Chapter 30 - Somatosensory System
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Primary somatosensory cortex organization for engineering artificial somatosensation
2024, Neuroscience ResearchSomatosensory deficits from stroke, spinal cord injury, or other neurologic damage can lead to a significant degree of functional impairment. The primary (SI) and secondary (SII) somatosensory cortices encode information in a medial to lateral organization. SI is generally organized topographically, with more discrete cortical representations of specific body regions. SII regions corresponding to anatomical areas are less discrete and may represent a more functional rather than topographic organization. Human somatosensory research continues to map cortical areas of sensory processing with efforts primarily focused on hand and upper extremity information in SI. However, research into SII and other body regions is lacking. In this review, we synthesize the current state of knowledge regarding the cortical organization of human somatosensation and discuss potential applications for brain computer interface. In addition to accurate individualized mapping of cortical somatosensation, further research is required to uncover the neurophysiological mechanisms of how somatosensory information is encoded in the cortex.
Multimodal anatomical mapping of subcortical regions in marmoset monkeys using high-resolution MRI and matched histology with multiple stains
2023, NeuroImageSubcortical nuclei and other deep brain structures play essential roles in regulating the central and peripheral nervous systems. However, many of these nuclei and their subregions are challenging to identify and delineate in conventional MRI due to their small size, hidden location, and often subtle contrasts compared to neighboring regions. To address these limitations, we scanned the whole brain of the marmoset monkeys in ex vivo using a clinically feasible diffusion MRI method, called the mean apparent propagator (MAP)-MRI, along with T2W and MTR (T1-like contrast) images acquired at 7 Tesla. Additionally, we registered these multimodal MRI volumes to the high-resolution images of matched whole-brain histology sections with seven different stains obtained from the same brain specimens. At high spatial resolution, the microstructural parameters and fiber orientation distribution functions derived with MAP-MRI can distinguish the subregions of many subcortical and deep brain structures, including fiber tracts of different sizes and orientations. The good correlation with multiple but distinct histological stains from the same brain serves as a thorough validation of the structures identified with MAP-MRI and other MRI parameters. Moreover, the anatomical details of deep brain structures found in the volumes of MAP-MRI parameters are not visible in conventional T1W or T2W images. The high-resolution mapping using novel MRI contrasts, combined and correlated with histology, can elucidate structures that were previously invisible radiologically. Thus, this multimodal approach offers a roadmap toward identifying salient brain areas in vivo in future neuroradiological studies. It also provides a useful anatomical standard reference for the region definition of subcortical targets and the generation of a 3D digital template atlas for the marmoset brain research (Saleem et al., 2023). Additionally, we conducted a cross-species comparison between marmoset and macaque monkeys using results from our previous studies (Saleem et al., 2021). We found that the two species had distinct patterns of iron distribution in subregions of the basal ganglia, red nucleus, and deep cerebellar nuclei, confirmed with T2W MRI and histology.
Sexual dimorphism in the dorsal root ganglia of neonatal mice identified by protein expression profiling with single-cell mass cytometry
2023, Molecular and Cellular NeuroscienceDevelopment of neuronal and glial populations in the dorsal root ganglia (DRG) is required for detection of touch, body position, temperature, and noxious stimuli. While female-male differences in somatosensory perception have been previously reported, no study has examined global sex differences in the abundance of DRG cell types, and the developmental origin of these differences has not been characterized. To investigate whether sex-specific differences in neuronal and glial cell types arise in the DRG during development, we performed single-cell mass cytometry analysis on sex-separated DRGs from 4 separate litter replicates of postnatal day 0 (P0) C57/BL6 mouse pups. In this analysis, we observed that females had a higher abundance of total neurons (p = 0.0266), as well as an increased abundance of TrkB+ (p = 0.031) and TrkC+ (p = 0.04) neurons for mechanoreception and proprioception, while males had a higher abundance of TrkA+ (p = 0.025) neurons for thermoreception and nociception. Pseudotime comparison of the female and male datasets indicates that male neurons are more mature and differentiated than female neurons at P0. These findings warrant further studies to determine whether these differences are maintained across development, and their impact on somatosensory perception.
Feasibility, Validity, and Reliability of Lower Limb Tactile and Body Awareness Assessments in Children With Upper Motor Neuron Lesions
2023, Archives of Physical Medicine and RehabilitationTo investigate the feasibility, discriminative and convergent validity, and inter-rater reliability of a lower limb tactile function and 2 body awareness assessments in children with upper motor neuron (UMN) lesions.
Cross-sectional psychometric study.
Pediatric rehabilitation center.
Forty individuals with UMN lesions (mean age 11.7 years, SD 3.4 years; 27 girls) and 40 neurotypically developing children of the same age participated (N=80).
Not applicable.
We assessed the tactile threshold (TT) with monofilaments and body awareness with tactile localization tasks (TLTs) for structural (TLTaction) and spatial (TLTperception) body representation at the foot sole. We compared the test outcomes between children with UMN lesions and neurotypically developing children with the Wilcoxon signed-rank test. Furthermore, we quantified the relations between the 3 tests with Spearman correlations (rs) and the interrater reliability with quadratic weighted kappa (κQW).
About 80% of the children with UMN lesions perceived the tests easy to perform. The children with UMN lesions had significantly reduced somatosensory function compared with the neurotypically developing children. For the more affected leg, we found good relations between the TT and the TLTaction (rs=0.71; P<.001) and between the 2 TLTs (rs=0.66; P<.001), and a fair relation between the TT and the TLTperception (rs=0.31; P=.06). The inter-rater reliability analyses for the sum scores showed almost perfect agreement for the TT (κQW more affected leg 0.86; less affected leg 0.81), substantial agreement for TLTaction (κQW more affected leg 0.76; less affected leg 0.63), and almost perfect agreement for TLTperception (κQW more affected leg 0.88; less affected leg 0.74).
The 3 tests are feasible to assess lower limb somatosensory function in children with UMN lesions. Discriminative and convergent validity and reliability of the 3 tests were confirmed. Further studies should investigate responsiveness and association with motor function of these outcome measures.
A bioinspired flexible artificial mechanoreceptor based on VO<inf>2</inf> insulator-metal transition memristor
2022, Journal of Alloys and CompoundsInspired by biological mechanoreceptors, we present a flexible artificial mechanoreceptor (FAM) based on high-performance VO2 insulator-metal transition (IMT) memristor with the functions of sensing, spikes coding and information fusion for the anthropomorphic neurorobotics. The flexible VO2 IMT memristors with the structure of Ti/Pt/VO2/Pt via-hole show bi-directional threshold switching performance, good endurance (>2 ×109) and excellent flexibility (>103 bending cycles). The FAM comprised of three receptors (flexible pressure sensors) and one flexible VO2 IMT memristor is able to detect, code and fuse the pressure information from different receptors into spike trains similar to the biological SA-Ⅰ mechanoreceptors, laying the foundation for the flexible electronic skin of anthropomorphic neurorobotics in the future.
High-resolution mapping and digital atlas of subcortical regions in the macaque monkey based on matched MAP-MRI and histology
2021, NeuroImageSubcortical nuclei and other deep brain structures are known to play an important role in the regulation of the central and peripheral nervous systems. It can be difficult to identify and delineate many of these nuclei and their finer subdivisions in conventional MRI due to their small size, buried location, and often subtle contrast compared to neighboring tissue. To address this problem, we applied a multi-modal approach in ex vivo non-human primate (NHP) brain that includes high-resolution mean apparent propagator (MAP)-MRI and five different histological stains imaged with high-resolution microscopy in the brain of the same subject. By registering these high-dimensional MRI data to high-resolution histology data, we can map the location, boundaries, subdivisions, and micro-architectural features of subcortical gray matter regions in the macaque monkey brain. At high spatial resolution, diffusion MRI in general, and MAP-MRI in particular, can distinguish a large number of deep brain structures, including the larger and smaller white matter fiber tracts as well as architectonic features within various nuclei. Correlation with histology from the same brain enables a thorough validation of the structures identified with MAP-MRI. Moreover, anatomical details that are evident in images of MAP-MRI parameters are not visible in conventional T1-weighted images. We also derived subcortical template “SC21” from segmented MRI slices in three-dimensions and registered this volume to a previously published anatomical template with cortical parcellation (Reveley et al., 2017; Saleem and Logothetis, 2012), thereby integrating the 3D segmentation of both cortical and subcortical regions into the same volume. This newly updated three-dimensional D99 digital brain atlas (V2.0) is intended for use as a reference standard for macaque neuroanatomical, functional, and connectional imaging studies, involving both cortical and subcortical targets. The SC21 and D99 digital templates are available as volumes and surfaces in standard NIFTI and GIFTI formats.