MR-Eyetracker: a new method for eye movement recording in functional magnetic resonance imaging

We present a method for recording saccadic and pursuit eye movements in the magnetic resonance tomograph designed for visual functional magnetic resonance imaging (fMRI) experiments. To reliably classify brain areas as pursuit or saccade related it is important to carefully measure the actual eye movements. For this purpose, infrared light, created outside the scanner by light-emitting diodes (LEDs), is guided via optic fibers into the head coil and onto the eye of the subject. Two additional fiber optical cables pick up the light reflected by the iris. The illuminating and detecting cables are mounted in a plastic eyepiece that is manually lowered to the level of the eye. By means of differential amplification, we obtain a signal that covaries with the horizontal position of the eye. Calibration of eye position within the scanner yields an estimate of eye position with a resolution of 0.2° at a sampling rate of 1000 Hz. Experiments are presented that employ echoplanar imaging with 12 image planes through visual, parietal and frontal cortex while subjects performed saccadic and pursuit eye movements. The distribution of BOLD (blood oxygen level dependent) responses is shown to depend on the type of eye movement performed. Our method yields high temporal and spatial resolution of the horizontal component of eye movements during fMRI scanning. Since the signal is purely optical, there is no interaction between the eye movement signals and the echoplanar images. This reasonably priced eye tracker can be used to control eye position and monitor eye movements during fMRI

Role of proprioception and vision in handwriting

The objective of this study is to better understand the role of proprioception in handwriting and test earlier conclusions stating that the automated shaping of letters was not impaired by the removal of visual control in deafferentation. To this aim we compared the performance of the deafferented patient GL, who suffers from a complete loss of cutaneous and proprioceptive sensation, with that of eight healthy age- and sex-matched subjects. The word “Parallele”, written within a short sentence with and without visual control, was quantified using a digital writing tablet. Three of the 13 analyzed parameters were strikingly different in patient GL compared to healthy subjects, both with and without vision: increase of number of pen touches, increase in number of inversions in velocity, and decrease of mean stroke frequency. The changes in these three parameters indicate a strong impairment in automated behaviour in the absence of proprioception and touch. This impairment is also supported by the significantly longer movement duration, which is also significantly increased by the removal of visual control. The present study provides for the first time a quantification of handwriting in a completely deafferented patient and reveals the central role of proprioception for the storage, updating, and maintenance of skilled motor programs. The fact that the deficits are already present with visual feedback suggests that the role of vision in handwriting is only secondary

Improved sensorimotor performance via stochastic resonance

Several studies about noise-enhanced balance control in humans support the hypothesis that stochastic resonance can enhance the detection and transmission in sensorimotor system during a motor task. The purpose of the present study was to extend these findings in a simpler and controlled task. We explored whether a particular level of a mechanical Gaussian noise (0–15 Hz) applied on the index finger can improve the performance during compensation for a static force generated by a manipulandum. The finger position was displayed on a monitor as a small white point in the center of a gray circle. We considered a good performance when the subjects exhibited a low deviation from the center of this circle and when the performance had less variation over time. Several levels of mechanical noise were applied on the manipulandum. We compared the performance between zero noise (ZN), optimal noise (ON), and high noise (HN). In all subjects (8 of 8) the data disclosed an inverted U-like graph between the inverse of the mean variation in position and the input noise level. In other words, the mean variation was significantly smaller during ON than during ZN or HN. The findings suggest that the application of a tactile-proprioceptive noise can improve the stability in sensorimotor performance via stochastic resonance. Possible explanations for this improvement in motor precision are an increase of the peripheral receptors sensitivity and of the internal stochastic resonance, causing a better sensorimotor integration and an increase in corticomuscular synchronization