Convolutional Neural Network Based Frameworks for Fast Automatic Segmentation of Thalamic Nuclei from Native and Synthesized Contrast Structural MRI.

7 Tesla MPRAGE Imaging of the Intracranial Arterial Vasculature: Nonenhanced versus Contrast-Enhanced

The thalamic reticular nucleus is a layer of GABAergic neurons that occupy a strategic position between the thalamus and cortex. Here we used laser scanning photostimulation to compare in young mice (9-12 days old) the organization of the reticular inputs to first- and higher-order somatosensory relays, namely, the ventral posterior lateral nucleus and posterior nucleus, respectively. The reticulothalamic input footprints to the ventral posterior lateral nucleus neurons consisted of small, single, topographically organized elliptical regions in a tier away from the reticulothalamic border. In contrast, those to the posterior nucleus were complicated and varied considerably among neurons: although almost all contained a single elliptical region near the reticulothalamic border, in most cases, they consisted of additional discontinuous regions or relatively diffuse regions throughout the thickness of the thalamic reticular nucleus. Our results suggest two sources of reticular inputs to the posterior nucleus neurons: one that is relatively topographic from regions near the reticulothalamic border and one that is relatively diffuse and convergent from most or all of the thickness of the thalamic reticular nucleus. We propose that the more topographic reticular input is the basis of local inhibition seen in posterior nucleus neurons and that the more diffuse and convergent input may represent circuitry through which the ventral posterior lateral and posterior nuclei interact.

To improve anatomical definition and stereotactic precision of thalamic targets in neurosurgical treatments of chronic functional disorders, a new atlas of the human thalamus has been developed. This atlas is based on multiarchitectonic parcellation in sections parallel or perpendicular to the standard intercommissural reference plane. The calcium-binding proteins parvalbumin (PV), calbindin D-28K (CB), and calretinin (CR) were used as neurochemical markers to further characterize thalamic nuclei and delimit subterritories of functional significance for stereotactic explorations. Their overall distribution reveals a subcompartmentalization of thalamic nuclei into several groups. Predominant PV immunostaining characterizes primary somatosensory, visual and auditory nuclei, the ventral lateral posterior nucleus, reticular nucleus (R), and to a lesser degree also, lateral part of the centre median nucleus, and anterior, lateral, and inferior divisions of the pulvinar complex. In contrast, CB immunoreactivity is prevalent in medial thalamic nuclei (intralaminar and midline), the posterior complex, ventral posterior inferior nucleus, the ventral lateral anterior nucleus, ventral anterior, and ventral medial nuclei. The complementary distributions of PV and CB appear to correlate with distinct lemniscal and spinothalamic somatosensory pathways and to cerebellar and pallidal motor territories, respectively. Calretinin, while overlapping with CB in medial thalamic territories, is also expressed in R and limbic associated anterior group nuclei that contain little or no CB. Preliminary analysis indicates that interindividual nuclear variations cannot easily be taken into account by standardization procedures. Nevertheless, some corrections in antero-posterior coordinates in relation to different intercommissural distances are proposed.

The ventral posterior lateral nucleus (VPL) of the monkey thalamus was investigated by histochemical staining for cytochrome oxidase (CO) activity and by immunocytochemical staining for the calcium-binding proteins parvalbumin and 28 kDa calbindin. Anterograde and retrograde tracing experiments were used to correlate patterns of differential distribution of CO activity and of parvalbumin and calbindin cells with the terminations of spinothalamic tract fibers and with the types of cells projecting differentially to superficial and deeper layers of primary somatosensory cortex (SI). VPL is composed of CO-rich and CO-weak compartments. Cells are generally smaller in the CO-weak compartment. Parvalbumin-immunoreactive cells and parvalbumin-immunoreactive medial lemniscal fiber terminations are confined to the CO-rich compartment. Calbindin-immunoreactive cells are found in both the CO-rich and CO-weak compartments. The CO-weak compartment, containing only calbindin cells, forms isolated zones throughout VPL and expands as a cap covering the posterior surface of the ventral posterior medial nucleus (VPM). Spinothalamic tract terminations tend to be concentrated in the CO-weak compartment, especially in the posterior cap. Other CO-weak, parvalbumin-negative, calbindin-positive nuclei, including the posterior, ventral posterior inferior, and anterior pulvinar and the small-celled matrix of VPM are also associated with concentrations of spinothalamic and caudal trigeminothalamic terminations. Parvalbumin cells are consistently larger than calbindin cells and are retrogradely labeled only after injections of tracers in middle and deep layers of SI. The smaller calbindin cells are the only cells retrogradely labeled after placement of retrograde tracers that primarily involve layer I of SI. The compartmental organization of VPL is similar to but less rigid than that previously reported in VPM. VPL and VPM relay cells projecting to different layers of SI cortex can be distinguished by differential immunoreactivity for the two calcium-binding proteins. The small-celled, CO-weak, calbindin-positive zones of VPL and VPM appear to form part of a wider system of smaller thalamic neurons unconstrained by traditional nuclear boundaries that are preferentially the targets of spinothalamic and caudal trigeminal inputs, and that may have preferential access to layer I of SI.

This study was to assess the usefulness of newer three-dimensional (3D)-T1 sampling perfection with application optimized contrast using different flip-angle evolutions (SPACE) and 3D-T2 fluid-attenuated inversion recovery (FLAIR) sequences in evaluation of meningeal abnormalities. 78 patients who presented with high suspicion of meningeal abnormalities were evaluated using post-contrast 3D-T2-FLAIR, 3D-T1 magnetization-prepared rapid gradient-echo (MPRAGE) and 3D-T1-SPACE sequences. The images were evaluated independently by two radiologists for cortical gyral, sulcal space, basal cisterns and dural enhancement. The diagnoses were confirmed by further investigations including histopathology. Post-contrast 3D-T1-SPACE and 3D-T2-FLAIR images yielded significantly more information than MPRAGE images (p < 0.05 for both SPACE and FLAIR images) in detection of meningeal abnormalities. SPACE images best demonstrated abnormalities in dural and sulcal spaces, whereas FLAIR was useful for basal cisterns enhancement. Both SPACE and FLAIR performed equally well in detection of gyral enhancement. In all 10 patients, where both SPACE and T2-FLAIR images failed to demonstrate any abnormality, further analysis was also negative. The 3D-T1-SPACE sequence best demonstrated abnormalities in dural and sulcal spaces, whereas FLAIR was useful for abnormalities in basal cisterns. Both SPACE and FLAIR performed holds good for detection of gyral enhancement. Post-contrast SPACE and FLAIR sequences are superior to the MPRAGE sequence for evaluation of meningeal abnormalities and when used in combination have the maximum sensitivity for leptomeningeal abnormalities. The negative-predictive value is nearly 100%, where no leptomeningeal abnormality was detected on these sequences. Advances in knowledge: Post-contrast 3D-T1-SPACE and 3D-T2-FLAIR images are more useful than 3D-T1-MPRAGE images in evaluation of meningeal abnormalities.

Lateral geniculate nucleus volumetry at 3T and 7T: Four different optimized magnetic-resonance-imaging sequences evaluated against a 7T reference acquisition

1. Extracellular and intracellular methods were used to record from fibers and neurons in the ventral lateral (VL) and adjacent nuclei of the cat thalamus. The receptive fields of the recorded units were analyzed and the units tested for inputs from the medial lemniscus (ML) and spinothalamic tract (STT) by electrical stimulation of the dorsal columns (DC) and ventrolateral funiculus (VLF) at the C2-3 spinal level. 2. Thirty-eight STT fibers were isolated in the thalamus. Their conduction velocities ranged from 15 to 75 m/s (mode 36 m/s). Adequate stimuli were found for 23 of these fibers. Seventeen were low-threshold (LT), 3 were wide-dynamic-range (WDR), and 3 were high-threshold (HT) units. 3. Five STT fibers were intra-axonally injected. Three were sufficiently well filled for analysis of their terminal fields. An intermediate-velocity STT fiber (conduction velocity 38 m/s) had a 4.3-microns axon and a single large terminal field in the central lateral nucleus (CL). The other two STT fibers were smaller, with diameters of 2.5 and 2.3 microns, conduction velocities of 15 and 19 m/s, and terminal fields made up of a few small boutons at the borders of the ventral posterior lateral nucleus (VPL). 4. Of 319 neurons isolated, 14 out of 129 (10.8%) in VL, 14 out of 76 (18.4%) in the VPL or ventral posterior medial (VPM) nucleus, 27 out of 64 (42.2%) in the CL nucleus, and 5 out of 50 (10%) in the reticular nucleus (R) responded at latencies less than 50 ms to VLF stimuli. A train of three pulses was more effective in driving VLF-responding neurons in all these nuclei than a single pulse. VLF-responding cells were widely dispersed in VL, concentrated in a focus in CL, and distributed around the borders of VPL. Most of those in VL and a small number in CL could be antidromically activated by stimulation of motor cortex. 5. Latencies of presynaptic responses (STT fibers) to VLF stimulation were short and varied from 0.8 to 3.9 ms (mode 1.6 ms). Despite this, very few fast-responding neurons were found. These were six VPL neurons (2.5 to 4 ms), one VL neuron (3 ms), and four CL neurons (3-4 ms). The initial spike latencies of the majority of thalamic neurons responding to VLF stimulation appeared in two peaks, one between 6 and 8 ms and the other at 10-15 ms.(ABSTRACT TRUNCATED AT 400 WORDS)

Three-dimensional (3D) MP-RAGE (magnetization-prepared rapid gradient-echo) imaging was evaluated as a high-resolution 3D T1-weighted brain imaging technique for patients with suspected neurologic disease. Fourteen patients were studied. In five, 3D MP-RAGE images were compared with 3D FLASH (fast low-angle shot) images. Signal difference--to-noise ratios and T1 contrast were not statistically different for 3D MP-RAGE images as opposed to 3D FLASH images. Advantages intrinsic to the application of 3D MP-RAGE sequences include decreased imaging time and decreased motion artifact. With this technique, it is possible to perform a relatively motion-insensitive, T1-weighted screening brain study with voxel resolution of 1.0 x 1.4 x 2.0 mm or smaller, in an imaging time of 5.9 minutes or less--permitting offline (poststudy) reconstruction of high-resolution images in any desired plane.

Differential synaptic distribution of AMPA receptor subunits in the ventral posterior and reticular thalamic nuclei of the rat

Thalamic afferent and efferent connectivity to cerebral cortical areas with direct projections to identified subgroups of trigeminal premotoneurons in the rat

It is generally agreed that cerebellar and lemniscal pathways project to largely separate areas of the thalamus and influence different functional areas of the cerebral cortex. Cerebellar afferents arise from neurones in the deep cerebellar nuclei and terminate in the ventral lateral group of thalamic nuclei or the "motor thalamus," whereas lemniscal afferents arise from the dorsal column nuclei and terminate in the adjacent ventral posterior group of thalamic nuclei or "sensory thalamus." However, it remains unclear whether or not these pathways converge onto thalamic neurones in the border zone between motor and sensory thalamus. The aim of this study was to compare directly the locations of cerebellar interposed and dorsal column nuclei terminals in the rat thalamus by using a double anterograde labelling technique. Microinjections of dextran-tetramethylrhodamine and dextran-fluorescein were made into the interposed and dorsal column nuclei, and labelled terminals in the thalamus were examined in the same sections. The labelled cerebellar and lemniscal terminals were located in separate areas throughout most of the ventral lateral and ventral posterior lateral nuclei, and there was only a limited region around the rostral border between these nuclei where the two groups of terminals came in close proximity to each other. In this common projection zone, however, cerebellar and lemniscal terminals seldom intermingled, and they mostly occupied separate, discreet areas. The results show that cerebellar and lemniscal fibres do indeed project to the border zone between the sensory and cerebellar thalamic nuclei, but they show practically no overlap in this region and are likely to influence separate thalamic neurones.

We previously reported that neurons in the mediodorsal thalamic nucleus (MD) are topographically organized and express spatial and nonspatial coding properties similar to those of the prefrontal areas with which they are connected. In the course of mapping the dorsal thalamus, we also studied neurons in a subset of thalamic nuclei (the caudal part of the ventral lateral nucleus (VLc), the oral part of the ventral posterior lateral nucleus (VPLo), the parvocellular part of the ventral anterior nucleus (VApc)) lateral to the MD and just across the internal medullary lamina. We compared these "paralaminar" neurons to MD neurons by having monkeys perform the same spatial and nonspatial cognitive tasks as those used to investigate the MD; these included two saccadic tasks-one requiring delayed and the other immediate responses-and one picture fixation task. Of the paralaminar thalamic neurons modulated by the saccadic tasks, a majority had saccade-related activity, and this was nearly always spatially tuned. Also, for about half of these neurons, the saccade-related activity occurred exclusively during the delayed-response task. No neurons with event-related activity in the saccadic tasks were preferentially modulated by specific picture stimuli, although other neurons were. All of these results were similar to what we had found for MD neurons. However, in contrast to the high proportion of presaccadic responses observed in the MD, the majority of saccade-related neurons in paralaminar thalamus exhibited mid- or postsaccadic activity, i.e., that started during or after the saccade. Our findings suggest that neurons in the paralaminar thalamus may be possible conduits of oculomotor feedback signals, especially during memory-guided saccades.

Nucleus- and species-specific properties of the slow (<1 Hz) sleep oscillation in thalamocortical neurons

The results of the present anatomical study on macaque monkeys concern some aspects of the dorsal column nuclei, their projection to the thalamus and the cytoarchitecture and topography of the recipient areas in the thalamus for the somatosensory pathways. Some observations regarding the cytoarchitecture of the dorsal column nuclei are reported; the gracile nucleus differs cytoarchitectonically over the rostrocaudal dimension in a way similar to the feline nucleus; the cuneate nucleus has a distinct pars rotunda (Ferraro and Barrera, '35) which might be analogous to a similar structure in the raccoon shown to be activated by afferents from the volar side of the hand and digits (Johnson et al., '68). Cytoarchitectonic observations and other arguments suggesting the presence of the nucleus Z in the monkey are presented.In Nissl stained frontal sections, cut in the stereotaxic frontal plane as well as in sections cut perpendicular to the long axis of the brain stem the cytoarchitecture and topography of the posteromedial, ventroposterior and centrolateral thalamic nuclei of the macaque were analysed. The posteromedial nucleus (POm) has been found to include portions of Olszewski's ('52) magnocellular medial geniculate, suprageniculate and pulvinar nuclei. The nucleus ventralis posterolateralis (VPL) corresponds to the main portion of Olszewski's VPLc, whereas most of his VPLo corresponds to the nucleus ventralis intermedius of Hassler ('59) and Mehler ('71).Electrolytic lesions were used to study the projection from the gracile and cuneate nuclei to the thalamus. With postoperative survival periods of 6 to 14 days the resulting degeneration was studied in frontal sections stained according to the Wiitanen modification of the Fink‐Heimer method. Both the gracile and cuneate nuclei project profusely to the contralateral nucleus ventralis posterolateralis and more sparsely to the contralateral posteromedial nucleus and the zona incerta. A distinct somatotopic organization exists in the projection to the ventroposterior nucleus, but not in that to the other target areas. The projection to the ventroposterior nucleus is very dense and evenly distributed except rostrally and dorsally, where it is more scattered.It is concluded that the posteromedial and the ventroposterior thalamic nuclei are very similar in monkeys and cats regarding cytoarchitecture, topography and afferent projections from the dorsal column nuclei.

Background and Purpose:Neuropathic pain (NP) is a debilitating condition following spinal cord injury (SCI). The role of periaqueductal gray (PAG) in NP development following SCI remains underexplored. Using resting-state functional MRI (rsfMRI), our study aimed to demonstrate the alterations in functional connectivity (FC) of PAG in NP following SCI.Methods:Ten SCI patients (SCI + NP, n = 7, and SCI − NP, n = 3), alongside 10 healthy controls (HCs), were enrolled. rsfMRI was conducted followed by seed-to-voxel analysis using PAG as the seed region and then group-based analysis comprising three groups (SCI + NP, SCI − NP, and HC). Age and gender were considered as confounding variables.Results:Compared to HCs, SCI + NP demonstrated decreased FC between PAG and right insula, right frontal orbital cortex, right pallidum, dorsal raphe nucleus (DRN), red nuclei (RN), substantia nigra (SN), and ventral posterolateral (VPL) thalamic nuclei. Compared to SCI − NP, SCI + NP demonstrated increased FC between PAG and posterior cingulate cortex (PCC), hippocampus, cerebellar vermis lobules IV and V, and thalamic structures (posterior and lateral pulvinar, the mediodorsal nuclei, and the ventral lateral nuclei). Additionally, decreased FC between the PAG and VPL, geniculate bodies, intralaminar nuclei of thalamus, DRN, RN, SN, and prefrontal cortex was observed in this comparison.Conclusions:Altered FC between PAG and right anterior insula, VPL, DRN, RN, SN, cerebellar vermis lobules IV and V, frontal cortex, and PCC was associated with NP sequelae of SCI. Additionally, SCI was independently associated with decreased FC between PAG and right posterior insula, cerebellar lobules IV and V, and cerebellar vermis lobules III, IV, and V.