Eye-hand coordination during reaching. II. An analysis of the relationships between visuomanual signals in parietal cortex and parieto-frontal association projections

The relationships between the distribution of visuomanual signals in parietal cortex and that of parieto-frontal projections are the subject of the present study. Single cell recording was performed in areas PEc and V6A, where different anatomical tracers were also injected. The monkeys performed a variety of behavioral tasks, aimed at studying the visual and motor properties of parietal cells, as well as the potential combination of retinal-, eye- and hand-related signals on cell activity. The activity of most cells was related to the direction of movement and the active position of the hand. Many of these reach-related cells were influenced by eye position information. Fewer cells displayed relationships to saccadic eye movements. The activity of most neurons related to a combination of both hand and eye signals. Many cells were also modulated during preparation for hand movement. Light-dark differences of activity were common and interpreted as related to the sight and monitoring of hand motion and/or position in the visual field. Most cells studied were very sensitive to moving visual stimuli and also responded to optic flow stimulation. Visual receptive fields were generally large and extended to the periphery of the visual field. For most neurons, the orientation of the preferred directions computed across different epochs and tasks conditions clustered within a limited sector of space, the field of global tuning. This can be regarded as an ideal frame to combine spatially congruent eye- and hand-related information for different forms of visuomanual behavior. All these properties were common to both PEc and V6A. Retinal, eye- and hand-related activity types, as well as parieto-frontal association cells, were distributed in a periodic fashion across the tangential domain of areas PEc and V6A. These functional and anatomical distributions were characterized and compared through a spectral and coherency analysis, which revealed the existence of a selective 'match' between activity types and parieto-frontal connections. This match depended on where each individual efferent projection was addressed. The results of the present and of the companion study can be relevant for a re-interpretation of optic ataxia as the consequence of the breakdown of the combination of retinal-, eye- and hand-related directional signals within the global tuning fields of parietal neurons.     

Temporal evolution and strength of neural activity in parietal cortex during eye and hand movements

The role of area 7a in eye-hand movement was studied by recording from individual neurons while monkeys performed 7 different tasks, aimed at assessing the relative influence of retinal, eye, and hand information on neural activity. Parietal cell activity was modulated by visuospatial signals about target location, as well as by information concerning eye and/or hand movement, and position. The highest activity was elicited when the hand moved to the fixation point. The population activities across different memory tasks showed common temporal peaks when aligned to the visual instruction (visuospatial peak) or Go signal (motor peak) for eye, hand, and coordinated eye-hand movement. The motor peak was higher for coordinated eye-hand movement, and it was absent in a No-Go task. Two activation maxima were also observed during visual reaching. They had the same latency of the visuospatial and motor peaks seen in the memory tasks. Therefore, area 7a seems to operate through a common neural mechanism underlying eye, hand, or combined eye-hand movement. This mechanism is revealed by invariant temporal activity profiles and is independent from the effector selected and from the presence or absence of a visible target during movement. For comparative purposes, we have studied the temporal evolution of the population activity in the superior parietal lobule (SPL) during the same reaching tasks and during a saccade task. In SPL, the population activity was characterized by a single peak, time locked to the Go signal for eye, hand, or combined eye-hand movement. As in IPL, the time of occurrence of this peak was effector independent. The population activity remained unchanged when the position of the eye changed, suggesting that SPL is mostly devoted to the hand motor behavior.     

Psychomotor control in a virtual laparoscopic surgery training environment: gaze control parameters differentiate novices from experts

Background  

Surgical simulation is increasingly used to facilitate the adoption of technical skills during surgical training. This study sought to determine if gaze control parameters could differentiate between the visual control of experienced and novice operators performing an eye-hand coordination task on a virtual reality laparoscopic surgical simulator (LAP Mentor™). Typically adopted hand movement metrics reflect only one half of the eye-hand coordination relationship; therefore, little is known about how hand movements are guided and controlled by vision.     

Construct validity for eye–hand coordination skill on a virtual reality laparoscopic surgical simulator

Background This study was carried out to investigate whether eye-hand coordination skill on a virtual reality laparoscopic surgical simulator (the LAP Mentor) was able to differentiate among subjects with different laparoscopic experience and thus confirm its construct validity. Methods A total of 31 surgeons, who were all right-handed, were divided into the following two groups according to their experience as an operator in laparoscopic surgery: experienced surgeons (more than 50 laparoscopic procedures) and novice surgeons (fewer than 10 laparoscopic procedures). The subjects were tested using the eye-hand coordination task of the LAP Mentor, and performance was compared between the two groups. Assessment of the laparoscopic skills was based on parameters measured by the simulator. Results The experienced surgeons completed the task significantly faster than the novice surgeons. The experienced surgeons also achieved a lower number of movements (NOM), better economy of movement (EOM) and faster average speed of the left instrument than the novice surgeons, whereas there were no significant differences between the two groups for the NOM, EOM and average speed of the right instrument. Conclusions Eye-hand coordination skill of the nondominant hand, but not the dominant hand, measured using the LAP Mentor was able to differentiate between subjects with different laparoscopic experience. This study also provides evidence of construct validity for eye-hand coordination skill on the LAP Mentor.     

The over-representation of contralateral space in parietal cortex: a positive image of directional motor components of neglect?

The activity of single cells was recorded in behaving monkeys while they performed several eye-hand directional motor tasks. The results revealed that in parietal area 7a there exists a directional representation of eye and hand motor space that, contrary to that of superior parietal, premotor and motor cortex, is highly skewed toward the contralateral workspace. In man, the loss of this representation after parietal lesions might explain the emergence of the directional movement disorders of neglect. In fact, although unilateral neglect is consequence of damage to different brain structures, it is more common and enduring after right inferior parietal cortex lesions. Neglect patients ignore and avoid interacting with events occurring in the contralesional part of their physical and mental space. Current theories distinguish perceptual from motor components of neglect. One key feature of the latter is directional hypokinesia, an impaired representation of space for action, evident as difficulty to plan hand movements toward the contralesional part of egocentric space. An impairment of a similar nature is also observed for eye movements. In this study, we offer an interpretation of directional movement disorders of neglect from a physiological perspective, i.e. by focusing on the mechanisms underlying the representation of visuomotor space in parietal cortex.     

Perceptual impairment and psychomotor control in virtual laparoscopic surgery

Background  

It is recognised that one of the major difficulties in performing laparoscopic surgery is the translation of two-dimensional video image information to a three-dimensional working area. However, research has tended to ignore the gaze and eye-hand coordination strategies employed by laparoscopic surgeons as they attempt to overcome these perceptual constraints. This study sought to examine if measures related to tool movements, gaze strategy, and eye-hand coordination (the quiet eye) differentiate between experienced and novice operators performing a two-handed manoeuvres task on a virtual reality laparoscopic surgical simulator (LAP Mentor™).     

Pontine reference frames for the sensory guidance of movement

The pontine nuclei (PN) are the major intermediary elements in the corticopontocerebellar pathway. Here we asked if the PN may help to adapt the spatial reference frames used by cerebrocortical neurons involved in the sensory guidance of movement to a format potentially more appropriate for the cerebellum. To this end, we studied movement-related neurons in the dorsal PN (DPN) of monkeys, most probably projecting to the cerebellum, executing fixed vector saccades or, alternatively, fixed vector hand reaches from different starting positions. The 83 task-related neurons considered fired movement-related bursts before saccades (saccade-related) or before hand movements (hand movement-related). About 40% of the SR neurons were "oculocentric," whereas the others were modulated by eye starting position. A third of the HMR neurons encoded hand reaches in hand-centered coordinates, whereas the remainder exhibited different types of dependencies on starting positions, reminiscent in general of cortical responses. All in all, pontine reference frames for the sensory guidance of movement seem to be very similar to those in cortex. Specifically, the frequency of orbital position gain fields of SR neurons is identical in the DPN and in one of their major cortical inputs, lateral intraparietal area (LIP).     

A model of movement coordinates in the motor cortex: posture-dependent changes in the gain and direction of single cell tuning curves.

This article outlines a methodology for investigating the coordinate systems by which movement variables are encoded in the firing rates of individual motor cortical neurons. Recent neurophysiological experiments have probed the issue of underlying coordinates by examining how cellular preferred directions (as determined by the center-out task) change with posture. Several key experimental findings have resulted that constrain hypotheses about how motor cortical cells encode movement information. But while the significance of shifts in preferred direction is well known and widely accepted, posture-dependent changes in the depth of modulation of a cell's tuning curve--that is, gain changes--have not been similarly identified as a means of coordinate inference. This article develops a vector field framework in which the preferred direction and the gain of a cell's tuning curve are viewed as dual components of a unitary response vector. The formalism can be used to compute how each aspect of cell response covaries with posture as a function of the coordinate system in which a given cell is hypothesized to encode its movement information. Such an integrated approach leads to a model of motor cortical cell activity that codifies the following four observations: (i) cell activity correlates with hand movement direction; (ii) cell activity correlates with hand movement speed; (iii) preferred directions vary with posture; and (iv) the modulation depth of tuning curves varies with posture. Finally, the model suggests general methods for testing coordinate hypotheses at the single-cell level and simulates an example protocol for three possible coordinate systems: Cartesian spatial, shoulder-centered, and joint angle.     

Motion control skill assessment based on kinematic analysis of robotic end‐effector movements

Background

The performance of robotic end‐effector movements can reflect the user's operation skill difference in robot‐assisted minimally invasive surgery. This study quantified the trade‐off of speed–accuracy–stability by kinematic analysis of robotic end‐effector movements to assess the motion control skill of users with different levels of experience.

Methods

Using ‘MicroHand S’ system, 10 experts, 10 residents and 10 novices performed single‐hand test and bimanual coordination test. Eight metrics based on the movements of robotic end‐effectors were applied to evaluate the users' performance.

Results

In the single‐hand test, experts outperformed other groups except for movement speed; in the bimanual coordination test, experts also performed better except for movement time and movement speed. No statistically significant difference in performance was found between residents and novices.

Conclusions

The kinematic differences obtained from the movements of robotic end‐effectors can be applied to assess the motion control skill of users with different skill levels.     

Human cortical networks for new and familiar sequences of saccades.

Visual exploration is organized in sequences of saccadic eye movements that depend on both perceptual and cognitive context. Using functional magnetic resonance imaging, we studied the neural basis of sequential oculomotor behavior and its dependence on different types of memory by analyzing cerebral activity during performance of newly learned and familiar sequences of eye movements. Compared to a resting condition, both types of sequences activated a common fronto-parietal network, including frontal and supplementary eye fields, and several parietal areas. Within this network, newly learned sequences induced stronger activation than familiar sequences, probably reflecting higher attentional demands. In addition, specific regions were recruited for the performance of new sequences, including pre-supplementary eye fields, the precuneus and the caudate nucleus. This indicates that in addition to attentional modulation, novelty of saccadic sequences requires specific cortical resources, probably related to effortful sequence preparation and coordination as well as to spatial working memory. For familiar sequences, recalled from long-term memory, we observed specific right medial temporo-occipital activation in the vicinity of the boundary between the parahippocampal and lingual gyri, as well as an activation site in the parieto-occipital fissure. We conclude that neuronal resources recruited by the gaze system can change with the familiarity of the scanpath to be executed. This study is important to better understand how the brain implements memorized scanpaths for visual exploration and orienting.     

Functional anatomy of biological motion perception in posterior temporal cortex: an FMRI study of eye, mouth and hand movements

Passive viewing of biological motion engages extensive regions of the posterior temporal-occipital cortex in humans, particularly within and nearby the superior temporal sulcus (STS). Relatively little is known about the functional specificity of this area. Some recent studies have emphasized the perceived intentionality of the motion as a potential organizing principle, while others have suggested the existence of a somatotopy based upon the limb perceived in motion. Here we conducted an event-related functional magnetic resonance imaging experiment to compare activity elicited by movement of the eyes, mouth or hand. Each motion evoked robust activation in the right posterior temporal-occipital cortex. While there was substantial overlap of the activation maps in this region, the spatial distribution of hemodynamic response amplitudes differentiated the movements. Mouth movements elicited activity along the mid-posterior STS while eye movements elicited activity in more superior and posterior portions of the right posterior STS region. Hand movements activated more inferior and posterior portions of the STS region within the posterior continuing branch of the STS. Hand-evoked activity also extended into the inferior temporal, middle occipital and lingual gyri. This topography may, in part, reflect the role of particular body motions in different functional activities.     

A quiet hand for microneurosurgery: twiddle your thumb. Technical note

Fatigue is both the most tremor-producing factor and the constant companion of a busy neurosurgeon. Because of the difficulty in controlling tremor-generating factors, the authors sought to develop a means of manipulating surgical instruments with minimal muscle movement while allowing accurate and repeatable movements in all conditions. The "quiet hand technique" is an isolation technique that creates a stable platform by forming the four fingers into a salute that thenceforth moves as one. Fine movements are supplied by the thumb. For instruments that open and close, the thumb abducts and adducts. For suture placement using a round needle holder, the thumb flexes and extends. Because only the thumb moves, the extent of movement is decreased and therefore momentum and inertia are limited as well. Previously, microsurgeons favored ballistic movements. With the quiet hand technique, however, tension movements are easy. The greater control makes tying 10-0 and 11-0 sutures more predictable. Although the quiet hand technique was developed for use in small-vessel anastomosis, the neurophysiological principles on which it is based apply to movement at all levels and are applicable to working a bipolar coagulator, pickups, a vascular clip holder, or other soft-tissue manipulators.     

Enhanced cortical activation in the contralesional hemisphere of chronic stroke patients in response to motor skill challenge

The brain processes involved in the restoration of motor skill after hemiparetic stroke are not fully understood. The current study compared cortical activity in chronic stroke patients who successfully recovered hand motor skill and normal control subjects during performance of kinematically matched unskilled and skilled hand movements using functional magnetic resonance imaging. We found that cortical activation during performance of the unskilled movement was increased in the patients relative to controls in the contralesional primary sensorimotor cortex. Performance of the skilled movement elicited increased activation in the patients relative to controls in the contralesional primary sensorimotor cortex, ventral premotor cortex, supplementary motor area/cingulate, and occipitoparietal cortex. Further, the activation change in the contralesional occipitoparietal cortex was greater in the patients relative to controls with the increase in motor skill challenge. Kinematic differences, mirror movements, and residual motor deficits did not account for the enhanced activation in the contralesional cortices in the patients. These results suggest that activation in the contralesional cortical network was enhanced as a function of motor skill challenge in stroke patients with good motor recovery. The findings of the current study suggest that successful recovery of motor skill after hemiparetic stroke involves participation of the contralesional cortical network.     

Neural correlates of the spontaneous phase transition during bimanual coordination

Repetitive bimanual finger-tapping movements tend toward mirror symmetry: There is a spontaneous transition from less stable asymmetrical movement patterns to more stable symmetrical ones under frequency stress but not vice versa. During this phase transition, the interaction between the signals controlling each hand (cross talk) is expected to be prominent. To depict the regions of the brain in which cortical cross talk occurs during bimanual coordination, we conducted event-related functional magnetic resonance imaging using a bimanual repetitive-tapping task. Transition-related activity was found in the following areas: the bilateral ventral premotor cortex, inferior frontal gyrus, middle frontal gyrus, inferior parietal lobule, insula, and thalamus; the right rostral portion of the dorsal premotor cortex and midbrain; the left cerebellum; and the presupplementary motor area, rostral cingulate zone, and corpus callosum. These regions were discrete from those activated by bimanual movement execution. The phase-transition-related activation was right lateralized in the prefrontal, premotor, and parietal regions. These findings suggest that the cortical neural cross talk occurs in the distributed networks upstream of the primary motor cortex through asymmetric interhemispheric interaction.     

Mental gait training -- effectiveness of a therapy method in the rehabilitation after hip-replacement

PURPOSE: New neurophysiological findings cover the effectiveness of movement images to the movement learning and deliver the theoretical base for the reasonable application of mental training forms in orthopaedic rehabilitation. In support of the mental training set-up in the high-performance sport, suitable movement images are developed and trained systematically in the mental gait training. The present study examines the question of the effectiveness of mental gait training. METHOD: A randomised control group study [experimental group: mental walking training; control group: no treatment (treatment additional to the customary physiotherapy)] with measuring repetition was carried out. With 24 patients after total hip replacement surgery the relevant kinematic data were collected by applying the procedure SIMI Motion to the walking movement. RESULTS: The experimental group improved in comparison to the control group in the variable stride length, as well as in the factor variable kinematics significantly. CONCLUSION: It can be stated that this study gives further proof for the reasonable application of mental training forms in rehabilitation. Further studies on the application of mental training forms to the movement learning (concerning different movements and further syndromes) must follow to provide further support of the effective and efficient application of these procedures within the context of rehabilitation.     

Waking-sleep modulation of paroxysmal activities induced by partial cortical deafferentation

We investigated the dependency of electrical seizures produced by cortical undercut upon behavioral states of vigilance in chronically implanted cats. Experiments were performed 1-12 weeks after white matter transection. Multisite field potentials and intracellular activity were recorded from suprasylvian and marginal gyri. Paroxysmal activity developed within days and consisted of spike-wave complexes at 3-4 Hz occurring during the waking state (correlated with eye movements), being enhanced during slow-wave sleep (SWS) and blocked during rapid eye movement (REM) sleep. Prolonged hyperpolarizing events were seen not only during SWS (which is the case in normal animals) but also during both waking and REM, thus resulting in bimodal distribution of the membrane potential in all 3 natural states of vigilance. The increased synchrony of field potential activity expressed by shorter time of propagation over the cortical surface and the tendency toward generalization are ascribed to changes in intrinsic neuronal properties and potential disinhibition following cortical undercut.     

The representation of blinking movement in cingulate motor areas: a functional magnetic resonance imaging study

Recent anatomical evidence from nonhuman primates indicates that cingulate motor areas (CMAs) play a substantial role in the cortical control of upper facial movement. Using event-related functional magnetic resonance imaging in 10 healthy subjects, we examined brain activity associated with volitional eye closure involving primarily the bilateral orbicularis oculi. The findings were compared with those from bimanual tapping, which should identify medial frontal areas nonsomatotopically or somatotopically related to bilateral movements. In a group-level analysis, the blinking task was associated with rostral cingulate activity more strongly than the bimanual tapping task. By contrast, the bimanual task activated the caudal cingulate zone plus supplementary motor areas. An individual-level analysis indicated that 2 foci of blinking-specific activity were situated in the cingulate or paracingulate sulcus: one close to the genu of the corpus callosum (anterior part of rostral cingulate zone) and the posterior part of rostral cingulate zone. The present data support the notion that direct cortical innervation of the facial subnuclei from the CMAs might control upper face movement in humans, as previously implied in nonhuman primates. The CMAs may contribute to the sparing of upper facial muscles after a stroke involving the lateral precentral motor regions.     

Timing of muscle activation in a hand movement sequence

Recent studies have described muscle synergies as overlapping, multimuscle groups defined by synchronous covariation in activation intensity. A different approach regards a synergy as a fixed temporal sequence of bursts of activity across groups of motoneurons. To pursue this latter definition, the present study used a principal component (PC) analysis tailored to reveal the across-muscle temporal synergies of human hand movement. Electromyographic (EMG) activity was recorded as subjects used a manual alphabet to spell a list of words. The analysis was applied to the EMG waveforms from 27 letter-to-letter transitions of equal duration. The first PC (of 27) represented the main temporal synergy; after practice, it began to account for more of the EMG variance (up to 40%). This main synergy began with a burst in the 4-finger extensor and a silent period in the flexors. There were then progressively later and shorter bursts in the thumb abductor, thumb flexor, little finger abductor, and finally the finger flexors. The results suggest that hand movements may be generated by activity waves unfolding in time. Because finger muscles are under relatively direct cortical control, this suggests a specific form of cortical pattern generation.     

A neural model of motion processing and visual navigation by cortical area MST

Cells in the dorsal medial superior temporal cortex (MSTd) process optic flow generated by self-motion during visually guided navigation. A neural model shows how interactions between well-known neural mechanisms (log polar cortical magnification, Gaussian motion-sensitive receptive fields, spatial pooling of motion-sensitive signals and subtractive extraretinal eye movement signals) lead to emergent properties that quantitatively simulate neurophysiological data about MSTd cell properties and psychophysical data about human navigation. Model cells match MSTd neuron responses to optic flow stimuli placed in different parts of the visual field, including position invariance, tuning curves, preferred spiral directions, direction reversals, average response curves and preferred locations for stimulus motion centers. The model shows how the preferred motion direction of the most active MSTd cells can explain human judgments of self-motion direction (heading), without using complex heading templates. The model explains when extraretinal eye movement signals are needed for accurate heading perception, and when retinal input is sufficient, and how heading judgments depend on scene layouts and rotation rates.