Manabu Honda

Functional relevance of cross-modal plasticity in blind humans.

Functional imaging studies of people who were blind from an early age have revealed that their primary visual cortex can be activated by Braille reading and other tactile discrimination tasks. Other studies have also shown that visual cortical areas can be activated by somatosensory input in blind subjects but not those with sight. The significance of this cross-modal plasticity is unclear, however, as it is not known whether the visual cortex can process somatosensory information in a functionally relevant way. To address this issue, we used transcranial magnetic stimulation to disrupt the function of different cortical areas in people who were blind from an early age as they identified Braille or embossed Roman letters. Transient stimulation of the occipital (visual) cortex induced errors in both tasks and distorted the tactile perceptions of blind subjects. In contrast, occipital stimulation had no effect on tactile performance in normal-sighted subjects, whereas similar stimulation is known to disrupt their visual performance. We conclude that blindness from an early age can cause the visual cortex to be recruited to a role in somatosensory processing. We propose that this cross-modal plasticity may account in part for the superior tactile perceptual abilities of blind subjects.

Cerebral processes related to visuomotor imagery and generation of simple finger movements studied with positron emission tomography.

Positron emission tomography was used to compare the functional anatomy of visual imagination and generation of movement. Subjects were asked to generate visual images of their finger movement in response to a preparatory signal. Four conditions were tested: in two, no actual movement was required; in the other two, a second signal prompted the subjects to execute the imagined movement. Which movement to imagine was either specified by the preparatory stimulus or freely selected by the subjects. Compared with a rest condition, tasks involving only imagination activated several cortical regions (inferoparietal cortex, presupplementary motor area, anterior cingulate cortex, premotor cortex, dorsolateral prefrontal cortex) contralateral to the imagined movement. Tasks involving both imagination and movement additionally increased activity in the ipsilateral cerebellum, thalamus, contralateral anteroparietal, and motor cortex and decreased activity in the inferior frontal cortex. These results support the hypothesis that distinct functional systems are involved in visuomotor imagination and generation of simple finger movements: associative parietofrontal areas are primarily related to visuomotor imagination, with inferior frontal cortex likely engaged in active motor suppression, and primary motor structures contribute mainly to movement execution.

Enhanced lateral premotor activity during paradoxical gait in Parkinson's disease.

Parkinsons disease (PD) patients often show marked improvement of hypokinetic gait when exposed to special stimuli. To investigate physiological mechanisms underlying this “paradoxical gait” induced by visual cues in PD patients, we examined regional cerebral blood flow changes during gait on a treadmill guided by two different visual cues, the lines oriented transversely to the direction of walk (TL) and the lines parallel to it (PL). Ten PD patients and 10 age‐matched controls received injections of 99mTc‐hexamethylpropyleneamine oxime twice, once during each walking condition. Brain perfusion images were obtained by single‐photon emission computed tomography. When affected by TL, PD patients showed marked improvement of gait parameters, mainly reduction of cadence. In regional cerebral blood flow analysis, when TL was compared with PL, both groups had common activation in the posterior parietal cortex and cerebellar hemispheres. Especially in the right lateral premotor cortex, PD patients showed enhanced activation induced by TL to a significantly greater degree than the controls. The present study indicates that the network dedicated to visuomotor control, particularly the lateral premotor cortex, plays an important role in the development of the paradoxical gait induced by special visual stimuli in PD patients. Ann Neurol 1999;45:329–336

Dissociation between contingent negative variation (CNV) and Bereitschaftspotential (BP) in patients with parkinsonism.

In order to clarify the generator mechanism of the late component of contingent negative variation (CNV), we compared the late CNV with Bereitschaftspotential (BP) in patients with parkinsonism (Parkinsons disease and progressive supranuclear palsy). In patients with mild symptoms (Hoehn Yahr grade I and II) both the late CNV and BP were clearly seen. In patients with severe symptoms (Hoehn Yahr grade III, IV and V) the BP was normally seen, but the late CNV was significantly smaller or absent (P < 0.001 at Cz) and it was also significantly smaller than that obtained from age-matched normals. In one patient (H-Y grade II) who had normal BP, the late CNV was diminished selectively at the midline area. Since it was reported that the late CNV arises from at least the supplementary motor area (SMA), selective diminution of the late CNV at the midline could be explained by the decreased activity of the SMA in parkinsonism. It was also previously reported that the BP was absent but the late CNV was normally present in a patient with cerebellar efferent lesion (Ikeda et al., 1994). Taken together with the experimental results indicating that movement-related neurons in the putamen behave contingent on external stimuli, it is suggested that subcortical generating mechanism is different for the late CNV and BP although both commonly share at least some cortical generators, and that the basal ganglia are most likely responsible for the generation of the late CNV and the cerebellar efferent system for the generation of the BP.

Movement-related cortical potentials and regional cerebral blood flow change in patients with stroke after motor recovery

We investigated brain activity during the self-initiated, simple, repetitive hand movement in two patients with hemiparesis due to stroke, who showed relatively good motor recovery, using movement-related cortical potential (MRCP) and regional cerebral blood flow (rCBF) measurements with positron emission tomography (PET). One patient had cortical lesions in the left premotor and left parietal cortices due to cerebral thrombosis, and the other had lesions in the right Rolandic area and several subcortical areas due to the occlusion of the right internal carotid artery. MRCPs in both patients showed lack of the contralateral predominance in amplitude of the late component of slow negative shift prior to the movement of the recovered hand. PET activation study showed increased rCBF in the ipsilateral hemisphere during the movement of the recovered hand. These findings suggest that the ipsilateral hemisphere to the recovered hand may play an important role in the process of motor recovery in patients with cortical infarction, especially within the time period of several hundred ms before the onset of each movement.

Toward Neuroanatomical Models of Analogy: A Positron Emission Tomography Study of Analogical Mapping ☆

Several brain regions associated with analogical mapping were identified using (15)O-positron emission tomography with 12 normal, high intelligence adults. Each trial presented during scanning consisted of a source picture of colored geometric shapes, a brief delay, and a target picture of colored geometric shapes. Analogous pictures did not share similar geometric shapes but did share the same system of abstract visuospatial relations. Participants judged whether each source-target pairing was analogous (analogy condition) or identical (literal condition). The results of the analogy-literal comparison showed activation in the dorsomedial frontal cortex and in the left hemisphere; the inferior, middle, and medial frontal cortices; the parietal cortex; and the superior occipital cortex. Based on these results as well as evidence from relevant cognitive neuroscience studies of reasoning and of executive working memory, we hypothesize that analogical mapping is mediated by the left prefrontal and inferior parietal cortices.

Comparison of auditory, somatosensory, and visually instructed and internally generated finger movements: a PET study.

We sought to determine how the pattern of cerebral activation, and in particular in frontal motor areas, during the performance of conditional motor tasks is dependent upon the modality of instruction (visual, auditory, or somatosensory). Regional cerebral blood flow (rCBF) changes with externally instructed movements were also compared with internally generated, self-paced, movements. We used positron emission tomography (PET) with the tracer H2(15O) to measure rCBF in 22 healthy volunteers. External stimuli consisted of the randomized presentation of single or double impulses using a single modality for each condition. In the movement scans, the subjects used the index and middle fingers of their right hands to press a left button for a single and a right button for a double impulse, respectively. In the control scans, subjects were required to covertly distinguish a single from a double stimulus without a motor response. Data were analyzed using conventional subtraction techniques with a statistical threshold of Z > 2.33 with corrections for multiple comparisons. When the activation differences between the three externally instructed movement conditions were statistically compared, nonsignificant trends toward increased rCBF in the sensory cortex of the modality of the cue were observed but no differential activity in cortical motor areas. Internally generated movements, when compared to externally triggered movements, were associated with enhanced activation in bilateral medial and lateral premotor, dorsolateral prefrontal and superior parietal regions, largely confirming previous reports. The data indicate that, on a regional level, modality-specific processing in a conditional motor task does not occur in frontal motor areas and is probably confined to sensory areas.

Functional mapping of human medial frontal motor areas

Abstract. Two functional brain-mapping techniques, functional magnetic resonance imaging (fMRI) and cortical stimulation by chronically implanted subdural electrodes, were used in combination for presurgical evaluation of three patients with intractable, partial motor seizures. Brain mapping was focused on characterizing motor-related areas in the medial frontal cortex, where all patients had organic lesions. Behavioral tasks for fMRI involved simple finger and foot movements in all patients and mental calculations in one of them. These tasks allowed us to discriminate several medial frontal motor areas: the presupplementary motor areas (pre-SMA), the somatotopically organized SMA proper, and the foot representation of the primary motor cortex. All patients subsequently underwent cortical stimulation through subdural electrodes placed onto the medial hemispheric wall. In each patient, the cortical stimulation map was mostly consistent with that patients brain map by fMRI. By integrating different lines of information, the combined fMRI and cortical stimulation map will contribute not only to safe and effective surgery but also to further understanding of human functional neuroanatomy.

Modulation of the Visual Word Retrieval System in Writing: A Functional MRI Study on the Japanese Orthographies

We used functional magnetic resonance imaging (fMRI) to examine whether the act of writing involves different neuro-psychological mechanisms between the two script systems of the Japanese language: kanji (ideogram) and kana (phonogram). The main experiments employed a 2 2 factorial design that comprised writing-to-dictation and visual mental recall for kanji and kana. For both scripts, the actual writing produced a widespread fronto-parietal activation in the left hemisphere. Especially, writing of kanji activated the left posteroinferior temporal cortex (lPITC), whereas that of kana also yielded a trend of activation in the same area. Mental recall for both scripts activated similarly the left parieto-temporal regions including the lPITC. The writing versus mental recall comparison revealed greater activations in the left sensorimotor areas and right cerebellum. The kanji versus kana comparison showed increased responses in the left prefrontal and anterior cingulate areas. Especially, the lPITC showed a significant task-by-script interaction. Two additional control tasks, repetition (REP) and semantic judgment (SJ), activated the bilateral perisylvian areas, but enhanced the lPITC response only weakly. These results suggest that writing of the ideographic and phonographic scripts, although using the largely same cortical regions, each modulates the visual word-retrieval system according to their graphic features. Furthermore, comparisons with two additional tasks indicate that the activity of the lPITC increases especially in expressive language operations regardless of sensory modalities of the input stimulus.

Desynchronization and synchronization of central 20-Hz rhythms associated with voluntary muscle relaxation: a magnetoencephalographic study.

Abstract. To clarify the cortical mechanisms involved in motor inhibition, modulation of cortical rhythms around 20xa0Hz during voluntary muscle relaxation was compared to that during muscle contraction in ten normal volunteers, using a whole head type neuromagnetometer. Each subject relaxed or contracted the right forearm muscles, from which electromyograms were recorded. After band-pass filtering magnetoencephalographic signals into frequency bands of 6–10, 10–14, 14–18, 18–22, 22–26, and 26–30xa0Hz, the signals of each frequency band were rectified and averaged with respect to the onset of motor trial. The relaxation task showed movement-related 20-Hz desynchronization over bilateral central areas beginning a few seconds before the termination of muscle contraction. Twenty-hertz desynchronization was present also for the contraction task at the same location within each subject. The two tasks had a positive correlation among subjects in both the percent decrease (r2=0.76, P<0.01) and the peak time (r2=0.61, P<0.05) for the contralateral 20-Hz desynchronization. After the muscle relaxation, desynchronization was followed by conspicuous movement-related synchronization of the 20-Hz passband in the contralateral central areas, which was significantly larger than that after the contraction (P<0.001). The results suggest that the voluntary muscle relaxation involves the modulation of central rhythms starting a few seconds before the actual event, and the 20-Hz desynchronization has a similar temporal property in the muscle relaxation and contraction. The 20-Hz synchronization in the contralateral central area after the muscle relaxation may be associated with the temporally arrayed termination of the ongoing muscle contraction.