As an extension of previous studies (Urbanczyk, Angel, & Kennelly, 1988) examining the effects of unimanual finger tapping on lateralized cognitive tasks, lateral body orienting was added to an established dual task paradigm to generate differential hemispheric activation and shifts of attention. One hundred twenty university students retained sequences of digits or spatial locations for 20 seconds either alone or during finger tapping. By turning both head and eyes left or right, the hemisphere congruent with the sequences (LH for digits, RH for locations) or incongruent (vice versa) was activated. Activation had little effect on retention means but greatly affected resource composition supporting task performance. Congruent orientation produced significantly higher positive correlations between digit and location tasks than incongruent orientation. Females showed higher sequence retention correlations than males across both orienting groups. For females, congruent activation enhanced tapping rates and retention-tapping correlations. For males, activation affected neither of these. Discussed in light of neuroanatomical research, these results suggest that congruent attentional orienting may integrate regions of the less activated hemisphere into networks of the more activated hemisphere. This unification may occur more readily across the female corpus callosum, producing a greater dependence upon a general attentional resource than for males, who appear to depend more upon hemispheric resources.

When exploring movement production, motor control researchers have been interested in investigating the relative contributions to different types of movement. In a research setting, a startling acoustic stimulus (SAS) can be used as a tool to explore the neural processes that are occurring when preparing and initiating a movement. Additionally, suprathreshold TMS is another tool which can induce a suppression of the cortical region of the brain, resulting in RT delays which provides us with the ability to assess the corticospinal contributions to a particular movement. The aim of the current study was to investigate potential differences in the planning and execution of bimanual versus unimanual wrist extension movements. It was of particular interest as to whether bimanual coupling occurs at the cortical level or in lower parts of the output pathway (reticulospinal). Participants (N=6) were instructed to complete a unimanual or bimanual wrist extension following a control go-signal or a SAS. For subset of trials, in order to explore the level of corticospinal excitability of the movement, suprathreshold TMS was applied over the left M1 during the task to induce a cortical silent period (CSP). Results revealed that theimpact of TMS on response initiation was not significantly different for unimanual task versus a bimanual task. Furthermore, the SP (silent period) only had an impact on the right limb and not the left during the bilateral task. Lastly, SAS did lead to shorter RTs for both the unimanual and bimanual wrist extension task, but the RT delay induced by TMS in the right limb was not shorter in SAS trials compared to control. The findings of the present study suggest that bimanual coupling may be occurring at the cortical level and in lower parts of the output pathway as there may be correlated neural activity in the two hemispheres occurring during bimanual wrist extension movements.

Made available in DSpace on 2016-06-02T20:18:22Z (GMT). No. of bitstreams: 1 5877.pdf: 9914755 bytes, checksum: 449c8d0ab2defc77d6b0d5a4ea1b20bb (MD5) Previous issue date: 2014-06-11 / Universidade Federal de Minas Gerais / The effect of using the non-preferred hand on manual preference and motor performance was assessed in two experiments. Experiment 1 investigated the short-term effect of lateralized experience on manual preference and motor performance in infants reaching. Four- and seven-month-olds were induced to use the non-preferred hand through reaching for toys contralaterally to the preferred hand. Reassessment of manual preference in reaching at the central position revealed that infants used the nonpreferred hand more frequently. That behavior was similar between both age groups. Kinematic analysis of reaching did not indicate variations coherent with shift of manual preference. Experiment 2 tested the effect of practice with the non-preferred hand on manual preference and intermanual asymmetries of performance, comparing children and adults. Different tasks requiring reaching and manipulation were practiced. Manual preference was assessed through reaching toward cards at different positions on the right and left of the participant, and inserting the card into a slot. Results showed that use of the nonpreferred hand increased after practice in both age groups. There was no effect of practice on intermanual asymmetries of performance. Results indicate that manual preference is flexible and modulated by immediate lateralized experiences. / O efeito do uso da mão não-preferida sobre a preferência manual específica à tarefa e desempenho motor foi avaliado em dois experimentos. O experimento 1 objetivou investigar o efeito de curto-prazo de experiências lateralizadas sobre a preferência manual e o desempenho motor no alcance em bebês. Bebês aos 4 e 7 meses foram induzidos ao uso mais frequente da mão não-preferida por meio do oferecimento de brinquedos em posição contralateral à mão preferida. A reavaliação da preferência manual no alcance em posição medial revelou que os bebês passaram a usar mais frequentemente a mão não-preferida, sendo esse comportamento similar entre ambos os grupos etários. A análise cinemática dos alcances não indicou variações coerentes com a mudança de preferência manual. O objetivo do experimento 2 foi testar o efeito da prática com a mão não-preferida sobre preferência manual e assimetrias intermanuais de desempenho, comparando crianças e adultos. Foram praticadas tarefas que exigiam alcance e manipulação de objetos variados. A preferência manual foi avaliada no alcance de cartas em diferentes posições à direita e esquerda do participante e subsequente depósito em uma urna. Houve aumento no uso da mão não-preferida após a prática em ambos os grupos etários. Não foi encontrado nenhum efeito da prática lateralizada sobre as assimetrias intermanuais de desempenho. Os resultados indicam que a preferência manual é flexível e modulada por experiências lateralizadas imediatamente anteriores.

Tool actions are characterized by a transformation between movements and their resulting consequences in the environment. This transformation has to be taken into account when tool actions are planned and executed. We investigated how angular shift transformations between circling movements and their visual feedback affect the coordination of this feedback with visual events in the environment. We used a task that required participants to coordinate the visual feedback of a circular hand movement (presented on the right side of a screen) with a circling stimulus (presented on the left side of a screen). Four stimulus-visual feedback relations were instructed: same or different rotations of stimulus and visual feedback, either in same or different y-directions. Visual speed was varied in three levels (0.8, 1, and 1.2 Hz). The movement-visual feedback relation was manipulated using eight angular shifts: (-180, -135, -90, -45, 0, 45, 90, and 135°). Participants were not able to perform the different rotation/different y-direction pattern, but instead fell into the different rotation/same y-direction pattern. The different rotation/same y-direction pattern and the same rotation/same y-direction pattern were performed equally well, performance was worse in the same rotation/different y-direction pattern. Best performance was observed with angular shifts 0 and -45° and performance declined with larger angular shifts. Further, performance was better with negative angular shifts than with positive angular shifts. Participants did not fully take the angular shift transformation into account: when the angular shifts were negative the visual feedback was more in advance, and when angular shifts were positive the visual feedback was less in advance of the stimulus than in 0° angular shift. In conclusion, the presence and the magnitude of angular shift transformations affect performance. Internal models do not fully take the shift transformation into account.

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Il existe des projections corticospinales (CS) vers les motoneurones (MNs) aussi bien contra- (c) qu’ipsilatérales (i). Les influences CSc sur les MNs du poignet sont connues pour être modulées entre autres par la position du poignet et les afférences cutanées. Pour cette raison, notre objectif était de vérifier si ces caractéristiques sont aussi valides pour les influences CSi. En utilisant la stimulation transcrânienne magnétique au niveau du cortex primaire droit, nous avons tout d’abord comparé les influences CSi sur les MNs des fléchisseurs du poignet à des positions maintenues de flexion et d’extension durant une tâche uni-manuelle ainsi que deux tâches bimanuelles, ceci chez des sujets droitiers (n=23). Nous avons ensuite comparé les influences CSi dans cinq tâches bi-manuelles de tenue d’objet durant lesquelles les sujets avaient à tenir entre leurs mains un bloc à la surface soit lisse, soit rugueuse, dont le poids était supporté ou non, ceci en position de flexion (n=21). Dans une tâche, un poids était ajouté au bloc lisse en condition non supportée pour amplifier les forces de préhension requises. Une modulation positiondépendante était observée au niveau des potentiels évoqués moteurs (iPEM), mais seulement lors de la tâche bi-manuelle quand les deux mains interagissaient via un bloc (p= 0.01). Une modulation basée sur la texture était également présente, quel que soit le support de poids, et le bloc lisse était associé avec des iPEMs plus importants en comparaison avec le bloc rugueux (p= 0.001). Ainsi, les influences CSi sur les MNs n’étaient modulées que lors des tâches bi-manuelles et dépendaient de la manière dont les mains interagissaient. De plus, les afférences cutanées modulaient les influences CSi facilitatrices et pourraient ainsi participer à la prise en main des objets. Il en est conclu que les hémisphères droit et gauche coopèrent durant les tâches bimanuelles impliquant la tenue d’objet entre les mains, avec la participation potentielle de projections mono-, et poly-synaptiques, transcallosales inclues. La possibilité de la contribution de reflexes cutanés et d’étirement (spinaux et transcorticaux) est discutée sur la base de la notion que tout mouvement découle du contrôle indirect, de la « référence » (referent control). Ces résultats pourraient être essentiels à la compréhension du rôle des interactions interhémisphériques chez les sujets sains et cliniques. / There are both contra- (c) and ipsilateral (i) corticospinal (CS) projections to motoneurons (MNs). There is evidence that cCS influences on wrist MNs are modulated by wrist position and cutaneous afferents. Thus, we aimed to test whether these findings are valid for iCS influences as well. Using transcranial magnetic stimulation applied over the right primary motor cortex, we first compared iCS influences on wrist flexor MNs at actively maintained flexion and extension wrist positions in one uni- and two bimanual tasks in right-handed subjects (n=23). We further compared iCS influences in five bimanual holding tasks in which subjects had to hold a smooth or coarse block between their hands, with or without its weight being supported, in flexion position (n=21). In one task, a weight was added to the unsupported smooth block to increase load forces. A position-dependent modulation of the short-latency motor evoked potential (iMEP) was observed, but only in the bimanual task when the two hands interacted through a block (p=0.01). A texture-dependent modulation was present regardless of the weight supported, and the smooth block was associated with larger iMEPs in comparison to the coarse block (p=0.001). Hence, iCS influences on MNs were modulated only in bimanual tasks and depended on how the two hands interacted. Furthermore, cutaneous afferents modulated facilitatory iCS influences and thus may participate to grip forces scaling and maintaining. It is concluded that the left and right cortices cooperate in bimanual tasks involving holding an object between the hands, with possible participation of mono- and poly-synaptic, including transcallosal projections to MNs. The possible involvement of spinal and trans-cortical stretch and cutaneous reflexes in bimanual tasks when holding an object is discussed based on the notion that indirect, referent control underlies motor actions. Results might be essential for the understanding of the role of intercortical interaction in healthy and neurological subjects.