Loss of Katnal2 leads to ependymal ciliary hyperfunction and autism-related phenotypes in mice.

Autism spectrum disorders (ASD) frequently accompany macrocephaly, which often involves hydrocephalic enlargement of brain ventricles. Katnal2 is a microtubule-regulatory protein strongly linked to ASD, but it remains unclear whether Katnal2 knockout (KO) in mice leads to microtubule- and ASD-related molecular, synaptic, brain, and behavioral phenotypes. We found that Katnal2-KO mice display ASD-like social communication deficits and age-dependent progressive ventricular enlargements. The latter involves increased length and beating frequency of motile cilia on ependymal cells lining ventricles. Katnal2-KO hippocampal neurons surrounded by enlarged lateral ventricles show progressive synaptic deficits that correlate with ASD-like transcriptomic changes involving synaptic gene down-regulation. Importantly, early postnatal Katnal2 re-expression prevents ciliary, ventricular, and behavioral phenotypes in Katnal2-KO adults, suggesting a causal relationship and a potential treatment. Therefore, Katnal2 negatively regulates ependymal ciliary function and its deletion in mice leads to ependymal ciliary hyperfunction and hydrocephalus accompanying ASD-related behavioral, synaptic, and transcriptomic changes.

No replication of direct neuronal activity-related (DIANA) fMRI in anesthetized mice.

Direct imaging of neuronal activity (DIANA) by functional magnetic resonance imaging (fMRI) could be a revolutionary approach for advancing systems neuroscience research. To independently replicate this observation, we performed fMRI experiments in anesthetized mice. The blood oxygenation level-dependent (BOLD) response to whisker stimulation was reliably detected in the primary barrel cortex before and after DIANA experiments; however, no DIANA-like fMRI peak was observed in individual animals' data with the 50 to 300 trials. Extensively averaged data involving 1050 trials in six mice showed a flat baseline and no detectable neuronal activity-like fMRI peak. However, spurious, nonreplicable peaks were found when using a small number of trials, and artifactual peaks were detected when some outlier-like trials were excluded. Further, no detectable DIANA peak was observed in the BOLD-responding thalamus from the selected trials with the neuronal activity-like reference function in the barrel cortex. Thus, we were unable to replicate the previously reported results without data preselection.

Mapping cerebral perfusion in mice under various anesthesia levels using highly sensitive BOLD MRI with transient hypoxia.

Cerebral perfusion is critical for the early detection of neurological diseases and for effectively monitoring disease progression and treatment responses. Mouse models are widely used in brain research, often under anesthesia, which can affect vascular physiology. However, the impact of anesthesia on regional cerebral blood volume and flow in mice has not been thoroughly investigated. In this study, we have developed a whole-brain perfusion MRI approach by using a 5-second nitrogen gas stimulus under inhalational anesthetics to induce transient BOLD dynamic susceptibility contrast (DSC). This method proved to be highly sensitive, repeatable within each imaging session, and across four weekly sessions. Relative cerebral blood volumes measured by BOLD DSC agree well with those by contrast agents. Quantitative cerebral blood volume and flow metrics were successfully measured in mice under dexmedetomidine and various isoflurane doses using both total vasculature-sensitive gradient-echo and microvasculature-sensitive spin-echo BOLD MRI. Dexmedetomidine reduces cerebral perfusion, while isoflurane increases cerebral perfusion in a dose-dependent manner.

No Replication of Direct Neuronal Activity-related (DIANA) fMRI in Anesthetized Mice.

Toi et al. (Science, 378, 160-168, 2022) reported direct imaging of neuronal activity (DIANA) by fMRI in anesthetized mice at 9.4 T, which could be a revolutionary approach for advancing systems neuroscience research. There have been no independent replications of this observation to date. We performed fMRI experiments in anesthetized mice at an ultrahigh field of 15.2 T using the identical protocol as in their paper. The BOLD response to whisker stimulation was reliably detected in the primary barrel cortex before and after DIANA experiments; however, no direct neuronal activity-like fMRI peak was observed in individual animals' data with the 50-300 trials used in the DIANA publication. Extensively averaged data involving 1,050 trials in 6 mice (1,050×54 = 56,700 stimulus events) and having a temporal signal-to-noise ratio of 7,370, showed a flat baseline and no detectable neuronal activity-like fMRI peak. Thus we were unable to replicate the previously reported results using the same methods, despite a much higher number of trials, a much higher temporal signal-to-noise ratio, and a much higher magnetic field strength. We were able to demonstrate spurious, non-replicable peaks when using a small number of trials. It was only when performing the inappropriate approach of excluding outliers not conforming to the expected temporal characteristics of the response did we see a clear signal change; however, these signals were not observed when such a outlier elimination approach was not used.

Baseline Correction of the Human 1H MRS(I) Spectrum Using T2* Selective Differential Operators in the Frequency Domain.

The baseline distortion caused by water and fat signals is a crucial issue in the 1H MRS(I) study of the human brain. This paper suggests an effective and reliable preprocessing technique to calibrate the baseline distortion caused by the water and fat signals exhibited in the MRS spectral signal. For the preprocessing, we designed a T2* (or linewidth within the spectral signal) selective filter for the MRS(I) data based on differential filtering within the frequency domain. The number and types for the differential filtering were determined by comparing the T2* selectivity profile of each differential operator with the T2* profile of the metabolites to be suppressed within the MRS(I) data. In the performance evaluation of the proposed differential filtering, the simulation data for MRS spectral signals were used. Furthermore, the spectral signal of the human 1H MRSI data obtained by 2D free induction decay chemical shift imaging with a typical water suppression technique was also used in the performance evaluation. The absolute values of the average of the filtered dataset were quantitatively analyzed using the LCModel software. With the suggested T2* selective (not frequency selective) filtering technique, in the simulated MRS data, we removed the metabolites from the simulated MRS(I) spectral signal baseline distorted by the water and fat signal observed in the most frequency band. Moreover, in the obtained MRSI data, the quantitative analysis results for the metabolites of interest showed notable improvement in the uncertainty estimation accuracy, the CRLB (Cramer-Rao Lower Bound) levels.

The thalamocortical inhibitory network controls human conscious perception.

Although conscious perception is a fundamental cognitive function, its neural correlates remain unclear. It remains debatable whether thalamocortical interactions play a decisive role in conscious perception. To clarify this, we used functional magnetic resonance imaging (fMRI) where flickering red and green visual cues could be perceived either as a non-fused colour or fused colour. Here we show significantly differentiated fMRI neurodynamics only in higher-order thalamocortical regions, compared with first-order thalamocortical regions. Anticorrelated neurodynamic behaviours were observed between the visual stream network and default-mode network. Its dynamic causal modelling consistently provided compelling evidence for the involvement of higher-order thalamocortical iterative integration during conscious perception of fused colour, while inhibitory control was revealed during the non-fusion condition. Taken together with our recent magnetoencephalography study, our fMRI findings corroborate a thalamocortical inhibitory model for consciousness, where both thalamic inhibitory regulation and integrative signal iterations across higher-order thalamocortical regions are essential for conscious perception.

Postnatal age-differential ASD-like transcriptomic, synaptic, and behavioral deficits in Myt1l-mutant mice.

Myelin transcription factor 1 like (Myt1l), a zinc-finger transcription factor, promotes neuronal differentiation and is implicated in autism spectrum disorder (ASD) and intellectual disability. However, it remains unclear whether Myt1l promotes neuronal differentiation in vivo and its deficiency in mice leads to disease-related phenotypes. Here, we report that Myt1l-heterozygous mutant (Myt1l-HT) mice display postnatal age-differential ASD-related phenotypes: newborn Myt1l-HT mice, with strong Myt1l expression, show ASD-like transcriptomic changes involving decreased synaptic gene expression and prefrontal excitatory synaptic transmission and altered righting reflex. Juvenile Myt1l-HT mice, with markedly decreased Myt1l expression, display reverse ASD-like transcriptomes, increased prefrontal excitatory transmission, and largely normal behaviors. Adult Myt1l-HT mice show ASD-like transcriptomes involving astrocytic and microglial gene upregulation, increased prefrontal inhibitory transmission, and behavioral deficits. Therefore, Myt1l haploinsufficiency leads to ASD-related phenotypes in newborn mice, which are temporarily normalized in juveniles but re-appear in adults, pointing to continuing phenotypic changes long after a marked decrease of Myt1l expression in juveniles.

Track-Density Ratio Mapping With Fiber Types in the Cerebral Cortex Using Diffusion-Weighted MRI.

The nerve fibers are divided into three categories: projection, commissural, and association fibers. This study demonstrated a novel cortical mapping method based on these three fiber categories using MR tractography data. The MR fiber-track data were extracted using the diffusion-weighted 3T-MRI data from 19 individuals' Human Connectome Project dataset. Anatomical MR images in each dataset were parcellated using FreeSurfer software and Brainnetome atlas. The 5 million extracted tracks per subject by MRtrix software were classified based on the basic cortical structure (cortical area in the left and right hemisphere, subcortical area), after the tracks validation procedure. The number of terminals for each categorized track per unit-sized cortical area (1 mm3) was defined as the track-density in that cortical area. Track-density ratio mapping with fiber types was achieved by mapping the density-dependent color intensity for each categorized tracks with a different primary color. The mapping results showed a highly localized, unique density ratio map determined by fiber types. Furthermore, the quantitative group data analysis based on the parcellation information revealed that the majority of nerve fibers in the brain are association fibers, particularly in temporal, inferior parietal, and occipital lobes, while the projection and commissural fibers were mainly located in the superior part of the brain. Hemispheric asymmetries in the fiber density were also observed, such as long association fiber in the Broca's and Wernicke's areas. We believe this new dimensional brain mapping information allows us to further understand brain anatomy, function.

New analysis method for functional brain imaging: White noise removed T2* variation mapping using multi-echo EPI.

BACKGROUND: Generally, the analysis of functional magnetic resonance imaging (fMRI) using echo-planar imaging (EPI) data is based on independent component analysis (ICA) and the general linear model (GLM). The application of these two approaches is highly independent, like GLM is for task-related activation mapping, and ICA is for resting-state imaging. Herein, we propose white noise-removed T2*-variation mapping as a new analysis method for fMRI that integrates the two conventional mapping approaches. NEW METHOD: We derived the standard deviation to the mean-square ratio of the true T2* signal from the multi-echo EPI (ME-EPI) dataset. For the true T2*-variation-based value, we removed the S0 (initial signal intensity) and white noise component from the variation in the EPI signal using signal-coherence analysis of the echo time (TE) dataset and slope analysis of the TE-variated coefficient of variation of the ME-EPI dataset. RESULTS: The activation mapping for a visual task and resting-state imaging by the proposed method showed the reliable activation map in the visual cortex area and area for the typical default mode network, with white noise and the S0 component removed. COMPARISON WITH EXISTING METHODS: Conventional analyses for fMRI cannot be applied to both activation mapping and resting-state imaging, with white noise removed, while the proposed method can be applied. CONCLUSIONS: We demonstrated white noise-removed true T2*-variation-based mapping as a new functional brain analysis approach. We expect the method allows studying in which that the association between task timing and brain activity is somewhat uncertain, such as studies of emotion and awareness.

Proposal for human visual pathway in the extrastriate cortex by fiber tracking method using diffusion-weighted MRI.

The extrastriate cortex in the human visual cortex is divided into two distinct clusters: the "what-information" processing area and the "where-information" processing area. It is widely accepted that the "what-information" cluster is processed through the ventral stream to the temporal cortex, and the "where-information" cluster through the dorsal stream to the parietal cortex. In human neuroanatomy, fiber bundles for the ventral stream (such as the inferior longitudinal fasciculus) are well defined, whereas fibers for the dorsal stream are poorly understood. In this study, we attempted to trace the dorsal stream fibers using a fiber tracking method using 7.0T diffusion-weighted MRI. We used data from a healthy male subject as well as from an unbiasedly selected nine-subject dataset in the Human Connectome Project. The surface of the visual area, including V1, V2, V3, V4, MT, was determined from the Brainnetome atlas (Fan et al., 2016), which is the connectivity-based parcellation framework of the human brain. The resulting visual pathway indicated that the putative pathway for the classical dorsal stream is unlikely to exist. Instead, we demonstrated that fiber connections exist between the angular gyrus with MT in the visual cortex, and between the angular gyrus and IT in the temporal cortex. Through that, we composed a two-pathway model for where-information processing that passes through the angular gyrus. Finally, we proposed a modified human visual pathway model based on our fiber tracking results in this report. The modified where-information pathway will provide a new aspect for the study of human visual processing.

Fiber-distance-based unsupervised clustering of MR tractography data.

BACKGROUND: MR tractography from diffusion tensor imaging provides a non-invasive way to explore white matter pathways in the human brain. However, a challenge to extracting reliable anatomical information from these data is the use of reliable and effective clustering methodologies. In this paper, we implemented a new version of a robust unsupervised clustering method from MR tractography data using the density-based spatial clustering of applications with noise (DBSCAN) algorithm. NEW METHOD: Conventional DBSCAN clustering methods for MR tractography data use each fiber's start and end point as well as the distance between start and end points. Instead, in this study, we extracted and used a fiber-distance matrix generated for all fiber combinations from the tractography dataset in DBSCAN clustering. The two DBSCAN parameters-minimum point number and maximum radius of the neighborhood-were selected according to the value generated with the cluster stability index (CSI). RESULTS: Performing the proposed CSI-optimized DBSCAN-based clustering method on MR tractography data of the superior longitudinal fasciculus generated 6 robust, non-overlapping, clusters that are neuroanatomically related. COMPARISON WITH EXISTING METHODS: Conventional DBSCAN-based clustering methods have intrinsic error potential in the clustering results due to deviations in fiber shape and fiber location. The proposed method did not exhibit clustering error caused by deviation in fiber trajectory or fiber location. CONCLUSIONS: We implemented a new, robust DBSCAN-based fiber clustering method for MR tractography data. The CSI-optimized DBSCAN-based unsupervised clustering is applicable to investigation of the neuroconnectome and the fiber structure of the brain.

Papez Circuit Observed by in vivo Human Brain With 7.0T MRI Super-Resolution Track Density Imaging and Track Tracing.

The Papez circuit has been considered as an important anatomical substrate involved in emotional experience. However, the circuit remains difficult to elucidate in the human brain due to the resolution limit of current neuroimaging modalities. In this article, for the first time, we report the direct visualization of the Papez circuit with 7-Tesla super-resolution magnetic resonance tractography. Two healthy, young male subjects (aged 30 and 35 years) were recruited as volunteers following the guidelines of the institutional review board (IRB). Track density imaging (TDI) generation with track tracing was performed using MRtrix software package. With these tools, we were able to visualize the entire Papez circuit. We believe this is the first study to visualize the complete loop of the Papez circuit, including the perforant path (PP), thalamocortical fibers of the anterior nucleus (AN), and mammillothalamic tract (MTT), which were hitherto difficult to visualize by conventional imaging techniques.

Newly observed anterior thalamocortical fiber of the thalamus using 7.0T super-resolution magnetic resonance tractography and its implications for the classical Papez circuit.

Here, we have employed recently developed super-resolution tractography using 7.0T-MRI to analyze the fine structures involved in thalamocortical connections, something that has proved difficult using conventional techniques. We detail a newly observed thalamocortical pathway connecting the anterior nucleus of the thalamus and the cingulate cortex not via the internal capsule but via the septal area. The observed pathway is believed to be a classical pathway of the Papez circuit but had not been previously identified.

A Newly Identified Frontal Path from Fornix in Septum Pellucidum with 7.0T MRI Track Density Imaging (TDI) - The Septum Pellucidum Tract (SPT).

The high anatomical contrast achieved with the newly emerging MRI tractographic technique of super-resolution track density imaging (TDI) encouraged us to search for a new fiber tract in the septum pellucidum. Although this septum pellucidum tract (SPT) has been observed previously, its connections were unclear due to ambiguity and limited resolution of conventional MRI images. It is now possible to identify detailed parts of SPT with the increased resolution of TDI, which involves diffusion MRI imaging, whole-brain tractography, and voxel subdivision using the track-count information. Four healthy male subjects were included in the study. The experiment was performed with 7.0T MRI, following the guidelines of the institute's institutional review board. Data were processed with the super-resolution TDI technique to generate a tractographic map with 0.18 mm isotropic resolution. The SPT was identified in all subjects. Based on additional seed tracking method with inter-axis correlation search, we have succeeded in identifying a new frontal lobe pathway in the SPT. We hypothesize that the tract is connected as a superior dorsal branch of the fornix that leads to the prefrontal cortex.

Pictorial review of in vivo human brain: from anatomy to molecular imaging.

Recent advances in neuroimaging demonstrated many markedly improved images hitherto unavailable, specifically the areas that lie deep in the brain. The anatomic images of the deep brain structure taken in vivo using 7.0 T magnetic resonance imaging (MRI) and the molecular images using high resolution research tomography positron emission tomography, as well as the fusion images using state-of-art neuroimaging techniques can contribute to the noninvasive treatment of neurologic and psychiatric diseases. We present a pictorial review with selected brain images obtained from 7.0 T MRI, and the images of brain metabolic function accompanied with high resolution anatomic information obtained using the positron emission tomography-MRI fusion technique. In addition, we present some recent results of the cerebral microvasculature and diffusion tractography imaging for the deep brain areas acquired with 7.0 T MRI.

Anterior commissure--posterior commissure revisited.

OBJECTIVE: The anterior commissure (AC) and posterior commissure (PC) are the two distinct anatomic structures in the brain which are difficult to observe in detail with conventional MRI, such as a 1.5T MRI system. However, recent advances in ultra-high resolution MRI have enabled us to examine the AC and PC directly. The objective of the present study is to standardize the shape and size of the AC and PC using a 7.0T MRI and to propose a new brain reference line. MATERIALS AND METHODS: Thirty-four, 21 males and 13 females, healthy volunteers were enrolled in this study. After determining the center of each AC and PC, we defined the connection of these centers as the central intercommissural line (CIL). We compared the known extra- and intra-cerebral reference lines with the CIL to determine the difference in the angles. Additionally, we obtained horizontal line from flat ground line of look front human. RESULTS: The difference in angle of the CIL and the tangential intercommissural line (TIL) from the horizontal line was 8.7 ± 5.1 (11 ± 4.8) and 17.4 ± 5.2 (19.8 ± 4.8) degrees in males and females, respectively. The difference in angle between the CIL and canthomeatal line was 10.1 in both male and female, and there was no difference between both sexes. Likewise, there was no significant difference in angle between the CIL and TIL between both sexes (8.3 +/- 1.1 in male and 8.8 +/- 0.7 in female). CONCLUSION: In this study, we have used 7.0T MRI to define the AC and PC quantitatively and in a more robust manner. We have showed that the CIL is a reproducible reference line and serves as a standard for the axial images of the human brain.

Intermixed structure of voxels with different hemispheric characteristics in the fusiform face area.

The fusiform face area, a high-level visual area, is pivotal in processing facial information. This area receives inputs from the left and right visual fields unlike the primary visual area, which only receives inputs from its contralateral visual field. Response of the fusiform face area to ipsilateral stimulation depends on the signals crossing over at the corpus callosum. We investigated the distribution of voxel-wise activation to determine whether ipsilateral-dominant voxels exist in the fusiform face area using high spatial resolution functional MRI at 7 T. We further examined the possible functional differences between ipsilateral-dominant and contralateral-dominant voxels. By unilateral visual field stimulation, we detected ipsilateral-dominant voxels in the right fusiform face area. Their distribution was spatially heterogeneous. We tested upright and inverted facial stimulation confined to unilateral visual fields and found that these ipsilateral-dominant voxels had a different functional nature from contralateral-dominant voxels.

Identification and morphologic assessment of mesocoelic recess by in vivo human brain imaging with 7.0-T magnetic resonance imaging.

OBJECTIVE: The mesocoelic recess (MCR) is found in the brain of human embryos and fetuses. The mesocoelic recess seems to be functionally related to the subcommissural organ that is one of neurosecretory organs involved in osmoregulation on the basis of data from other species. Subsequently, recent speculation as to the importance of the subcommissural organ in the development of congenital hydrocephalus has been raised. Yet unlike other mammals, MCR is known to be a vestigial structure in the adult human brain. Here, we performed the in vivo imaging identification of this space to investigate functional and clinical correlations. METHODS: We studied adult human brains using a 7.0-T magnetic resonance imaging (MRI). Twenty healthy individuals aged 22 to 30 years were selected, and they were all volunteers. The parasagittal images through the intercommissural line were examined. We determined the type of shape of the MCR; a triangular C shape was classified as type 1, and a trapezoidal concave shape was classified as type 2. RESULTS: In 14 brains, the recesses were radiologically demonstrated just rostral to the tectal plate of the midbrain and covered the ventral aspect of the posterior commissure and pointed the opening into the aqueduct. The average size of the circumference of the MCR measured from the end point of the C-shaped cup was 6.82 mm. CONCLUSIONS: This study on the anatomy of the MCR of adult brains in vivo is the first of its kind, thanks to the availability of 7.0-T MRI because it has been barely discernible even in autopsy specimens as well as in radiology owing to the resolution limit of the currently available imaging system. The current study raises awareness of the MCR, an important but little-known anatomic structure in adult human brain. This visualization of MCR in human in vivo with ultrahigh-field MRI will certainly provide us important clues including the functional information of MCR, a mystery of modern neurological science.

Classification of the venous architecture of the pineal gland by 7T MRI.

Magnetic resonance imaging (MRI) at 7.0 Tesla (7T) can show many details of anatomical structures with unprecedented resolution and contrast. In this report, we describe for the first time the unexpected wide variation in pineal gland structure, as visualized by MR images obtained with 7T in a group of healthy young volunteers. A total of 34 volunteers (22 men and 12 women) were enrolled in the study. Their 7T MR images revealed such wide variations in pineal gland shape that it led us to attempt to classify the patterns seen in these pineal glands. Indeed, they were successfully correlated with a previous human cadaver study of venous structures by Tamaki et al., who classified the venous structures of the pineal gland into three categories. This is the first human in vivo pineal vein imaging study using 7T MRI. Pineal venous imaging may permit the early diagnosis of a pineal tumor.

Involvement of low-level visual areas in hemispheric superiority for face processing.

Previous studies on laterality in face processing have indicated superiority of the right hemisphere in discriminating and recognizing faces; however, the reasons for this feature are poorly understood. We employed functional MRI (fMRI) to elucidate the origin of this feature and used a paired-stimulus paradigm in which face pairs were presented unilaterally at the left or right visual hemifield of the participants. Each face in a pair was at a different position in the visual field. Refractory suppression in the fMRI response was observed bilaterally at the fusiform face area (FFA) for the same face pairs when pictures were presented in the left visual hemifield. In contrast, suppression was observed bilaterally at the FFA for the different as well as for the same face pairs when pictures were presented in the right visual hemifield. This pattern indicated inferior discrimination ability for paired stimuli presented to the right visual hemifield. These observations, along with changes in bilaterally interlocked responses at the FFA, suggest that low-level visual areas, and not high-level face areas, are strongly associated with the superiority of the right hemisphere in face processing.