Toshiharu Nakai

Temperature mapping using the water proton chemical shift: Self- referenced method with echo-planar spectroscopic imaging

An echo‐planar spectroscopic imaging method of temperature mapping is proposed. This method is sufficiently faster than the so‐called 3D magnetic resonance spectroscopic imaging (3D‐MRSI) method and does not require image subtractions, unlike the conventional phase mapping method when an internal reference signal is detectable. The water proton chemical shift measured by using the tissue lipid as an internal reference clearly visualized the temperature change in a porcine liver sample in vitro. It was also demonstrated that the internally referenced echo‐planar spectroscopic imaging method could markedly reduce a temperature error caused by a simple, translational motion between scans compared with the phase‐mapping method. Magn Reson Med 43:220–225, 2000.

Finger movements lighten neural loads in the recognition of ideographic characters.

The role of finger writing movements in recognizing Japanese ideographic characters (Kanji) was investigated using functional magnetic resonance imaging at 3 T. A total of 12 healthy native Japanese-speaking volunteers were studied while counting the number of strokes in ideographic characters. In experiment 1, a representation of the pronunciation of an ideographic character was displayed using Japanese syllabic characters. Volunteers were required to count the strokes of the ideographic character corresponding to the displayed phonogram. This procedure included retrieval and generation of ideographic characters. In experiment 2, the ideographic character itself was displayed and the volunteers counted its strokes. This procedure focused on visuospatial imagery processes. Each experiment was conducted under two different motor conditions. One condition allowed the subject to use finger movements to count the strokes, while the other disallowed any finger movements. In both experiments, movement-allowed conditions duly activated the primary motor area. The phonogram-displayed and movement-disallowed condition induced an augmented activation in a part of the left premotor area, which was assumed to be Exners area. This area might have been activated by a demand for sequential generation of character graphemes that corresponded to the phonogram displayed. The ideographic-character-displayed and movement-disallowed condition activated the dorsal occipitoparietal areas and the primary visual area, which might be involved in the visuospatial mental imagery processes. These results suggest that execution of finger movements during stroke counting of ideographic characters lightens the neural loads for grapheme generation on Exners area and for the visuospatial imagery processes on the dorsal pathway.

Visual language and handwriting movement: functional magnetic resonance imaging at 3 tesla during generation of ideographic characters

A functional magnetic resonance imaging experiment at 3 tesla was performed to investigate the collaborative mechanism between visuospatial processing and motor execution in performing visual language generation tasks. Japanese Kanji, ideographic characters, were utilized to design tasks. The bilateral border portions between the inferior parietal lobule and the occipital lobe were involved during a Kanji puzzle task, which required subjects to combine several parts into a Kanji. The higher motor areas, such as the premotor areas and the pre-supplementary motor areas, were also activated bilaterally during the puzzle task. The parieto-occipital activation may be related to analysis of configuration or segmentation/integration of Kanji figures. Activation in the higher motor areas may be induced by cognitive components related to motor function to perform the visuospatial language task, such as intense reference for displayed characters and finding a proper character for puzzle solution. A collaborative mechanism in these areas may explain the effectiveness of tactile reading in letter recognition by patients with pure alexia or kinesthetic facilitation by Kanji users when recalling difficult Kanji.

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.

Post-stimulus response in hemodynamics observed by functional magnetic resonance imaging—difference between the primary sensorimotor area and the supplementary motor area

The blood oxygen level dependency (BOLD) contrast is a useful tool for functional neuroimaging based on the hemodynamic response to neuronal activation. We observed different hemodynamic responses in the BOLD signal between the primary sensorimotor area (SM1) and the supplementary motor area (SMA) in the sequential finger movement task. In the SMA, a stronger initial overshoot and a post-stimulus overshoot were observed. It was hypothesized from the time course analysis that the stronger initial overshoot reflected the activation of the SMA for motor control programming in the initial phase. Although the post-stimulus overshoot may be partially explained by cerebral blood flow (CBF) cerebral blood volume (CBV) uncoupling, its mechanism remained unknown. In the SM1, only the initial overshoot was observed and the level of BOLD signal was almost constant after the initial overshoot during the task period. These observations suggested that the BOLD signal is characterized by both CBF-CBV uncoupling and the neuronal activation characteristics in each region.

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.

Activation during endogenous orienting of visual attention using symbolic pointers in the human parietal and frontal cortices: a functional magnetic resonance imaging study.

Brain activation induced by endogenous orienting with a motor response was investigated by functional magnetic resonance imaging. We conducted four cued-attention experiments in which peripheral attention was caused by one of three symbolic pointers (eyes, squares as artificial eyes, or an arrow) that was predictive or not predictive of the target location. Attentional shift caused by the predictive and non-predictive cues induced right and left parietal activation across cue modalities, respectively. Regardless of the predictability of the target location, the eyes and arrow induced left parietal and frontal activation, and the arrow induced left parietal activation more than the squares. These results suggested that the left parieto-frontal network was involved in motor attention caused by natural or familiar pointers, whereas the right parietal cortex was involved in endogenous orienting.

The effect of task block arrangement on the detectability of activation in fMRI

The effect of task block arrangements on the detection of brain activation was investigated. Sessions of functional magnetic resonance imaging (fMRI) including the same number of two different task conditions but with different arrangements were compared. The two task conditions were, A) Ellipse-shaped black and white checkerboard flicker stimulation at 4.2 Hz covering the bilateral visual field, and B) the same flicker stimuli covering only the left visual field. In the rest blocks (0), the subjects looked at a fixation point. Four different task block arrangements were compared, 1) A0 (0A0A0A0) and B0 (0B0B0B0), 2) A0B0 (0A0B0A0B0A0B0), 3) AB0 (0AB0AB0AB0) and 4) AB (0ABABAB). Bilateral V1, V2, V3 and the left V5 were activated by condition A, and the right V1 and V2 by B. The activation in the left visual field by A0 was larger than in the other three conditions. In a differential analysis between conditions A and B, activation in the left V3 and V5 was declined by AB0 or AB. When rest blocks were located in the post-stimulus undershoot phase, the % signal change of the BOLD signal was emphasized, which caused augmented significance in the detection of the activity. It was indicated that the outcome of the activation map was influenced by the arrangement of task blocks, even though the same number of task blocks were repeated within the sessions. In fMRI studies, task conditions should be carefully compared within or across sessions considering the characteristics of hemodynamic response functions.

Orthography effect on brain activities in the working memory process for phonologically ambiguous syllables: a functional magnetic resonance imaging study using Japanese speakers

English /l/ and /r/ sounds are not distinctive for Japanese speakers and they are loosely associated with corresponding graphemes. The purpose of this study was to investigate the brain activities in the memory process for the graphemes containing l and r in Japanese speakers. Two functional magnetic resonance imaging (at 1.5 T) experiments was conducted using syllable working memory tasks. The task using l and r syllables was coupled with either task using b and n syllables (l/r versus b/n block-designed experiment), or d and n syllables (l/r versus d/n block-designed experiment). The results revealed that the l/r working memory tasks induced augmented activation specifically in the right middle frontal gyrus (BA9, 46) and the right superior parietal lobule (BA7), compared with the b/n or d/n tasks. The results indicate that a visually-biased memory process (i.e. excessive visual rehearsal or monitoring) was executed for phonologically ambiguous syllables. Significant activation in the left inferior frontal gyrus was not observed only in the b/n task, probably because articulatory contrast between /b/ and /n/ sounds was highly clear for Japanese speakers.