Correlation between the sizes of Mauthner neurons and the preference of goldfish to turn to the right or left

Three-dimensional computer reconstruction working from serial histological sections was used to study the morphology of the right and left Mauthner neurons (MN) in goldfish fry showing marked preferences to turn stably to the right or left in a narrow water channel or showing no asymmetry in their choice of side during turns. Visually, fish with left-sided motor asymmetry had larger MN on the right side, while fish with right-sided motor asymmetry had larger MN on the left side. Fish with symmetrical turns to the right and left showed no differences in MN size. Quantitative assessment of the MN of fish with preferences for turns to one side or the other revealed significant differences in the sizes of the somatic part, the axon hillock, and the axons of neurons located on the contralateral side of the medulla oblongata. Analysis of the statistical relationships between the functional (motor) asymmetry of fish and the morphological asymmetry of the somatic parts of MN in the same fish revealed a stable correlation (0.69) between these measures. Given that MN initiate unilateral turns of the body in free movement, the data obtained here lead to the conclusion that the larger neuron is more frequently activated in natural conditions as compared with the smaller, contralateral, neuron. __________ Translated from Morfologiya, Vol. 127, No. 2, pp. 16–19, March–April, 2005.     

Anticipatory planning deficits and task context effects in hemiparetic cerebral palsy

Individuals with hemiparetic cerebral palsy (HCP) display deviant motor output, predominantly on one side of the body. The question pursued here is whether HCP participants have the ability to anticipate the forthcoming perceptual-motor demands of the goal of an action sequence. Such anticipatory planning was necessary to successfully perform the tasks that were studied. In experiment I, HCP participants had to grasp a hexagonal knob with their unimpaired hand by choosing one of five possible grasping patterns (free choice) and consequently rotate it 60°, 120°, or 180° clockwise or counterclockwise. HCP participants showed a large amount of task failures that were persistent throughout the task. These findings suggest a deficit in anticipatory planning. No such task failures were observed for the control group. In addition, the instructed degree of rotation had less effect on the selected grasping pattern for the HCP participants than for the controls. In experiment II, we investigated if HCP participants are prone to use context information that is directly available in the task, instead of planning the forthcoming perceptual-motor demands. To that aim, an arrow was inserted at one of the sides of the hexagon in a position that had no relevance for the action to be planned and executed. The location of this arrow significantly affected the grip selected in the HCP participants, but not in controls. Overall, the results suggest an anticipatory planning deficit in HCP participants that may be caused by an impairment at the motor imagery level. Consequently, as an alternative strategy, performance in HCP participants was predominantly based on information directly available in the task context.     

An investigation into manual asymmetries in grasp behavior and kinematics during an object manipulation task

Manual asymmetries in the control of movements have been investigated in a variety of experimental paradigms. Initial studies demonstrated that the dominant right hand has advantages over the non-dominant left hand in many aspects of motor control. However, more recent studies have shown that the presence and extent of these asymmetries depends on the task context and accuracy demands. Typically, manual asymmetries on a motor planning and motor execution level are examined separately. However, given that recent research has demonstrated that specific task constraints do not influence both levels equally, the purpose of the present experiment was to investigate manual asymmetries in motor planning and execution. To this end, initial grasp behavior (motor planning) and kinematics (motor execution) were examined in thirteen right-handed participants during a unimanual grasping and placing task. We specifically manipulated grasping hand, target location, object end orientation, and object grasp time at the start location. There were three main findings. First, motor planning or movement execution was similar regardless of grasping hand. Second, prospectively planned actions were influenced by target location and the required end orientation of the object. Third, the amount of time spent in an initial posture did not influence initial grasp postures. However, it did alter the movement kinematics during the grasping (approach phase) and placing (transport phase) portion of the task. We posit that grasping and placing movements are comprised of an initial grasp and a transport component, which are differentially influenced by task constraints.     

Delay activity and sensory-motor translation during planned eye or hand movements to visual or tactile targets

To perform eye or hand movements toward a relevant location, the brain must translate sensory input into motor output. Recent studies revealed segregation between circuits for translating visual information into saccadic or manual movements, but less is known about translation of tactile information into such movements. Using human functional magnetic resonance imaging (fMRI) in a delay paradigm, we factorially crossed sensory modality (vision or touch) and motor effector (eyes or hands) for lateralized movements (gaze shifts to left or right or pressing a left or right button with the corresponding left or right hand located there). We investigated activity in the delay-period between stimulation and response, asking whether the currently relevant side (left or right) during the delay was encoded according to sensory modality, upcoming motor response, or some interactive combination of these. Delay activity mainly reflected the motor response subsequently required. Irrespective of visual or tactile input, we found sustained activity in posterior partial cortex, frontal-eye field, and contralateral visual cortex when subjects would later make an eye movement. For delays prior to manual button-press response, activity increased in contralateral precentral regions, again regardless of stimulated modality. Posterior superior temporal sulcus showed sustained delay activity, irrespective of sensory modality, side, and response type. We conclude that the delay activations reflect translation of sensory signals into effector-specific motor circuits in parietal and frontal cortex (plus an impact on contralateral visual cortex for planned saccades), regardless of cue modality, whereas posterior STS provides a representation that generalizes across both sensory modality and motor effector.     

Effects of transcranial direct current stimulation on the excitability of the leg motor cortex

Although locomotion and prehension are commonly coordinated in everyday life, little previous research has focused on this form of coordination. To address this neglected topic, we asked participants to stand a variable distance from a table, walk up to the table, and move an object on the tabletop to a new tabletop position, either to the right or to the left of the object’s initial position and near or far from that initial position. For large manual displacements, which required a step after picking up the object, subjects preferred to stand on the foot opposite the direction of forthcoming manual displacement. By contrast, for small manual displacements, which did not require a step after picking up the object, subjects showed no support-leg preference when they grasped the object prior to manual displacement. The support-leg preferences at grasp time were apparently anticipated by participants as they walked up to the table, indicating considerable long-range planning of entire body positions associated with forthcoming object transfers.This work is based on the Master’s thesis of the first author at the University of Maastricht, which was completed under the supervision of the second author while the first author spent an internship at the first author’s lab.     

Evidence for context sensitivity of grasp representations in human parietal and premotor cortices

Grasp-related responses in neurons of the macaque rostral inferior parietal lobule [PF/PFG and the anterior intraparietal area (AIP)] are modulated by task context. Event-related functional MRI was used to determine whether this is true in putative homologs of the human cortex, the rostral inferior parietal lobule (rIPL) and the anterior intraparietal sulcus (aIPS). Fifteen healthy, right-handed adults were required to select prospectively the most comfortable way to grasp a horizontally oriented handle using the cued hand (left or right). In the "no-rotation" condition, the task was simply to grasp the handle, whereas in the "rotation" condition, the goal was to plan to grasp and rotate it into a vertical orientation with the cued end (medial or lateral) pointing downward. In both conditions, participants remained still and indicated their grip preferences by pressing foot pedals. As in overt grasping, participants' grip preferences were significantly influenced by anticipation of the demands associated with handle rotation. Activity within the aIPS and rIPL increased bilaterally in both the rotation and no-rotation conditions. Importantly, these responses were significantly greater in the rotation vs. no-rotation condition. Similar context effects were detected in the presupplementary motor area, caudal intraparietal sulcus/superior parietal lobule, and bilateral dorsal and left ventral premotor cortices. Grasp representations within the rIPL and aIPS are sensitive to predicted task demands and play a role in context-sensitive grip selection. Moreover, the findings provide additional evidence that areas involved in the sensorimotor control of grasp also contribute to feedforward planning.     

Random walks on the mental number line

The direction of influence between conceptual and motor activation, and its relevance for real-life activities, is still unclear. Here, we use the frequently reported association between small/large numbers and left/right space to investigate this issue during walking. We asked healthy adults to generate random numbers as they made lateral turns and found that (1) lateral turn decisions are predicted by the last few numbers generated prior to turning; (2) the intention to turn left/right makes small/large numbers more accessible; and (3) magnitude but not order of auditorily presented numbers influences the listener’s turn selection. Our findings document a bidirectional influence between conceptual and motor activation and point to a hierarchically organized conceptual–motor activation.     

Cerebral lateralization and spatial ability

Frequencies of three cerebral dominance genotypes who show right or left ear superiority on a verbal dichotic listening test and left or right field superiority on a tachistoscopic lateral field test of perceptual dominance are deduced. A hypothesis is offered relating direction of cerebral dominance, as defined by genotype, to degree of lateral specialization and perceptual ability, and a theoretical distribution of subjects according to spatial-perceptual ability and lateralization is derived. This distribution corresponds almost exactly with empirical data, thus confirming the proposed correlation between lateralization and spatial-perceptual capacity.     

The relative effects of external spatial and motoric factors on the bimanual coordination of discrete movements

The ability to coordinate the two hands effectively is a fundamental requirement for many everyday tasks. To investigate how bimanual coordination is achieved we asked subjects to perform discrete bimanual key-press responses under conditions in which the motoric (i.e., muscles employed) and external spatial (i.e., direction of movement in external space) relationships between the actions of the left and right index fingers were systematically varied. Subjects made simultaneous right and left index finger key-presses in response to an auditory tone. The right finger always made downward flexion movements whilst the left finger either flexed in a downward/upward direction, or extended in a downward/upward direction. Unimanual control trials of each movement type for both hands were also performed. Reaction times for each hand (RTs) and the inter-response interval (IRI) were recorded . Right hand RTs were significantly affected only when the left finger performed motorically different actions, but were unaffected by the external spatial direction in which the left hands actions were made. The IRI results followed a similar pattern with the worst coordination (highest IRI) occurring when the left finger performed different motor actions to the right finger regardless of the direction of the left hand movement. In contrast to other recent results from experiments examining oscillatory tasks (e.g., Mechsner et al. 2001), our results suggest that in discrete tasks there is a dominance of the motor relationship between the hands over the external spatial relationship.     

Manual asymmetries in grasp pre-shaping and transport–grasp coordination

Few studies have directly compared the visuo-motor transformation of grasp pre-shaping or transport–grasp coordination of reach-to-grasp movements between the two hands. Our objective was to determine if there are manual asymmetries in right-handed adults as a foundation to investigate hemispheric specialization in individuals post-stroke. Twelve non-disabled right-handed adults performed rapid reach-to-grasp movements to cylinders of three sizes as vision of the arm and hand was partially occluded. We reasoned that the hand system (left or right) that is superior in anticipatory planning of aperture scaling and movement preparation would be more likely to exhibit early grasp pre-shaping under this experimental manipulation. Movement time, hand path, transport velocity, and aperture were derived from 3D electromagnetic sensor data. The visuo-motor transformation of object sizes into an action of aperture pre-shaping was quantified using the correlations between initial aperture velocity and object diameter, and peak aperture and object diameter. Coordination between hand transport and aperture grasping was quantified using the cross-correlation between transport velocity and aperture size. Peak aperture and object diameter were strongly correlated for both hands. However, early aperture velocity and object diameter were correlated only for left-hand movements. Cross-correlation analyses revealed a strong association between transport velocity and aperture only for right-hand movements. Together, these results suggest earlier anticipatory control for the left hand in the visuo-motor transformation of grasp pre-shaping and a stronger transport–grasp linkage for the right hand. Further, initial aperture velocity was a more sensitive measure of these manual asymmetries than peak aperture. Our findings compliment the specialization previously observed for pointing movements of the dominant and non-dominant hemispheric/limb system and the coordinated control of complex movements and visuo-spatial components, respectively.     

Integration of cortical areas during performance of a catching ball task

The study aimed to elucidate electrophysiological and cortical mechanisms involved in anticipatory actions when healthy subjects had to catch balls in free drop; specifically through quantitative electroencephalography (qEEG) alpha absolute power changes. Our hypothesis is that during the preparation of motor action (i.e., 2 s before ball’s drop) occurred integration among left medial frontal, left primary somatomotor and left posterior parietal cortices, showing a differentiated activity involving expectation, planning and preparedness. This hypothesis supports a lateralization of motor function. Although we contend that in right-handers the left hemisphere takes on a dominant role for the regulation of motor behavior. The sample was composed of 23 healthy subjects (13 male and 10 female), right handed, with ages varying between 25 and 40 years old (32.5 ± 7.5), absence of mental and physical illness, right handed, and do not make use of any psychoactive or psychotropic substance at the time of the study. The experiment consisted of a task of catching balls in free drop. The three-way ANOVA analysis demonstrated an interaction between moment and position in left medial frontal cortex (F3 electrode), somatomotor cortex (C3 electrode) and posterior parietal cortex (P3 electrode; p < 0.001). Summarizing, through experimental task employed, it was possible to observe integration among frontal, central and parietal regions. This integration appears to be more predominant in expectation, planning and motor preparation. In this way, it established an absolute predominance of this mechanism under the left hemisphere.     

Holding an object: neural activity associated with fingertip force adjustments to external perturbations

When you hold an object, a sudden unexpected perturbation can threaten the stability of your grasp. In such situations grasp stability is maintained by fast reflexive-like grip-force responses triggered by the somatosensory feedback. Here we use functional magnetic resonance imaging (fMRI) to investigate the neural mechanisms involved in the grip-force responses associated with unexpected increases (loading) and decreases (unloading) in the load force. Healthy right-handed subjects held an instrumented object (of mass 200 g) between the tips of right index finger and thumb. At some time during an interval of 8 to 45 s the weight of the object was suddenly increased or decreased by 90 g. We analyzed the transient increases in the fMRI signal that corresponded precisely in time to these grip-force responses. Activity in the left primary motor cortex was associated with the loading response, but not with unloading, suggesting that sensorimotor processing in this area mediates the sensory-triggered reflexive increase in grip force during loading. Both the loading and the unloading events activated the cingulate motor area and the medial cerebellum. We suggest that these regions could participate in the updating of the sensorimotor representations of the fingertip forces. Finally, the supplementary somatosensory area located on the medial wall of the parietal lobe showed an increase in activity only during unloading, indicating that this area is involved in the sensorimotor processing generating the unloading response. Taken together, our findings suggest different central mechanisms for the grip-force responses during loading and unloading.     

Asymmetrical cognitive differences associated with hemiparkinsonism

The question of whether Parkinson's disease (PD) patients who have left (LPD) or right (RPD) motor predominance also exhibit cognitive differences is controversial. We examined this issue using a neuropsychological battery designed to provide a balanced sampling of both right- and left-hemispheric functions. RPD patients were impaired relative to LPD patients on verbally mediated tasks (left hemisphere function), but there was no group difference for visuospatial tasks (right-hemispheric function). In addition, there was a significant correlation between the extent of right side motor predominance and performance on verbal tasks, but there was no relationship between left side motor symptoms and performance on visuospatial tasks. The controversy related to cognitive differences in hemiparkinsonism may be due to the balance of the assessment procedure, the severity of motor asymmetry, or both.     

On the link between action planning and motor imagery: a developmental study

We examined the link between action planning and motor imagery in 6- and 8-year-old children. Action planning efficiency was assessed with a bar transport task. Motor imagery and visual imagery abilities were measured using a hand mental rotation task and a number (i.e., non-body stimuli) mental rotation task, respectively. Overall, results showed that performance varied with age in all tasks, performance being progressively refined with development. Importantly, action planning performance was correlated with motor imagery, whereas no relationship was evident between action planning and visual imagery at any age. The results showed that the ability to engage sensorimotor mechanisms when solving a motor imagery task was concomitant with action planning efficiency. The present work is the first demonstration that evaluating the consequences of the upcoming action in grasping depends on children’s abilities to mentally simulate the response options to choose the most efficient grasp.     

膝骨性关节炎患者动态平衡能力变化

背景：膝骨性关节炎患者屈膝肌力及伸膝肌力均有不同程度的下降,进而影响患者的平衡控制能力。 目的：探讨膝骨性关节炎患者动态平衡功能的变化特征。 方法：纳入22例膝骨性关节炎患者(膝骨性关节炎组)和20例健康正常人(正常组),应用动态平衡仪进行动态平衡能力测试,包括总体稳定指数、前后方向稳定指数和左右方向稳定指数;稳定性测试：包括完成稳定性测试全部随机目标跟踪的时间,平均方向控制能力和前、后、右、左、前右、前左、后右、后左8个方向上的控制能力。 结果与结论：膝骨性关节炎组在睁眼双足站立、闭眼双足站立状态下总体稳定指数、前后方向稳定指数、左右方向稳定指数均高于正常组(P < 0.01),平均方向控制能力、前方控制能力、后方控制能力、左方控制能力、后右方控制能力测试值低于正常组,而完成该测试所需时间明显增加(P < 0.01)。说明膝骨性关节炎患者动态平衡能力下降。     

Lateralization of emotionality in right parietal cortex of the rat

Lesions of right parietal cortex in the rat increase activity in the open field compared with left parietal lesions, especially after section of the corpus callosum. Left or right motor or medial frontal cortex lesions do not have a lateralized effect. This evidence of a localized asymmetry between the cerebral hemispheres strongly implies that right parietal cortex has a role in emotionality in this species. Our findings suggest a functional similarity to right parietal cortex in man.     

Eye dominance and somatosensory asymmetry in relation to motor asymmetry: Evidence from hemiplegic children

Fifty‐four children with congenital hemiplegia (25 left and 29 right hemiplegics) were administered a battery of sensory and perceptual tests, the results of which were related to measures of motor asymmetry obtained from the same children. Asymmetries of visual acuity and eye dominance were largely independent of motor asymmetry. Asymmetries of stereognosis and finger identification, but not graphesthesia, were associated with various measures of motor asymmetry. It appears that the association between tactile and motor asymmetries varies with the motor demands of the tactile task and that there is little intrinsic relationship between somatosensory and motor asymmetry. Even though the development of motor skill in these children was more impaired by left‐hemisphere damage than by right‐hemisphere damage, left‐and right‐hemisphere damage produced equivalent deficits in their sensory and perceptual ability.     

Neuroanatomical correlates of motor acquisition and motor transfer

The acquisition of new motor skills is dependent on task practice. In the case of motor transfer, learning can be facilitated by prior practice of a similar skill. Although a multitude of studies have investigated the brain regions contributing to skill acquisition, the neural bases associated with the savings seen at transfer have yet to be determined. In the current study, we used functional MRI to examine how brain activation differs during acquisition and transfer of a visuomotor adaptation task. Two groups of participants adapted manual aiming movements to three different rotations of the feedback display in a sequential fashion, with a return to baseline display conditions between each rotation. Subjects showed a savings in the rate of adaptation when they had prior adaptive experiences (i.e., positive transfer of learning). This savings was associated with a reduction in activity of brain regions typically recruited early in the adaptation process, including the right inferior frontal gyrus, primary motor cortex, inferior temporal gyrus, and the cerebellum (medial HIII). Moreover, although these regions exhibit activation that is correlated across subjects with the rate of acquisition, the degree of savings at transfer was correlated with activity in the right cingulate gyrus, left superior parietal lobule, right inferior parietal lobule, left middle occipital gyrus, and bilaterally in the cerebellum (HV/VI). The cerebellar activation was in the regions surrounding the posterior superior fissure, which is thought to be the site of storage for acquired internal models. Thus we found that motor transfer is associated with brain activation that typically characterizes late learning and storage. Transfer seems to involve retrieval of a previously formed motor memory, allowing the learner to move more quickly through the early stage of learning.     

Activity of pyramidal tract neurons in the cat during postural corrections

The dorsal side-up body orientation in quadrupeds is maintained by a postural control system. We investigated participation of the motor cortex in this system by recording activity of pyramidal tract neurons (PTNs) from limb representations of the motor cortex during postural corrections. The cat was standing on the platform periodically tilting in the frontal plane, and maintained equilibrium at different body configurations: with the head directed forward (symmetrically alternating loading of the left and right fore limbs), or with the head voluntary turned to the right or to the left (asymmetrical loading). We found that postural corrective responses to tilts included an increase of the contact forces and activity of limb extensors on the side moving down, and their decrease on the opposite side. The activity of PTNs was strongly modulated in relation to the tilt cycle. Phases of activity of individual PTNs were distributed over the cycle. Thus the cortical output mediated by PTNs appeared closely related to a highly automatic motor activity, the maintenance of the body posture. An asymmetrical loading of limbs, caused by head turns, resulted in the corresponding changes of motor responses to tilts. These voluntary postural modifications were also well reflected in the PTNs' activity. The activity of a part of PTNs correlated well with contact forces, in some others with the limb muscle activity; in still others no correlation with these variables was observed. This heterogeneity of the PTNs population suggests a different functional role of individual PTNs.     

Correlation of the sizes of Mauthner neurons with the preference in the goldfish to turn rightwards or leftwards

Using the three-dimensional computer reconstruction from serial histological sections, the morphology of right and left Mauthner cells (MC) was examined in the goldfish fry which demonstrated clearly pronounced preference to turn to the right or to the left in a narrow water channel or which did not show any asymmetry in choosing the side of turning. Visually, the goldfish with left-sided motor asymmetry seemed to possess larger right MC, while in the goldfish with right-sided motor asymmetry left MC were larger. In fish with symmetric proportion of right or left turnings, the sizes of MC did not differ. Quantitative evaluation of MC in fish showing the preference of turning side has revealed significant differences in the sizes of cell bodies, axon hillock and axons of MC, located contralaterally in medulla oblongata. Analysis of a statistic relations between functional (motor) and morphological asymmetry of MC cell body in the same fish indicated the existence of a stable correlation (0,69) between them. Taking into consideration that MC initiate unilateral body turn during free swimming of fish, it may be concluded that the larger size of neuron predetermines its more frequent natural activation in comparison with the contrlateral neuron, that has smaller size.