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Existence of automaticity in anomalous bundle of Wolff-Parkinson-White syndrome.

Przybylski, J; Chiale, P A; Halpern, M S; Lázzari, J O; Elizari, M V; Rosenbaum, M B
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /06/1978 Português
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Escape beats probably arising from the anomalous bundle were documented in 2 patients with the Wolff-Parkinson-White (WPW) syndrome. A third patient, in whom complete AV block developed both in the anomalous bundle and the normal pathway, showed the occurrence of escape beats (an escape-bigeminy pattern), as well as a regular idioventricular rhythm arising from the anomalous bundle. Phase 4 block in the anomalous bundle occurred in 7 other patients, in 4 of them spontaneously and in 3 only after the administration of ajmaline or amiodarone. Only 4 of 14 fully investigated patients (out of a total number of 23) showed absence of both escape beats and phase 4 block. The escape beats were considered as direct evidence, and the phase 4 block as indirect evidence, for the existence of automaticity in the anomalous bundle. Such evidence supports the view that the anomalous bundle, like the His bundle-branch system, may be composed of specialised tissue endowed with the property of automaticity.

Effects of verapamil on ventricular tachycardias possibly caused by reentry, automaticity, and triggered activity.

Sung, R J; Shapiro, W A; Shen, E N; Morady, F; Davis, J
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /07/1983 Português
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To define the role of verapamil in the treatment of ventricular tachycardia (VT), we studied 21 patients with chronic recurrent VT. Electrophysiologic studies were performed before and during intravenous infusion of verapamil (0.15 mg/kg followed by 0.005 mg/kg per min). On the basis of the mode of VT initiation and termination, we identified three groups of patients: (a) 11 patients had VT suggestive of reentry, as VT could be initiated with ventricular extrastimulation and terminated with overdrive ventricular pacing. Verapamil did not affect the inducibility and cycle length of VT. (b) 7 patients had VT suggestive of catecholamine-sensitive automaticity as VT could not be initiated with programmed electrical stimulation but could be provoked by isoproterenol infusion. Moreover, the VT could not be converted to a sustained sinus rhythm with overdrive ventricular pacing and it resolved only with discontinuing isoproterenol infusion. Verapamil exerted no effects on VT. (c) 3 patients had VT with electrophysiologic characteristics suggestive of triggered activity related to delayed afterdepolarizations. Characteristically, after attaining a range of cycle lengths, the sinus, atrial or ventricular paced rhythm could initiate VT without ventricular extrastimulation. The first beat of VT invariably occurred late in the cardiac cycle with a premature coupling interval 0-80 ms shorter than the preceding QRS cycle length; the premature coupling interval gradually decreased as the sinus...

Physiological role of endogenous amines in the modulation of ventricular automaticity in the guinea-pig.

Hume, J; Katzung, B G
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /12/1980 Português
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1. Current-clamp experiments were carried out with guinea-pig papillary muscles to determine the dependence of depolarization-induced automaticity on endogenous catecholamines. 2. Catecholamine depletion was produced by pre-treatment of animals with 6-hydroxydopamine and confirmed by fluorimetric assay of right ventricular tissue. Papillary muscles from depleted animals demonstrated a marked suppression of depolarization-induced automaticity for maximum diastolic potentials less negative than -55 mV. This suppression was completely reversed by noradrenaline but not by tyramine. 3. In normal tissue, noradrenaline and tyramine had much smaller effects on automaticity arising from maximum diastolic potentials negative to -55 mV than on repetitive activity arising positive to this level. 4. L-propranolol in concentrations of 2-3 x 10(-7) M reduced repetitive activity in the less negative range of maximum diastolic potential. No evidence of direct membrane depression was observed at these doses and the effect was reversed by application of noradrenaline. 5. D-propranolol, the isomer with much lower beta-receptor blocking potency, required twentyfold higher concentrations to depress automaticity and this was accompanied by evidence of direct membrane depression...

A dual model for cardiac arrhythmias: coexistence of re-entry and abnormal automaticity and effects of antiarrhythmic agents.

Wu, K. M.; Hunter, T.; Proakis, A.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /09/1989 Português
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1. We have developed a dual model for arrhythmia anaesthetized dogs. The model consists of an inducible re-entrant atrial tachycardia and spontaneous ventricular ectopies in the same heart. 2. The model for re-entrant atrial tachycardia was created by crushing the right atrium longitudinally in the intercaval region and transversely in the front free wall parallel to the atrioventricular groove. Ventricular abnormal automaticity was produced by prior (20 approximately 24 h) left anterior descending coronary artery occlusion. The ventricular arrhythmia was partially suppressed during rapid pacing-induced atrial tachycardia and resumed after atrial re-entry was terminated. 3. Mapping experiments indicate that the atrial tachycardia was due to circus movement occurring in the tissue around the tricuspid ring. This re-entrant circuit was identical to that induced in the model created by the incision method. 4. Clofilium (0.75 mg kg-1, n = 5) increased the cycle length of atrial re-entry by 14 +/- 4% from 139 +/- 12 to 159 +/- 18 ms (P less than 0.05). Flecainide (1.8 +/- 0.9 mg kg-1, n = 5) prolonged the cycle length of the tachycardia by 114 +/- 57% from 158 +/- 11 to 332 +/- 66 ms (P less than 0.05). 5. Both drugs terminated the atrial arrhythmia...

The 2008 Carl Ludwig Lecture: retrotrapezoid nucleus, CO2 homeostasis, and breathing automaticity

Guyenet, Patrice G.
Fonte: American Physiological Society Publicador: American Physiological Society
Tipo: Artigo de Revista Científica
Português
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The retrotrapezoid nucleus (RTN) contains 2,000 glutamatergic neurons that innervate selectively the respiratory centers of the pontomedullary region. These cells are at the ventral medullary surface in a previously identified chemosensitive region. RTN neurons are highly sensitive to acid in vitro and vigorously activated by inputs from the carotid body and from the hypothalamus in vivo. Mutations of the transcription factor Phox2b cause the congenital hypoventilation syndrome (CCHS), a disease characterized by extremely reduced chemoreflexes and the loss of breathing automaticity during sleep. RTN neurons express Phox2b and develop poorly in a mouse model of CCHS, which lacks chemoreflexes. Based on these and other data, I propose that the RTN is a critical nodal point for the homeostatic regulation of arterial Pco2 and that the nucleus operates as follows. RTN always contributes a major fraction of the tonic excitatory drive to the respiratory centers. RTN neurons derive their activity from two sources: a chemosensory drive (intrinsic chemosensitivity and inputs from the carotid bodies) and synaptic inputs from higher brain centers (non-chemosensory drive). Under anesthesia or non-rapid eye movement sleep, the chemosensory drive to RTN neurons dominates...

Role of sarcolemmal ATP-sensitive K+ channels in the regulation of sinoatrial node automaticity: an evaluation using Kir6.2-deficient mice

Fukuzaki, Koichi; Sato, Toshiaki; Miki, Takashi; Seino, Susumu; Nakaya, Haruaki
Fonte: Blackwell Science Inc Publicador: Blackwell Science Inc
Tipo: Artigo de Revista Científica
Português
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The role of cardiac sarcolemmal ATP-sensitive K+ (KATP) channels in the regulation of sinoatrial node (SAN) automaticity is not well defined. Using mice with homozygous knockout (KO) of the Kir6.2 (a pore-forming subunit of cardiac KATP channel) gene, we investigated the pathophysiological role of KATP channels in SAN cells during hypoxia. Langendorff-perfused mouse hearts were exposed to hypoxic and glucose-free conditions (hypoxia). After 5 min of hypoxia, sinus cycle length (CL) was prolonged from 207 ± 10 to 613 ± 84 ms (P < 0.001) in wild-type (WT) hearts. In Kir6.2 KO hearts, CL was slightly prolonged from 198 ± 17 to 265 ± 32 ms. The CL of spontaneous action potentials of WT SAN cells, recorded in the current-clamp mode, was markedly prolonged from 410 ± 56 to 605 ± 108 ms (n = 6, P < 0.05) with a decrease of the slope of the diastolic depolarization (SDD) after the application of the K+ channel opener pinacidil (100 μm). Pinacidil induced a glibenclamide (1 μm)-sensitive outward current, which was recorded in the voltage-clamp mode, only in WT SAN cells. During metabolic inhibition by 2,4-dinitrophenol, CL was prolonged from 292 ± 38 to 585 ± 91 ms (P < 0.05) with a decrease of SDD in WT SAN cells but not in Kir6.2 KO SAN cells. Diastolic Ca2+ concentration...

Retrotrapezoid nucleus, respiratory chemosensitivity and breathing automaticity

Guyenet, Patrice G.; Bayliss, Douglas A.; Stornetta, Ruth L.; Fortuna, Michal G.; Abbott, Stephen B.; Depuy, Seth D.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Português
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Breathing automaticity and CO2 regulation are inseparable neural processes. The retrotrapezoid nucleus (RTN), a group of glutamatergic neurons that express the transcription factor Phox2b, may be a crucial nodal point through which breathing automaticity is regulated to maintain CO2 constant. This review updates the analysis presented in prior publications. Additional evidence that RTN neurons have central respiratory chemoreceptor properties is presented but this is only one of many factors that determine their activity. The RTN is also regulated by powerful inputs from the carotid bodies and, at least in the adult, by many other synaptic inputs. We also analyze how RTN neurons may control the activity of the downstream central respiratory pattern generator. Specifically, we review the evidence which suggests that RTN neurons a) innervate the entire ventral respiratory column, and b) control both inspiration and expiration. Finally, we argue that the RTN neurons are the adult form of the parafacial respiratory group in neonate rats.

The Calcium and Voltage Clocks in Sinoatrial Node Automaticity

Joung, Boyoung; Ogawa, Masahiro; Lin, Shien-Fong; Chen, Peng-Sheng
Fonte: The Korean Society of Cardiology Publicador: The Korean Society of Cardiology
Tipo: Artigo de Revista Científica
Português
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Recent evidence indicates that the voltage (cyclic activation and deactivation of membrane ion channels) and Ca2+ clocks (rhythmic spontaneous sarcoplasmic reticulum Ca2+ release) jointly regulate sinoatrial node (SAN) automaticity. Since the intact SAN is a heterogeneous structure that includes multiple different cell types interacting with each other, the relative importance of the voltage and Ca2+ clocks for pacemaking may be variable in different regions of the SAN. Recently, we performed optical mapping in isolated and Langendorff-perfused canine right atria. We mapped the intracellular calcium (Cai) and membrane potentials of the intact SAN simultaneously. Using previously described criteria of the timing of the late diastolic Cai elevation (LDCAE) relative to the action potential upstroke to detect Ca2+ clock activity, we demonstrated that the sinus rate increased and the leading pacemaker shifted to the superior SAN with the robust LDCAE during β-adrenergic stimulation. We also showed that the LDCAE was caused by spontaneous diastolic SR Ca2+ release and was closely related with heart rate changes. We conclude that the Ca2+ and voltage clocks work synergistically to generate SAN automaticity.

Modeling of Arrhythmogenic Automaticity Induced by Stretch in Rat Atrial Myocytes

Youm, Jae Boum; Leem, Chae Hun; Zhang, Yin Hua; Kim, Nari; Han, Jin; Earm, Yung E.
Fonte: The Korean Physiological Society and The Korean Society of Pharmacology Publicador: The Korean Physiological Society and The Korean Society of Pharmacology
Tipo: Artigo de Revista Científica
Português
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Since first discovered in chick skeletal muscles, stretch-activated channels (SACs) have been proposed as a probable mechano-transducer of the mechanical stimulus at the cellular level. Channel properties have been studied in both the single-channel and the whole-cell level. There is growing evidence to indicate that major stretch-induced changes in electrical activity are mediated by activation of these channels. We aimed to investigate the mechanism of stretch-induced automaticity by exploiting a recent mathematical model of rat atrial myocytes which had been established to reproduce cellular activities such as the action potential, Ca2+ transients, and contractile force. The incorporation of SACs into the mathematical model, based on experimental results, successfully reproduced the repetitive firing of spontaneous action potentials by stretch. The induced automaticity was composed of two phases. The early phase was driven by increased background conductance of voltage-gated Na+ channel, whereas the later phase was driven by the reverse-mode operation of Na+/Ca2+ exchange current secondary to the accumulation of Na+ and Ca2+ through SACs. These results of simulation successfully demonstrate how the SACs can induce automaticity in a single atrial myocyte which may act as a focus to initiate and maintain atrial fibrillation in concert with other arrhythmogenic changes in the heart.

Cortical and basal ganglia contributions to habit learning and automaticity

Ashby, F. Gregory; Turner, Benjamin O.; Horvitz, Jon C.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Português
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The 20th century was dominated by the view that novel behaviors are mediated primarily in cortex and that the development of automaticity is a process of transferring control to subcortical structures. Much evidence suggests however, that subcortical structures, such as the striatum, make significant contributions to initial learning. More recently, evidence has been accumulating that neurons in the associative striatum are selectively activated during early learning, whereas those in the sensorimotor striatum are more active after automaticity has developed. At the same time, other recent reports suggest that automatic behaviors are striatum- and dopamine-independent, and may be mediated entirely within cortex. Resolving this apparent conflict should be a major goal of future research.

A novel quantitative explanation for the autonomic modulation of cardiac pacemaker cell automaticity via a dynamic system of sarcolemmal and intracellular proteins

Maltsev, Victor A.; Lakatta, Edward G.
Fonte: American Physiological Society Publicador: American Physiological Society
Tipo: Artigo de Revista Científica
Português
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Classical numerical models have attributed the regulation of normal cardiac automaticity in sinoatrial node cells (SANCs) largely to G protein-coupled receptor (GPCR) modulation of sarcolemmal ion currents. More recent experimental evidence, however, has indicated that GPCR modulation of SANCs automaticity involves spontaneous, rhythmic, local Ca2+ releases (LCRs) from the sarcoplasmic reticulum (SR). We explored the GPCR rate modulation of SANCs using a unique and novel numerical model of SANCs in which Ca2+-release characteristics are graded by variations in the SR Ca2+ pumping capability, mimicking the modulation by phospholamban regulated by cAMP-mediated, PKA-activated signaling. The model faithfully predicted the entire range of physiological chronotropic modulation of SANCs by the activation of β-adrenergic receptors or cholinergic receptors only when experimentally documented changes of sarcolemmal ion channels are combined with a simultaneous increase/decrease in SR Ca2+ pumping capability. The novel numerical mechanism of GPCR rate modulation is based on numerous complex synergistic interactions between sarcolemmal and intracellular processes via membrane voltage and Ca2+. Major interactions include changes of diastolic Na+/Ca2+ exchanger current that couple earlier/later diastolic Ca2+ releases (predicting the experimentally defined LCR period shift) of increased/decreased amplitude (predicting changes in LCR signal mass...

Functional roles of Cav1.3, Cav3.1 and HCN channels in automaticity of mouse atrioventricular cells: Insights into the atrioventricular pacemaker mechanism

Marger, Laurine; Mesirca, Pietro; Alig, Jacqueline; Torrente, Angelo; Dubel, Stefan; Engeland, Birgit; Kanani, Sandra; Fontanaud, Pierre; Striessnig, Jörg; Shin, Hee-Sup; Isbrandt, Dirk; Ehmke, Heimo; Nargeot, Joël; Mangoni, Matteo E
Fonte: Landes Bioscience Publicador: Landes Bioscience
Tipo: Artigo de Revista Científica
Português
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The atrioventricular node controls cardiac impulse conduction and generates pacemaker activity in case of failure of the sino-atrial node. Understanding the mechanisms of atrioventricular automaticity is important for managing human pathologies of heart rate and conduction. However, the physiology of atrioventricular automaticity is still poorly understood. We have investigated the role of three key ion channel-mediated pacemaker mechanisms namely, Cav1.3, Cav3.1 and HCN channels in automaticity of atrioventricular node cells (AVNCs). We studied atrioventricular conduction and pacemaking of AVNCs in wild-type mice and mice lacking Cav3.1 (Cav3.1−/−), Cav1.3 (Cav1.3−/−), channels or both (Cav1.3−/−/Cav3.1−/−). The role of HCN channels in the modulation of atrioventricular cells pacemaking was studied by conditional expression of dominant-negative HCN4 channels lacking cAMP sensitivity. Inactivation of Cav3.1 channels impaired AVNCs pacemaker activity by favoring sporadic block of automaticity leading to cellular arrhythmia. Furthermore, Cav3.1 channels were critical for AVNCs to reach high pacemaking rates under isoproterenol. Unexpectedly, Cav1.3 channels were required for spontaneous automaticity, because Cav1.3−/− and Cav1.3−/−/Cav3.1−/− AVNCs were completely silent under physiological conditions. Abolition of the cAMP sensitivity of HCN channels reduced automaticity under basal conditions...

Automaticity in Anxiety Disorders and Major Depressive Disorder

Teachman, Bethany A.; Joormann, Jutta; Steinman, Shari; Gotlib, Ian H.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Português
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In this paper we examine the nature of automatic cognitive processing in anxiety disorders and Major Depressive Disorder (MDD). Rather than viewing automaticity as a unitary construct, we follow a social cognition perspective (Bargh, 1994) that argues for four theoretically independent features of automaticity: unconscious (processing of emotional stimuli occurs outside awareness), efficient (processing emotional meaning uses minimal attentional resources), unintentional (no goal is needed to engage in processing emotional meaning), and uncontrollable (limited ability to avoid, alter or terminate processing emotional stimuli). Our review of the literature suggests that most anxiety disorders are characterized by uncontrollable, and likely also unconscious and unintentional, biased processing of threat-relevant information. In contrast, MDD is most clearly typified by uncontrollable, but not unconscious or unintentional, processing of negative information. For the anxiety disorders and for MDD, there is not sufficient evidence to draw firm conclusions about efficiency of processing, though early indications are that neither anxiety disorders nor MDD are characterized by this feature. Clinical and theoretical implications of these findings are discussed and directions for future research are offered. In particular...

The mitochondrial Na+-Ca2+ exchanger, NCLX, regulates automaticity of HL-1 cardiomyocytes

Takeuchi, Ayako; Kim, Bongju; Matsuoka, Satoshi
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
Publicado em 26/09/2013 Português
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Mitochondrial Ca2+ is known to change dynamically, regulating mitochondrial as well as cellular functions such as energy metabolism and apoptosis. The NCLX gene encodes the mitochondrial Na+-Ca2+ exchanger (NCXmit), a Ca2+ extrusion system in mitochondria. Here we report that the NCLX regulates automaticity of the HL-1 cardiomyocytes. NCLX knockdown using siRNA resulted in the marked prolongation of the cycle length of spontaneous Ca2+ oscillation and action potential generation. The upstrokes of action potential and Ca2+ transient were markedly slower, and sarcoplasmic reticulum (SR) Ca2+ handling were compromised in the NCLX knockdown cells. Analyses using a mathematical model of HL-1 cardiomyocytes demonstrated that blocking NCXmit reduced the SR Ca2+ content to slow spontaneous SR Ca2+ leak, which is a trigger of automaticity. We propose that NCLX is a novel molecule to regulate automaticity of cardiomyocytes via modulating SR Ca2+ handling.

The contributions of vocabulary and letter writing automaticity to word reading and spelling for kindergartners

Kim, Young-Suk; Al Otaiba, Stephanie; Puranik, Cynthia; Folsom, Jessica Sidler; Gruelich, Luana
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Português
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In the present study we examined the relation between alphabet knowledge fluency (letter names and sounds) and letter writing automaticity, and unique relations of letter writing automaticity and semantic knowledge (i.e., vocabulary) to word reading and spelling over and above code-related skills such as phonological awareness and alphabet knowledge. These questions were addressed using data from 242 English-speaking kindergartners and employing structural equation modeling. Results showed letter writing automaticity was moderately related to and a separate construct from alphabet knowledge fluency, and marginally (p = .06) related to spelling after accounting for phonological awareness, alphabet knowledge fluency, and vocabulary. Furthermore, vocabulary was positively and uniquely related to word reading and spelling after accounting for phonological awareness, alphabet knowledge fluency, and letter writing automaticity.

Re-Examining the Automaticity and Directionality of the Activation of the Spatial-Valence "Good is Up" Metaphoric Association

Huang, Yanli; Tse, Chi-Shing
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em 13/04/2015 Português
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According to the Conceptual Metaphor Theory, people understand abstract concepts depending on the activation of more concrete concepts, but not vice versa. The present research aims to investigate the role of directionality and automaticity regarding the activation of the conceptual metaphor “good is up”. Experiment 1 tested the automaticity of the spatial-to-valence metaphoric congruency effect by having participants judge the valence of a positive or negative word that appeared either at the top or at the bottom of the screen. They performed the task concurrently with a 6-digit verbal rehearsal task in the working-memory-load (WML) blocks and without this task in the non-WML blocks. The spatial-to-valence metaphoric congruency effect occurred for the positive words in the non-WML blocks (i.e., positive words are judged more quickly when they appeared at the top than at the bottom of the screen), but not in the WML blocks, suggesting that this metaphoric association might not be activated automatically. Experiments 2-6 investigated the valence-to-spatial metaphoric association and its automaticity. Participants processed a positive or negative prime, which appeared at the center of the screen, and then identified a letter (p/q) that subsequently appeared at the top or bottom of the screen. The valence-to-spatial metaphoric congruency effect did not occur in the WML (6-digit verbal rehearsal) or non-WML blocks...

Automaticity of walking: functional significance, mechanisms, measurement and rehabilitation strategies

Clark, David J.
Fonte: Frontiers Media S.A. Publicador: Frontiers Media S.A.
Tipo: Artigo de Revista Científica
Publicado em 05/05/2015 Português
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Automaticity is a hallmark feature of walking in adults who are healthy and well-functioning. In the context of walking, “automaticity” refers to the ability of the nervous system to successfully control typical steady state walking with minimal use of attention-demanding executive control resources. Converging lines of evidence indicate that walking deficits and disorders are characterized in part by a shift in the locomotor control strategy from healthy automaticity to compensatory executive control. This is potentially detrimental to walking performance, as an executive control strategy is not optimized for locomotor control. Furthermore, it places excessive demands on a limited pool of executive reserves. The result is compromised ability to perform basic and complex walking tasks and heightened risk for adverse mobility outcomes including falls. Strategies for rehabilitation of automaticity are not well defined, which is due to both a lack of systematic research into the causes of impaired automaticity and to a lack of robust neurophysiological assessments by which to gauge automaticity. These gaps in knowledge are concerning given the serious functional implications of compromised automaticity. Therefore, the objective of this article is to advance the science of automaticity of walking by consolidating evidence and identifying gaps in knowledge regarding: (a) functional significance of automaticity; (b) neurophysiology of automaticity; (c) measurement of automaticity; (d) mechanistic factors that compromise automaticity; and (e) strategies for rehabilitation of automaticity.

Stay Focused! The Effects of Internal and External Focus of Attention on Movement Automaticity in Patients with Stroke

Kal, E. C.; van der Kamp, J.; Houdijk, H.; Groet, E.; van Bennekom, C. A. M.; Scherder, E. J. A.
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em 28/08/2015 Português
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Dual-task performance is often impaired after stroke. This may be resolved by enhancing patients’ automaticity of movement. This study sets out to test the constrained action hypothesis, which holds that automaticity of movement is enhanced by triggering an external focus (on movement effects), rather than an internal focus (on movement execution). Thirty-nine individuals with chronic, unilateral stroke performed a one-leg-stepping task with both legs in single- and dual-task conditions. Attentional focus was manipulated with instructions. Motor performance (movement speed), movement automaticity (fluency of movement), and dual-task performance (dual-task costs) were assessed. The effects of focus on movement speed, single- and dual-task movement fluency, and dual-task costs were analysed with generalized estimating equations. Results showed that, overall, single-task performance was unaffected by focus (p = .341). Regarding movement fluency, no main effects of focus were found in single- or dual-task conditions (p’s ≥ .13). However, focus by leg interactions suggested that an external focus reduced movement fluency of the paretic leg compared to an internal focus (single-task conditions: p = .068; dual-task conditions: p = .084). An external focus also tended to result in inferior dual-task performance (β = -2.38...

Evidence for a cooperation between adenosine A2 receptors and beta 1-adrenoceptors on cardiac automaticity in the isolated right ventricle of the rat.

Hernandez, J.; Pinto, F.; Figueira, M. A.; Riberio, J. A.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /04/1994 Português
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1. The effects of the adenosine receptor agonists, 5'-N-ethyl-carboxamidoadenosine (NECA) and 2-[4-(2-carboxyethyl)phenethylamino]-5'-N-ethylcarboxamidoadenosin e (CGS-21680) on ventricular automaticity induced by a local injury in the isolated right ventricle of the rat were studied. 2. In concentrations ranging from 0.1 to 100 nM, NECA significantly increased ventricular automaticity. This effect was more reproducible when the adenosine receptor antagonist 1,3-dipropyl-8-cyclopentylxanthine (DPCPX) was present at 5 nM, a concentration that blocks A1 adenosine receptors. 3. The excitatory effect of NECA was not observed when DPCPX was present at a concentration of 10 microM, which antagonizes both A1 and A2 adenosine receptors, as well as when rats were reserpinized. 4. In reserpinized rats, NECA increased ventricular automaticity in the presence of isoprenaline and the beta 2-adrenoceptor antagonist, ICI-118,551, but not in the presence of the beta 1-adrenoceptor antagonists, bisoprolol or atenolol. 5. The A 2s-selective adenosine receptor agonist, CGS-21680 (0.1 nM-10 microM) was devoid of excitatory effect on ventricular automaticity. Binding studies of this compound to the rat ventricular membranes revealed that in the preparation there was no specific binding. 6. These results suggest that the excitatory effect of NECA on ectopic ventricular automaticity is dependent on endogenous catecholamines and is mediated by an A2 adenosine receptor which is in some way 'linked' to the beta 1-adrenoceptor. These A2 receptors do not appear to be of the A2a adenosine receptor subtype.

Freezing of gait in Parkinson's disease: disturbances in automaticity and control

Vandenbossche, Jochen; Deroost, N.; Soetens, E.; Coomans, D.; Spildooren, J.; Vercruysse, S.; Nieuwboer, A.; Kerckhofs, E.
Fonte: Frontiers Media S.A. Publicador: Frontiers Media S.A.
Tipo: Artigo de Revista Científica
Publicado em 10/01/2013 Português
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Recent studies emphasize a key role of controlled operations, such as set-shifting and inhibition, in the occurrence of freezing of gait (FOG) in Parkinson's disease (PD). However, FOG can also be characterized as a de-automatization disorder, showing impairments in both the execution and acquisition of automaticity. The observed deficits in automaticity and executive functioning indicate that both processes are malfunctioning in freezers. Therefore, to explain FOG from a cognitive-based perspective, we present a model describing the pathways involved in automatic and controlled processes prior to a FOG episode. Crucially, we focus on disturbances in automaticity and control, regulated by the frontostriatal circuitry. In complex situations, non-freezing PD patients may compensate for deficits in automaticity by switching to increased cognitive control. However, as both automatic and controlled processes are more severely impaired in freezers, this hampers cognitive compensation in FOG, resulting in a potential breakdown. Future directions for cognitive rehabilitation are proposed, based on the cognitive model we put forward.