Dominique Chapuis

Multisensory Mechanisms in Temporo-Parietal Cortex Support Self-Location and First-Person Perspective

Self-consciousness has mostly been approached by philosophical enquiry and not by empirical neuroscientific study, leading to an overabundance of diverging theories and an absence of data-driven theories. Using robotic technology, we achieved specific bodily conflicts and induced predictable changes in a fundamental aspect of self-consciousness by altering where healthy subjects experienced themselves to be (self-location). Functional magnetic resonance imaging revealed that temporo-parietal junction (TPJ) activity reflected experimental changes in self-location that also depended on the first-person perspective due to visuo-tactile and visuo-vestibular conflicts. Moreover, in a large lesion analysis study of neurological patients with a well-defined state of abnormal self-location, brain damage was also localized at TPJ, providing causal evidence that TPJ encodes self-location. Our findings reveal that multisensory integration at the TPJ reflects one of the most fundamental subjective feelings of humans: the feeling of being an entity localized at a position in space and perceiving the world from this position and perspective.

Design of a simple MRI/fMRI compatible force/torque sensor

Force/torque sensors compatible with magnetic resonance imaging (MRI) are required to develop haptic interfaces for neuroscientific investigations and robotic tools for interventional MRI. In this paper, we analyze the mechanical structure of classical and MRI compatible sensors from literature and demonstrate the critical role of the mechanical design on the sensing performance. A simple and efficient torque sensor based on light intensity measurement over optical fibers is introduced, which allows to place the electronic components outside the scanner room. By using a self-guiding flexible structure and optimal mirror placement, the sensitivity to transverse torque is reduced to 0.03% of the desired output torque.

Sensors for Applications in Magnetic Resonance Environments

This paper analyzes sensing methods compatible with magnetic resonance imaging (MRI) and functional MRI (fMRI) reported in the literature, and presents the three generations of MR-compatible force/torque sensors we have developed for robotic systems to interact with human motion. Conventional sensors such as camera-based measurement systems, strain gauges or commercial force/torque sensors, and optical encoders may be used, if placed sufficiently away from the imaging region and equipped with adequate shielding and filtering in order to minimize electromagnetic interference caused by electric cables, the transducer, and electronics of surrounding equipment. However, electromagnetic interference can be avoided by using light transmission over optical fibers, in which case sensitive and noisy electronic components can be placed outside the MR room, and the MR compatibility issue is restricted to the used materials. Good performance can be obtained with sensing elements made from materials adapted to the location of use, combined with reflected or differential light intensity measurement over optical fibers. We have developed various force and position sensors based on this principle, ranging from MR Safe (for a definition and discussion of the terms MR Safe and MR Conditional, see Gassert , IEEE Eng. Med. Biol. Mag., pp. 12--14, May/Jun. 2008) milled polymer probes to MR Conditional assemblies combining beryllium copper blades with a polymer body, as well as smaller aluminum probes realized through a combination of milling and electric discharge machining. It appears that, in contrast to actuators, good performance is not in tradeoff with MR compatibility.

A 2-DOF fMRI compatible haptic interface to investigate the neural control of arm movements

This paper describes a two-degrees-of-freedom haptic interface to investigate the brain mechanisms of human motor control, which is capable of safely and gently interacting with human arm motion during functional magnetic resonance imaging (fMRI). A hydrostatic transmission separates the interface into a master and an MR compatible slave system, allowing the placement of all interfering components outside the electromagnetic shield of the MR room. The transmission mirrors force and motion of the master actuators on the slave system placed close to the MR scanner. The parallel architecture takes advantage of the linear MR compatible actuators and allows human subjects to perform reaching movements comfortably in the small workspace limited by the dimensions of the MR scanner and the biomechanics of the arm. The kinematic structure of the slave interface was optimized with respect to the available space and types of movements to be investigated. Materials were chosen based on their MR compatibility, their stiffness and weight. The interaction force with the subject is measured over two optical force sensors, located close to the output of the interface. Two shielded optoelectronic encoders measure the extension of the slave hydraulic pistons. Detailed tests demonstrated the fMRI compatibility even during movement of the interface

fMRI compatible haptic interface actuated with traveling wave ultrasonic motor

We are developing haptic interfaces compatible with functional magnetic resonance imaging (fMRI) for neuroscience studies. The presented prototype with one rotary degree of freedom is actuated by a traveling wave ultrasonic motor operating under admittance control. Torque is sensed from the deflection of an elastic polymer probe via light intensity measurement over optical fibers. This concept allows us to place all electronic components outside the shielded MR room. Hence, the device can be used in conjunction with fMRI, providing torque and motion feedback simultaneously with imaging. Its compactness and simplicity facilitate the construction of multiple degree of freedom systems.

Sensing Glove for Brain Studies: Design and Assessment of Its Compatibility for fMRI With a Robust Test

In this paper, we describe a biomimetic-fabric-based sensing glove that can be used to monitor hand posture and gesture. Our device is made of a distributed sensor network of piezoresistive conductive elastomers integrated into an elastic fabric. This solution does not affect natural movement and hand gestures, and can be worn for a long time with no discomfort. The glove could be fruitfully employed in behavioral and functional studies with functional MRI (fMRI) during specific tactile or motor tasks. To assess MR compatibility of the system, a statistical test on phantoms is introduced. This test can also be used for testing the compatibility of mechatronic devices designed to produce different stimuli inside the MR environment. We propose a statistical test to evaluate changes in SNR and time-domain standard deviations between image sequences acquired under different experimental conditions. fMRI experiments on subjects wearing the glove are reported. The reproducibility of fMRI results obtained with and without the glove was estimated. A good similarity between the activated regions was found in the two conditions.

A Haptic Knob for Rehabilitation of Stroke Patients

The strong impairment of motor functions in stroke survivors affects daily activities such as eating, manipulating objects or writing. Our goal is to induce long lasting improvements in such tasks by having patients perform systematic exercises using haptic interfaces. This paper describes a novel two-degrees-of-freedom interface which we have developed to help stroke patients gradually recover the ability to open and close the hand and manipulate knobs. Different solutions are studied and a design consisting of two parallelogram structures interacting with the fingers is proposed. The mechanical design offers the possibility to adapt the interface to various hand sizes and finger orientations, and to right or left-handed subjects. Design kinematics as well as actuation and system control are described. Several knobs are proposed to interact with patients, especially a cone mechanism to train a complete opening movement from a strongly contracted and closed hand to a large opened position. The interaction force with the subject is measured over four force sensors located close to the output of the interface. A preliminary study has been performed to evaluate the performances of the haptic interface

Investigation of a Cable Transmission for the Actuation of MR Compatible Haptic Interfaces

This paper investigates a cable transmission to remotely actuate MR compatible robots over a distance of several meters. Such a transmission could be an interesting solution for haptic interfaces for neuroscience studies performing force feedback during functional magnetic resonance imaging (fMRI), as well as for robots for interventional MRI. MR compatible components, transmission length and bandwidth as well as cable properties are discussed. Experiments performed on an MR compatible test bench allowing variable transmission length up to 9 meters show a mechanical bandwidth of over 30 Hz. Transmission performances and flexibility are compared with those of a hydrostatic transmission

Supplementary motor area and anterior intraparietal area integrate fine-graded timing and force control during precision grip.

We investigated the neuronal processing of the physiologically particularly important precision grip (opposition of index finger and thumb) by the combination of functional magnetic resonance imaging (fMRI) and an MR‐compatible haptic interface. Ten healthy subjects performed isometric precision grip force generation with visual task instruction and real‐time visual feedback in a block design. In a 2 × 2 two‐factorial design, both the timing and force could be either constant or varying (identical average timing and force). As we expected only small changes in the fMRI response for the different fine‐graded motor control conditions, we maximized the sensitivity of the data analysis and implemented a volumes of interest (VOI) restricted general linear model analysis including non‐explanatory force regressors to eliminate directly force‐related low‐level activations. The VOIs were defined based on previous studies. We found significant associations: timing variation (variable vs. constant) and primary motor area (M1) and dorsal premotor area (PMd); force variation (variable vs. constant) and primary somatosensory area (S1), anterior intraparietal area (AIP) and PMd; interaction of timing and force and supplementary motor area (SMA) and AIP. We conclude that SMA and AIP integrate fine‐graded higher‐level timing and force control during precision grip. M1, S1 and PMd process lower‐level timing and force control, yet not their integration. These results are the basis for a detailed assessment of manual motor control in a variety of motor diseases. The detailed behavioural assessment by our MR‐compatible haptic interface is particularly valuable in patients due to expected larger inter‐individual variation in motor performance.

A Haptic Knob with a Hybrid Ultrasonic Motor and Powder Clutch Actuator

In haptics, the forces to be displayed vary widely in terms of magnitude and bandwidth. A single actuator can hardly comply with these requirements. It has thus been proposed to combine electrical motors and passive devices in a hybrid actuator to cover a larger range of display able forces. In this paper, different hybrid actuators are reviewed and a novel hybrid USM/clutch actuator is presented. It has been developed for haptic applications and its principle is adaptable to MR compatible robots. The complementary dynamic properties of the USM, which is a velocity source, and a torque controlled clutch, lead to a simple mechanism offering more control modes and lower power consumption than previous hybrid actuators. A haptic knob is designed and realized to test this approach. It includes a differential gear that allows the powder brake to mimic the behavior of a clutch. Haptic effects such as springs or walls have been implemented and successfully tested on the prototype