Browsing by Subject "Motor Neurons"

Now showing 1 - 6 of 6
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    Composition and topographic organization of signals sent from the frontal eye field to the superior colliculus.
    (J Neurophysiol, 2000-04) Sommer, MA; Wurtz, RH
    The frontal eye field (FEF) and superior colliculus (SC) contribute to saccadic eye movement generation, and much of the FEF's oculomotor influence may be mediated through the SC. The present study examined the composition and topographic organization of signals flowing from FEF to SC by recording from FEF neurons that were antidromically activated from rostral or caudal SC. The first and most general result was that, in a sample of 88 corticotectal neurons, the types of signals relayed from FEF to SC were highly diverse, reflecting the general population of signals within FEF rather than any specific subset of signals. Second, many neurons projecting from FEF to SC carried signals thought to reflect cognitive operations, namely tonic discharges during the delay period of a delayed-saccade task (delay signals), elevated discharges during the gap period of a gap task (gap increase signals), or both. Third, FEF neurons discharging during fixation were found to project to the SC, although they did not project preferentially to rostral SC, where similar fixation neurons are found. Neurons that did project preferentially to the rostral SC were those with foveal visual responses and those pausing during the gap period of the gap task. Many of the latter neurons also had foveal visual responses, presaccadic pauses in activity, and postsaccadic increases in activity. These two types of rostral-projecting neurons therefore may contribute to the activity of rostral SC fixation neurons. Fourth, conduction velocity was used as an indicator of cell size to correct for sampling bias. The outcome of this correction procedure suggested that among the most prevalent neurons in the FEF corticotectal population are those carrying putative cognitive-related signals, i.e., delay and gap increase signals, and among the least prevalent are those carrying presaccadic burst discharges but lacking peripheral visual responses. Fifth, corticotectal neurons carrying various signals were biased topographically across the FEF. Neurons with peripheral visual responses but lacking presaccadic burst discharges were biased laterally, neurons with presaccadic burst discharges but lacking peripheral visual responses were biased medially, and neurons carrying delay or gap increase signals were biased dorsally. Finally, corticotectal neurons were distributed within the FEF as a function of their visual or movement field eccentricity and projected to the SC such that eccentricity maps in both structures were closely aligned. We conclude that the FEF most likely influences the activity of SC neurons continuously from the start of fixation, through visual analysis and cognitive manipulations, until a saccade is generated and fixation begins anew. Furthermore, the projection from FEF to SC is highly topographically organized in terms of function at both its source and its termination.
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    Corollary discharge across the animal kingdom.
    (Nat Rev Neurosci, 2008-08) Crapse, Trinity B; Sommer, Marc A
    Our movements can hinder our ability to sense the world. Movements can induce sensory input (for example, when you hit something) that is indistinguishable from the input that is caused by external agents (for example, when something hits you). It is critical for nervous systems to be able to differentiate between these two scenarios. A ubiquitous strategy is to route copies of movement commands to sensory structures. These signals, which are referred to as corollary discharge (CD), influence sensory processing in myriad ways. Here we review the CD circuits that have been uncovered by neurophysiological studies and suggest a functional taxonomic classification of CD across the animal kingdom. This broad understanding of CD circuits lays the groundwork for more challenging studies that combine neurophysiology and psychophysics to probe the role of CD in perception.
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    Phosphatase and tensin homologue/protein kinase B pathway linked to motor neuron survival in human superoxide dismutase 1-related amyotrophic lateral sclerosis.
    (Brain : a journal of neurology, 2011-02) Kirby, Janine; Ning, Ke; Ferraiuolo, Laura; Heath, Paul R; Ismail, Azza; Kuo, Su-Wei; Valori, Chiara F; Cox, Laura; Sharrack, Basil; Wharton, Stephen B; Ince, Paul G; Shaw, Pamela J; Azzouz, Mimoun
    Gene expression profiling has been used previously with spinal cord homogenates and laser capture microdissected motor neurons to determine the mechanisms involved in neurodegeneration in amyotrophic lateral sclerosis. However, while cellular and animal model work has focused on superoxide dismutase 1-related amyotrophic lateral sclerosis, the transcriptional profile of human mutant superoxide dismutase 1 motor neurons has remained undiscovered. The aim of this study was to apply gene expression profiling to laser captured motor neurons from human superoxide dismutase 1-related amyotrophic lateral sclerosis and neurologically normal control cases, in order to determine those pathways dysregulated in human superoxide dismutase 1-related neurodegeneration and to establish potential pathways suitable for therapeutic intervention. Identified targets were then validated in cultured cell models using lentiviral vectors to manipulate the expression of key genes. Microarray analysis identified 1170 differentially expressed genes in spinal cord motor neurons from superoxide dismutase 1-related amyotrophic lateral sclerosis, compared with controls. These genes encoded for proteins in multiple functional categories, including those involved in cell survival and cell death. Further analysis determined that multiple genes involved in the phosphatidylinositol-3 kinase signalling cascade were differentially expressed in motor neurons that survived the disease process. Functional experiments in cultured cells and primary motor neurons demonstrate that manipulating this pathway by reducing the expression of a single upstream target, the negative phosphatidylinositol-3 kinase regulator phosphatase and tensin homology, promotes a marked pro-survival effect. Therefore, these data indicate that proteins in the phosphatidylinositol-3 kinase pathway could represent a target for therapeutic manipulation in motor neuron degeneration.
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    Potential involvement of intracellular pH in a mouse model of amyotrophic lateral sclerosis.
    (Amyotrophic lateral sclerosis & frontotemporal degeneration, 2014-03) Kuo, Su-Wei; Jiang, Mingchen; Heckman, Cj
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    The role of the thalamus in motor control.
    (Curr Opin Neurobiol, 2003-12) Sommer, Marc A
    Two characteristics of the thalamus--its apparently simple relay function and its daunting multinuclear structure--have been customarily viewed as good reasons to study something else. Yet, now that many other brain regions have been explored and neurophysiologists are turning to questions of how larger circuits operate, these two characteristics are starting to seem more attractive. First, the relay nature of thalamic neurons means that recording from them, like tapping into a wire, can reveal the signals carried by specific circuits. Second, the concentration of like relay neurons into nuclei means that inactivating or stimulating them can efficiently test the functions of the circuits. Recent studies implementing these principles have revealed pathways through the thalamus that contribute to generating movements and to monitoring one's own actions (corollary discharge).
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    What the brain stem tells the frontal cortex. II. Role of the SC-MD-FEF pathway in corollary discharge.
    (J Neurophysiol, 2004-03) Sommer, Marc A; Wurtz, Robert H
    One way we keep track of our movements is by monitoring corollary discharges or internal copies of movement commands. This study tested a hypothesis that the pathway from superior colliculus (SC) to mediodorsal thalamus (MD) to frontal eye field (FEF) carries a corollary discharge about saccades made into the contralateral visual field. We inactivated the MD relay node with muscimol in monkeys and measured corollary discharge deficits using a double-step task: two sequential saccades were made to the locations of briefly flashed targets. To make second saccades correctly, monkeys had to internally monitor their first saccades; therefore deficits in the corollary discharge representation of first saccades should disrupt second saccades. We found, first, that monkeys seemed to misjudge the amplitudes of their first saccades; this was revealed by systematic shifts in second saccade end points. Thus corollary discharge accuracy was impaired. Second, monkeys were less able to detect trial-by-trial variations in their first saccades; this was revealed by reduced compensatory changes in second saccade angles. Thus corollary discharge precision also was impaired. Both deficits occurred only when first saccades went into the contralateral visual field. Single-saccade generation was unaffected. Additional deficits occurred in reaction time and overall performance, but these were bilateral. We conclude that the SC-MD-FEF pathway conveys a corollary discharge used for coordinating sequential saccades and possibly for stabilizing vision across saccades. This pathway is the first elucidated in what may be a multilevel chain of corollary discharge circuits extending from the extraocular motoneurons up into cerebral cortex.