19 research outputs found
Hijerarhije sinergija u ljudskim pokretima
This brief review addresses the problem of motor redundancy, which exists at many levels of the neuro-motor hierarchies involved in the production of voluntary movements. An approach to this problem is described based on the principle of abundance. This approach offers an operational definition for motor synergies using the framework of the uncontrolled manifold hypothesis. It is shown that hierarchical systems have inherent trade-offs between synergies at different control levels. These trade-offs have been demonstrated in experimental studies of human multi-finger pressing and prehension. They are likely to be present in other hierarchical systems, for example, those involved in the control of large groups of muscles. The framework of the equilibrium-point hypothesis offers a physiologically based mechanism, which may form the basis for hierarchies of synergies.Ovaj se pregledni rad bavi problemom motoriÄke redundancije (zalihosti) koja postoji na viÅ”e razina neuromotoriÄkih hijerarhija ukljuÄenih u realizaciju voljnih pokreta. Opisan je pristup utemeljen na principu obilja (brojnosti). Pristup nudi operativnu definiciju za motoriÄke sinergije koriÅ”tenjem okvira Å”to ga pruža hipoteza neupravljanih slojeva (ljusaka). Pokazuje se da hijerarhijski sustavi posjeduju inherentne kompromise izmeÄu sinergija na razliÄitim razinama upravljanja. Ti se kompromisi mogu pokazati pomoÄu eksperimentalnih studija pritiska prstima ljudske Å”ake. Vjerojatno je da su isti prisutni i u drugim hijerarhijskim sustavima, npr. onima ukljuÄenima u upravljanje velikim skupinama miÅ”iÄa. Okvir hipoteze ravnotežne toÄke nudi fizioloÅ”ki utemeljen mehanizam koji može predstavljati osnovu za hijerarhije sinergija.
Problem motoriÄke redundancije
Svi neuromotoriÄki procesi unutar ljudskoga ti-jela povezani s izvoÄenjem prirodnih voljnih pokreta ukljuÄuju nekoliko preslikavanja (mapiranja) tipa āod nekoliko na viÅ”eā, kakva se uobiÄajeno smatraju problemom redundancije. Drugim rijeÄima, ograniÄenja definirana ulazom (npr. zadatkom) ne definiraju jednoznaÄno uzorak izlaza (npr. uzorci rotacije zglobova, miÅ”iÄne sile, aktivacije motoriÄkih neurona itd.) na naÄin da postoji viÅ”e (beskonaÄan broj, uobiÄajeno) rjeÅ”enja. Problem je uoÄio Bernstein (1935, 1967), smatrajuÄi ga srediÅ”njim problemom motoriÄkog upravljanja: āNa koji naÄin srediÅ”nji živÄani sustav (SŽS) odabire jednoznaÄna rjeÅ”enja iz brojnih, naizgled jednakih moguÄnosti?ā
Tradicionalni naÄin shvaÄanja problema motoriÄke redundancije pretpostavljao je da SŽS rabi skup kriterija da bi pronaÅ”ao jednoznaÄna rjeÅ”enja takvih problema. Konkretno, mnoÅ”tvo optimizacijskih tehnika uporabljeno je za pristup tim problemima ukljuÄujuÄi optimizaciju funkcija troÅ”kovi-korist, temeljenu na mehaniÄkim, psihologijskim i neuropsihologijskim varijablama (vidjeti pregled u Prilutsky, 2000; Osenbaum i sur., 1993; Latash, 1993).
Princip obilja
Gelfand i Tselin (1966) su usporedili mnoge ele-mente ukljuÄene na bilo kojem koraku generiranja pokreta s razredom studenata koji žele sa Å”to manje rada izvrÅ”iti zadatak. Uveli su princip minimalnog meÄudjelovanja da bi opisali takve oblike velikih skupina elemenata. Prema tom naÄelu svaki element nastoji minimizirati svoje meÄudjelovanje s ostalima, s upravljaÄkim dijelom te s okolinom. Drugim rijeÄima, svaki element nastoji minimizirati ulaz koji prima iz svih spomenutih izvora.
Taj je princip u novije vrijeme razvijen u princip obilja (Gelfand i Latash, 1998). Prema njemu su problemi motoriÄke redundancije pogreÅ”no formulirani. Preslikavanja tipa āod nekoliko na viÅ”eā, tipiÄna za takve probleme, ne bi trebalo gledati kao problem raÄunalne naravi za upravljaÄki sustav, nego pak viÅ”e kao svojevrsni luksuz koji dozvoljava kombiniranje stabilnog funkcioniranja zadatka uz obavljanje ostalih zadataka i reagiranje na moguÄe ometajuÄe utjecaje okoline. RjeÅ”avanje problema motoriÄke redundancije ne ukljuÄuje izbor jednoznaÄnog, optimalnog rjeÅ”enja, nego prije olakÅ”a-vanje Äitave obitelji rjeÅ”enja koje mogu biti jedna-ko uspjeÅ”ne u rjeÅ”avanju problema. Broj tih obitelji rjeÅ”enja puno je manji od ukupnog broja moguÄih rjeÅ”enja, Å”to znaÄi da se ipak dogaÄa neka vrsta selekcije. Taj pomak od traženja jedinstvenog rjeÅ”enja prema definiranju pravila kojima se organiziraju obitelji rjeÅ”enja rezultirao je novim pogledom na motoriÄke sinergije, paradigmatskim pomakom koji je doveo do izvedbene definicije sinergija i do stvaranja novog raÄunalnog pristupa identifikaciji i kvantifikaciji sinergija.
Sinergija - radna definicija
RijeÄ āsinergijaā rabila se u studijima ljudskog kretanja, kao i za opis motoriÄkih poremeÄaja viÅ”e od stotinu godina. OpÄenito, definicija je bila sukladna s grÄkim prijevodom āraditi zajednoā. U posljednje vrijeme, meÄutim, ta je rijeÄ poprimila odreÄenije znaÄenje ukorijenjeno u principu obilja (detalj-no vidjeti u Latash, 2008). Postoje, naime, tri vrste sinergija. Prvo, kada je u zadatak ukljuÄen privi-dno redundantni skup elemenata, odabire se srednji uzorak raspodjele koji Äe karakterizirati prosjeÄni doprinos svakog elementa. Drugo, kada se analizira nekoliko pokuÅ”aja izvedbe zadatka, izlazi elemenata mogu kovarirati, Å”to je za zadatak korisno, tj. smanjuje se varijabilnost važne varijable u usporedbi sa situacijom koja bi se mogla oÄekivati kada kovarijacije ne bi bilo. To se svojstvo ponekad naziva kompenzacijom pogreÅ”ke ili stabilnoÅ”Äu. TreÄe, isti skup elemenata može se rabiti za formiranje razliÄitih sinergija, tj. razliÄitih uzoraka kovarijacije koji su povoljni za razliÄite varijable cjelokupnog sustava. To se svojstvo može nazvati stabilnoÅ”Äu. Samo sustavi koji mogu pokazati sva tri svojstva nazivat Äe se sinergijama. Nema apstraktnih sinergija ā one uvijek neÅ”to Äine.
Sinergija se, prema tomu, definira kao neuralna organizacija skupa elementarnih varijabla s ciljem osiguranja svojevrsnih svojstava stabilnosti (stabilizirati ili destabilizirati) varijable koja je izlaz sustava kao cjeline.
Hipoteza neupravljanih ljusaka (UCM ā uncontrolled manifold hypothesis) i hijerarhijsko upravljanje
Uvedena definicija sinergije zahtijeva kvantitativnu metodu koja bi mogla razlikovati sinergiju od nesinergije, kao i kvantificirati sinergije. Takva je metoda razvijena u sklopu nekontroliranih viŔeslojnih hipoteza. Ona pretpostavlja da neuralni kontroler djeluje u prostoru elementarnih varijabla
i u tom prostoru izabire potprostore koji odgovaraju željenoj vrijednosti uspjeÅ”no izvedene varijable. Nadalje, kontroler organizira interakcije meÄu elementima tako da je varijanca meÄu elementarnim varijablama uglavnom ograniÄena UCM-om. Bilo je nekoliko pokuÅ”aja da se ponude mehanizmi koji mogu organizirati takvu vrstu kontrole ā feedback perifernih senzora, feedback koji koristi uparivanje centralnih i povratnih neuralnih petlji, kontrolni anticipacijski program.
Pojam referentne konfiguracije pruža privlaÄan okvir za analizu motoriÄkih sinergija. Taj okvir pretpostavlja hijerarhijski kontrolni sustav u kojemu je , na svakom stupnju hijerarhije, taj sustav redundantan, tj. proizvodi puno viÅ”e izlaznih varijabli od broja ograniÄenja specificiranih ulaznim varijablama (kao na slici 3). Ostale karakteristike akcije mogu varirati na temelju sekundarnih zakonitosti, koje vjerojatno odražavaju optimizaciju nekih osobina izvedbe. Zato Å”to je sustav redundantan, referentna konfiguracija na viÅ”em hijerarhijskom stupnju ne specificira sasvim nedvojbeno sve referentne konfiguracije na nižim stupnjevima. Izranjanje odreÄenih nižerazinskih referentnih trajektorija može se temeljiti na mehanizmu povratne sprege ili na mehanizmu anticipacije (feed-forward). Stoga se hijerarhija kontrolnih razina, gdje svaka razina funkcionira na na-Äelu kontrole ravnotežne toÄke, Äini vrlo vjerojatnom strukturom koja podržava motoriÄke sinergije
Sitting Time and Future Health Expectations in African American and Hispanic or Latina Women
Purpose: In Lee et al. (2012; J Obesity), a hypothesis relating increased sitting time and lower stress levels was introduced. The aim of this analysis is to evaluate the relationship between measures of sedentary behavior and mental health outcomes.
Method: The current study was a secondary analysis using data from the Health Is Power (HIP) study. Four hundred ten community dwelling African American (n = 263), and Hispanic/Latina (n = 147) women aged 25-60 participated in HIP, a longitudinal, community-based, randomized controlled trial to increase physical activity. Women who met inclusionary criteria gave informed consent and completed health assessments measuring physical activity, mental health status, and demographics. Data were collected at baseline (T1) and after six months of HIP intervention (T2). Interviewer administered questionnaires measured sitting time using items from the International Physical Activity Questionnaire (IPAQ) and self-assessed health status. Ethnicity, household income, and education questions were adapted from the Maternal Infant Health Assessment (MIHA) survey.
Results: Women reported high levels of weekday (414.9 Ā± 13.1 minutes) and weekend (323.5 Ā± 11.9 minutes) sitting time at baseline. Over half (n = 248, 63%) reported one or more days that physical health or emotional problems interfered with usual activities, and most (n = 348, 89%) did not expect their health to get worse. Both weekday (r = 0.11; p = 0.036) and weekend sitting time (r = 0.09; p = 0.087) were associated with positive future health expectations. After controlling for age, education, parental education, ethnicity, and income, linear regression models revealed that increased weekday (p = 0.05) and weekend sitting time (p = 0.044) were associated with positive future health expectations at T1, but not at T2. At T2, weekday (-60 Ā± 25 minutes) and weekend sit time (-49 Ā± 21 minutes) were significantly reduced compared to T1 (p \u3c 0.05); however, this change was not related to positive future health expectations.
Conclusions: Increased weekday and weekend sitting time was associated with positive future health expectations in minority women. This effect was extinguished after the intervention period, suggesting that sedentary behaviors, but not health expectations, can be mitigated by behaviorally-based health intervention
Bimanual force coordination in Parkinson's disease patients with bilateral subthalamic deep brain stimulation.
Studies of bimanual actions similar to activities of daily living (ADLs) are currently lacking in evaluating fine motor control in Parkinson's disease patients implanted with bilateral subthalamic deep brain stimulators. We investigated basic time and force characteristics of a bimanual task that resembles performance of ADLs in a group of bilateral subthalamic deep brain stimulation (DBS) patients.Patients were evaluated in three different DBS parameter conditions off stimulation, on clinically derived stimulation parameters, and on settings derived from a patient-specific computational model. Model-based parameters were computed as a means to minimize spread of current to non-motor regions of the subthalamic nucleus via Cicerone Deep Brain Stimulation software. Patients were evaluated off parkinsonian medications in each stimulation condition.The data indicate that DBS parameter state does not affect most aspects of fine motor control in ADL-like tasks; however, features such as increased grip force and grip symmetry varied with the stimulation state. In the absence of DBS parameters, patients exhibited significant grip force asymmetry. Overall UPDRS-III and UPDRS-III scores associated with hand function were lower while patients were experiencing clinically-derived or model-based parameters, as compared to the off-stimulation condition.While bilateral subthalamic DBS has been shown to alleviate gross motor dysfunction, our results indicate that DBS may not provide the same magnitude of benefit to fine motor coordination
Do synergies improve accuracy? A study of speed-accuracy trade-offs during finger force production
We explored possible effects of negative covariation among finger forces in multifinger accurate force production tasks on the classical Fitts's speed-accuracy trade-off. Healthy subjects performed cyclic force changes between pairs of targets ""as quickly and accurately as possible."" Tasks with two force amplitudes and six ratics of force amplitude to target size were performed by each of the four fingers of the right hand and four finger combinations. There was a close to linear relation between movement time and the log-transformed ratio of target amplitude to target size across all finger combinations. There was a close to linear relation between standard deviation of force amplitude and movement time. There were no differences between the performance of either of the two ""radial"" fingers (index and middle) and the multifinger tasks. The ""ulnar"" fingers (little and ring) showed higher indices of variability and longer movement times as compared with both ""radial"" fingers and multifinger combinations. We conclude that potential effects of the negative covariation and also of the task-sharing across a set of fingers are counterbalanced by an increase in individual finger force variability in multifinger tasks as compared with single-finger tasks. The results speak in favor of a feed-forward model of multifinger synergies. They corroborate a hypothesis that multifinger synergies are created not to improve overall accuracy, but to allow the system larger flexibility, for example to deal with unexpected perturbations and concomitant tasks
Mean (SD) volume of tissue activated by the clinically-determined and patient-specific model-derived stimulation parameters, averaged across all patients.
<p>Note that STN refers to the subthalamic nucleus.</p
Schematics of the testing device.
<p><b><i>A:</i></b> The dynamic (upper) and static (lower) transducers are indicated. <b><i>B:</i></b> Depiction of the task being performed with the Non-Rotation method. <b><i>C:</i></b> Depiction of the task being performed with the Rotation method.</p
Patient demographics, UPDRS-III scores in each of the three stimulation states, and testing session order.
<p>Patient demographics, UPDRS-III scores in each of the three stimulation states, and testing session order.</p
Mean and standard error of force production.
<p>Significant differences in the forces exerted on the two transducers (Dynamic vs Static) are shown in each panel. Significant differences among the three DBS parameter conditions can be found in panels A-C, whereas a difference between transducers is shown in panel D. <b><i>A:</i></b> Average grip force. <b><i>B:</i></b> Rate of grip force production. <b><i>C:</i></b> Maximum grip force. <b><i>D:</i></b> Within-hand grip-load force correlation.</p
Clinically-determined and patient-specific model-derived stimulation parameters for all patients.
<p>Note that STN refers to the subthalamic nucleus.</p
Mean and standard error UPDRS-III scores and task time.
<p><b><i>A:</i></b> Fine and total UPDRS-III scores. Significant reductions in both the fine and total UPDRS-III scores were found for the on-stimulation states as compared to the Off DBS state. <b><i>B:</i></b> Task time, averaged across stimulation state. A significant decrease in task time in Non-Rotational actions and in Disconnect-type tasks were found as compared to Rotational actions and Connect-type tasks.</p