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Journal of Neurophysiology Oct 2021The connectivity among architectonically defined areas of the frontal, parietal, and temporal cortex of the macaque has been extensively mapped through tract-tracing...
The connectivity among architectonically defined areas of the frontal, parietal, and temporal cortex of the macaque has been extensively mapped through tract-tracing methods. To investigate the statistical organization underlying this connectivity, and identify its underlying architecture, we performed a hierarchical cluster analysis on 69 cortical areas based on their anatomically defined inputs. We identified 10 frontal, four parietal, and five temporal hierarchically related sets of areas (clusters), defined by unique sets of inputs and typically composed of anatomically contiguous areas. Across the cortex, clusters that share functional properties were linked by dominant information processing circuits in a topographically organized manner that reflects the organization of the main fiber bundles in the cortex. This led to a dorsal-ventral subdivision of the frontal cortex, where dorsal and ventral clusters showed privileged connectivity with parietal and temporal areas, respectively. Ventrally, temporofrontal circuits encode information to discriminate objects in the environment, their value, emotional properties, and functions such as memory and spatial navigation. Dorsal parietofrontal circuits encode information for selecting, generating, and monitoring appropriate actions based on visual-spatial and somatosensory information. This organization may reflect evolutionary antecedents, in which the vertebrate pallium, which is the ancestral cortex, was defined by a ventral and lateral olfactory region and a medial hippocampal region. The study of cortical connectivity is crucial for understanding brain function and disease. We show that temporofrontal and parietofrontal networks in the macaque can be described in terms of circuits among clusters of areas that share similar inputs and functional properties. The resulting overall architecture described a dual subdivision of the frontal cortex, consistent with the main cortical fiber bundles and an evolutionary trend that underlies the organization of the cortex in the macaque.
Topics: Animals; Cluster Analysis; Frontal Lobe; Macaca; Nerve Net; Parietal Lobe; Temporal Lobe
PubMed: 34379536
DOI: 10.1152/jn.00092.2021 -
Developmental Cognitive Neuroscience Dec 2023Hemispherectomy is a surgical procedure in which an entire hemisphere of a patient's brain is resected or functionally disconnected to manage seizures in individuals...
Hemispherectomy is a surgical procedure in which an entire hemisphere of a patient's brain is resected or functionally disconnected to manage seizures in individuals with drug-resistant epilepsy. Despite the extensive loss of both ventral and dorsal visual pathways in one hemisphere, pediatric patients who have undergone hemispherectomy show a remarkably high degree of perceptual function across many domains. In the current study, we sought to understand the extent to which functions of the ventral and dorsal visual pathways reorganize to the contralateral hemisphere following childhood hemispherectomy. To this end, we collected fMRI data from an equal number of left and right hemispherectomy patients who completed tasks that typically elicit lateralized responses from the ventral or the dorsal pathway, namely, word (left ventral), face (right ventral), tool (left dorsal), and global form (right dorsal) perception. Overall, there was greater evidence of functional reorganization in the ventral pathway than in the dorsal pathway. Importantly, because ventral and dorsal reorganization was tested within the very same patients, these results cannot be explained by idiosyncratic factors such as disease etiology, age at the time of surgery, or age at testing. These findings suggest that because the dorsal pathway may mature earlier, it may have a shorter developmental window of plasticity than the ventral pathway and, hence, be less malleable after perturbation.
Topics: Humans; Child; Hemispherectomy; Visual Pathways; Brain; Magnetic Resonance Imaging
PubMed: 37976921
DOI: 10.1016/j.dcn.2023.101323 -
NeuroImage Feb 2021Neurophysiological and anatomical data suggest the existence of several functionally distinct regions in the lower arcuate sulcus and adjacent postarcuate convexity of...
Neurophysiological and anatomical data suggest the existence of several functionally distinct regions in the lower arcuate sulcus and adjacent postarcuate convexity of the macaque monkey. Ventral premotor F5c lies on the postarcuate convexity and consists of a dorsal hand-related and ventral mouth-related field. The posterior bank of the lower arcuate contains two additional premotor F5 subfields at different anterior-posterior levels, F5a and F5p. Anterior to F5a, area 44 has been described as a dysgranular zone occupying the deepest part of the fundus of the inferior arcuate. Finally, area GrFO occupies the most rostral portion of the fundus and posterior bank of inferior arcuate and extends ventrally onto the frontal operculum. Recently, data-driven exploratory approaches using resting-state fMRI data have been suggested as a promising non-invasive method for examining the functional organization of the primate brain. Here, we examined to what extent partitioning schemes derived from data-driven clustering analysis of resting-state fMRI data correspond with the proposed organization of the fundus and posterior bank of the macaque arcuate sulcus, as suggested by invasive architectonical, connectional and functional investigations. Using a hierarchical clustering analysis, we could retrieve clusters corresponding to the dorsal and ventral portions of F5c on the postarcuate convexity, F5a and F5p at different antero-posterior locations on the posterior bank of the lower arcuate, area 44 in the fundus, as well as part of area GrFO in the most anterior portion of the fundus. Additionally, each of these clusters displayed distinct whole-brain functional connectivity, in line with previous anatomical tracer and seed-based functional connectivity investigations of F5/44 subdivisions. Overall, our data suggests that hierarchical clustering analysis of resting-state fMRI data can retrieve a fine-grained level of cortical organization that resembles detailed parcellation schemes derived from invasive functional and anatomical investigations.
Topics: Animals; Brain Mapping; Cluster Analysis; Female; Image Processing, Computer-Assisted; Macaca mulatta; Magnetic Resonance Imaging; Male; Motor Cortex; Neural Pathways
PubMed: 33338618
DOI: 10.1016/j.neuroimage.2020.117647 -
World Neurosurgery Nov 2021The far-lateral suboccipital approach and its variants, including the transcondylar, supracondylar, and paracondylar approaches, are essential skull base techniques for...
The far-lateral suboccipital approach and its variants, including the transcondylar, supracondylar, and paracondylar approaches, are essential skull base techniques for the neurosurgeon to expose and treat pathologies located at the ventral and ventrolateral craniovertebral junction. An understanding of the surgical anatomy and technical nuances of these approaches is vital for preventing catastrophic brainstem or spinal cord injury, neurovascular injury, and/or cranial nerve injury. This is achieved by carefully studying the location, the rostral-caudal and lateral extents of the lesion itself, and the anatomy of the surrounding structures on preoperative imaging. The amount of bony exposure should be tailored to each specific lesion to avoid unnecessary bone drilling and therefore decrease the risk of potential craniocervical instability. Minimizing retraction of the cerebellum, brainstem, and spinal cord is important for preventing neurologic injury; therefore, appropriate intraoperative head positioning and adequate bony exposure should be ensured, especially for more ventrally located lesions. A thorough knowledge of the anatomy of the extradural and intradural segments of the vertebral artery, and the lower cranial nerves, in relation to the lesion is also critical. For almost all lesions, the far-lateral suboccipital route with no or minimal condylar drilling is more than adequate for removing the most ventral lesions. Herein, we discuss the indications, general and preoperative considerations, and surgical anatomy and technical nuances of this approach.
Topics: Humans; Neurosurgical Procedures; Skull Base; Skull Base Neoplasms; Treatment Outcome; Vertebral Artery
PubMed: 34724749
DOI: 10.1016/j.wneu.2021.08.018 -
Frontiers in Neural Circuits 2022In male Poeciliid fishes, the modified anal fin (i.e., gonopodium) and its axial and appendicular support are repositioned within the axial skeleton, creating a novel...
In male Poeciliid fishes, the modified anal fin (i.e., gonopodium) and its axial and appendicular support are repositioned within the axial skeleton, creating a novel sexually dimorphic ano-urogenital region. During copulation, the relative location of the gonopodium is crucial for successful insemination. Therefore, the repositioning of these structures and organ relied on the reorganization of the efferent circuitry that controls spinal motor neurons innervating appendicular muscles critical for the movement of the gonopodium, including the fast and synchronous torque-trust motion during insemination attempts. Copulation occurs when a male positions himself largely outside a female's field of view, circumducts his gonopodium, and performs a rapid, complex maneuver to properly contact the female urogenital sinus with the distal tip of the gonopodium and transfers sperm. Although understanding of the efferent circuitry has significantly increased in the last 24 years, nothing is known about the cutaneous receptors involved in gonopodium movement, or how the afferent signals are processed to determine the location of this organ during copulation. Using Western mosquitofish, , as our model, we attempt to fill this gap in knowledge. Preliminary data showed cutaneous nerves and sensory neurons innervating superficial neuromasts surrounding the base of adult male gonopodium; those cutaneous nerves projected ventrally from the spinal cord through the 14th dorsal root ganglion and its corresponding ventral root towards the base and fin rays of the gonopodium. We asked what role the cutaneous superficial neuromasts play in controlling the positioning and timing of the gonopodium's fast and synchronous movements for effective sperm transfer. First, we found a greater number of superficial neuromasts surrounding the base of the male's gonopodium compared to the base of the female's anal fin. Second, we systemically removed superficial neuromasts surrounding the gonopodium base and observed significant impairment of the positioning and timing of gonopodial movements. Our findings provide a first step to supporting the following hypothesis: during radical reorganization of the Poeciliid body plan, superficial neuromasts have been partially co-opted as proprioceptors that allow the gonopodium to control precise positioning and timing during copulatory attempts.
Topics: Animals; Copulation; Cyprinodontiformes; Female; Male; Motor Neurons; Semen; Sensory Receptor Cells
PubMed: 36082109
DOI: 10.3389/fncir.2022.921568 -
Journal of Morphology May 2022Whip spiders (Arachnida, Amblypygi), like many other soil arthropods, transfer their spermatozoa indirectly via a stalked spermatophore. While the complex courtship...
Whip spiders (Arachnida, Amblypygi), like many other soil arthropods, transfer their spermatozoa indirectly via a stalked spermatophore. While the complex courtship behavior as well as the morphological differences of spermatophores and corresponding female genitalia between taxa have received great attention in the past, comparative research on the internal reproductive system is lacking so far. In this study, the morphology of the male whip spiders of four neoamblypygid taxa has been comparatively studied via computer tomography and subsequent 3D reconstruction. We investigated four species belonging to the Neoamblypygi, that is, the phrynichid species Damon medius (Damoninae), and Euphrynichus bacillifer (Phrynichidae), the phrynid species Phrynus hispaniolae (Phrynidae), and the charontid species Charon grayi (Charontidae). The male reproductive organs consist of paired testes and two pairs of accessory glands, the ventral and lateral glands, which project their ducts anteriorly into the ventrally located unpaired spermatophore producing organ where the respective seminal and secretory reservoirs are located. While this general organization of the male reproductive system is similar among all investigated taxa, there are some notable differences in some structures. The most surprising findings include the complete absence of ventral glands in D. medius, the presence of unique spherical ventral gland reservoirs in C. grayi as well as differences in the organization of the seminal and secretory reservoirs and their connections to the inner genital slit. In addition, the secretory products of both, ventral and lateral glands, are stored in combined secretory reservoirs in E. bacillifer and P. hispaniolae. This study is the first to show that there is some morphological variation in the male reproductive system in Neoamblypygi. These results are the basis for the reconstruction of the Bauplan for the reproductive organs of the whip spiders.
Topics: Animals; Arachnida; Female; Genitalia, Male; Male; Spermatogonia; Spiders; Testis
PubMed: 35094422
DOI: 10.1002/jmor.21458 -
Der Nervenarzt Aug 2023Ventral cervical spondylophytes can lead to severe dysphagia if they are of sufficient extent and height localization and represent an important differential diagnosis... (Review)
Review
BACKGROUND
Ventral cervical spondylophytes can lead to severe dysphagia if they are of sufficient extent and height localization and represent an important differential diagnosis of neurogenic dysphagia, especially in older patients.
OBJECTIVE
Presentation of various etiologies of ventral cervical spondylophytes, specific symptoms and abnormalities of the swallowing function caused by spondylophytes, their manifestation in the instrumental swallowing diagnostics and an outlook on treatment options.
MATERIAL AND METHODS
Summary of the current literature on spondylophyte-related dysphagia and an overview of research results regarding differential diagnostic aspects of neurogenic dysphagia.
RESULTS
The manifestation forms of ventral cervical spondylophytes can be very diverse. With respect to dysphagia, disorders of pharyngeal bolus transfer and an increased tendency to aspiration have been observed. The occurrence and severity of the symptoms depend primarily on the extent of the bony attachments and their height localization.
CONCLUSION
In some cases, symptomatic ventral cervical spondylophytes can be a relevant differential diagnosis of neurogenic dysphagia. For a more precise evaluation of the dysphagic symptoms and their association with the spondylophytic outgrowths, a video fluoroscopy of swallowing (VFS) should be added to the fiber endoscopic evaluation (FEES). In most cases, a resection of the bone spurs leads to a significant improvement or even to a complete restitution of the swallowing disorders.
Topics: Humans; Aged; Deglutition Disorders; Diagnosis, Differential; Deglutition; Endoscopy; Pharynx
PubMed: 36897376
DOI: 10.1007/s00115-023-01456-w -
Journal of Morphology Jun 2022The classic view of the vertebrate dorsal root ganglion is that it arises from trunk neural crest cells that migrate to positions lateral to the spinal cord, sending...
The classic view of the vertebrate dorsal root ganglion is that it arises from trunk neural crest cells that migrate to positions lateral to the spinal cord, sending axons dorsally into the spinal cord and dendrites ventrally to meet with motor axons in the ventral root to form spinal nerves. As a result, the ganglion ends up lying in the dorsal root of the spinal nerve. Serial histological sections of parts of the trunk of juveniles of different snake species revealed that the ganglia lie distal to the junction of dorsal and ventral roots of spinal nerves and outside the neural canal. The anatomical position of spinal ganglia in snakes suggests that regulation of trunk neural crest migration in snakes differs from that in the model endotherms in which it has been most thoroughly explored. Dorsal roots have no distinct rootlets and the span of root entry to the spinal cord is short compared to that of ventral rootlets in the same segment. Comparing early developmental stages to juvenile spinal cords shows an increased separation of spinal nerve root sites and ventral migration of the ganglion in later development. Dorsal rami of the spinal nerves leave directly from the dorsal edge of the ganglion, and the ventral ramus leaves from the ventral tip of the ganglion. How these features relate to the developmental regulation of ganglion form and position and the extraordinary locomotor capabilities of the snake trunk are unclear.
Topics: Animals; Ganglia, Spinal; Neural Crest; Snakes; Spinal Cord; Spinal Nerve Roots
PubMed: 35510680
DOI: 10.1002/jmor.21481 -
WIREs Mechanisms of Disease Sep 2021The spinal cord is functionally and anatomically divided into ventrally derived motor circuits and dorsally derived somatosensory circuits. Sensory stimuli originating... (Review)
Review
The spinal cord is functionally and anatomically divided into ventrally derived motor circuits and dorsally derived somatosensory circuits. Sensory stimuli originating either at the periphery of the body, or internally, are relayed to the dorsal spinal cord where they are processed by distinct classes of sensory dorsal interneurons (dIs). dIs convey sensory information, such as pain, heat or itch, either to the brain, and/or to the motor circuits to initiate the appropriate response. They also regulate the intensity of sensory information and are the major target for the opioid analgesics. While the developmental mechanisms directing ventral and dorsal cell fates have been hypothesized to be similar, more recent research has suggested that dI fates are specified by novel mechanisms. In this review, we will discuss the molecular events that specify dorsal neuronal patterning in the spinal cord, thereby generating diverse dI identities. We will then discuss how this molecular understanding has led to the development of robust stem cell methods to derive multiple spinal cell types, including the dIs, and the implication of these studies for treating spinal cord injuries and neurodegenerative diseases. This article is categorized under: Neurological Diseases > Stem Cells and Development.
Topics: Cell Differentiation; Interneurons; Neurons; Spinal Cord; Touch
PubMed: 34730293
DOI: 10.1002/wsbm.1520 -
Development (Cambridge, England) Oct 2023Closed spinal dysraphisms are poorly understood malformations classified as neural tube (NT) defects. Several, including terminal myelocystocele, affect the distal...
Closed spinal dysraphisms are poorly understood malformations classified as neural tube (NT) defects. Several, including terminal myelocystocele, affect the distal spine. We have previously identified a NT closure-initiating point, Closure 5, in the distal spine of mice. Here, we document equivalent morphology of the caudal-most closing posterior neuropore (PNP) in mice and humans. Closure 5 forms in a region of active FGF signalling, and pharmacological FGF receptor blockade impairs its formation in cultured mouse embryos. Conditional genetic deletion of Fgfr1 in caudal embryonic tissues with Cdx2Cre diminishes neuroepithelial proliferation, impairs Closure 5 formation and delays PNP closure. After closure, the distal NT of Fgfr1-disrupted embryos dilates to form a fluid-filled sac overlying ventrally flattened spinal cord. This phenotype resembles terminal myelocystocele. Histological analysis reveals regional and progressive loss of SHH- and FOXA2-positive ventral NT domains, resulting in OLIG2 labelling of the ventral-most NT. The OLIG2 domain is also subsequently lost, eventually producing a NT that is entirely positive for the dorsal marker PAX3. Thus, a terminal myelocystocele-like phenotype can arise after completion of NT closure with localised spinal mis-patterning caused by disruption of FGFR1 signalling.
Topics: Animals; Humans; Mice; Neural Tube Defects; Phenotype; Spinal Cord; Spinal Dysraphism; Spine; Receptor, Fibroblast Growth Factor, Type 1
PubMed: 37756583
DOI: 10.1242/dev.202139