The corpus callosum provides a physical and functional connection between the two hemispheres of the brain allowing interactions between homologous cognitive, sensory and motor areas. In humans, the integrity of transcallosal connections between motor cortices can be evaluated quickly and non-invasively using transcranial magnetic stimulation (TMS) via the ipsilateral silent period (iSP). While the technique has been known for 20 years, many issues remain unsolved regarding which methods are best to elicit the iSP as an index of transcallosal inhibition. In addition, there is still limited information regarding the influence of individualized factors such as age on iSP measurements. This thesis investigates how common physiological and methodological factors influence the iSP in order to establish this method as a reliable index to assess the integrity of the transcallosal pathway linking primary motor cortices. In the first series of experiments, we used a previously described TMS protocol to elicit iSPs [1] to investigate changes in motor transcallosal inhibition in relation to individual factors linked to age, hand preference and history of concussions. A second series of methodological experiments examined the effects of stimulation intensity on the iSP and to determine its inter-session reliability. Our first series of experiments provided evidence that advancing age and history of concussions in young athletes were each independently associated with alterations in transcallosal inhibition. This was evidenced by changes in the duration of transcallosal inhibition (DTI) and in the latency of transcallosal inhibition (LTI) derived from iSP measurements. These experiments also revealed that the degree of hand preference in young adults was reflected in measures of transcallosal inhibition, so that mixed-handed individuals (i.e., ambidextrous) exhibited evidence of more efficient transcallosal transmission than either strong right or left handed individuals. The second series of experiments focusing on methodological aspects showed that the iSP duration (though not its onset) was influenced by stimulation intensity, increasing linearly with intensity up to 140% of the resting motor threshold (RMT). Our analysis further revealed that the probability of eliciting detectable iSP also increased with increasing intensity up to 130% RMT before reaching a plateau. A stimulation intensity of 130% of RMT appears to be optimal to elicit iSPs in healthy participants. In a subsequent study, we showed that iSP elicited at this stimulation intensity (i.e., 130% RMT) had good inter-session reliability. In light of these investigations, we recommend for future studies that, in addition to contraction of the homologous muscles of the opposite hand as proposed by Giovannelli et al 2009, that an intensity of 130% RMT should be used to elicit the iSP when assessing transcallosal inhibition between motor cortices.

The aim of this study is to contribute to the standardization of the new diagnostic tools assessing the motor manifestations of laterality in adults and children aged 8 to 10 years, both in terms of determining the theoretical concept and the selection of appropriate items, and the verification of structural hypotheses concerning the design of acceptable models, including the diagnostic quality of individual parts of the test battery. Moreover in this study we try to suggest new approach in assessing of motor laterality manifestation by means of relationship between cerebellar dominance and hand performance. The first part of this thesis deals with the concept of laterality, its manifestations and meaning in non-living systems and living organisms. As a human characteristic, laterality is manifested in a variety of functional and structural asymmetries. This part also discusses ways of diagnosing motor manifestations of laterality and the issue of cerebellar dominance, including its reflection in the form of asymmetry of the extinction physiological syndrome of upper limbs. The second part focuses on the process of the standardization study, the statistical method of structural equation modelling, and the actual design of test battery construction. The last part of this thesis presents the results...

This investigation attempted to determine the relationship of the site of contact ulcers and subject’s handedness. Literature concerned with contact ulcers has indicated that cerebral dominance tends to determine the site of the lesion. Four research questions were posed, two questions were presented in the form of the null hypothesis. The questions were: (1) Is the proportion of right-handed subjects with left-sided ulcers equal to the proportion of left-handed subjects with left-sided ulcers? (2) Is the proportion of right-handed subjects with right-sided ulcers equal to the proportion of left-handed subjects with right-sided ulcers? (3) Will the site of contact ulcers be able to be predicted from subject’s handedness? And (4) Is there a significant relationship between the factors of age, sex and occupation of the sample studied and the occurrence of contact ulcers?

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The aim of this study is to contribute to the standardization of the new diagnostic tools assessing the motor manifestations of laterality in adults and children aged 8 to 10 years, both in terms of determining the theoretical concept and the selection of appropriate items, and the verification of structural hypotheses concerning the design of acceptable models, including the diagnostic quality of individual parts of the test battery. Moreover in this study we try to suggest new approach in assessing of motor laterality manifestation by means of relationship between cerebellar dominance and hand performance. The first part of this thesis deals with the concept of laterality, its manifestations and meaning in non-living systems and living organisms. As a human characteristic, laterality is manifested in a variety of functional and structural asymmetries. This part also discusses ways of diagnosing motor manifestations of laterality and the issue of cerebellar dominance, including its reflection in the form of asymmetry of the extinction physiological syndrome of upper limbs. The second part focuses on the process of the standardization study, the statistical method of structural equation modelling, and the actual design of test battery construction. The last part of this thesis presents the results...

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This work examines the effect of participants' gender and handedness on the perception of short intervals of time. The time estimation task consisted of an empty production procedure with forty trials at each of four intervals of one, three, seven, and twenty seconds. The four target intervals represent a natural logarithmic progression and a series that bracket important temporal thresholds. The order of presentation of those intervals was randomized across participants but yoked across the sexes in each of the respective dominant hand groups. The two between-subject factors, with two levels each, were sex and handedness. Participants produced forty estimates at each of the required intervals, which was the first within-subject factor, estimated interval being the other. T-tests were conducted on the dependent measures, the time estimates in terms of their variability and their central tendency with respect to the target duration. If handedness plays a significant role in timing, this may indicate differences between hemispheric functioning as a possible causal mechanism. If there is cerebral asymmetry in time perception, namely if one hemisphere is more competent regarding time perception, accuracy in judging duration should be higher for the contralateral hand. The results of the present study indicated that there are no significant differences in performance between right-handed and left-handed participants, or between male and female participants, in the estimation of short intervals of time.

<p dir="ltr">Ninety percent of humans are right-handed, and this is often construed to mean that the right hand is better than the left at all tasks, in the right-handed individuals. However, we often ignore the important role played by the left-hand when performing certain bimanual tasks. For instance, when slicing a bread loaf, stabilizing the bread with the left hand is as important as slicing it with the right hand. This implies that each hand is dominant in different types of tasks. The influential dynamic dominance theory posits that each hand’s specific dominance arises from the contralateral hemisphere specialization. The dominant (right) arm produces well-coordinated movements because the left hemisphere is superior at predictive control, and the non-dominant (left) arm shows better stabilizing performance because the right hemisphere is superior at impedance control. This theory has been proposed by studying arm movements. However, it is unclear whether the features of this theory extend to grip force control during object manipulation. This is an important gap in our knowledge; identifying the differences in hand-specific control of grip force would improve our understanding of sensorimotor control of skilled bimanual manipulations. Therefore, the goal of my dissertation was to investigate whether the features of dynamic dominance extend to the control of grip forces in bimanual object manipulation.</p><p dir="ltr">In this dissertation, I performed two studies to investigate the control of complex, bimanual object manipulation tasks. Participants held an object in each hand. The two objects were connected by a spring. The grip forces of each hand accounted not only for the dynamics of the object that the hand manipulated, but also for the destabilizing forces that arose from the actions of the other hand that were transmitted by the spring. This experimental design mimics ecological tasks like slicing bread to the first degree of approximation. The goals were to determine whether the features of hand-specific specialization of control observed in wrist movements is also evident in the movement of hand-held objects and in the control of grip forces during movement execution (study 1) and planning (study 2). Furthermore, I investigated how task uncertainty interacts with hemispheric specialization in modes of grip forces control in both studies.</p><p dir="ltr">In study 1, I investigated whether grip force characteristics differ between hands during an ongoing bimanual manipulation. The right hand produced accurate object movement performance accompanied by stronger modulations in grip force in response to dynamics of loads associated with object movement compared to the left hand. In contrast, the left hand stabilized the object’s position better by exerting a higher grip force on the object. The main contribution of this study is that it suggests that the left hemisphere specializes in predicting dynamics of loads associated with object movements whereas the right hemisphere specializes in ensuring object’s stability by increasing its impedance.</p><p dir="ltr">In study 2, I investigated anticipatory modulations in grip force before an impending bimanual object manipulation task. I studied how each hand prepared grip force for the expected increase in load force, thereby uncovering differences in underlying motor planning processes of each hand. Grip force increased in both hands; however, this increase was greater in the left hand. This result indicates that the right hemisphere relies more on impedance control during planning. The main contribution of this study is that it suggests that even the motor planning processes that prepare each hand for an impending motor action are specialized in a way consistent with the predictions of dynamic dominance theory.</p><p dir="ltr">This dissertation adds to the existing knowledge about hemispheric specialization of arm movement control and extends it to grip force control. Future studies should focus on how the control of arm movements and grip force interact in each hemisphere. Furthermore, building on this dissertation, future work on pathology- and age-related dexterity loss could potentially lead to better interventions that improve the quality of life in these populations.</p>

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