Biomedical subjects

F Lacquaniti

Publications and source records attributed to F Lacquaniti.

At least 37 records · Page 2Linked to original sources

PubMed1999

Effect of gaze on postural responses to neck proprioceptive and vestibular stimulation in humans.

1. We studied the effect of gaze orientation on postural responses evoked by vibration of neck dorsal muscles or by galvanic stimulation of the vestibular system during quiet standing in healthy humans. Various gaze orientations were obtained by different combinations of horizontal head-on-feet (-90, -45, 0, 45, 90 deg) and eye-in-orbit (-30, 0, 30 deg) positions. The instantaneous centre of foot pressure was recorded with a force platform. 2. With a symmetrical position of the vibrator relative to the spine, neck muscle vibration elicited a body sway in the direction of the head naso-occipital axis when the eyes were aligned with it. The same result was obtained both during head rotations and when the head and trunk were rotated together. 3. For lateral eye deviations, the direction of the body sway was aligned with gaze orientation. The effect of gaze was present both with eyes open and eyes closed. After long-lasting (1 min) lateral fixation of the target the effect of gaze decreased significantly. 4. Postural responses to galvanic vestibular stimulation tended to occur orthogonal to the head naso-occipital axis (towards the anodal ear) but in eight of the 11 subjects the responses were also biased by the direction of gaze. 5. The prominent effect of gaze in reorienting automatic postural reactions indicates that both neck proprioceptive and vestibular stimuli are processed in the context of visual control of posture. The results point out the importance of a viewer-centred frame of reference for processing multisensory information.

Adult↗

PubMed1999

Basal ganglia and gait control: apomorphine administration and internal pallidum stimulation in Parkinson's disease.

Gait coordination was analyzed (four-camera 100 Hz ELITE system) in two groups of idiopathic Parkinson disease (PD) patients. Five patients underwent continuous infusion of apomorphine and were recorded in two different sessions (APO OFF and APO ON) in the same day. Three patients with a previous chronic electrode implantation in both internal globi pallidi (GPi) were recorded in the same experimental session with the electrodes on and off (STIM ON and STIM OFF). The orientation of both the trunk and the lower-limb segments was described with respect to the vertical in the sagittal plane. Lower-limb inter-segmental coordination was evaluated by analyzing the co-variation between thigh, shank, and foot elevation angles by means of orthogonal planar regression. At least 30 gait cycles per experimental condition were processed. We found that the trunk was bent forward in STIM OFF, whereas it was better aligned with the vertical in STIM ON in both PD groups. The legs never fully extended during the gait cycle in STIM OFF, whereas they extended before heel strike in STIM ON. The multisegmental coordination of the lower limb changed almost in parallel with the changes in trunk orientation. In STIM OFF, both the shape and the spatial orientation of the planar gait loops (thigh angle vs. shank angle vs. foot angle) differed from those of physiological locomotion, whereas in STIM ON the gait loop tended to resume features closer to the control. Switching the electrodes on and off in patients with GPi electrodes resulted in quasi-parallel changes of the trunk inclination and of the planar gait loop. The bulk of the data suggest that the basal-ganglia circuitry may be relevant in locomotion by providing an appropriate spatio-temporal framework for the control of posture and movement in a gravity-based body-centered frame of reference. Pallido-thalamic and/or pallido-mesencephalic pathways may influence the timing of the inter-segmental coordination for gait.

Aged↗

PubMed1999

Viewer-centered and body-centered frames of reference in direct visuomotor transformations.

It has been hypothesized that the end-point position of reaching may be specified in an egocentric frame of reference. In most previous studies, however, reaching was toward a memorized target, rather than an actual target. Thus, the role played by sensorimotor transformation could not be disassociated from the role played by storage in short-term memory. In the present study the direct process of sensorimotor transformation was investigated in reaching toward continuously visible targets that need not be stored in memory. A virtual reality system was used to present visual targets in different three-dimensional (3D) locations in two different tasks, one with visual feedback of the hand and arm position (Seen Hand) and the other without such feedback (Unseen Hand). In the Seen Hand task, the axes of maximum variability and of maximum contraction converge toward the mid-point between the eyes. In the Unseen Hand task only the maximum contraction correlates with the sight-line and the axes of maximum variability are not viewer-centered but rotate anti-clockwise around the body and the effector arm during the move from the right to the left workspace. The bulk of findings from these and previous experiments support the hypothesis of a two-stage process, with a gradual transformation from viewer-centered to body-centered and arm-centered coordinates. Retinal, extra-retinal and arm-related signals appear to be progressively combined in superior and inferior parietal areas, giving rise to egocentric representations of the end-point position of reaching.

Adult↗

PubMed1999

Parieto-frontal coding of reaching: an integrated framework.

In the last few years, anatomical and physiological studies have provided new insights into the organization of the parieto-frontal network underlying visually guided arm-reaching movements in at least three domains. (1) Network architecture. It has been shown that the different classes of neurons encoding information relevant to reaching are not confined within individual cortical areas, but are common to different areas, which are generally linked by reciprocal association connections. (2) Representation of information. There is evidence suggesting that reach-related populations of neurons do not encode relevant parameters within pure sensory or motor "reference frames", but rather combine them within hybrid dimensions. (3) Visuomotor transformation. It has been proposed that the computation of motor commands for reaching occurs as a simultaneous recruitment of discrete populations of neurons sharing similar properties in different cortical areas, rather than as a serial process from vision to movement, engaging different areas at different times. The goal of this paper was to link experimental (neurophysiological and neuroanatomical) and computational aspects within an integrated framework to illustrate how different neuronal populations in the parieto-frontal network operate a collective and distributed computation for reaching. In this framework, all dynamic (tuning, combinatorial, computational) properties of units are determined by their location relative to three main functional axes of the network, the visual-to-somatic, position-direction, and sensory-motor axis. The visual-to-somatic axis is defined by gradients of activity symmetrical to the central sulcus and distributed over both frontal and parietal cortices. At least four sets of reach-related signals (retinal, gaze, arm position/movement direction, muscle output) are represented along this axis. This architecture defines informational domains where neurons combine different inputs. The position-direction axis is identified by the regular distribution of information over large populations of neurons processing both positional and directional signals (concerning the arm, gaze, visual stimuli, etc.) Therefore, the activity of gaze- and arm-related neurons can represent virtual three-dimensional (3D) pathways for gaze shifts or hand movement. Virtual 3D pathways are thus defined by a combination of directional and positional information. The sensory-motor axis is defined by neurons displaying different temporal relationships with the different reach-related signals, such as target presentation, preparation for intended arm movement, onset of movements, etc. These properties reflect the computation performed by local networks, which are formed by two types of processing units: matching and condition units. Matching units relate different neural representations of virtual 3D pathways for gaze or hand, and can predict motor commands and their sensory consequences. Depending on the units involved, different matching operations can be learned in the network, resulting in the acquisition of different visuo-motor transformations, such as those underlying reaching to foveated targets, reaching to extrafoveal targets, and visual tracking of hand movement trajectory. Condition units link these matching operations to reinforcement contingencies and therefore can shape the collective neural recruitment along the three axes of the network. This will result in a progressive match of retinal, gaze, arm, and muscle signals suitable for moving the hand toward the target.

Animals↗

PubMed1998

Short-term memory for reaching to visual targets: psychophysical evidence for body-centered reference frames.

Pointing to a remembered visual target involves the transformation of visual information into an appropriate motor output, with a passage through short-term memory storage. In an attempt to identify the reference frames used to represent the target position during the memory period, we measured errors in pointing to remembered three-dimensional (3D) targets. Subjects pointed after a fixed delay to remembered targets distributed within a 22 mm radius volume. Conditions varied in terms of lighting (dim light or total darkness), delay duration (0.5, 5.0, and 8.0 sec), effector hand (left or right), and workspace location. Pointing errors were quantified by 3D constant and variable errors and by a novel measure of local distortion in the mapping from target to endpoint positions. The orientation of variable errors differed significantly between light and dark conditions. Increasing the memory delay in darkness evoked a reorientation of variable errors, whereas in the light, the viewer-centered variability changed only in magnitude. Local distortion measurements revealed an anisotropic contraction of endpoint positions toward an "average" response along an axis that points between the eyes and the effector arm. This local contraction was present in both lighting conditions. The magnitude of the contraction remained constant for the two memory delays in the light but increased significantly for the longer delays in darkness. These data argue for the separate storage of distance and direction information within short-term memory, in a reference frame tied to the eyes and the effector arm.

Anisotropy↗

PubMed1998

Early motor influences on visuomotor transformations for reaching: a positive image of optic ataxia.

Coding of reaching in the cerebral cortex is based on the operation of distributed populations of parietal and frontal neurons, whose main functional characteristics reside in their combinatorial power, i.e., in the capacity for combining different information related to the spatial aspects of reaching. The tangential distribution of reach-related neurons endowed with different functional properties changes gradually in the cortex and defines, in the parieto-frontal network, trends of functional properties. These visual-to-somatic gradients imply the existence of cortical regions of functional overlaps, i.e., of combinatorial domains, where the integration of different reach-related signals occurs. Studies of early coding of reaching in the mesial parietal areas show how somatomotor information, such as that related to arm posture and movement, influences neuronal activity in the very early stages of the visuomotor transformation underlying the composition of the motor command and is not added "downstream" in the frontal cortex. This influence is probably due to re-entrant signals traveling through fronto-parietal-association connections. Together with the gradient architecture of the network and the reciprocity of cortico-cortical connections, this implies that coding of reaching cannot be regarded as a top-down, serial sequence of coordinate transformation, each performed by a given cortical area, but as a recursive process, where different signals are progressively matched and further elaborated locally, due to intrinsic cortical connections. This model of reaching is also supported by psychophysical studies stressing the parallel processing of the different relevant parameters and the "hybrid" nature of the reference frame where they are combined. The theoretical frame presented here can also offer a background for a new interpretation of a well-known visuomotor disorder, due to superior parietal lesions, i.e., optic ataxia. More than a disconnection syndrome, this can now be interpreted as the consequence of the breakdown of the operations occurring in the combinatorial domains of the superior parietal segment of the parieto-frontal network.

Animals↗

PubMed1998

Individual characteristics of human walking mechanics.

Twenty-four subjects walked at different speeds (V) from 0.4 to 2.6 m s-1, while motion and ground reaction forces were recorded in 3-D space. The total mechanical energy of each body segment was computed as the sum of the gravitational potential, translation and rotation kinetic energies. Energy profiles reveal that there are inter-individual differences, particularly at moderate and fast V. In some subjects, the energy excursions are less pronounced, and tend to evolve out of phase at the lower limbs and trunk. As a consequence, there is a better transfer of energy between the trunk and the leg segments, resulting in smaller oscillations of the net energy of the whole body. There is a threefold variation of the rate of increment of lnPu (the mass-specific mean absolute power) with lnV across subjects. We show that this variability cannot be simply explained on the basis of the different biomechanical characteristics of the subjects, but that it depends on the different kinematic strategies. Subjects differ in their ability to minimize energy oscillations of their body segments and to transfer mechanical energy between the trunk and the limbs. Individual characteristics of the mechanical energy expenditure were correlated with the corresponding kinematic characteristics. The changes of the elevation angles of the lower limb segments covary along a plane in all subjects. Plane orientation (quantified by the direction cosine of the normal with the thigh axis, u3t) at any V is not the same in all subjects, but correlates with the net power output: smaller values of u3t tend to be associated with smaller values of Pu, and vice versa.

Adult↗

PubMed1998

Reference frames and internal models for visuo-manual coordination: what can we learn from microgravity experiments?

Gravity plays a role in many different levels of human motor behavior. It dictates the laws of motion of our body and limbs, as well as of the objects in the external world with which we wish to interact. The dynamic interaction of our body with the world is molded within gravity's constraints. The task of catching a ball that has been thrown toward a human subject typifies the kind of constraints that the nervous system must take into consideration during visuo-manual coordination on earth. By dissecting and examining the components of this task, one can see what kinds of problems must be solved by the central nervous system to generate coordinated motor actions in response to incoming sensory information. In this review, we use the example of a ball catching task to outline various issues in the field of human motor control and to ask the question as to how the microgravity environment of lower earth orbit can be used to probe the functioning of the human motor system.

Hand↗

PubMed1998

Virtual reality: a tutorial.

Virtual reality (VR) technology is complex and relies on multidisciplinary knowledge. VR applications are attracting an increasing interest among neuroscientists, in particular in the study of the human brain. Here we present a brief tutorial in which we address aspects of VR methodology that are most relevant to neurophysiology applications. After a brief survey of possible applications to neurophysiology, we discuss the following issues in VR: display technology, visual stimulus presentation techniques, visual spatial resolution and accuracy, devices for real-time interaction with the virtual environment and force-feedback.

Humans↗

PubMed1998

Visuo-motor transformations for arm reaching.

Visuomanual co-ordination requires the merging of ocular and arm information in a common frame of reference. Here we consider behavioural evidence in humans for the use of a viewer-centred frame in the specification of end point positions of reaching. We then review anatomical and neurophysiological data in the non-human primate that indicate a prominent role of the parietal cortex in the process of multisensory fusion that leads to egocentric representations of space. Finally, we discuss the functional anatomy of the human parietal cortex in visuomanual co-ordination as revealed by neuroimaging.

Animals↗

PubMed1998

Kinematic coordination in human gait: relation to mechanical energy cost.

Twenty-four subjects walked at different, freely chosen speeds (V) ranging from 0.4 to 2.6 m s-1, while the motion and the ground reaction forces were recorded in three-dimensional space. We considered the time course of the changes of the angles of elevation of the trunk, pelvis, thigh, shank, and foot in the sagittal plane. These angles specify the orientation of each segment with respect to the vertical and to the direction of forward progression. The changes of the trunk and pelvis angles are of limited amplitude and reflect the dynamics of both right and left lower limbs. The changes of the thigh, shank, and foot elevation are ample, and they are coupled tightly among each other. When these angles are plotted one versus the others, they describe regular loops constrained on a plane. The plane of angular covariation rotates, slightly but systematically, along the long axis of the gait loop with increasing V. The rotation, quantified by the change of the direction cosine of the normal to the plane with the thigh axis (u3t), is related to a progressive phase shift between the foot elevation and the shank elevation with increasing V. As a next step in the analysis, we computed the mass-specific mean absolute power (Pu) to obtain a global estimate of the rate at which mechanical work is performed during the gait cycle. When plotted on logarithmic coordinates, Pu increases linearly with V. The slope of this relationship varies considerably across subjects, spanning a threefold range. We found that, at any given V > 1 m s-1, the value of the plane orientation (u3t) is correlated with the corresponding value of the net mechanical power (Pu). On the average, the progressive rotation of the plane with increasing V is associated with a reduction of the increment of Pu that would occur if u3t remained constant at the value characteristic of low V. The specific orientation of the plane at any given speed is not the same in all subjects, but there is an orderly shift of the plane orientation that correlates with the net power expended by each subject. In general, smaller values of u3t tend to be associated with smaller values of Pu and vice versa. We conclude that the parametric tuning of the plane of angular covariation is a reliable predictor of the mechanical energy expenditure of each subject and could be used by the nervous system for limiting the overall energy expenditure.

Adult↗

PubMed1998

Motor patterns for human gait: backward versus forward locomotion.

Seven healthy subjects walked forward (FW) and backward (BW) at different freely chosen speeds, while their motion, ground reaction forces, and electromyographic (EMG) activity from lower limb muscles were recorded. We considered the time course of the elevation angles of the thigh, shank, and foot segments in the sagittal plane, the anatomic angles of the hip, knee, and ankle joints, the vertical and longitudinal ground reaction forces, and the rectified EMGs. The elevation angles were the most reproducible variables across trials in each walking direction. After normalizing the time course of each variable over the gait cycle duration, the waveforms of all elevation angles in BW gait were essentially time reversed relative to the corresponding waveforms in FW gait. Moreover, the changes of the thigh, shank, and foot elevation covaried along a plane during the whole gait cycle in both FW and BW directions. Cross-correlation analysis revealed that the phase coupling among these elevation angles is maintained with a simple reversal of the delay on the reversal of walking direction. The extent of FW-BW correspondence also was good for the hip angle, but it was smaller for the knee and ankle angles and for the ground reaction forces. The EMG patterns were drastically different in the two movement directions as was the organization of the muscular synergies measured by cross-correlation analysis. Moreover, at any given speed, the mean EMG activity over the gait cycle was generally higher in BW than in FW gait, suggesting a greater level of energy expenditure in the former task. We argue that conservation of kinematic templates across gait reversal at the expense of a complete reorganization of muscle synergies does not arise from biomechanical constraints but may reflect a behavioral goal achieved by the central networks involved in the control of locomotion.

Adult↗

PubMed1997

Visuomotor transformations for reaching to memorized targets: a PET study.

Positron emission tomography (PET) was used to identify cortical and subcortical regions involved in the control of reaching to visual targets. Regional cerebral blood flow (rCBF) was measured in eight healthy subjects using H2(15)O PET during the performance of three different tasks. All tasks required central fixation while a 400-ms target was flashed every 5 s at a random location around a virtual circle centered on the fixation target. Additional instructions differed according to the task: (i) visual detection of the target without overt responses; (ii) immediate pointing to the most recent target in the sequence, and (iii) pointing to the previous target in the sequence. By design, the two motor tasks differed in the cognitive processing required. In each trial of immediate pointing, the spatial location of only the most recent target needed to be processed. In each trial of pointing to the previous, instead, while the most recent target was stored in memory for the movement of the next trial, the previous target had to be retrieved from memory to direct the current movement. Limb trajectories were comparable between the two motor tasks in terms of most spatiotemporal parameters examined. Significant rCBF increases were identified using analysis of covariance and t statistics. Compared with visual detection there was activation of primary sensorimotor cortex, ventrolateral precentral gyrus, inferior frontal gyrus in the opercular region, supramarginal gyrus, and middle occipital gyrus, all these sites in the hemisphere (left) contralateral to the moving limb, and cerebellar vermis, during both immediate pointing and pointing to the previous. During immediate pointing there was additional activation of left inferior parietal lobule close to the intraparietal sulcus, and when compared with pointing to the previous, dorsolateral prefrontal cortex bilaterally. During pointing to the previous, instead, there was additional activation of supplementary motor cortex, anterior and midcingulate, and inferior occipital gyrus in the left hemisphere; superior parietal lobule, supramarginal gyrus, and posterior hippocampus in the right hemisphere; lingual gyri and cerebellar hemispheres bilaterally; anterior thalamus; and pulvinar. The activation of two partially distinct cerebral networks in these two motor tasks reflects the different nature of signal processing involved. In particular, the specific activation of intraparietal sulcus and prefrontal cortex in immediate pointing appears characteristic of a network for visuospatial working memory. By contrast, the corticolimbic network engaged in pointing to the previous could mediate spatial attention and the sequence of encoding, recording, and decoding of spatial memories required by a dual task with two competing targets.

Adult↗

PubMed1997

Visual control of hand-reaching movement: activity in parietal area 7m.

The activity of single neurons was studied in parietal area 7m while monkeys performed an instructed-delay reaching task to visual targets under normal light conditions and in darkness. The task was aimed at assessing the influence of vision of hand position on the neural activity of 7m related either to static posture and movement of the hand or to eye position in the orbit. The results show the existence of preparatory, movement-related and postural activity for the control of reaching, all of which are strongly modulated by vision. The activity of many 7m neurons, otherwise insensitive to pure visual stimuli, seems to reflect complex interactions between gaze angle and hand position in the visual field.

Animals↗

PubMed1997

Combination of hand and gaze signals during reaching: activity in parietal area 7 m of the monkey.

The role of area 7 m has been studied by recording the activity of single neurons of monkeys trained to fixate and reach toward peripheral targets. The target was randomly selected from eight possible locations on a virtual circle, of radius 30 degrees visual angle from a central target. Three tasks were employed to dissociate hand- from eye-related contributions. In the first task, animals looked and reached to the peripheral target. In a second task, the animal reached to the peripheral target while maintaining fixation on the central target. In the third task, the monkey maintained fixation on peripheral targets that were spatially coincident with those of the reaching tasks. The results show that cell activity in area 7 m relates, for some cells to eye position, for others to hand position and movement, and for the majority of cells to a combination of visuomanual and oculomotor information. This area, therefore, seems to perform an early combination of information in the processing leading from target localization to movement generation.

Animals↗

PubMed1997

Viewer-centered frame of reference for pointing to memorized targets in three-dimensional space.

Pointing to a remembered visual target involves the transformation of binocular visual information into an appropriate motor output. Errors generated during pointing tasks may indicate the reference frames used by the CNS for the transformation and storage of the target position. Previous studies have proposed eye-, shoulder-, or hand-centered reference frames for various pointing tasks, depending on visual conditions. We asked subjects to perform pointing movements to remembered three-dimensional targets after a fixed memory delay. Pointing movements were executed under dim lighting conditions, allowing vision of the fingertip against a uniform black background. Subjects performed repeated movements to targets distributed uniformly within a small (radius 25 mm) workspace volume. In separate blocks of trials, subjects pointed to different workspace regions that varied in terms of distance and direction from the head and shoulder. Additional blocks were performed that differed in terms of starting position, effector hand, head rotation, and memory delay duration. Final pointing positions were quantified in terms of the constant and variable errors in three dimensions. The orientation of these errors was examined as a function of workspace location to identify the underlying reference frames. Subjects produced anisotropic patterns of variable error, with greater variability for endpoint distances from the body. The major axes of the variable-error tolerance ellipsoids pointed toward the eyes of the subject, independent of workspace region, effector hand (left or right), initial hand position, and head rotations. Constant errors were less consistent across subjects, but also tended to point toward the head and body. Both overshoots and undershoots of the target position were observed. Increasing the duration of the memory delay period increased the size but did not alter the orientation of the variable-error ellipsoids. Variability of the endpoint positions increased equally in all three Cartesian directions as the memory delay increased from 0.5 to 8.0 s. The anisotropy of variable errors indicates a viewer-centered reference frame for pointing to remembered visual targets with vision of the finger. The anisotropy of pointing variability stems from variability in egocentric binocular cues as opposed to reliance on allocentric visual references or to specific approximations in the sensorimotor transformation. Nevertheless, observed increases in variability with longer memory delays indicate that the short-term storage of the target position does not simply mirror the retinal and ocular sensory signals of the visually acquired target location. Thus spatial memory is carried out in an internal representation that is viewer-centered but that may be isotropic with respect to Cartesian space.

Adult↗

PubMed1997

Posture and movement: coordination and control.

Studies are reviewed that address the problem of the variables controlled in the maintenance of body posture and generation of limb movement. Vestibulospinal and neck reflexes cancel each other in response to roll, but not in response to pitch of the animal. In pitch trunk orientation is not effectively stabilized in space. Instead, limb length and orientation relative to the vertical are accurately controlled in normal cats pitched statically and dynamically by variable angles. Control of limb geometry may even take precedence over the control of the projected centre of mass. Coordinate transformation results in a constraint of planar covariation of the elevation angles at all limb segments in cat posture. Because the same constraint applies also to human locomotion, we suggest that sharing the same laws of intersegmental coordination for the control of posture and locomotion helps to assure the maintenance of dynamic equilibrium during movement. Moreover, because several neural sites encode posture and movement in gravity-based reference frames, alignment in register of spatial information derived from multiple sensors and directed to multiple effectors is made possible.

Animals↗

PubMed1997

A callosal disconnection syndrome of vascular origin.

OBJECTIVE: To study the after-effects of a selective lesion of the corpus callosum on the capacity in transferring spatial information on arm posture derived from kinesthesia and vision. DESIGN: Neuropsychological and psychophysical evaluations of a patient with callosal damage. SETTING: Institute of Neurology, University of "Tor Vergata", Rome, Italy and Research Centre, IRCCS "S. Lucia", Rome, Italy. PATIENT: P.V., a 59 years old man suffering from a vascular lesion of the left half of corpus callosum and left callosal radiations. MEASURES: Sensori-motor and cognitive tasks. Exo- and egocentric pointing abilities tasks. RESULTS: Impairments due to a disconnection between the two cerebral hemispheres were pointed out. About pointing abilities, errors were greater when each hand pointed to the remembered location of the other hand. Errors decreased dramatically with eyes open for right hand pointing to remembered location of left and right hand, and left hand pointing to remembered location of left hand. Open eyes left hand pointing to remembered location of right hand remained as poor as with eyes closed. CONCLUSIONS: The results appear compatible with the following network: visual information from striate and extrastriate cortex is passed forward to parietal cortex bilaterally (even in PV due to the splenium sparing). Kinesthetic information from parietal cortex of left and right hemisphere converge on a single visuokinesthetic center, lateralized to the left hemisphere. Information about limb position in three-dimensional space is then encoded in body-centered coordinates and passed forward to motor and premotor cortex in the frontal lobe. These frontal regions are those disconnected in PV.

Brain Ischemia↗