Direct and fast detection of neuronal activation in the human brain with diffusion MRI

Using MRI, we found that a slowly diffusing water pool was expanding (1.7 +/- 0.3%) upon activation on the human visual cortex at the detriment of a faster diffusing pool. The time course of this water phase transition preceded the activation-triggered vascular response detected by usual functional MRI by several seconds. The observed changes in water diffusion likely reflect early biophysical events that take place in the activated cells, such as cell swelling and membrane expansion. Although the exact mechanisms remain to clarify, access to such an early and direct physiological marker of cortical activation with MRI will provide opportunities for functional neuroimaging of the human brain.

[Focal cortical dysplasia at the primary somatosensory cortex could manifest both intractable partial epilepsy and cortical reflex myoclonus]

We report a 31-year-old patient who suffered from the left foot motor seizure since 6 years of age. In addition to spontaneous seizures, the seizures tended to be triggered by somatosensory stimulus to the left foot. Recently, he developed irregular myoclonic jerks of the left foot. Neurologically, he had mild impairment of fine movements of the left foot, but otherwise no weakness or sensory disturbance was noted. Interictal spikes were frequently recorded at the vertex region, where ictal discharges also started during the video-EEG monitoring. Electrical stimulation of the left tibial nerve evoked giant cortical components of somatosensory evoked potentials and C-reflex. Magnetoencephalographic study of both interictal and jerk-locked averaged spikes located the equivalent current dipole of both activities at the left foot primary somatosensory cortex (SI), where 3 tesla MRI revealed a focal abnormality consistent with focal cortical dysplasia. The present non-invasive investigation suggests that focal cortical dysplasia at SI could manifest intrinsic, autonomous, epileptogenicity as well as extrinsic, stimulus-sensitive, hyperexcitability, which are clinically manifested as spontaneous seizures and cortical reflex myoclonus, respectively.

Comparison of 3.0- and 1.5-T Three-dimensional Time-of-Flight MR Angiography in Moyamoya Disease: Preliminary Experience

PURPOSE

To prospectively compare 3.0- and 1.5-T three-dimensional (3D) time-of-flight (TOF) magnetic resonance (MR) angiography in patients with moyamoya disease, with special emphasis on the visualization of abnormal netlike vessels (moyamoya vessels).

MATERIALS AND METHODS

Study protocols were approved by the local ethics committee; written informed consent was obtained from all patients. The study included 24 consecutive patients with moyamoya disease (four male and 20 female patients). Patients ranged in age from 17 to 66 years (mean age, 41 years). Moyamoya disease had been diagnosed in all patients before they were entered into the study. All patients underwent 3D TOF MR angiography at both 3.0 and 1.5 T; imaging examinations were performed within 14 days of each other. Maximum intensity projections (MIPs) obtained with MR angiography performed at both 3.0 and 1.5 T were evaluated by two neuroradiologists; the visualization of moyamoya vessels was graded according to a 4-point scale. For both 3.0- and 1.5-T imaging, the number of high-signal-intensity areas and the summation of cross-sectional areas of high signal intensity on source images obtained at the same level of MR angiography were compared quantitatively by using the Wilcoxon matched-pair signed-rank test.

RESULTS

Moyamoya vessels were better visualized on MIPs obtained with 3.0-T imaging than on MIPs obtained with 1.5-T imaging (P < .001). At the identical level of the source image, 3.0-T imaging depicted more high-signal-intensity areas than did 1.5-T imaging. Wider cross-sectional areas of moyamoya vessels were visualized with 3.0-T imaging than with 1.5-T imaging (P < .001).

CONCLUSION

Moyamoya vessels are better depicted with MR angiography at 3.0 T than at 1.5 T.

Effect of Benzodiazepine Hypnotic Triazolam on Relationship of Blood Pressure and Paco2 to Cerebral Blood Flow During Human Non-Rapid Eye Movement Sleep

We sought to clarify the effect of short-acting benzodiazepine hypnotic on the relationship of arterial blood pressure and arterial partial pressure of carbon dioxide (Paco2) to regional cerebral blood flow (rCBF) during human non-rapid-eye-movement (non-REM) sleep. Nine young normal volunteers were treated in a randomized, crossover design with triazolam or placebo and underwent positron emission tomography at night. During wakefulness and stage 2 and slow wave (stages 3 and 4) sleep, we measured mean arterial blood pressure (MAP), Paco2, and absolute CBF. With triazolam compared to placebo, MAP reduced gradually. During stage 2 sleep, Paco2 increased and whole-brain mean CBF decreased. With triazolam, relative rCBF of the left orbital basal forebrain decreased more during stage 2 than slow wave sleep, whereas absolute CBF of the occipital cortex and cerebral white matter remained constant. During triazolam-induced stage 2 sleep, absolute CBF of the cerebral white matter correlated more strongly to both MAP and Paco2 than during placebo sleep and also correlated more strongly to both MAP and Paco2 than absolute CBF of the occipital cortex. In the frontal white matter, during triazolam-induced stage 2 sleep compared to wakefulness, absolute CBF was significantly better correlated to MAP, but not to Paco2. During triazolam-induced stage 2, the cerebral white matter may receive a modulated CBF regulation having the strengthened relationship of Paco2 to CBF and, more locally, the frontal white matter may depend precariously on CBF regulation.

Regional cerebral blood flow in Parkinson disease with nonpsychotic visual hallucinations

BACKGROUND

Patients with Parkinson disease (PD) often experience visual hallucinations (VH) with retained insight (nonpsychotic) but the precise mechanism remains unclear.

OBJECTIVE

To clarify which neural substrates participate in nonpsychotic VH in PD, the authors evaluated regional cerebral blood flow (rCBF) changes in patients with PD and VH.

METHODS

The authors compared 24 patients with PD who had nonpsychotic VH (hallucinators) and 41 patients with PD who had never experienced VH (non-hallucinators) using SPECT images with N-isopropyl-p-[(123)I]iodoamphetamine. There were no significant differences in age, sex, duration of disease, doses of PD medications, Hoehn and Yahr scale, or Mini-Mental State Examination (MMSE) scores between the two groups. The rCBF data were analyzed using statistical parametric mapping (SPM).

RESULTS

The rCBF in the right fusiform gyrus was lower in the hallucinators than in the non-hallucinators (corrected p < 0.05 at cluster levels). The hallucinators revealed higher rCBF in the right superior and middle temporal gyri than the non-hallucinators (uncorrected p < 0.001). These significant differences were demonstrated after MMSE scores and duration of disease, which are the relevant factors associated with VH, were covariated out.

CONCLUSIONS

Nonpsychotic visual hallucinations in Parkinson disease (PD) may be associated with hypoperfusion in the right fusiform gyrus and hyperperfusion in the right superior and middle temporal gyri. These temporal regions are important for visual object recognition and these regional cerebral blood flow changes are associated with inappropriate visual processing and are responsible for nonpsychotic visual hallucinations in PD.

Early Experience with 3-T Magnetic Resonance Tractography in the Surgery of Cerebral Arteriovenous Malformations in and around the Visual Pathway

OBJECTIVE

To evaluate of the role of magnetic resonance (MR) tractography on the optic radiation with a 3-T MR unit in the surgery of cerebral arteriovenous malformation (AVM) in and around the visual pathway.

METHODS

Of the 322 patients with cerebral AVMs admitted to our clinic between 1978 and 2005, a study of MR tractography was made on 29 patients. Ten of those patients had AVMs in and around the visual pathway and were included in this study. There were two men and eight women ranging in age from 15 to 64 years (mean age, 34.5 +/- 14.8 yr). All of the patients underwent 3-T tractography of optic radiation (OR) and neuro-ophthalmologic evaluation. Four of the 10 patients underwent surgical resection of the AVM. A postoperative 3-T MR study and a neuro-ophthalmologic evaluation was performed 1 month after surgery in most patients.

RESULTS

The preoperative patients for whom tractography demonstrated a continuous bundle of OR from the medial temporal region to the primary visual cortex had minimal or no visual field loss, whereas the patients for whom the tractography did not show a continuous bundle of OR had significant visual loss. The patients for whom tractography in the postoperative study demonstrated a bundle of OR experienced no postoperative deterioration of the visual field loss, whereas the patients for whom tractography did not demonstrate a bundle of OR exhibited significant visual field loss.

CONCLUSION

This technique is thought to be useful in confirming the integrity of and localizing deviated tract and in evaluating the surgical risk, especially for nonhemorrhagic AVMs in and around the visual pathways, taking some limitations of this method into consideration.

MR imaging of Liliequist's membrane

Liliequist's membrane is an arachnoid structure well-known to neurosurgeons. However, the importance of this membrane had been lost until the development of endoscopic third ventriculostomy (ETV). ETV is superior in its minimal invasiveness, but in some subgroups of hydrocephalus, the effectiveness of ETV may be reduced. Liliequist's membrane may block the cerebrospinal fluid (CSF) flow from the defect of the third ventricle floor, which may cause failure of ETV. Liliequist's membrane can be visualized on magnetic resonance (MR) imaging in normal healthy individuals, however, its visibility is different among individuals. CSF artifacts exist to varying degrees, but do not impede visualization of Liliequist's membrane in most subjects. Since Liliequist's membrane is a cisternal structure, the three-dimensional (3D) constructive interference in steady state (CISS) sequence is useful. The outcome of ETV could be predicted with MR imaging findings of Liliequist's membrane in a patient with obstructive hydrocephalus. High-field (> or =3 Tesla) MR imaging of Liliequist's membrane also offers superior resolution and is expected to provide additional information about Liliequist's membrane.

Right hemispheric predominance in the segregation of mistuned partials

To elucidate the central mechanisms of sound segregation, we compared responses to a harmonic sound and a mistuned sound using a whole-head magnetoencephalography system. The harmonic sound was composed of a 200-Hz tone and its 2nd to 12th harmonics. The mistuned sound had, instead of the 600-Hz harmonic, a 696-Hz tone. In the right hemisphere, the amplitude of N100m responses evoked by the mistuned sound was significantly larger and the peak latency significantly longer than that evoked by the harmonic sound, suggesting that the right hemisphere plays a more important role than the left in detecting mistuned partials.

Diffusion-tensor fiber tractography: intraindividual comparison of 3.0-T and 1.5-T MR imaging

PURPOSE

To prospectively evaluate the depiction of brain fiber tracts at 3.0- versus 1.5-T diffusion-tensor (DT) fiber tractography performed with parallel imaging.

MATERIALS AND METHODS

Institutional review board approval was obtained, and each subject provided written informed consent. Subjects were 30 healthy volunteers (15 men, 15 women; mean age, 28 years; age range, 21-46 years). Single-shot spin-echo echo-planar magnetic resonance (MR) sequences with parallel imaging were applied. Four fiber tracts were reconstructed: corticospinal tract (CST), superior longitudinal fasciculus (SLF), corpus callosum (CC), and fornix. Two neuroradiologists compared 3.0- and 1.5-T tractography in terms of fiber tract depiction by using five depiction scores (scores 0-4) and numbers of reconstructed tract fibers and in terms of lateral asymmetry in the CST by using numbers of reconstructed fibers. The Wilcoxon signed rank test was applied for statistical analysis.

RESULTS

Visual scores for both CST hemispheres (P < .001), the right SLF (P = .005), the CC (P = .01), and the right fornix (P = .04) were higher at 3.0-T DT tractography. Larger numbers of CST (right, P = .008; left, P < .001), SLF (right, P = .001; left, P = .02), and fornix (bilaterally, P = .02) tract fibers were depicted at 3.0 T. The asymmetry index for the CST was lower (P < .001) at 3.0 T. Visual scores for the left SLF and the left fornix and numbers of CC tract fibers were not significantly different.

CONCLUSION

Depiction of most fiber tracts was improved at 3.0-T DT tractography compared with depiction at 1.5-T tractography.

Rapid recovery from coma with multifocal PLEDs in a patient with severe dementia and transient hypoxemia

We report a patient with severe dementia who acutely developed transient coma following possible acute anoxic encephalopathy, and presented multifocal periodic lateralized epileptiform discharges (PLEDs) on EEG, who had a good recovery from the acute state. Two EEGs were recorded from this patient. In the first EEG taken immediately after admission, multifocal PLEDs were prominent, and the background activity consisted of low voltage, continuous and irregular theta activity (4-6 Hz). The patient recovered from coma (GCS-3) to the conscious state (GCS-15) within 14 hours and was not associated with newly developed focal or global neurological deficits except for stable severe dementia which had developed in the previous several years. Another EEG taken 5 days later showed disappearance of multifocal PLEDs. Transient appearance of multifocal PLEDs might represent at least the transient, vulnerability associated with underlying dementia in this particular patient. We concluded that multifocal PLEDs do not always indicate a poor outcome in patients with possible acute anoxic encephalopathy, and rapid diagnosis and appropriate treatment should be done even if the initial EEG shows multifocal PLEDs.

Clinical outcome of patients with SREDA (subclinical rhythmic EEG discharge of adults)

OBJECTIVE

To clarify the clinical significance of subclinical rhythmic EEG discharge of adults' (SREDA) by analyzing characteristics of SREDA and the outcome of patients based on retrospective analysis of EEG data base.

METHODS

EEGs were recorded soon after the onset of patient's initial symptoms and repeatedly recorded at various intervals of 2-3 months in all 4 patients. Neurological findings, MRI and SPECT were also investigated.

SUBJECTS

Out of 340 consecutive inpatient population who had EEGs, 4 patients (1.2%) showed SREDA. They had a diagnosis of syncope, transient global amnesia, generalized tonic-clonic seizure and right temporal lobe epilepsy for each.

RESULTS

There was no consistent abnormality in the brain MRI, CT or SPECT among the 4 patients. The acute and transient symptoms disappeared and did not recur within the follow-up period of 28 months in any patient. In 2 patients SREDA disappeared in the follow-up EEG taken 7-14 days after the first EEG showing SREDA. In the other 2 patients, the follow-up EEGs taken 5 days after the first EEG with SREDA when clinical symptoms disappeared showed less frequent occurrence of SREDA.

CONCLUSION

Being different from the previous reports suggesting the relation with cardiogenic insults or persistent ischemic abnormality, SREDA can occur in patients with various acute brain dysfunctions followed by a favorable clinical outcome.

Cortical mechanisms of unilateral voluntary motor inhibition in humans

While motor control is very often a goal-oriented event, little is known about the mechanisms underlying the termination of motor performance. To investigate what type of cortical activation underlies the muscle relaxation required to terminate the act, we performed single- and double-pulse transcranial magnetic stimulation (TMS) studies during voluntary muscle relaxation in nine normal volunteers. Subjects maintained a weak isometric contraction of the right first dorsal interosseous muscle (FDI), and either increased the level of contraction (Contraction), terminated the contraction (Relaxation), or maintained it (No-go) depending on a visual cue. Motor evoked potentials (MEP) and the silent period (SP) were recorded from the FDI during motor activity. To measure intra-cortical inhibition (ICI), we also performed double-pulse TMS, applying subthreshold conditioning stimuli at interstimulus intervals of 2 ms. When single-pulse TMS was given just prior to muscle relaxation (-21 to -70 ms), the MEP was reduced while the SP was unchanged. Intra-cortical inhibition was smaller just prior to the muscle relaxation. Unilateral voluntary muscle relaxation may not be associated with activation of the intracortical inhibitory system, but rather with the possible excitation of the corticospinal system, which can inhibit motoneurons disynaptically. These findings suggest that multiple inhibitory mechanisms act in diverse ways to achieve motor inhibition.

Hemispheric asymmetry emerges at distinct parts of the occipitotemporal cortex for objects, logograms and phonograms: A functional MRI study

Behavioral and neuropsychological studies have suggested that the right hemisphere has a special advantage in the visual recognition of logograms. While this long-standing 'right hemisphere hypothesis' has never been investigated systematically by previous neuroimaging studies, a candidate neural substrate of such asymmetry might be found within the occipitotemporal cortex that is known to exhibit lateralized response to a certain class of stimuli, such as letters and faces. The present study examined the hemispheric specialization of brain activation during naming of objects, logograms and phonograms using functional magnetic resonance imaging. The three types of stimuli overall produced left-predominant activation of the perisylvian and inferior parietal regions relative to the resting baseline. This inter-hemispheric difference was significant irrespective of the stimuli type. In the occipitotemporal cortex, six subregions showing lateralized response were identified. That is, the three stimuli commonly produced left-lateralized response in the posterior fusiform and superior temporal gyri and right-lateralized response in the extrastriate cortex. Only logograms and objects produced a distinct cluster showing right-lateralized activation in the medial anterior fusiform gyrus associated with semantic knowledge, whereas only phonograms produced a left-lateralized activation in the posterior middle temporal cortex close to the site associated with visual perception of alphabetical letters. These findings suggest that while these stimuli similarly recruit the left perisylvian language area as a common neural component for naming, processing of objects and logograms becomes left-lateralized only in the downstream of the occipitotemporal cortex. By contrast, visual processing of phonograms is specialized to the left hemisphere in earlier stages of the area. The present data provide further evidence suggesting that both the left-right and anterior-posterior axes of the occipitotemporal cortex are differentially tuned according to the specific features of visual stimuli.

In Vivo Epileptogenicity of Focal Cortical Dysplasia: A Direct Cortical Paired Stimulation Study

PURPOSE

Alternation of the intracortical inhibitory and excitatory mechanisms in focal cortical dysplasia (FCD) has not been well elucidated in vivo in humans. We investigated in vivo alternation of these mechanisms in epileptogenesis of FCD by means of paired-pulse direct cortical electrical stimulation.

METHODS

A 31-year-old man with FCD at the left foot primary somatosensory (SI) and motor areas who underwent invasive monitoring with subdural electrodes was studied. By means of subdural electrodes, paired-pulse electrical stimulation was performed at the epileptic focus (foot SI) and control cortex (hand SI) with interstimulus interval (ISI) of 1-100 ms. Instead of using motor evoked potentials to investigate the degree of cortical excitability in response to motor cortex stimulation, we evaluated the size change of corticocortical evoked potentials (CCEPs), which are elicited at the adjacent cortex by direct cortical stimulation via fiber projection and thus reflect direct and indirect excitation of corticocortical projection neurons at the site of stimulation.

RESULTS

During the interictal state, paired-pulse stimulation of the focus revealed abnormally enhanced intracortical inhibition at ISI of 1-10 ms (maximum, 22%) compared with control stimulation of the hand SI (ISI of 1-2 ms; maximum, 18%) (p < 0.01). While the patient was having the somatosensory aura that later evolved into the left-leg clonic seizure, single and paired stimulation at the focus showed increased cortical excitability (enlarged CCEP) and decreased intracortical inhibition, respectively.

CONCLUSIONS

During the aura, interictally enhanced intracortical inhibition at the focus was replaced by increased cortical excitability and decreased intracortical inhibition, suggesting increased net intrinsic epileptogenicity during seizure generation in this patient with FCD.

[Temporal changes of diffusion-weighted MR images in a patient with transient global amnesia]

The pathogenesis of transient global amnesia (TGA) remains uncertain, although it is featured by characteristic clinical symptoms. We present a patient with TGA, in which diffusion-weighted MR image showed a punctuate hyperintense lesion in the left CA1 subfield of the hippocampus adjoining the lateral ventricle 24 hours after the onset. This lesion was observed with FLAIR image after 9 days from the onset, and therefore was considered to be a delayed ischemic lesion. A SPECT and PET studies 7 days after the onset showed a decrease of the CBF, CMRO2 and CMRglu, and was compatible with a delayed ischemic lesion. However, there were no cardiovascular risk factors nor abnormalities of vascular supply, and therefore the reason for microcirculatory disturbances remained unclear.

Surgical resection of an epileptogenic cortical dysplasia in the deep foot sensorimotor area

Epileptogenic foci in the foot/leg motor area of cortex are rarely resected, due to the risks of the surgical procedures. A 31-year-old right-handed man with cortical dysplasia deep in the central sulcus suffered from disturbances in walking due to frequent daily seizures. Following subdural electrode implantation to define the epileptogenic area and assess cortical function, limited regions of cortex were removed from the foot/leg primary motor and sensory areas under local anesthesia until the epileptiform discharges disappeared. Postoperative motor weakness and sensory disturbances completely resolved within 2 weeks and 2 months, respectively; the patient has been free from seizures for more than a year and a half postsurgery. Intraoperative examination demonstrated that small and moderate cortical dysplasia in the depths of the central sulcus exhibits both intrinsic epileptogenicity and function. Focused resection of the lower extremity of the sensorimotor area may be a surgical strategy for intractable epilepsy if resolution of clinical symptoms with minimal dysfunction due to the limited size of the resection is expected to follow surgery.

The high prognostic value of the histologic grade at the deep invasive front of tongue squamous cell carcinoma

BACKGROUND

Although many histopathologic factors in squamous cell carcinoma of the tongue predict the prognosis, the major predictive factors have not been identified clearly. This study analyzed the prognostic value of the histologic grade at the deep invasive front of tongue squamous cell carcinoma.

METHODS

The clinicopathologic features of 124 consecutive patients seen between January 1985 and December 1999 with previously untreated squamous cell carcinoma of the tongue were reviewed. Their mean age was 58.5 years (range: 23-90) and the male-female ratio was 1.8: 1 (79 men and 45 women). There were 41, 40, 30, and 13 cases at stage I to stage IV, respectively. The clinicopathologic factors, especially the histologic grade at the deep invasive front (invasive front grade, IFG), were analyzed to determine factors predicting prognosis.

RESULTS

The 5-year disease-free survival rate of the patients treated with curative aim only was 66.7%. Clinicopathologic factors significantly associated with the prognosis were T classification, tumor size, stage classification, tumor depth, macroscopic appearance, cervical lymph node metastasis (nodal metastasis), microvascular invasion, and IFG. In a multivariate analysis, patients with tumor depth >/=4 mm, IFG >/=8 points, and nodal metastasis had a reduced disease-free survival and IFG >/=11 points had a predictive value for nodal metastasis (odds ratio: 7.34; P = 0.0019).

CONCLUSION

This study found that a high IFG malignancy score had a high prognostic value for squamous cell carcinoma of the tongue.

Processing of Japanese morphogram and syllabogram in the left basal temporal area: electrical cortical stimulation studies

Language functions in the left basal temporal area (LBTA) were investigated using electrical cortical stimulation during functional mapping in six Japanese patients with refractory epilepsy. This study provides the first direct evidence that kana (Japanese syllabogram) is processed in the LBTA. Electrical stimulation of some areas within LBTA induced disturbance in overt reading of kana words only in the first trials, with no errors in the subsequent trials. By contrast, stimulation of the same area caused obvious disturbance in kana non-word reading in all trials. Since a kana word carries both meaning and sound while a kana non-word carries only sounds of a letter string, the contrasting results of partial and complete disturbance imply a possibility that there are two distinct pathways for kana reading: one dealing with both phonological and semantic aspects of the words and the other dealing only with phonological aspect. Kanji words (Japanese morphogram) and objects/pictures were found to be processed in an area different from the area for the kana non-word processing. Furthermore, the present study also identified the common area for processing kanji reading and object/picture naming. There were no errors in matching pictures with kanji words, indicating that concepts of pictures and meanings of kanji words were not interfered by the electrical stimulation of that area. The new insight provides a clue for partial description of processing pathways for language-related visual information in LBTA. Three types of information (morphological, phonological, and semantic) are conveyed together at some stages and are separated into different routes at some other stages.

Frontal nonconvulsive status epilepticus manifesting somatic hallucinations

Somatic hallucinations are subjective experience of false, strange sensations of things occurring in or to the body. They can be seen in psychotic disorders, but have not been well described as an ictal psychosis in patients with nonconvulsive status epilepticus (NCSE) of frontal origin. We reported a 69-year-old woman who had NCSE of frontal origin manifesting prolonged somatic hallucinations mimicking a psychiatric disorder and initially treated as such. Ictal EEG revealed the frontal focus and ictal single-photon emission computed tomography (SPECT) showed the activation, not only in the frontal area but also in the parietal area as the projected regions, both of which might be associated with the development of her symptoms. She also had two generalized tonic-chronic seizures out of psychosis. Her psychosis and ictal rhythmic discharges on EEG ceased with valproate and she has since remained free from the symptoms. The current case suggests that long-lasting somatic hallucinations could be an ictal psychosis in frontal NCSE and thus an EEG study is needed for an early diagnosis and treatment.

A brainstem variant of reversible posterior leukoencephalopathy syndrome

Reversible posterior leukoencephalopathy syndrome (RPLS) is caused by various heterogeneous factors, the commonest being hypertension, followed by nonhypertensive causes such as eclampsia, renal diseases and immunosuppressive therapy. Patients with RPLS exhibit bilateral white and gray matter abnormalities in the posterior aspects of the cerebral hemispheres. However, this syndrome may affect the brainstem predominantly, and these cases are designated as hypertensive brainstem encephalopathy. We present here two patients with reversible brainstem encephalopathy: one with hypertension and the other without hypertension. These patients presented with swelling and diffuse hyperintensities of the brainstem in fluid-attenuated inversion-recovery (FLAIR) and T2-weighted MRI, but with relatively mild clinical symptoms. They recovered without major neurological deficits, but had residual lacunar lesions in the pons. Reversible brainstem encephalopathy with characteristic MRI features was found in both hypertensive and nonhypertensive patients. These patients were diagnosed with a brainstem variant of RPLS, which is potentially fully reversible after an adequate treatment, and therefore should be carefully differentiated from other brainstem disease conditions.

Involvement of V5/MT+ in object substitution masking: evidence from repetitive transcranial magnetic stimulation

The visibility of a briefly presented target can be reduced by a subsequent weak mask that does not touch it, when the target is encoded in low spatiotemporal resolution. This phenomenon, called object substitution masking, has recently been proposed to reflect information updating in object-level representation, with perception of the target and the mask belonging to a single object through apparent motion. We investigated this issue by applying repetitive transcranial magnetic stimulation over V5/MT+, specialized in visual motion processing. The transient functional disruption of V5/MT+ produced by repetitive transcranial magnetic stimulation attenuated object substitution masking, while sham stimulation did not. Our results suggest that object substitution masking is mediated by normal functioning of V5/MT+. We conclude that repetitive transcranial magnetic stimulation of V5/MT+ impaired perceived object continuity and reduced object substitution masking accordingly.

Neural mechanisms underlying the processing of Chinese words: An fMRI study

The present study employed functional magnetic resonance imaging (fMRI) to investigate the neural mechanisms underlying orthographic, phonological and semantic processing of single character Chinese words. Twelve right-handed native Chinese speakers participated in the study. Three fundamental linguistic tasks including orthographic judgment, phonological matching and semantic association task were used. Our results demonstrated robust activation in the left posterior inferior temporal cortex (BA 37) for all three tasks. While the phonological matching task produced left-lateralized activation in the inferior frontal and parietal regions, semantic association task showed considerable bilateral activation in the inferior frontal and occipito-parietal regions. Direct comparison between phonological matching and semantic association task yielded semantic related activation in the anterior portion of the left inferior frontal gyrus (BA 47) and the right inferior frontal region (Broca's homology; BA 45). Behaviorally, there was no difference in response time between phonological matching and semantic association task. Our findings suggested that differential neural pathways were involved in the processing of meaning and sound of single-character Chinese words. The present study provided systemic information of the neural substrates underlying the processing of different components of Chinese language.

Cerebral white matter blood flow is constant during human non-rapid eye movement sleep: a positron emission tomographic study

This study aimed to identify brain regions with the least decreased cerebral blood flow (CBF) and their relationship to physiological parameters during human non-rapid eye movement (NREM) sleep. Using [15O]H2O positron emission tomography, CBF was measured for nine normal young adults during nighttime. As NREM sleep progressed, mean arterial blood pressure and whole brain mean CBF decreased significantly; arterial partial pressure of CO2 and, selectively, relative CBF of the cerebral white matter increased significantly. Absolute CBF remained constant in the cerebral white matter, registering 25.9 ± 3.8 during wakefulness, 25.8 ± 3.3 during light NREM sleep, and 26.9 ± 3.0 (ml·100 g−1·min−1) during deep NREM sleep ( P = 0.592), and in the occipital cortex ( P = 0.611). The regression slope of the absolute CBF significantly differed with respect to arterial partial pressure of CO2 between the cerebral white matter (slope 0.054, R = − 0.04) and frontoparietal association cortex (slope − 0.776, R = − 0.31) ( P = 0.005) or thalamus (slope − 1.933, R = − 0.47) ( P = 0.004) and between the occipital cortex (slope 0.084, R = 0.06) and frontoparietal association cortex ( P = 0.021) or thalamus ( P < 0.001), and, with respect to mean arterial blood pressure, between the cerebral white matter (slope − 0.067, R = − 0.10) and thalamus (slope 0.637, R = 0.31) ( P = 0.044). The cerebral white matter CBF keeps constant during NREM sleep as well as the occipital cortical CBF, and may be specifically regulated by both CO2 vasoreactivity and pressure autoregulation.