Die Rolle vom Spiegelneuronensystem im motorischen Lernen

Following a classical perspective, acquiring a new motor skill implies moving from a declarative knowl-edge of the motor task to be learned to a procedural knowledge of it. Some recent research on the motor system challenges this view. In the ventral premotor cortex of a monkey, neurons have been discovered that discharge both when an animal executes a specific goal-directed action (i.e. grasping a piece of food) and when it observes the same or a similar action executed by a conspecific or an experimenter. These neurons are called “mirror neurons”. In humans the mirror neuron system code for the execution and observation of goal-directed actions is executed with different biological effectors like the hand, the mouth, and the foot. The mirror neuron system has been demonstrated to be involved in action recognition, motor imagery and on line imitation of simple movements, which are already present in the motor repertoire of the acting indi-viduals. Furthermore, in a very recent functional magnetic resonance image (fMRI) study, the involvement of this system in learning novel, complex hand actions has been tested. In the experiment musically naïve participants were asked to learn to play different guitar chords, after observing models given by an expert guitarist. The mirror neuron system has been found active in all phases of the motor learning process, namely from the observation of the model till the execution of it by the participants. These results strongly support the notion that learning a new motor pattern implies re-arranging the elementary motor acts constituting it in order to fit a given model. This is an operation that the brain apparently does within the motor system, without the involvement of any specific associative areas.Uvod Pod pojmom “motoričko učenje” razumije se niz procesa povezanih s vježbanjem tijekom kojih osoba usvaja nova motorička znanja i razvija motoričke sposobnosti (Schmidt 1991). Tradicionalno je tumačenje da osoba tijekom usvajanja nove motoričke vještine prolazi tri različite faze: 1. kognitivnu fazu (učenje pravila specifične motoričke vještine); 2. asocijativnu fazu (raščlanjivanje motoričkog zadatka na elementarne motoričke komponente, razlučivanje relevantnih i irelevantnih informacija za izvođenje zadatka) i 3. automatsku fazu (uvježbanost i iskustvo u izvođenju motoričkog zadatka, tako da se zadatak izvodi automatski). Prema tom stajalištu, tijekom usvajanja novog motoričkog obrasca, osoba prelazi s deklarativnog znanja o motoričkom zadatku na proceduralno znanje o izvedbi. Novija istraživanja o motoričkom sustavu, međutim, osporavaju ovo gledište. Sustav zrcalnih neurona Sustav zrcalnih neurona kod majmuna Spoznaje o motoričkom sustavu kod čovjeka, kao i kod čovjekolikih majmuna, u novije su se vrijeme radikalno promijenile te se danas smatra da uključuje velik broj područja mozga. Jedno od njih, područje F5 ventralne premotoričke kore mozga čovjekolikih majmuna, sadrži motoričku reprezentaciju prema cilju usmjerenih radnji ustiju i šaka (Rizzolatti et al., 1988). U tom je području otkrivena skupina neurona kod kojih je prisutno izbijanje i kad sama životinja izvodi specifičnu, cilju usmjerenu radnju (npr. posezanje za komadom hrane), ali i u slučaju kad ona samo promatra jednaku ili sličnu radnju u izvođenju druge životinje ili pak istraživača (Gallese et al., 1996; Rizzolatti et al, 1996a). Ti se neuroni nazivaju zrcalnim neuronima jer se doima kao da se promatrana radnja “reflektira” u promatračevoj motoričkoj reprezentaciji iste radnje, kao u zrcalu. Od samog otkrića, pretpostavljalo se da zrcal-ni neuroni igraju važnu ulogu, kako u prepoznavanju radnje, tako i u motoričkom učenju (Jeannerod, 1994). Te je pretpostavke u potpunosti poduprlo recentno elektrofiziološko istraživanje (Umiltà et al., 2001). Jedan od novijih eksperimenata pokazao je da oko 15% zrcalnih neurona, osim na vizualna svojstva, reagira i na prezentaciju specifičnog zvuka određene radnje. Ti se neuroni nazivaju audio-vizualnim zrcalnim neuronima (Kohler et al., 2002). Sustav zrcalnih neurona kod čovjeka Sve je više dokaza o postojanju sustava zrcalnih neurona i kod čovjeka. Podaci na kojima se temelje ova saznanja proizlaze iz istraživanja provedenih korištenjem neurofizioloških i bihejvioralnih tehnika i metoda prikazivanja mozga (engl. brain imaging). Neurofiziološka istraživanja Prvi, iako samo indirektni, dokaz o postojanju sustava zrcalnih neurona kod čovjeka pružilo je istraživanje u kojem je primijenjena transkranijalna magnetska stimulacija (TMS) kod zdravih dobrovoljaca koji su promatrali istraživača u izvođenju različitih, cilju usmjerenih, kretnji šake (Fadiga et al., 1995). Ti su rezultati nedavno potvrđeni (Strafella and Paus, 2000; Gangitano et al., 2001). Daljnja istraživanja na tom području koristila su se magnetoencefalografijom (MEG) (Hari et al., 1998), kvantificiranom elektroencefalografijom (Cochin et al., 1999) i trajno implantiranim subduralnim elektrodama (Tremblay et al., 2004). Bihejvioralna istraživanja Brass i suradnici (2000) su, korištenjem paradigme kompatibilnosti podražaj-odgovor, ispitivali kako promatranje specifičnog pokreta može utjecati na samo izvođenje tog pokreta. Dobiveni rezultati pružili su čvrst dokaz o utjecaju promatranja pokreta na izvođenje istog pokreta. Slične rezultate dobili su Craighero i suradnici (2002). Istraživanja metodama prikaza mozga (brain imaging) U ranom istraživanju, usmjerenom na utvrđivanje područja mozga aktivnih tijekom promatranja radnji, u kojemu je korištena pozitronska emisijska tomografija (PET), Rizzolatti i suradnici (1996b) su otkrili aktivaciju u Brokinom području lijeve donje čeone vijuge, srednje sljepoočne vijuge i gornjeg sljepoočnog žlijeba. Ovo je istraživanje pružilo prvi dokaz o anatomskoj lokalizaciji sustava zrcalnih neurona za kretnje šake kod čovjeka. Nalazi vrlo recentnog istraživanja funkcionalnom magnetskom rezonancijom (fMRI) (Buccino et al., 2001) snažno podupiru tvrdnju da se, kao kod stvarnog izvođenja kretnje, i kod promatranja kretnje regrutiraju različiti, somatotopski organizirani čeono-tjemeni krugovi (Jeannerod et al., 1995; Rizzolatti et al., 1998b). Sustav zrcalnih neurona i motorička predodžba Motorička predodžba predstavlja voljno nastojanje osobe da zamisli sebe u izvođenju određene radnje. Motorička predodžba može pomoći u učenju novog motoričkog obrasca. Kada se od pojedinaca zatraži da stvore motoričku predodžbu, oni mogu primijeniti različite strategije. Oni mogu: (a) stvoriti vizualnu reprezentaciju ekstremiteta u pokretu (vizualna predodžba) ili (b) mentalno simulirati pokret, uz kinestetički osjećaj pokreta (kinetička predodžba). S obzirom na to da kinetička predodžba dijeli više fizioloških obilježja s izvođenjem pokreta od vizualne predodžbe, više je povezivana sa samim motoričkim funkcijama (Decety et al., 1994; Stephan, 1996; Porro et al, 1996; Fadiga, 1999; Rossini et al, 1999; Jeannerod, 2001; Gerardin, 2000; Hanakawa et al., 2003). Ukupno gledano, istraživanja u kojima su za prikazivanje mozga korištene PET ili fMRI, jedva da su pokazala razlike između vizualnih i kinetičkih predodžbi. Općenito, istraživanja su pokazala da se tijekom zadataka motoričkog predočavanja opsežno aktiviraju različita područja, uključujući ona koja pripadaju sustavu zrcalnih neurona. To sugerira postojanje složenog distribuiranog neuralnog kruga motoričke predodžbe koji uključuje i različita kortikalna područja u osnovi uključena u izvođenje i opažanje radnje. Uloga sustava zrcalnih neurona u imitaciji Paralelna (on line) imitacija jednostavnih pokreta Motorička imitacija se često smatra elementarnim kognitivnim zadatkom. Novija istraživanja pokazuju da ta tvrdnja nije točna. Postoje jasni dokazi o tome da je imitacija sposobnost koja je specifično razvijena kod čovjeka te je intrinzično povezana s jezikom i kulturom (Rizzolatti et al., 2002). Imitacija radnje inherentno uključuje motoričko opažanje (opservaciju), motoričku predodžbu i samo izvođenje pokreta. Uključenost sustava zrcalnih neurona u imitaciji nedavno je dokazana nizom istraživanja metodama prikaza mozga (Iacoboni et al., 1999; Koski et al., 2002; Grèzes et al., 2003; Nishitani and Hari, 2000, 2002; Heiser et al., 2003; Tanaka et al., 2002). U tim se istraživanjima od ispitanika tražilo da izravno, on line imitiraju visoko uvježbane, jednostavne pokrete koje je izvodila druga osoba. Pokreti koje je trebalo imitirati spadali su u već postojeći motorički repertoar opažača/ispitanika. Ukupno gledano, rezultati spomenutih studija snažno podupiru tvrdnju da se osnovni neuralni krug koji omogućuje imitaciju u velikoj mjeri preklapa s neuralnim krugom aktivnim tijekom opažanja radnje. Rezultati također ukazuju na to da se izravno stvaranje mape promatrane kretnje/radnje te njena motorička reprezentacija zbivaju u stražnjem dijelu donje čeone vijuge. Učenje imitacijom U recentnom istraživanju proučavalo se motoričko učenje novog motoričkog obrasca promatranjem kretnje (Buccino et al., 2004). Od glazbeno neobrazovanih ispitanika zatraženo je da nauče odsvirati različite gitarističke akorde na temelju promatranja i oponašanja profesionalnog gitarista koji je svirao akorde. Uočeno je da je sustav zrcalnih neurona bio aktivan u svim fazama procesa motoričkog učenja, tj. od opažanja primjera do samog izvođenja primjera od strane ispitanika. Ti rezultati snažno podupiru teoriju prema kojoj učenje novog motoričkog obrasca podrazumijeva preraspodjelu osnovnih motoričkih kretnji koje ga tvore radi uklapanja u zadani model. Čini se da je to operacija koju mozak izvodi u potpunosti unutar motoričkog sustava, bez uključivanja specifičnih asocijativnih područja. Zaključak Spomenuti rezultati istraživanja jasno pokazuju da motorički sustav nije uključen samo u izvođenje aktivnosti, nego i u druge kognitivne motoričke funkcije. Štoviše, ventralna premotorička kora i donji tjemeni režanj, kortikalna područja koja pripadaju sustavu zrcalnih neurona, također su uključeni u motoričku predodžbu radnji, kao i u imitaciju tuđih kretnji. Čak i prilikom učenja nove motoričke vještine, sustav zrcalnih neurona je aktivan od promatranja obrasca do izvođenja radnje koja odgovara obrascu. Učenje novog motoričkog obrasca bi, stoga, moglo predstavljati kombiniranje osnovnih motoričkih kretnji koje ga sačinjavaju na nov način. Izgleda da se ta rekombinacija zbiva unutar sustava zrcalnih neurona, bez uključivanja specifičnih asocijativnih područja.Vom klassischen Standpunkt gesehen, das Erwerben einer neuen motorischen Fertigkeit impliziert das Überwechseln von deklarativem Kenntnis einer zu lernenden motorischen Aufgabe auf deren verfahrens-technisches Kenntnis. Einige neueste Forschungen des motorischen Systems stellen diesen Standpunkt in Frage. Im ventralen prämotorischen Kortex einer Affe wurden die Neuronen entdeckt, die ausgeschüttelt werden, wenn das Tier eine spezifische auf das Ziel orientierte Aufgabe ausführt (z.B. Ergreifen eines Stückes des Nahrungsmittels) und wenn es entweder dieselbe oder ähnliche von einem anderen Affe oder einem Experimentator ausgeführte Bewegung realisiert. Diese Neuronen werden Spiegelneuronen genannt. Bei Menschen wird der Spiegelneuronensystem-Code für die Ausführung und Beobachtung von den auf ein Ziel orientierten Bewegungen, die mittels verschiedener biologischen Effektoren wie die Hand, der Mund oder der Fuß realisiert werden, realisiert. Das Spiegelneuronensystem zeigte sich in das Erkennen einer Bewegung, in der motorischen Vorstellung und in der parallelen Nachahmung von einfachen Bewegungen involviert zu sein, die schon im motorischen Repertoire von tätigen Individuen existiert. Außerdem in einer neuen Studie der funktionellen Magnet-Resonanz-Tomographie (fMRI) wurde die Rolle dieses Systems beim Erlernen neuer, komplexer Handbewegungen getestet. Im Experiment wurden die Teilnehmern, die sich in Musik nicht auskennen, gebeten, verschiedene Akkorde auf der Gitarre spielen zu lernen, nachdem sie die von einem Expert-Gitarristen durchgeführten Models beobachtet haben. Das Spiegelneuronensystem war aktiv in allen Phasen des motorischen Lernprozesses, d.h. angefangen von der Beobachtung eines Models bis zur dessen Ausführung. Diese Ergebnisse befürworten bedeutend die Ansicht, dass das Erlernen neuer motorischen Mustern eine Änderung von elementaren motorischen Bewegungen, die einen solchen Muster bilden, impliziert, um einem bestimmten Model zu entsprechen. Es handelt sich um eine Operation, die das Gehirn offensichtlich in dem motorischen System ausführt, ohne die Beteiligung von spezifischen assoziativen Bereichen

Chained activation of the motor system during language understanding

Two experiments were carried out to investigate whether and how one important characteristic of the motor system, that is its goal-directed organization in motor chains, is reflected in language processing. This possibility stems from the embodied theory of language, according to which the linguistic system re-uses the structures of the motor system. The participants were presented with nouns of common tools preceded by a pair of verbs expressing grasping or observational motor chains (i.e., grasp-to-move, grasp-to-use, look-at-to-grasp, and look-at-to-stare). They decided whether the tool mentioned in the sentence was the same as that displayed in a picture presented shortly after. A primacy of the grasp-to-use motor chain over the other motor chains in priming the participants' performance was observed in both the experiments. More interestingly, we found that the motor information evoked by the noun was modulated by the specific motor-chain expressed by the preceding verbs. Specifically, with the grasping chain aimed at using the tool, the functional motor information prevailed over the volumetric information, and vice versa with the grasping chain aimed at moving the tool (Experiment 2). Instead, the functional and volumetric information were balanced for those motor chains that comprise at least an observational act (Experiment 1). Overall our results are in keeping with the embodied theory of language and suggest that understanding sentences expressing an action directed toward a tool drives a chained activation of the motor system

Broken affordances, broken objects: A TMS study

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Language–motor interference reflected in MEG beta oscillations

AbstractThe involvement of the brain's motor system in action-related language processing can lead to overt interference with simultaneous action execution. The aim of the current study was to find evidence for this behavioural interference effect and to investigate its neurophysiological correlates using oscillatory MEG analysis. Subjects performed a semantic decision task on single action verbs, describing actions executed with the hands or the feet, and abstract verbs. Right hand button press responses were given for concrete verbs only. Therefore, longer response latencies for hand compared to foot verbs should reflect interference. We found interference effects to depend on verb imageability: overall response latencies for hand verbs did not differ significantly from foot verbs. However, imageability interacted with effector: while response latencies to hand and foot verbs with low imageability were equally fast, those for highly imageable hand verbs were longer than for highly imageable foot verbs. The difference is reflected in motor-related MEG beta band power suppression, which was weaker for highly imageable hand verbs compared with highly imageable foot verbs. This provides a putative neuronal mechanism for language–motor interference where the involvement of cortical hand motor areas in hand verb processing interacts with the typical beta suppression seen before movements. We found that the facilitatory effect of higher imageability on action verb processing time is perturbed when verb and motor response relate to the same body part. Importantly, this effect is accompanied by neurophysiological effects in beta band oscillations. The attenuated power suppression around the time of movement, reflecting decreased cortical excitability, seems to result from motor simulation during action-related language processing. This is in line with embodied cognition theories

Combining Action Observation Treatment with a Brain–Computer Interface System: Perspectives on Neurorehabilitation

Action observation treatment (AOT) exploits a neurophysiological mechanism, matching an observed action on the neural substrates where that action is motorically represented. This mechanism is also known as mirror mechanism. In a typical AOT session, one can distinguish an observation phase and an execution phase. During the observation phase, the patient observes a daily action and soon after, during the execution phase, he/she is asked to perform the observed action at the best of his/her ability. Indeed, the execution phase may sometimes be difficult for those patients where motor impairment is severe. Although, in the current practice, the physiotherapist does not intervene on the quality of the execution phase, here, we propose a stimulation system based on neurophysiological parameters. This perspective article focuses on the possibility to combine AOT with a brain–computer interface system (BCI) that stimulates upper limb muscles, thus facilitating the execution of actions during a rehabilitation session. Combining a rehabilitation tool that is well-grounded in neurophysiology with a stimulation system, such as the one proposed, may improve the efficacy of AOT in the treatment of severe neurological patients, including stroke patients, Parkinson’s disease patients, and children with cerebral palsy

Grasping the semantic of actions: a combined behavioral and MEG study

There is experimental evidence that the brain systems involved in action execution also play a role in action observation and understanding. Recently, it has been suggested that the sensorimotor system is also involved in language processing. Supporting results are slower response times and weaker motor-related MEG Beta band power suppression in semantic decision tasks on single action verbs labels when the stimulus and the motor response involve the same effector. Attenuated power suppression indicates decreased cortical excitability and consequent decreased readiness to act. The embodied approach forwards that the simultaneous involvement of the sensorimotor system in the processing of the linguistic content and in the planning of the response determines this language-motor interference effect. Here, in a combined behavioral and MEG study we investigated to what extent the processing of actions visually presented (i.e., pictures of actions) and verbally described (i.e., verbs in written words) share common neural mechanisms. The findings demonstrated that, whether an action is experienced visually or verbally, its processing engages the sensorimotor system in a comparable way. These results provide further support to the embodied view of semantic processing, suggesting that this process is independent from the modality of presentation of the stimulus, including language

Prefrontal involvement in imitation learning of hand actions : effects of practice and expertise.

In this event-related fMRI study, we demonstrate the effects of a single session of practising configural hand actions (guitar chords) on cortical activations during observation, motor preparation, and imitative execution. During the observation of non-practised actions, the mirror neuron system (MNS), consisting of inferior parietal and ventral premotor areas, was more strongly activated than for the practised actions. This finding indicates a strong role of the MNS in the early stages of imitation learning. In addition, the dorsolateral prefrontal cortex (DLPFC) was selectively involved during observation and motor preparation of the non-practised chords. This finding confirms Buccino et al.’s (2004a) model of imitation learning: for actions that are not yet part of the observer’s motor repertoire, DLPFC engages in operations of selection and combination of existing, elementary representations in the MNS. The pattern of prefrontal activations further supports Shallice’s (2004) proposal of a dominant role of the left DLPFC in modulating lower-level systems, and of a dominant role of the right DLPFC in monitoring operations