Space representation for eye movements is more contralateral in monkeys than in humans

Contralateral hemispheric representation of sensory inputs (the right visual hemifield in the left hemisphere and vice versa) is a fundamental feature of primate sensorimotor organization, in particular the visuomotor system. However, many higher-order cognitive functions in humans show an asymmetric hemispheric lateralization—e.g., right brain specialization for spatial processing—necessitating a convergence of information from both hemifields. Electrophysiological studies in monkeys and functional imaging in humans have investigated space and action representations at different stages of visuospatial processing, but the transition from contralateral to unified global spatial encoding and the relationship between these encoding schemes and functional lateralization are not fully understood. Moreover, the integration of data across monkeys and humans and elucidation of interspecies homologies is hindered, because divergent findings may reflect actual species differences or arise from discrepancies in techniques and measured signals (electrophysiology vs. imaging). Here, we directly compared spatial cue and memory representations for action planning in monkeys and humans using event-related functional MRI during a working-memory oculomotor task. In monkeys, cue and memory-delay period activity in the frontal, parietal, and temporal regions was strongly contralateral. In putative human functional homologs, the contralaterality was significantly weaker, and the asymmetry between the hemispheres was stronger. These results suggest an inverse relationship between contralaterality and lateralization and elucidate similarities and differences in human and macaque cortical circuits subserving spatial awareness and oculomotor goal-directed actions

Behavioral and electrophysiological correlates of cognitive control in ex-obese adults

Impaired cognitive control functions have been documented in obesity. It remains unclear whether these functions normalize after weight reduction. We compared ex-obese individuals, who successfully underwent substantial weight loss after bariatric surgery, to normal weight participants on measures of resistance to interference, cognitive flexibility and response inhibition, obtained from the completion of two Stroop tasks, a Switching task and a Go/NoGo task, respectively. To elucidate the underlying brain mechanisms, event-related potentials (ERPs) in the latter two tasks were examined. As compared to controls, patients were more susceptible to the predominant but task-irrelevant stimulus dimension (i.e., they showed a larger verbal Stroop effect), and were slower in responding on trials requiring a task-set change rather than a task-set repetition (i.e., they showed a larger switch cost). The ERP correlates revealed altered anticipatory control mechanisms (switch positivity) and an exaggerated conflict monitoring response (N2). The results suggest that cognitive control is critical even in ex-obese individuals and should be monitored to promote weight loss maintenance

How the Development of Handedness Could Contribute to the Development of Language

We propose a developmental process which may link the development of handedness with the development of hemispheric specialization for speech processing. Using Arbib’s proposed sequence of sensorimotor development of manual skills and gestures (that he considers to be the basis of speech gestures and proto-language), we show how the development of hand-use preferences in proto-reaching skills concatenate into object acquisition skills and eventually into role-differentiated bimanual manipulation skills (that reflect interhemispheric communication and coordination). These latter sensorimotor skills might facilitate the development of speech processing via their influence on the development of tool-using and object management abilities. ß 2013 Wiley Periodicals, Inc. Dev Psychobiol 55: 608–620, 201

Laterality and perceptual-motor skills in elite Australian Football

This thesis is a study of how within-individual and between-individual lateral preference affects the performance of perceptual-motor skills in Australian football (AF). Results in study 1 demonstrated that whereas AF players executed handballs using both their preferred and non-preferred side during professional games, kicks were performed by predominantly using the preferred side. Study 2 found that when sport-specific hand preference was considered, there were more mixed-hand preference players in the AF population compared to the expert basketball players, with a smaller proportion of mixed-footed and a higher proportion of right-footed players in AF compared to soccer. Study 3 demonstrated that participants were less accurate and had slower RTs when identifying the kicking foot of opposing team players, relative to their speed and accuracy at identifying teammates. Significantly lower discrimination accuracy was also evident in participants’ capability to identify left-footed opponents. Using a ‘snap-kick’ for goal, study 4 found that accuracy was greater with the preferred than the non-preferred foot and greater for easy than difficult kick angles, but there were no accuracy differences due to player footedness. In study 5.1, a set shot goal-kicking task revealed that left-footed AF players were more accurate than right-footed players from a more acute angle relative to the goal. Results in study 5.2 showed that the accuracy cost of ‘look away’ handball passes with the preferred hand was lower for left-handers compared to right-handers. Study 5.3 found reaction time to be faster when players used the preferred hand for handballing. Together, this series of studies indicated that AF skills on the non-preferred side were less developed than the preferred side, although player beliefs and patterns of handedness in games support a more dynamic view of laterality, potentially arising from evolution of the AF competition’s rules and team strategies

Does Handedness for Prehension Predict Handedness for Role-Differentiated Bimanual Manipulation During Infancy?

The clearly observable behaviors that identify infant hand-use preferences make the development of this sensorimotor form of lateralization a valuable model for evaluating the development of other forms of lateral asymmetries of function. The current study examined the relation of individual patterns of development of handedness for reaching for objects (prehension) to the emergence of handedness in role-differentiated bimanual manipulation (RDBM). RDBM requires each hand to perform different, but complementary, actions on one or more objects. Hand-use reference for reaching for and grasping objects was assessed in a sample of 85 infants from the period of 6- to 11-months of age using a validated handedness assessment that consists of a series of presentations of 34 common infant toys. At 11 and 14 months, hand-use preferences for RDBM were assessed while the infants were involved in semiplay activity in which they were presented with a series of 13 toys (20-40 s for each presentation). Results revealed no significant relationship between prehension handedness and handedness for RDBM. However, multi-level modeling of the prehension data revealed interesting developmental changes in prehension handedness that can only be identified by using monthly sampling intervals with longitudinal methods

Development of handedness for role-differentiated bimanual manipulation of objects in relation to the development of hand-use preferences for acquisition during infancy

Handedness development during infancy could be represented as a progressive expansion of a hand-use preference across a wider range of increasingly complex skills. The goal of the present study was to explore the development of role-differentiated bimanual manipulation (RDBM) during infancy as an expansion of the development of handedness for acquiring objects and unimanual manipulation. Infants were categorized according to their handedness status for acquiring objects (right-hand, left-hand, or no distinct hand-use preference). This status was determined from nine monthly assessments performed during 6-14 month period and resulted in a sample of 90 normally developing infants (30 right-handers, 30 left-handers, and 30 no preference infants). These infants were tested monthly from 9 to 14 months for unimanual manipulation and RDBM handedness. The results of the multilevel analyses showed that lateralization of handedness for toy acquisition increased during 6-12 month interval and decreased thereafter. Lateralization of handedness for unimanual manipulation and RDBM increased during 9-14 month period. Furthermore, handedness for toy acquisition was found to be positively related to handedness for unimanual manipulation, which, in its turn, was positively related to handedness for difficult, but not simple, RDBM. Also, handedness for toy acquisition was positively related to handedness for difficult RDBM. Thus, it was concluded that handedness for toy acquisition concatenates into unimanual handedness which further influences the development of RDBM handedness

Whole-brain estimates of directed connectivity for human connectomics

Connectomics is essential for understanding large-scale brain networks but requires that individual connection estimates are neurobiologically interpretable. In particular, a principle of brain organization is that reciprocal connections between cortical areas are functionally asymmetric. This is a challenge for fMRI-based connectomics in humans where only undirected functional connectivity estimates are routinely available. By contrast, whole-brain estimates of effective (directed) connectivity are computationally challenging, and emerging methods require empirical validation. Here, using a motor task at 7T, we demonstrate that a novel generative model can infer known connectivity features in a whole-brain network (>200 regions, >40,000 connections) highly efficiently. Furthermore, graph-theoretical analyses of directed connectivity estimates identify functional roles of motor areas more accurately than undirected functional connectivity estimates. These results, which can be achieved in an entirely unsupervised manner, demonstrate the feasibility of inferring directed connections in whole-brain networks and open new avenues for human connectomics

Event related potential correlates of movement production and the regulation and monitoring of actions

Humans have the ability to interact with the environment by producing voluntary movements and responding to relevant external events. Since human performance is rarely perfect, an important task of the human information processing system also concerns the monitoring of actions (Rabbitt, 1967). In this way departures from required performance are detected and adjustments can be made to eliminate, or reduce, errors. This thesis describes experiments on the planning, execution and evaluation of voluntary movement. To this end, brain activity in the electro-encephalogram (EEG) accompanying both hand and eye movements are examined

EEG and TMS-EEG Studies on the Cortical Excitability and Plasticity associated with Human Motor Control and Learning

More than half of the activities of daily living rely on upper limb functions (Ingram et al., 2008). Humans perform upper limb movements with great ease and flexibility but even simple tasks require complex computations in the brain and can be affected following stroke leaving survivors with debilitating movement impairments. Hemispheric asymmetries related to motor dominance, imbalances between contralateral and ipsilateral primary motor cortices (M1) activity and the ability to adapt movements to novel environments play a key role in upper limb motor control and can affect recovery. Motor learning and control are critical in neurorehabilitation, however to effectively integrate these concepts into upper limb recovery treatments, a deeper understanding of the basic mechanisms of unimanual control is needed. This thesis aimed to investigate hemispheric asymmetries related to motor dominance, to evaluate the relative contribution of the contralateral and ipsilateral M1 during unilateral reaching preparation and finally to identify the neural correlates underlying the formation of a predictive internal model enabling to adapt movements to new environments. To this end electroencephalography (EEG), transcranial magnetic stimulation (TMS), simultaneous TMS-EEG were employed during a simple motor and a highly standardised robot-mediated task. The first study used TMS-EEG to examine differences in cortical excitability related to motor dominance by applying TMS over the dominant and non-dominant M1 at rest and during contraction. No hemispheric asymmetries related to hand dominance were found. The second study assessed the temporal dynamics of bi-hemispheric motor cortical excitability during right arm reaching preparation. TMS was applied either to the ipsilateral or contralateral M1 during different times of movement preparation. Significant bilateral M1 activation during unilateral reaching preparation was observed, with no significant differences between the contralateral and ipsilateral M1. Unimanual reaching preparation was associated with significant interactions of excitatory and inhibitory processes in both motor cortices. The third study investigated the neural correlates of motor adaptation. EEG was recorded during a robot-mediated adaptation task involving right arm reaching movements and cortical excitability was assessed by applying TMS over the contralateral M1 and simultaneously recording TMS responses with EEG before and after motor adaptation. It was found that an error-related negativity (ERN) over fronto-central regions correlated with performance improvements during adaptation, suggesting that this neural activity reflects the formation of a predictive internal model. Motor adaptation underlay significant modulations in cortical excitability (i.e. neuroplasticity) in sensorimotor regions. Finally, it was shown that native cortical excitability was linked to motor learning improvements during motor adaptation and explained the variability in motor learning across individuals. These experiments demonstrated that even unimanual motor control relies on interactions between excitatory and inhibitory mechanisms not only in the contralateral M1 but in a wider range of brain regions, shown by a bi-hemispheric activity during movement preparation, the formation of a predictive model in fronto-central regions during motor adaptation and neuroplastic changes in sensorimotor regions underlying motor adaptation during unimanual reaching