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PubMed2003

Pyramidal tract mapping by diffusion tensor magnetic resonance imaging in multiple sclerosis: improving correlations with disability.

BACKGROUND: Current magnetic resonance imaging (MRI) outcome measures such as T2 lesion load correlate poorly with disability in multiple sclerosis. Diffusion tensor imaging (DTI) of the brain can provide unique information regarding the orientation and integrity of white matter tracts in vivo. OBJECTIVE: To use this information to map the pyramidal tracts of patients with multiple sclerosis, investigate the relation between burden of disease in the tracts and disability, and compare this with more global magnetic resonance estimates of disease burden. METHODS: 25 patients with relapsing-remitting multiple sclerosis and 17 healthy volunteers were studied with DTI. An algorithm was used that automatically produced anatomically plausible maps of white matter tracts. The integrity of the pyramidal tracts was assessed using relative anisotropy and a novel measure (L(t)) derived from the compounded relative anisotropy along the tracts. The methods were compared with both traditional and more recent techniques for measuring disease burden in multiple sclerosis (T2 lesion load and "whole brain" diffusion histograms). RESULTS: Relative anisotropy and L(t) were significantly lower in patients than controls (p < 0.05). Pyramidal tract L(t) in the patients correlated significantly with both expanded disability status scale (r = -0.48, p < 0.05), and to a greater degree, the pyramidal Kurtzke functional system score (KFS-p) (r = -0.75, p < 0.0001). T2 lesion load and diffusion histogram parameters did not correlate with disability. CONCLUSIONS: Tract mapping using DTI is feasible and may increase the specificity of MRI in multiple sclerosis by matching appropriate tracts with specific clinical scoring systems. These techniques may be applicable to a wide range of neurological conditions.

Adult↗

PubMed2007

Pyramidal tract degeneration in multiple system atrophy: the relevance of magnetization transfer imaging.

The clinical features of multiple system atrophy (MSA) include four domains: autonomic failure/urinary dysfunction, Parkinsonism, cerebellar ataxia, and corticospinal tract dysfunction. Although the diagnosis of definite MSA requires pathological confirmation, magnetic resonance imaging (MRI) studies have been shown to contribute to the diagnosis of MSA. Although pyramidal tract dysfunction is frequent in MSA patients, signs of pyramidal tract involvement are controversially demonstrated by MRI. We evaluated the pyramidal involvement in 10 patients (7 women) with clinically probable MSA, detecting the presence of spasticity, hyperreflexia, and Babinski sign, as well as demonstrating degeneration of the pyramidal tract and primary motor cortex by MRI in all of them. Our article also discusses key radiological features of this syndrome. In MSA, pyramidal tract involvement seems to be more frequent than previously thought, and the clinicoradiological correlation between pyramidal tract dysfunction and degeneration may contribute to the understanding of the clinical hallmarks of MSA. MRI may also add information regarding the differential diagnosis of this syndrome.

Female↗

PubMed1975

Projections of pyramidal tract cells to alpha-motoneurones innervating hind-limb muscles in the monkey.

1. We have investigated the spatial organization of monosynaptic corticospinal projections to hind-limb motoneurones, using near threshold stimulation of the surface of the precentral gyrus to activate pyramidal tract (PT) cells and intracellular recording from motoneurones to detect the resulting e.p.s.p.s. 2. Monosynaptic e.p.s.p.s. of cortical origin were seen in all motoneurone species investigated, those of distal as well as of proximal hind-limb muscles. The proportion of motoneurones in which the e.s.p.s. were evoked and the amplitudes of the latter indicated a more extensive cortical projection to motor nuclei for distal than for proximal muscles, as previously found for forelimb motoneurones. 3. Cortical areas from which monosynaptic e.p.s.p.s. were evoked in individual motoneurones were remarkably large, most often between 3 and 7 mm2. Several motoneurones appeared to have two or three separate areas within the hind-limb division of the motor cortex. 4. Areas of location of pyramidal tract cells projecting to various motoneurones innervating one muscle were usually not identical. They overlapped often only partially or did not overlap at all. 5. Areas of location of pyramidal tract cells projecting to motor nuclei for different muscles often showed an extensive overlap. When it occurred, various motoneurones of a given motor nucleus had common cortical projection areas with motoneurones of other motor nuclei, either to synergistic or to antagonistic muscles. Our results give further evidence for overlapping of areas of cortical projections to motoneurones and speak against a mosaic-like organization of pyramidal tract cells projecting to different motor nuclei. 6. The rise times of cortically evoked e.p.s.p.s. indicate that the corticospinal tract fibres terminate on motoneurones at approximately similar distances from the soma as group Ia afferents. The small amplitudes of the majority of e.p.s.p.s. evoked by near threshold cortical stimulation therefore suggest that unitary e.p.s.p.s of cortical origin are small and that the density of pyramidal tract cells projecting to individual motoneurones is usually low, even in the centrum of projection areas. 7. Effects of intracortical stimulation depended on the stimulus strength. With currents of 2-3 muA, e.p.s.p.s were usually evoked in one motoneurone species or in close synergists. With currents of 5-10 muA, largest e.p.s.p.s a number of other motoneurones. Latencies of descending volleys in the lumbar corticospinal tract indicated that intracortical stimuli activated pyramidal tract cells indirectly; the effects of these stimuli could thus not be used to indicate the location of pyramidal tract cells responsible for them.

Animals↗

PubMed2000

Plasticity in the distribution of the red nucleus output to forearm muscles after unilateral lesions of the pyramidal tract.

It has been hypothesized that the magnocellular red nucleus (RNm) contributes to compensation for motor impairments associated with lesions of the pyramidal tract. To test this hypothesis, we used stimulus triggered averaging (StTA) of electromyographic (EMG) activity to characterize changes in motor output from the red nucleus after lesions of the pyramidal tract. Three monkeys were trained to perform a reach and prehension task. EMG activity was recorded from 11 forearm muscles including one elbow, five wrist, and five digit muscles. Microstimulation (20 microA at 20 Hz) was delivered throughout the movement task to compute StTAs. Two monkeys served as controls. In a third monkey, 65% of the left pyramidal tract had been destroyed by an electrolytic lesion method five years before recording. The results demonstrate a clear pattern of postlesion reorganization in red nucleus-mediated output effects on forearm muscles. The normally prominent extensor preference in excitatory output from the RNm (92% in extensors) was greatly diminished in the lesioned monkey (59%). Similarly, suppression effects, which are normally much more prominent in flexor than in extensor muscles (90% in flexors), were also more evenly distributed after recovery from pyramidal tract lesions. Because of the limited excitatory output from the RNm to flexor muscles that normally exists, loss of corticospinal output would leave control of flexors particularly weak. The changes in RNm organization reported in this study would help restore function to flexor muscles. These results support the hypothesis that the RNm is capable of reorganization that contributes to the recovery of forelimb motor function after pyramidal tract lesions.

Action Potentials↗

PubMed2000

Ipsilateral hemiparesis after putaminal hemorrhage due to uncrossed pyramidal tract.

OBJECTIVE: Previous case reports supported the presence of the uncrossed pyramidal tract in exceptional patients. However, most of these case reports have not fully discussed involvement of the motor cortex controlling the ipsilateral limbs. DESIGN AND METHOD: The authors investigated a 62-year-old man who developed right hemiparesis after right putaminal hemorrhage by using MRI, transcranial magnetic stimulation, functional MRI (fMRI), and sensory evoked potentials. He had moderate weakness including the face, spasticity with brisk deep tendon reflexes and Babinski sign, and impaired vibration and position sense, all on the right side. RESULT: A MRI study showed hemorrhage in the right putamen and the wedge-shaped medulla. A fMRI study during a sequential finger opposition task showed activation in the motor cortex ipsilateral to the finger movements, but not on the contralateral side. Sensory evoked potentials showed cortical response ipsilateral to the side of stimulation. CONCLUSION: The pyramidal tract and the dorsal column-medial lemniscus pathway did not cross in the medulla in this patient. In view of the presence of the abnormal shape in the medulla and congenital scoliosis, a congenital factor might be responsible for the uncrossed pyramidal tract and dorsal column-medial lemniscus in this patient.

Brain Mapping↗

PubMed1991

Outgrowth of the pyramidal tract in the rat cervical spinal cord: growth cone ultrastructure and guidance.

In order to examine the mode of outgrowth of the pyramidal tract in the rat, the ultrastructure of its pathway in the dorsal funiculus of the spinal cord was analysed. The analysis was performed by means of serial sections of the third cervical segment before and during the arrival of pyramidal tract axons, and focussed on the morphology and microenvironment of the growth cones. Growth cones appear as elongated terminal enlargements without side branches. Two zones could be discerned: the distal, usually lamellipodial fine granular zone, containing no organelles, except for an occasional clear vesicle; and the proximal organelle-rich zone, which contains various organelles, such as agranular reticulum and vesicular structures. In addition, the proximal organelle-rich zone contains round or elliptic structures, limited by two concentric membranes, that enclose reticular and vesicular elements. The electron density of these structures varied from as low as the surrounding growth cone matrix to as dark as lysosomal structures, suggesting their involvement in turnover processes. At embryonic day 20, the most ventral part of the dorsal funiculus, where the first pyramidal tract axons are due to arrive within two days, is populated by axons that are relatively small compared to those in the rest of the dorsal funiculus. At birth, the arrival of the first pyramidal tract axons is marked by the presence of numerous large growth cone profiles in between small axons in the most ventral part of the dorsal funiculus; no circumscript bundle separated from the ascending sensory fiber tracts is present yet. The growth cones descend, club-shaped and 1 to 2 microns in diameter, without lamellipodia or filopodia. Within the same area a second growth cone type is present, which contains dense-core vesicles and has spread-out lamellipodia. Most of these growth cones are ascending and they probably belong to primary afferent or propriospinal fibers. At postnatal day 2, the pyramidal tract can be readily delineated from the adjacent fasciculus cuneatus where myelination has already started, but no glial boundary is present. The abundant growth cones are 1-2 microns wide and extend single unbranched lamellipodia, up to 15 microns long, which often enfold parallel axons or other growth cones. At postnatal day 4, growth cones are scarce in the tract. They measure 1 micron or less in diameter and each extends a single, straight lamellipodium or filopodium over 1 to 7 microns in the caudal direction.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1975

Variation in form of the pyramidal tract and its relationship to digital dexterity.

A morphometric analysis of the pyramidal tract's relation to digital dexterity was performed on data from 69 mammals. The results show that the variation in digital dexterity among mammals corresponds most closely to the variation in place of termination of pyramidal tract fibers within the spinal cord, corresponds less closely to the variation in the size of the tract itself and its constituent fibers, and does not correspond reliably with any other feature yet reported. Since the termination of pyramidal tract fibers on or very near spinal motor neurons is a prerequisite even for the peculiar kind of dexterity seen in some non-primates (e.g., raccoon, kinkajou), this one feature alone seems to be a critical factor.

Animals↗

PubMed1985

Fiber analysis of the pyramidal tract of the laboratory rat.

Light and electron microscopic study of the pyramidal tract of the laboratory rat at a midbulbar level revealed the total number of myelinated fibers on one side to be about 200,000. They ranged from 0.2 micron to more than 5 microns, but clustered strongly in the neighborhood of 1.0 micron (mode of 0.9 micron and mean of 1.2 micron), forming the highly skewed fiber spectrum so familiar for mammalian pyramidal tracts and other central fiber pathways. Numerous small clusters of unmyelinated axons were found scattered throughout the tract, adding another 100,000 axons to the estimated number. Not only were the fibers exceedingly small, but also the degree of myelination relative to axon diameter varied widely, suggesting that conduction speed within the tract is not optimal for all fibers. In fact, about half of the fibers in the pyramidal tract would, in theory, conduct faster if they had no myelin wrapping.

Animals↗

PubMed2004

Pyramidal tract lesions and movement-associated cortical recruitment in patients with MS.

Cortical functional changes, with the potential to limit the functional consequences of tissue injury, have been shown in patients with multiple sclerosis (MS). In this study, we assessed the influence of MS-related tissue damage of the brain portion of the left pyramidal tract on the corresponding movement-associated patterns of cortical recruitment in a large sample of MS patients when performing a simple motor task with their fully normal functioning right upper limbs. We investigated 76 right-handed patients with definite MS. In each subject, functional magnetic resonance imaging (fMRI) was acquired during the performance of a simple motor task with the dominant, right upper limb. During the same session, dual-echo, magnetization transfer (MT) and diffusion tensor (DT) MRI sequences were also obtained to quantify the extent and the severity of pyramidal tract damage. Lesions along the left pyramidal tract were identified in 43 patients. Compared to patients without pyramidal tract lesions, patients with such lesions had more significant activations of the contralateral primary sensorimotor cortex (SMC), secondary sensorimotor cortex (SII), inferior central sulcus, and cingulate motor area (CMA). They also showed more significant activations of several regions of the ipsilateral hemisphere, including the primary SMC and the precuneus. In these patients, T2 lesion load of left pyramidal tract was correlated with the extent of activation of the contralateral primary SMC (r2 = 0.25, P < 0.0001), whereas no correlations were found between the extent of fMRI activations and the severity of intrinsic lesion damage, as well as with left pyramidal tract normal-appearing white matter damage. This study shows that, in patients with MS, following injury of the motor pathways, there is an increased recruitment of a widespread sensorimotor network, which is likely to contribute to limit the appearance of overt clinical deficits.

Adult↗

PubMed1998

Wallerian degeneration of the pyramidal tract does not affect stroke rehabilitation outcome.

OBJECTIVE: To test whether Wallerian degeneration (WD) of the pyramidal tract as signaled by MRI affects rehabilitation outcome in patients with subcortical infarction (internal capsule or corona radiata). BACKGROUND: Recent radiologic evidence suggests that WD occurs no earlier than 3 months after a subcortical infarction. METHODS: A total of 77 consecutive patients with pure motor hemiparesis due to an initial subcortical infarction were assessed on admission and discharge with the Functional Independence Measure (FIM) for disability and Stroke Impairment Assessment Set (SIAS, full = 25) for impairment. WD was defined by a high-intensity area detected along the pyramidal tract below the level of lesion on T2-weighted MR image (WD+). RESULTS: Age, sex, side of stroke, Mini-Mental State Examination score, and volume of lesion were comparable for each group. Length of stay (LOS) was significantly longer (p < 0.05) in WD+ (130 days) than in WD- (105 days). There was no difference in the change of FIM (WD+, 99 to 111; WD-, 95 to 107) or SIAS measures (WD+, 12 to 16; WD-, 13 to 16) made on admission and discharge, nor was there any effect of the timing of the rehabilitation experience (< or = 90 days or >90 days after stroke). CONCLUSIONS: After stroke, apparent WD of the pyramidal tract may slow functional recovery but does not limit final rehabilitation outcome of pure motor hemiparesis. Study of the mechanisms of compensation for this delayed pyramidal tract degeneration will enhance the scientific basis for rehabilitation.

Cerebral Infarction↗

PubMed2002

Rhythm generation in monkey motor cortex explored using pyramidal tract stimulation.

We investigated whether stimulation of the pyramidal tract (PT) could reset the phase of 15-30 Hz beta oscillations observed in the macaque motor cortex. We recorded local field potentials (LFPs) and multiple single-unit activity from two conscious macaque monkeys performing a precision grip task. EMG activity was also recorded from the second animal. Single PT stimuli were delivered during the hold period of the task, when oscillations in the LFP were most prominent. Stimulus-triggered averaging of the LFP showed a phase-locked oscillatory response to PT stimulation. Frequency domain analysis revealed two components within the response: a 15-30 Hz component, which represented resetting of on-going beta rhythms, and a lower frequency 10 Hz response. Only the higher frequency could be observed in the EMG activity, at stronger stimulus intensities than were required for resetting the cortical rhythm. Stimulation of the PT during movement elicited a greatly reduced oscillatory response. Analysis of single-unit discharge confirmed that PT stimulation was capable of resetting periodic activity in motor cortex. The firing patterns of pyramidal tract neurones (PTNs) and unidentified neurones exhibited successive cycles of suppression and facilitation, time locked to the stimulus. We conclude that PTN activity directly influences the generation of the 15-30 Hz rhythm. These PTNs facilitate EMG activity in upper limb muscles, contributing to corticomuscular coherence at this same frequency. Since the earliest oscillatory effect observed following stimulation was a suppression of firing, we speculate that inhibitory feedback may be the key mechanism generating such oscillations in the motor cortex.

Algorithms↗

PubMed1985

Superposition of antidromic responses in pyramidal tract cell clusters.

Large-seeing-distance microelectrodes were used to record simultaneously the activity of several pyramidal tract neurons in cerebral cortex. When activated antidromically, these neurons responded simultaneously, forming a "stack" of superimposed spikes, rather than responding at different times within the 10-ms time interval during which they might be expected to respond. Using a variety of spike collision tests, we found that these individual spikes arose from separate sources and reflected the activity of individual, albeit neighboring, pyramidal tract neurons. The collaterals of neurons within a stack projected to different structures, further verifying that separate neurons were involved. Such synchrony of antidromic activity among neighboring pyramidal tract neurons is an exceedingly low-probability event, if neighboring fibers conduct independently of one another. Our results imply that fibers from small clusters of neurons in the cortex assemble to form synchronously conducting bundles of fibers within the pyramidal tract.

Animals↗

PubMed2001

Three-dimensional visualization of the pyramidal tract in a neuronavigation system during brain tumor surgery: first experiences and technical note.

OBJECTIVE: To integrate spatial three-dimensional information concerning the pyramidal tracts into a customized system for frameless neuronavigation during brain tumor surgery. METHODS: Four consecutive patients with intracranial tumors in eloquent areas underwent diffusion-weighted and anatomic magnetic resonance imaging studies within 48 hours before surgery. Diffusion-weighted datasets were merged with anatomic data for navigation purposes. The pyramidal tracts were segmented and reconstructed for three-dimensional visualization. The reconstruction results, together with the fused-image dataset, were available during surgery in the environment of a customized neuronavigation system. RESULTS: In all four patients, the combination of reconstructed data and fused images was a helpful additional source of information concerning the tumor seat and topographical interaction with the pyramidal tract. In two patients, intraoperative motor cortex stimulation verified the tumor seat with regard to the precentral gyrus. CONCLUSION: Diffusion-weighted magnetic resonance imaging allows individual estimation of large fiber tracts applicable as important information in intraoperative neuronavigation and in planning brain tumor resection. A three-dimensional representation of fibers associated with the pyramidal tract during brain tumor surgery is feasible with the presented technique and is a helpful adjunct for the neurosurgeon. The main drawbacks include the length of time required for the segmentation procedure, the lack of direct intraoperative control of the pyramidal tract position, and brain shift. However, mapping of large fiber tracts and its intraoperative use for neuronavigation have the potential to increase the safety of neurosurgical procedures and to reduce surgical morbidity.

Aged↗

PubMed1991

[MR evaluation of wallerian degeneration of the pyramidal tract].

This study is based on 135 magnetic resonance (MR) exams of 110 patients with wallerian degeneration of the pyramidal tract shown on MR images acquired on a mid field imaging scanner. The MR findings of wallerian degeneration were abnormal signal band along the course of the pyramidal tract and ipsilateral brain stem shrinkage. In all 110 cases an abnormal signal band was seen on T2-weighted spin-echo images, that is, a hypointense band in four exams between 30 days and 116 days after onset of symptoms, and hyperintense bands in 122 exams. The hyperintense signal on T2-weighted images was shown in most cases after 200 days from the onset. In one case a signal of the pyramidal tract showed a hyperintense band at 7 days, hypointense at 30 days, and hyperintense again at 123 days after onset. Sequential MR exams of another case showed gradual narrowing of the hyperintense signal band and progression of the ipsilateral brainstem shrinkage. The narrowing of the pyramidal tract and the ipsilateral brain stem shrinkage tended to be shown after 6 months from onset.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMed1993

Transient cortical pathways in the pyramidal tract of the neonatal ferret.

Anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) was used to study transient axons from the visual cortex in the pyramidal tract. Injections at birth restricted to the visual cortex labeled axons in the vicinity of the pontine nuclei. Two to eight days after birth, axons from the occipital cortex were found posterior to the pontine nucleus, their caudalmost stable target. Transient corticospinal axons from the presumptive primary visual cortex did not grow caudal to the pyramidal decussation. Innervation of more distal targets preceded innervation of proximal targets. Innervation of the pontine nucleus is initiated around 68 hours after birth, when the transient extension in the medullary pyramidal tract has attained its maximum caudal extent. Innervation of the superior colliculus begins 9 days after birth. Retrograde tracers were used to follow the developmental changes in the cortical distribution of the parent neurons giving rise to axons in the pyramidal tract. In the adult, labeled neurons following injection of retrograde tracer in the pyramidal tract occupied less than a third of the neocortex and were centred on the anterior part of the coronal and spleniocruciate gyri. In the immature brain, labeled neurons covered more than two-thirds of the neocortex. Areal density measurements in the neonate showed that peak labeling was centred in the anterior coronal and spleniocruciate gyri, where corticospinal cells in the adult are located. There was a marked rostral-caudal gradient so that labeled neurons were very scarce towards the occipital pole. These results, showing transient neocortical axons in the pyramidal tract in a carnivore, suggest that this may be a common feature of mammalian development. The finding that the adult pattern of corticospinal projections does not emerge from a uniform distribution is discussed with respect to the areal specification of cortical connectivity.

Animals↗

PubMed1980

Localization of the pyramidal tract in the internal capsule by whole brain dissection.

Six human brains were dissected by blunt technique and sectioned horizontally to establish the three-dimensional relationships of the pyramidal tract and the internal capsule. In all instances, the pyramidal tract entered the rostral capsule in the anterior half of the posterior limb and progressively shifted into the posterior half of the posterior limb in the more caudal horizontal sections. These observations resolve the current controversy about the exact anatomic location of the pyramidal tract in the posterior limb of the internal capsule. This controversy arose because previous authors failed to consider the changing rostrocaudal/anterior-posterior anatomy of the pyramidal tract as it courses through the posterior limb.

Dissection↗

PubMed1983

Responses of pyramidal tract neurons in the postcentral cortex to tactile inputs.

Pyramidal tract neurons were recorded from postcentral cortex of awake monkeys and their responses to step indentation and vibratory stimulus were studied. The majority of them exhibited slowly adapting response to the indentation stimulus but failed to show phase-locked response to 50-200 Hz vibrations. The response properties appeared to be in contrast to those of non-pyramidal tract neurons whose responses were largely quickly adapting.

Adaptation, Physiological↗

PubMed1979

Prolonged changes in excitability of pyramidal tract neurones in the cat: a post-synaptic mechanism.

1. Prolonged changes in the excitability of cortical neurones can be produced by altering their firing rates for brief periods. In the anaesthetized cat, increased firing of pyramidal tract cells induced by trains of antidromic conditioning shocks led to increases in cell excitability, as measured by the size of the mass response at the medullary pyramid to test shocks applied to the cortical surface. We have shown in two ways that post-synaptic mechanisms could be responsible. 2. In one experimental design, MgCl2 solution (1 mole/l.) was applied to the cortical surface in order to block synaptic activity throughout the cortical depth. Following antidromic conditioning trains, cell excitability was increased; the size of the mass response was up to 30% larger than the control values. This persisted undiminished for up to 3 hr. 3. In the second experimental design, synaptic activity was not blocked, but we compared the effects of antidromic plus synaptic activation of pyramidal tract cells with the effects of synaptic activation alone. Antidromic plus synaptic activation was obtained by applying conditioning trains to the pyramidal tract at the medulla ipsilateral to the cortical test shock; prolonged increases in the ipsilateral response to the test shock were produced. Synaptic activation alone was obtained by the same conditioning trains, but in those cells whose axons projected into the contralateral pyramidal tract; prolonged increases in the contralateral response to the cortical test shock were never seen. In many instances prolonged decreases in excitability were found. 4. We conclude that prolonged increases in excitability of pyramidal tract cells can occur in the absence of any synaptic input, demonstrating that the underlying mechanism is post-synaptic; this does not preclude the action of synaptic mechanisms when synaptic transmission is not blocked.

Animals↗