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The Journal of Neuroscience : the... Jul 2019The speed of motor reaction to an external stimulus varies substantially between individuals and is slowed in aging. However, the neuroanatomical origins of...
The speed of motor reaction to an external stimulus varies substantially between individuals and is slowed in aging. However, the neuroanatomical origins of interindividual variability in reaction time (RT) remain unclear. Here, we combined a cognitive model of RT and a biophysical compartment model of diffusion-weighted MRI (DWI) to characterize the relationship between RT and microstructure of the corticospinal tract (CST) and the optic radiation (OR), the primary motor output and visual input pathways associated with visual-motor responses. We fitted an accumulator model of RT to 46 female human participants' behavioral performance in a simple reaction time task. The non-decision time parameter () derived from the model was used to account for the latencies of stimulus encoding and action initiation. From multi-shell DWI data, we quantified tissue microstructure of the CST and OR with the neurite orientation dispersion and density imaging (NODDI) model as well as the conventional diffusion tensor imaging model. Using novel skeletonization and segmentation approaches, we showed that DWI-based microstructure metrics varied substantially along CST and OR. The of individual participants was negatively correlated with the NODDI measure of the neurite density in the bilateral superior CST. Further, we found no significant correlation between the microstructural measures and mean RT. Thus, our findings suggest a link between interindividual differences in sensorimotor speed and selective microstructural properties in white-matter tracts. How does our brain structure contribute to our speed to react? Here, we provided anatomically specific evidence that interindividual differences in response speed is associated with white-matter microstructure. Using a cognitive model of reaction time (RT), we estimated the non-decision time, as an index of the latencies of stimulus encoding and action initiation, during a simple reaction time task. Using an advanced microstructural model for diffusion MRI, we estimated the tissue properties and their variations along the corticospinal tract and optic radiation. We found significant location-specific correlations between the microstructural measures and the model-derived parameter of non-decision time but not mean RT. These results highlight the neuroanatomical signature of interindividual variability in response speed along the sensorimotor pathways.
Topics: Cognition; Decision Making; Diffusion Tensor Imaging; Female; Humans; Male; Pyramidal Tracts; Random Allocation; Reaction Time; White Matter; Young Adult
PubMed: 31123103
DOI: 10.1523/JNEUROSCI.2954-18.2019 -
Journal of Applied Physiology... Apr 2004Spinal tracts can be stimulated noninvasively in human subjects by passing a high-voltage stimulus between the mastoids or by magnetic stimulation over the back of the... (Review)
Review
Spinal tracts can be stimulated noninvasively in human subjects by passing a high-voltage stimulus between the mastoids or by magnetic stimulation over the back of the head. The stimulus probably activates the corticospinal tract at the cervicomedullary junction (pyramidal decussation) and evokes large, short-latency motor responses in the arm muscles. These responses have a large monosynaptic component. Responses in leg muscles can be elicited by cervicomedullary junction stimulation or by stimulation over the cervical or thoracic spine. Because nerve roots are more easily activated than spinal tracts, stimulus spread to motor axons can occur. Facilitation of responses by voluntary activity confirms that the responses are evoked synaptically. Stimulation of the corticospinal tract is useful in studies of central conduction and studies of the behavior of motoneurons during different tasks. It also provides an important comparison to allow interpretation of changes in responses to stimulation of the motor cortex. The major drawback to the use of electrical stimulation of the corticospinal tract is that each stimulus is transiently painful.
Topics: Electric Stimulation; Evoked Potentials; Humans; Leg; Magnetics; Muscle Contraction; Muscle Fatigue; Pyramidal Tracts
PubMed: 15016794
DOI: 10.1152/japplphysiol.01116.2003 -
Neurology India Dec 2000In 1896, Joseph Babinski, a French neurologist, first described the best known neurologic eponym 'the Babinski sign'. This sign is characterised by dorsiflexion of the... (Review)
Review
In 1896, Joseph Babinski, a French neurologist, first described the best known neurologic eponym 'the Babinski sign'. This sign is characterised by dorsiflexion of the big toe and recruitment of the extensor hallucis longus muscle, on stimulating the sole of the foot. He has emphasised from the outset, the intimate relationship between this sign and the shortening movement in other leg muscles, which form the flexion synergy of the lower limb. The Babinski sign is not a new reflex, rather it is released as a result of breakdown of the harmonious integration of the flexion and extension components of the normal defence reflex mechanism, due to pyramidal tract dysfunction. A pathological Babinski sign should be clearly distinguished from upgoing toes that may not always be a part of the flexion synergy. This article reviews the Babinski sign in detail, focusing on the historical perspectives, role of pyramidal tract dysfunction and art of elicitation and interpretation. The significance of assessing this phenomenon in the entire leg, and the clinical clues that will help to dispel the myths regarding the Babinski sign, have been emphasised.
Topics: Humans; Nervous System Diseases; Neurologic Examination; Pyramidal Tracts; Reflex, Babinski
PubMed: 11146592
DOI: No ID Found -
NeuroImage. Clinical 2021Microstructural alterations of corticospinal tract (CST) have been found in idiopathic normal pressure hydrocephalus (iNPH). No study, however, investigated the effect...
BACKGROUND
Microstructural alterations of corticospinal tract (CST) have been found in idiopathic normal pressure hydrocephalus (iNPH). No study, however, investigated the effect of ventricular dilatation on CST in Progressive Supranuclear Palsy (PSP).
OBJECTIVE
The aim of this study was to investigate CST diffusion profile in a large cohort of PSP patients with and without ventricular dilatation.
METHODS
Twenty-three iNPH patients, 87 PSP patients and 26 controls were enrolled. Evans index (EI) and ventricular volume (VV) were measured in all patients. CST tractography was performed to calculate FA, MD, AxD and RD in six different anatomical regions: medulla oblungata (MO), pons (P), cerebral peduncle (CP), posterior limb of internal capsule (PLIC), corona radiata (CR), subcortical white matter (SWM). ANCOVA was used for comparing CST diffusion profiles between the groups and association between CST microstructural metrics and measures of ventricular dilatation (EI and VV) was assessed.
RESULTS
Thirty-three PSP patients had ventricular dilatation (EI > 0.30, PSP-vd) while 54 PSP patients had normal ventricular system (EI ≤ 0.30, PSP-wvd). iNPH patients had the most marked FA and AxD increase in PLIC and CR of CST followed by PSP-vd, PSP-wvd and controls; RD was altered only in iNPH. A strong correlation was found between CST diffusion metrics and EI or VV.
CONCLUSIONS
Our findings confirm the microstructural changes of CST in iNPH patients and demonstrate for the first time similar alterations in PSP-vd patients, suggesting a crucial role of ventricular dilatation in the mechanical compression of CST.
Topics: Diffusion Tensor Imaging; Dilatation; Humans; Internal Capsule; Pyramidal Tracts; Supranuclear Palsy, Progressive
PubMed: 34688144
DOI: 10.1016/j.nicl.2021.102862 -
The Journal of Physiology Jan 1984A method is described for chronically implanting fine flexible microwires into cat motor cortex, which permitted extracellular recordings to be made from 165 single...
A method is described for chronically implanting fine flexible microwires into cat motor cortex, which permitted extracellular recordings to be made from 165 single neurones. Most units were recordable for 12 h and some for up to 2 days. Of the neurones tested, 57% were shown to project to the medullary pyramid (pyramidal tract neurones, p.t.n.s). Antidromic latencies corresponded to a range of conduction velocities from 63 to 9 m/s. In the animal at rest neurones discharged at rates from 0.5 to 44 impulses/s. During locomotion at 0.5 m/s (a slow walk) 56% of cells discharged faster than at rest and 80% showed frequency modulations time-locked to the step cycle. Most fired one discrete burst of impulses per step or one peak period superimposed on a maintained discharge. In different cells peak activity occurred at widely different times during the step cycle. A few cells peaked twice per step. Peak rates (averaged over twenty steps) ranged from 10 to over 120 impulses/s, the values for most slow-axon p.t.n.s (conduction velocity less than 21 m/s) being lower than for any of the fast-axon p.t.n.s. For locomotion at speeds between 0.37 and 1.43 m/s a roughly linear relationship existed between discharge rate and speed in 14% of cells. However, the changes were modest and in most cells both mean rate and peak rate were unrelated to speed. In some cells discharge phasing was fixed (relative to the step cycle in the contralateral forelimb); in others there were progressive phase shifts (or more complex changes) as speed increased. During locomotion up a 10 degrees incline discharge phasings were the same as on the flat in all of the twenty-seven neurones studied and most showed no substantial change in mean rate or peak rate (although there were substantial increases in limb muscle electromyogram amplitudes).
Topics: Action Potentials; Animals; Axons; Cats; Electrophysiology; Motor Activity; Motor Cortex; Motor Neurons; Neural Conduction; Pyramidal Tracts; Time Factors
PubMed: 6699782
DOI: 10.1113/jphysiol.1984.sp015036 -
NeuroImage. Clinical 2022Unconventional magnetic resonance imaging studies of the brainstem have recently acquired a growing interest in amyotrophic lateral sclerosis (ALS) pathology since they...
BACKGROUND
Unconventional magnetic resonance imaging studies of the brainstem have recently acquired a growing interest in amyotrophic lateral sclerosis (ALS) pathology since they provide a unique opportunity to evaluate motor tract degeneration and bulbar lower motor neuron involvement. The aim of this study was to investigate the role of brainstem structures as accurate biomarkers of disease severity and predictors of survival.
MATERIALS AND METHODS
A total of 60 ALS patients and 30 healthy controls subjects (CS) were recruited in this study. Patients were divided in two subgroups according to the onset of the disease: 42 spinal (S-ALS) and 18 bulbar (B-ALS). All subjects underwent 3D-structural MRI. Brainstem volume both of the entire cohort of ALS patients and S-ALS and B-ALS onset were compared with those of CS. In addition the two ALS subgroups were tested for differences in brainstem volumes. Volumetric, vertex-wise, and voxel-based approaches were implemented to assess correlations between MR structural features and clinical characteristics expressed as ALSFRS-r and its bulbar (ALSFSR-r-B) and spinal subscores (ALSFSR-r-S). ROC curves were performed to test the accuracy of midbrain, pons, and medulla oblongata volumes able to discriminate patients dichotomized into long and short survivors by using Two-Steps cluster analysis. Univariate and multivariate survival analyses were carried out to test the prognostic role of brainstem structures' volume, trichotomized by applying a k-means clustering algorithm.
RESULTS
Both the entire cohort of ALS patients and B-ALS and S-ALS showed significant lower volumes of both medulla oblongata and pons compared to CS. Furthermore, B-ALS showed a significant lower volume of medulla oblongata, compared to S-ALS. Lower score of ALSFRS-r correlated to atrophy in the anterior compartment of midbrain, pons, and medulla oblongata, as well as in the posterior portion of only this latter region. ALSFSR-r-S positively correlated with shape deformation and density reduction of the anterior portion of the entire brainstem, along the corticospinal tracts. ALSFSR-r-B instead showed a positive correlation with shape deformation of the floor of the fourth ventricle in the medulla oblongata and the crus cerebri in the midbrain. Only medulla oblongata volume demonstrated a significant accuracy to discriminate long and short survivors ALS patients (ROC AUC 0.76, p < 0.001). Univariate and multivariate analysis confirmed the survival predictive role of the medulla oblongata (log rank test p: 0.003).
DISCUSSIONS
Our findings suggest that brainstem volume may reflect the impairment of corticospinal and corticobulbar tracts as well as lower bulbar motor neurons. Furthermore, medulla oblongata could be used as an early predictor of survival in ALS patients.
Topics: Amyotrophic Lateral Sclerosis; Humans; Magnetic Resonance Imaging; Medulla Oblongata; Motor Neurons; Pyramidal Tracts
PubMed: 35561555
DOI: 10.1016/j.nicl.2022.103015 -
Nature Communications Oct 2017Pyramidal tract neurons (PTs) represent the major output cell type of the neocortex. To investigate principles of how the results of cortical processing are broadcasted...
Pyramidal tract neurons (PTs) represent the major output cell type of the neocortex. To investigate principles of how the results of cortical processing are broadcasted to different downstream targets thus requires experimental approaches, which provide access to the in vivo electrophysiology of PTs, whose subcortical target regions are identified. On the example of rat barrel cortex (vS1), we illustrate that retrograde tracer injections into multiple subcortical structures allow identifying the long-range axonal targets of individual in vivo recorded PTs. Here we report that soma depth and dendritic path lengths within each cortical layer of vS1, as well as spiking patterns during both periods of ongoing activity and during sensory stimulation, reflect the respective subcortical target regions of PTs. We show that these cellular properties result in a structure-function parameter space that allows predicting a PT's subcortical target region, without the need to inject multiple retrograde tracers.The major output cell type of the neocortex - pyramidal tract neurons (PTs) - send axonal projections to various subcortical areas. Here the authors combined in vivo recordings, retrograde tracings, and reconstructions of PTs in rat somatosensory cortex to show that PT structure and activity can predict specific subcortical targets.
Topics: Action Potentials; Animals; Dendrites; Male; Neuroanatomical Tract-Tracing Techniques; Pyramidal Tracts; Rats, Wistar
PubMed: 29021587
DOI: 10.1038/s41467-017-00971-0 -
The Journal of Physiology May 2013Most movements need to be accurate. The neuronal mechanisms controlling accuracy during movements are poorly understood. In this study we compare the activity of fast-...
Most movements need to be accurate. The neuronal mechanisms controlling accuracy during movements are poorly understood. In this study we compare the activity of fast- and slow-conducting pyramidal tract neurons (PTNs) of the motor cortex in cats as they walk over both a flat surface, a task that does not require accurate stepping and can be accomplished without the motor cortex, as well as along a horizontal ladder, a task that requires accuracy and the activity of the motor cortex to be successful. Fast- and slow-conducting PTNs are known to have distinct biophysical properties as well as different afferent and efferent connections. We found that while the activity of all PTNs changes substantially upon transition from simple locomotion to accurate stepping on the ladder, slow-conducting PTNs respond in a much more concerted manner than fast-conducting ones. As a group, slow-conducting PTNs increase discharge rate, especially during the late stance and early swing phases, decrease discharge variability, have a tendency to shift their preferred phase of the discharge into the swing phase, and almost always produce a single peak of activity per stride during ladder locomotion. In contrast, the fast-conducting PTNs do not display such concerted changes to their activity. In addition, upon transfer from simple locomotion to accurate stepping on the ladder slow-conducting PTNs more profoundly increase the magnitude of their stride-related frequency modulation compared with fast-conducting PTNs. We suggest that slow-conducting PTNs are involved in control of accuracy of locomotor movements to a greater degree than fast-conducting PTNs.
Topics: Animals; Cats; Female; Locomotion; Male; Neurons; Pyramidal Tracts
PubMed: 23381901
DOI: 10.1113/jphysiol.2012.232538 -
Magma (New York, N.Y.) Feb 2023Diffusion-weighted MRI can assist preoperative planning by reconstructing the trajectory of eloquent fiber pathways, such as the corticospinal tract (CST). However,...
OBJECTIVES
Diffusion-weighted MRI can assist preoperative planning by reconstructing the trajectory of eloquent fiber pathways, such as the corticospinal tract (CST). However, accurate reconstruction of the full extent of the CST remains challenging with existing tractography methods. We suggest a novel tractography algorithm exploiting unused fiber orientations to produce more complete and reliable results.
METHODS
Our novel approach, referred to as multi-level fiber tractography (MLFT), reconstructs fiber pathways by progressively considering previously unused fiber orientations at multiple levels of tract propagation. Anatomical priors are used to minimize the number of false-positive pathways. The MLFT method was evaluated on synthetic data and in vivo data by reconstructing the CST while compared to conventional tractography approaches.
RESULTS
The radial extent of MLFT reconstructions is comparable to that of probabilistic reconstruction: [Formula: see text] for the left and [Formula: see text] for the right hemisphere according to Wilcoxon test, while achieving significantly higher topography preservation compared to probabilistic tractography: [Formula: see text].
DISCUSSION
MLFT provides a novel way to reconstruct fiber pathways by adding the capability of including branching pathways in fiber tractography. Thanks to its robustness, feasible reconstruction extent and topography preservation, our approach may assist in clinical practice as well as in virtual dissection studies.
Topics: Diffusion Tensor Imaging; Image Processing, Computer-Assisted; Diffusion Magnetic Resonance Imaging; Algorithms; Pyramidal Tracts
PubMed: 35904612
DOI: 10.1007/s10334-022-01033-3 -
Nature Communications Jan 2021Processing within the anterior cingulate cortex (ACC) is crucial for the patterning of appropriate behavior, and ACC dysfunction following chronic drug use is thought to...
Processing within the anterior cingulate cortex (ACC) is crucial for the patterning of appropriate behavior, and ACC dysfunction following chronic drug use is thought to play a major role in drug addiction. However, cortical pyramidal projection neurons can be subdivided into two major types (intratelencephalic (IT) and pyramidal tract (PT)), with distinct inputs and projection targets, molecular and receptor profiles, morphologies and electrophysiological properties. Yet, how each of these cell populations modulate behavior related to addiction is unknown. We demonstrate that PT neurons regulate the positive features of a drug experience whereas IT neurons regulate the negative features. These findings support a revised theory of cortical function in addiction, with distinct cells and circuits mediating reward and aversion.
Topics: Animals; Cerebral Cortex; Cocaine; Electrophysiological Phenomena; Male; Pharmaceutical Preparations; Pyramidal Cells; Pyramidal Tracts; Rats; Rats, Sprague-Dawley; Reward
PubMed: 33420090
DOI: 10.1038/s41467-020-20526-0