Spinal Cord Injury Immediately Changes the State of the Brain
TL;DR: It is shown that a complete thoracic transection of the spinal cord produces immediate functional reorganization in the primary somatosensory cortex of anesthetized rats, and that this state change plays a critical role in the early cortical reorganization after spinal cord injury.
Abstract: Spinal cord injury can produce extensive long-term reorganization of the cerebral cortex. Little is known, however, about the sequence of cortical events starting immediately after the lesion. Here we show that a complete thoracic transection of the spinal cord produces immediate functional reorganization in the primary somatosensory cortex of anesthetized rats. Besides the obvious loss of cortical responses to hindpaw stimuli (below the level of the lesion), cortical responses evoked by forepaw stimuli (above the level of the lesion) markedly increase. Importantly, these increased responses correlate with a slower and overall more silent cortical spontaneous activity, representing a switch to a network state of slow-wave activity similar to that observed during slow-wave sleep. The same immediate cortical changes are observed after reversible pharmacological block of spinal cord conduction, but not after sham. We conclude that the deafferentation due to spinal cord injury can immediately (within minutes) change the state of large cortical networks, and that this state change plays a critical role in the early cortical reorganization after spinal cord injury.
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TL;DR: The results suggest interventions that presume substantial preservation of the neural retina will likely fail in late stages of the disease, and suggest fundamental work in the biology and mechanisms of disease progression are needed to support vision rescue strategies.
241 citations
Cites background from "Spinal Cord Injury Immediately Chan..."
...Furthermore, given the changes in retinal circuitry, there are implications for downstream changes in CNS in response to lesions (Boucard et al., 2009; Aguilar et al., 2010)....
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TL;DR: This review will focus on delineating the pathophysiological mechanisms of the brain plasticity changes following SCI, based on the existing neuroimaging and neurophysiological evidence in experimental models and humans.
153 citations
TL;DR: It is suggested that acute stroke activates unique pathways that can rapidly redistribute function within the spared cortical hemisphere within 30–50 min of stroke onset, and not merely loss of activity.
Abstract: Most processing of sensation involves the cortical hemisphere opposite (contralateral) to the stimulated limb. Stroke patients can exhibit changes in the interhemispheric balance of sensory signal processing. It is unclear whether these changes are the result of poststroke rewiring and experience, or whether they could result from the immediate effect of circuit loss. We evaluated the effect of mini-strokes over short timescales (<2 h) where cortical rewiring is unlikely by monitoring sensory-evoked activity throughout much of both cortical hemispheres using voltage-sensitive dye imaging. Blockade of a single pial arteriole within the C57BL6J mouse forelimb somatosensory cortex reduced the response evoked by stimulation of the limb contralateral to the stroke. However, after stroke, the ipsilateral (uncrossed) forelimb response within the unaffected hemisphere was spared and became independent of the contralateral forelimb cortex. Within the unaffected hemisphere, mini-strokes in the opposite hemisphere significantly enhanced sensory responses produced by stimulation of either contralateral or ipsilateral pathways within 30-50 min of stroke onset. Stroke-induced enhancement of responses within the spared hemisphere was not reproduced by inhibition of either cortex or thalamus using pharmacological agents in nonischemic animals. I/LnJ acallosal mice showed similar rapid interhemispheric redistribution of sensory processing after stroke, suggesting that subcortical connections and not transcallosal projections were mediating the novel activation patterns. Thalamic inactivation before stroke prevented the bilateral rearrangement of sensory responses. These findings suggest that acute stroke, and not merely loss of activity, activates unique pathways that can rapidly redistribute function within the spared cortical hemisphere.
135 citations
Cites background from "Spinal Cord Injury Immediately Chan..."
...However, this evidence for structural plasticity must reconcile the fact that rearrangements in the patterns of sensory-evoked activity can even occur at very short time points that are too early for the sprouting of connections to have an effect (21, 33, 59, 60)....
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TL;DR: It is not only necessary to better understand how the brain can reorganize after injury with or without therapy, it is also necessary to clarify when and why brain reorganization can be either "good" or "bad" in terms of its clinical consequences.
104 citations
Cites background from "Spinal Cord Injury Immediately Chan..."
...A complete thoracic spinal cord transection or hemisection in anesthetized rats immediately changes the state of the brain, decreasing cortical spontaneous activity as evidenced by a slowing of the frequency of anesthesia-induced oscillations (Aguilar et al., 2010; Yagüe et al., 2014)....
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...A uthor M anuscript A uthor M anuscript A uthor M anuscript A uthor M anuscript lesion (Aguilar et al., 2010; Yagüe et al., 2014)....
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...Figure reproduced from Aguilar et al. (2010), with permission....
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TL;DR: Cord atrophy predicts changes at the cortical level that lead to reduced excitability and increased inhibition, and cortical forearm motor representations may reorganize towards the intrinsic hand motor representation to maximize output to muscles of the impaired forearm following SCI.
Abstract: Functional imaging studies, using blood oxygen level-dependent signals, have demonstrated cortical reorganization of forearm muscle maps towards the denervated leg area following spinal cord injury (SCI) The extent of cortical reorganization was predicted by spinal atrophy We therefore expected to see a similar shift in the motor output of corticospinal projections of the forearm towards more denervated lower body parts in volunteers with cervical injury Therefore, we used magnetic resonance imaging-navigated transcranial magnetic stimulation (TMS) to non-invasively measure changes in cortical map reorganization of a forearm muscle in the primary motor cortex (M1) following human SCI We recruited volunteers with chronic cervical injuries resulting in bilateral upper and lower motor impairment and severe cervical atrophy and healthy control participants All participants underwent a T1-weighted anatomical scan prior to the TMS experiment The motor thresholds of the extensor digitorum communis muscle (EDC) were defined, and its cortical muscle representation was mapped The centre of gravity (CoG), the cortical silent period (CSP) and active motor thresholds (AMTs) were measured Regression analysis was used to investigate relationships between trauma-related anatomical changes and TMS parameters SCI participants had increased AMTs (P = 001) and increased CSP duration (P = 001) The CoG of the EDC motor-evoked potential map was located more posteriorly towards the anatomical hand representation of M1 in SCI participants than in controls (P = 003) Crucially, cord atrophy was negatively associated with AMT and CSP duration (r 2 ‡ 026, P < 005) In conclusion, greater spinal cord atrophy predicts changes at the cortical level that lead to reduced excitability and increased inhibition Therefore, cortical forearm motor representations may reorganize towards the intrinsic hand motor representation to maximize output to muscles of the impaired forearm following SCI
84 citations
Cites background from "Spinal Cord Injury Immediately Chan..."
..., 2004), changes in cortical AMT may reflect structural and functional alterations in cortico-cortical connectivity that result from degenerative processes affecting CS neurons (Aguilar et al., 2010)....
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...…results from activation of facilitatory inputs to CS neurons (Amassian et al., 1987; Shimazu et al., 2004), changes in cortical AMT may reflect structural and functional alterations in cortico-cortical connectivity that result from degenerative processes affecting CS neurons (Aguilar et al., 2010)....
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References
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01 Jan 1983
TL;DR: This paper presents a meta-analyses of the determinants of earthquake-triggered landsliding in the Czech Republic over a period of 18 months in order to establish a probabilistic framework for estimating the intensity of the earthquake.
Abstract: Preface. Acknowledgements. Introduction. References. List of Structures. Index of Abbreviations. Diagrams.
57,116 citations
"Spinal Cord Injury Immediately Chan..." refers methods in this paper
...A craniotomy was performed on the right side of the midline over the somatosensory cortex [AP: 1 to 4; ML: 1–5; atlas of Paxinos and Watson (1986)], and the cisterna magna was opened to guarantee the stability of the recordings....
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TL;DR: It is shown here how the response of the immune system to repeated exposure to high-energy radiation affects its ability to discriminate between healthy and diseased tissue.
11,002 citations
"Spinal Cord Injury Immediately Chan..." refers methods in this paper
...A craniotomy was performed on the right side of the midline over the somatosensory cortex [AP: 1 to 4; ML: 1–5; atlas of Paxinos and Watson (1986)], and the cisterna magna was opened to guarantee the stability of the recordings....
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TL;DR: These findings suggest that the BOLD contrast mechanism reflects the input and intracortical processing of a given area rather than its spiking output, and that LFPs yield a better estimate of BOLD responses than the multi-unit responses.
Abstract: Functional magnetic resonance imaging (fMRI) is widely used to study the operational organization of the human brain, but the exact relationship between the measured fMRI signal and the underlying neural activity is unclear. Here we present simultaneous intracortical recordings of neural signals and fMRI responses. We compared local field potentials (LFPs), single- and multi-unit spiking activity with highly spatio-temporally resolved blood-oxygen-level-dependent (BOLD) fMRI responses from the visual cortex of monkeys. The largest magnitude changes were observed in LFPs, which at recording sites characterized by transient responses were the only signal that significantly correlated with the haemodynamic response. Linear systems analysis on a trialby-trial basis showed that the impulse response of the neurovascular system is both animal- and site-specific, and that LFPs yield a better estimate of BOLD responses than the multi-unit responses. These findings suggest that the BOLD contrast mechanism reflects the input and intracortical processing of a given area rather than its spiking output.
6,140 citations
"Spinal Cord Injury Immediately Chan..." refers result in this paper
...Since BOLD, VSD, and LFP responses to sensory stimuli are reasonably related (Logothetis et al., 2001; Arthurs and Boniface, 2003; Petersen et al., 2003; Goloshevsky et al., 2008), our findings likely represent the early electrophysiological counterpart of the results of Endo et al. (2007) and…...
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TL;DR: In this paper, it was shown that reticular activation is associated with the activation of the reticular formation of the brain stem, and that reticulus activation can be induced by low frequency stimulation of the diffuse thalamic projection system, rather than intra-cortical spread following the arrival of afferent impulses at the sensory receiving areas of the cortex.
4,014 citations
TL;DR: The NE-LC system may globally bias the responsiveness of target neurons and thereby influence overall behavioral orientation, generally consistent with previous proposals that the NE- LC system is involved in regulating cortical and behavioral arousal.
Abstract: Spontaneous discharge of norepinephrine-containing locus coeruleus (NE-LC) neurons was examined during the sleep-walking cycle (S-WC) in behaving rats. Single unit and multiple unit extracellular recordings yielded a consistent set of characteristic discharge properties. (1) Tonic discharge co-varied with stages of the S-WC, being highest during waking, lower during slow wave sleep, and virtually absent during paradoxical sleep. (2) Discharge anticipated S-WC stages as well as phasic cortical activity, such as spindles, during slow wave sleep. (3) Discharge decreased within active waking during grooming and sweet water consumption. (4) Bursts of impulses accompanied spontaneous or sensory-evoked interruptions of sleep, grooming, consumption, or other such ongoing behavior. (5) These characteristic discharge properties were topographically homogeneous for recordings throughout the NE-LC. (6) Phasic robust activity was synchronized markedly among neurons in multiple unit populations. (7) Field potentials occurred spontaneously in the NE-LC and were synchronized with bursts of unit activity from the same electrodes. (8) Field potentials became dissociated from unit activity during paradoxical sleep, exhibiting their highest rates in the virtual absence of impulses. These results are generally consistent with previous proposals that the NE-LC system is involved in regulating cortical and behavioral arousal. On the basis of the present data and those described in the following report (Aston-Jones, G., and F. E. Bloom (1981) J. Neurosci.1: 887-900), we conclude that these neurons may mediate a specific function within the general arousal framework. In brief, the NE-LC system may globally bias the responsiveness of target neurons and thereby influence overall behavioral orientation.
1,809 citations