepts of objects and events in the external world. Using event-related functional magnetic resonance imaging (fMRI) in humans, we measured transient brain responses to auditory/visual binding, as evidenced by a sound-induced change in visual motion perception. Identical auditory and visual stimuli were presented in all trials, but in some trials they were perceived to be bound together and in others they were perceived as unbound unimodal events. Cross-modal binding was associated with higher activity in multimodal areas, but lower activity in predominantly unimodal areas. This activation pattern suggests that a reciprocal and 'competitive' interaction between multimodal and unimodal areas underlies the perceptual interpretation of simultaneous signals from multiple sensory modalities.

Acoustic Stimulation↗

PubMed2003

Functional properties of brain areas associated with motor execution and imagery.

Imagining motor acts is a cognitive task that engages parts of the executive motor system. While motor imagery has been intensively studied using neuroimaging techniques, most studies lack behavioral observations. Here, we used functional MRI to compare the functional neuroanatomy of motor execution and imagery using a task that objectively assesses imagery performance. With surface electromyographic monitoring within a scanner, 10 healthy subjects performed sequential finger-tapping movements according to visually presented number stimuli in either a movement or an imagery mode of performance. We also examined effects of varied and fixed stimulus types that differ in stimulus dependency of the task. Statistical parametric mapping revealed movement-predominant activity, imagery-predominant activity, and activity common to both movement and imagery modes of performance (movement-and-imagery activity). The movement-predominant activity included the primary sensory and motor areas, parietal operculum, and anterior cerebellum that had little imagery-related activity (-0.1 ~ 0.1%), and the caudal premotor areas and area 5 that had mild-to-moderate imagery-related activity (0.2 ~ 0.7%). Many frontoparietal areas and posterior cerebellum demonstrated movement-and-imagery activity. Imagery-predominant areas included the precentral sulcus at the level of middle frontal gyrus and the posterior superior parietal cortex/precuneus. Moreover, activity of the superior precentral sulcus and intraparietal sulcus areas, predominantly on the left, was associated with accuracy of the imagery task performance. Activity of the inferior precentral sulcus (area 6/44) showed stimulus-type effect particularly for the imagery mode. A time-course analysis of activity suggested a functional gradient, which was characterized by a more "executive" or more "imaginative" property in many areas related to movement and/or imagery. The results from the present study provide new insights into the functional neuroanatomy of motor imagery, including the effects of imagery performance and stimulus-dependency on brain activity.

Adult↗

PubMed2002

Functional MRI in human motor control studies and clinical applications.

Functional magnetic resonance imaging (fMRI) has been a useful tool for the noninvasive mapping of brain function associated with various motor and cognitive tasks. Because fMRI is based on the blood oxygenation level dependent (BOLD) effect, it does not directly record neural activity. With the fMRI technique, distinguishing BOLD signals created by cortical projection neurons from those created by intracortical neurons appears to be difficult. Two major experimental designs are used in fMRI studies: block designs and event-related designs. Block-designed fMRI presupposes the steady state of regional cerebral blood flow and has been applied to examinations of brain activation caused by tasks requiring sustained or repetitive movements. By contrast, the more recently developed event-related fMRI with time resolution of a few seconds allows the mapping of brain activation associated with a single movement according to the transient aspects of the hemodynamic response. Increasing evidence suggests that multiple motor areas are engaged in a networked manner to execute various motor acts. In order to understand functional brain maps, it is important that one understands sequential and parallel organizations of anatomical connections between multiple motor areas. In fMRI studies of complex motor tasks, elementary parameters such as movement length, force, velocity, acceleration and frequency should be controlled, because inconsistency in those parameters may alter the extent and intensity of motor cortical activation, confounding interpretation of the findings obtained. In addition to initiation of movements, termination of movements plays an important role in the successful achievement of complex movements. Brain areas exclusively related to the termination of movements have been, for the first time, uncovered with an event-related fMRI technique. We propose the application of fMRI to the elucidation of the pathophysiology of movement disorders, particularly dystonia, which exhibits involuntary co-contraction of agonist and antagonist muscles and manifests abnormal posture or slow repetition of movements.

Brain Mapping↗

PubMed2002

Generators of movement-related cortical potentials: fMRI-constrained EEG dipole source analysis.

To clarify the precise location and timing of the mo tor cortical activation in voluntary movement, dipole source analysis integrating multiple constraints wa conducted for the movement-related cortical potentia (MRCP). Six healthy subjects performed single self paced extensions of the right index finger at about 15-intervals during EEG and event-related fMRI acquisi tions. EEG was recorded from 58 scalp electrodes, and fMRI of the entire brain was obtained every 2.6 s. Coordinates of the two methods were coregistered us ing anatomical landmarks. During dipole source mod eling, a realistic three-layer head model was used as a volume conductor. To identify the number of uncorre lated source s in the MRCP, principal component (PC analysis was performed, which was consistent with the existence of six sources in the left (Lt SM1) and right (Rt SMI) sensorimotor and medial frontocentral (MFC) areas. After dipoles were seeded at the acti vated spots revealed by fMRI, dipole orientations were fixed based on the interpretation of the topography of distribution of the PC. The strength of the six dipoles (three dipoles in Lt SMI, two in Rt SMI, and one in MFC) was then computed over time. Within the bilat eral SM1, activation of the precentral gyrus occurs bilaterally with similar strength from -1.2 s, followed by that of the precentral bank from -0.5 s with con tralateral preponderance. Subsequently, the postcen tral bank becomes active only on the contralateral side at 0.1 s after movement. Activation of the MFC shows timing similar to that of the bilateral precentral gyri These deduced patterns of activation are consis tent with previous studies of electrocorticography in humans.

Adult↗

PubMed2002

Second somatosensory area (SII) plays a significant role in selective somatosensory attention.

In order to explore human cortical areas involved in active attention toward a somatosensory modality, somatosensory evoked cortical magnetic fields were recorded in ten healthy adults with a 122-channel whole-head magnetometer while the subjects performed the selective attention task. Two kinds of stimulus modality, somatosensory and auditory, were presented independently in the same session. For the somatosensory modality, a randomized sequence of strong (P=0.45) and weak (P=0.05) electric stimuli was delivered to the right median nerve at the wrist. For the auditory modality, a randomized sequence of 900-Hz (P=0.45) and 950-Hz (P=0.05) tones was delivered to both ears. Subjects were requested to pay attention to the specified stimulus modality (either somatosensory or auditory) and to count the number of rare stimuli of the attended modality (weak stimuli in the somatosensory or 950-Hz tone in the auditory modality). A total of 12 sessions were performed for each subject, among which the order of attended modality was changed alternately and counterbalanced among subjects. In the data analysis, somatosensory evoked fields for frequent stimuli (strong electric stimuli) were compared between the two conditions; attend somatosensory condition (ATS) and attend auditory condition (non-attend somatosensory condition; NATS). In six out of the ten subjects, somatosensory evoked fields showed attention-related change. The magnitude of the estimated generator source in SII, but not in SI, significantly increased from NATS to ATS while keeping the same locations. Moreover, a simulation study using the estimated sources in SII in NATS supported the enhancement of the activity in the SII rather than participation of additional sources in the selective attention task. These results suggest that the SII plays a main role in selective somatosensory attention.

Acoustic Stimulation↗

PubMed2002

Movement rate effect on activation and functional coupling of motor cortical areas.

We investigated changes in the activation and functional coupling of bilateral primary sensorimotor (SM1) and supplementary motor (SMA) areas with different movement rates in eight normal volunteers. An auditory-cued repetitive right-thumb movement was performed at rates of 0.5, 0.75, 1, 2, 3, and 4 Hz. As a control condition, subjects listened to pacing tones with no movements. Electroencephalogram (EEG) was recorded from 28 scalp electrodes and electromyogram was obtained from the hand muscles. The event-related changes in EEG band-power (ERpow: activation of each area) and correlation (ERcor: functional coupling between each pair of cortical areas) were computed every 32 ms. Modulations of ERpow and ERcor were inspected in alpha (8-12 Hz) and beta (16-20 Hz) bands. Motor cortical activation and coupling was greater for faster movements. With increasing movement rate, the timing relationship between movement and tone switched from synchronization (for 0.5-1 Hz) to syncopation (for 3-4 Hz). The results suggested that for slow repetitive movements (0.5-1 Hz), each individual movement is separately controlled, and EEG activation and coupling of the motor cortical areas were immediately followed by transient deactivation and decoupling, having clear temporal modulation locked to each movement. In contrast, for fast repetitive movements (3-4 Hz), it appears that the rhythm is controlled and the motor cortices showed sustained EEG activation and continuous coupling.

Adult↗