Biomedical subjects

Carine Michel

Publications and source records attributed to Carine Michel.

3 recordsLinked to original sources

PubMed2006

Simulating unilateral neglect in normals: myth or reality?

Hemispatial neglect is a neurological deficit of perception, attention, representation, and/or performing actions within the left-sided space. The condition also produces many functional debilitating effects on everyday life, and is associated with poor functional recovery and inability to benefit from treatment. Numerous methods of rehabilitation (sensory stimulations or active training) have been proposed to alleviate neglect condition. It has been recently shown that visuo-manual adaptation to rightward optical shift leads to profound and enduring improvements of neglect symptoms. Based on the different methods commonly used in the rehabilitation of neglect, several techniques have been employed to simulate neglect symptoms in healthy subjects with a view to better understand the physiopathology of neglect. The present paper reviews studies of neglect-like behaviour in healthy individuals and in particular the use of prism adaptation as a procedure for simulating various symptoms of clinical neglect in normals. Neglect-like symptoms following prism adaptation offer insights as to the mechanisms of spatial neglect and provide an understanding of the interaction between low level sensorimotor processes and spatial cognition. Implications for the functional mechanisms and the anatomical substrates of prism adaptation are discussed in terms of inter-sensory plasticity and sensorimotor coordination and the way these may affect higher-level representations of space.

Adaptation, Physiological↗

PubMed2003

Simulating unilateral neglect in normals using prism adaptation: implications for theory.

Rightward deviation on line bisection is considered one of the most classic clinical signs of unilateral visual neglect--a cognitive disorder of spatial processing that commonly follows right brain damage. Recently, short-term adaptation to wedge prisms has been shown to significantly reduce neglect on this and other conventional diagnostic tasks. Our previous study has shown that visuomotor adaptation in normals produces a similar pattern of directional bias on a line bisection task. Based on the good working knowledge of how neglect patients perform on different versions of the standard diagnostic task, we showed here that using leftward-deviating prisms in normals, it is possible to produce: (1) a reliable bias on line bisection, (2) a rightward specific deviation, (3) a modulation of rightward deviation, which depends on the relative spatial location of the target lines and (4) a line length effect. A final experiment confirmed that these after-effects are specific to prism adaptation rather than passive prism exposure. Collectively, these findings confirm that adaptation to left-deviating prisms in normals produces a reliable right-sided bias and as shown by a previous visuospatial judgement task, these findings cannot be adequately explained by the symmetric sensori-motor effects of prism adaptation. Taken together with the improvement of spatial neglect shown by right-deviating prisms only, the present study suggests that low level sensori-motor adaptations play a greater role in right hemisphere organisation for spatial cognition than previously thought.

Adaptation, Physiological↗

PubMed2002

After-effects of visuo-manual adaptation to prisms on body posture in normal subjects.

Postural equilibrium is known to be controlled by sensorimotor reflexes and automatic control loops but also depends on high-level body representation in space, probably implicating the right temporoparietal cortex. Indeed, short-term prism adaptation to a 10 degrees rightward visual shift has been shown to reduce predominant postural imbalance in patients with right hemisphere damage, as it did for neglect symptoms. These effects are likely to be explained by a high level effect of prism adaptation on body and space representation, rather than by a sensorimotor effect. Cognitive after-effects of prism adaptation to a leftward visual shift, suggesting neglect-like symptoms, have also recently been shown in normal subjects on line bisection tasks. In the present study, we investigated the effect of wedge prism adaptation on postural control in normal subjects. Two groups of seven healthy subjects were either adapted to a leftward or a rightward visual shift. Results showed that our procedure induced changes in lateral postural control in normal subjects. Furthermore, this lateral postural after-effect was dependent on direction of prism adaptation. Indeed, only adaptation to a leftward visual shift induced significant rightward postural bias in normal subjects. The rightward postural lateral displacement was negatively correlated with the visual vertical. Both transfer and direction specific effect of visuo-manual adaptation to prisms on postural control suggest that effects of adaptation act more on high-level postural control linked to body representation in space or at least reveal close interaction between sensorimotor plasticity and body representation.

Adolescent↗