SENSORIMOTOR PLASTICITY AND COGNITION: prism adaptation can affect various levels of space representation
COMMUNICATION
TOPIC:
REHABILITATION
COMMUNICATION
TOPIC:
REHABILITATION
Authors:
Yves Rossettia**, Gilles Rodea**, Laure Pisella*, Alessandro Farné*, Ling
Li**, Dominique Boissona***Institut National de la Santé Et de la Recherche Médicale, Unité 94:
ESPACE ET ACTION, 16 avenue Lépine, Case 13, 69676 Bron - France
**Service de Rééducation Neurologique, Hospices Civils de Lyon and
Université Claude Bernard, Lyon- France
fax: (33) 472 91 34 01
E-mail: rossetti@lyon151.inserm.fr
The improvement of hemispatial neglect described in the present reportsuggests that virtually all levels of space representations can be affectedby a simple sensori-motor adaptation procedure, and that, despite theirfrequent dissociations (Rossetti 1998), sensori-motor and higher-levelspatial functions share a common level of space representation that islinked to multisensory integration.REFERENCESPrism adaptation
Exposure to an optical alteration of the visual field is known to producean initial disorganisation of visuo-motor behaviour, which can be correctedthrough visuo-motor adaptation. Such adaptation has been used widely todemonstrate the plasticity of coordinate transformations involved inmultisensory and sensori-motor integration (e.g. Rossetti et al. 1993). Onemajor compensative effect of short-term wedge-prism exposure is a shift ofproprioceptive representations, which can be demonstrated by requiringsubjects to point straight-ahead in the dark (e.g. Redding and Wallace1995, 1996). After adaptation, this finger straight-ahead demonstration isshifted in a direction opposite to the optical deviation, indicating thatinternal visual and proprioceptive 'maps' have been realigned. The aim ofour study was to investigate the effect of prism adaptation on variousneglect symptoms, including the manual demonstration of the subjectivemidline.Hemispatial neglect
A large proportion of right-hemisphere stroke patients show hemispatialneglect - a neurological deficit of perception, representation, and/orperforming actions within their left-sided space. The frequent parietallocus of the lesion producing neglect reflects the impairment of coordinatetransformation used by the nervous system to represent extrapersonal space.Given that prism adaptation can be considered as a way to stimulate neuralstructures responsible for the transformation of sensorimotor coordinates,the aim of our study was to investigate the effect of prism adaptation onvarious neglect symptoms, including the pathological shift of thesubjective midline to the right.Prism adaptation and hemispatial neglect
Sixteen right brain-damaged patients with a persistent, left hemispatialneglect participated in experiment 1 and 2 (Rossetti et al. 1998). All hadbeen admitted to a neurological rehabilitation hospital for a moderate tosevere hemiplegia and various degrees of somatosensory dysfunction. Allpatients were right-handed and had a documented, single unilateralhemispheric lesion, and no past history of previous stroke. None of thepatients suffered from impaired vigilance, confusion, general mentaldeterioration or psychiatric disorders. Testing took place between 3 weeksand 14 months post-onset.Experiment 1 was aimed at measuring the adaptability of neglect patientsto a lateral shift of the visual field. Manual body-midline demonstrationwas used to evaluate adaptation to base-left wedge prisms (inducing a 10°shift of the visual field to the right) by a simple target-pointing task. Agroup of eight neglect patients and a group of five control subjectsproduced 10 straight-ahead pointing trials before and after a short periodof adaptation. The patient's mean straight-ahead was initially shifted tothe right. Following the adaptation, straight-ahead were shifted to theleft in both groups, and thus the patient's pathological deviation wasgreatly improved. This first result demonstrated that neglect patients caneasily adapt to a lateral shift of the visual field to the right.
A second experiment investigated whether prism adaptation could alsoimprove the main clinical manifestations of neglect. Twelve neglectpatients were randomly assigned to the prism group and the control group.All patients underwent a similar procedure. A series of traditionalneuropsychological tests (Halligan and Marshall 1989) was performed onthree sessions. After the first session (Pre-test), patients had to performthe elementary pointing task with the prismatic goggles used in experiment1, in order to adapt to the visual-proprioceptive discrepancy. Patients inthe Prism group were exposed to the optical deviation to the right.Patients in the Control group wore neutral goggles with thick flat glasses.Immediately after removing the goggles, a second session was performed withthe same battery of tests (Post-test). Patients were again tested after adelay of about two hours following the goggle exposure (Late-test). Thestandard neuropsychological procedure included: line bisection, linecancellation, copying a simple drawing, drawing of a daisy from memory, andreading a simple text.
Figure 1: Copying test.All patients in the Prism group exhibited a clear improvement followingprism exposure. A dramatic improvement was observed for all tests followingprism exposure and was fully maintained two hours later. By contrast, therewas no significant improvement in the Control group. Figure 2 shows resultsobtained for the copying test (Gainotti, 1972) by one representativepatient of each group.
Figure 2: Mental representation. More recent experiments have focused on the exploration of other levels ofspace representation, ranging from postural control and wheel-chair drivingto mental representations of space. Our preliminary results suggest thatvarious other levels of space representation can be altered by prismadaptation in patients. Figure 3 shows the effect of adaptation on mentalrepresentation of a geographic space. The patient was asked to mentallyvisualise the map of France, and was then given 2 minutes to name as manytowns of France as possible. A clear neglect of the western part of the mapwas initally observed (see Rode and Perenin 1994), and the map was moreextensively explored after adaptation.
Acknowledgements:This work was supported by Région Rhône-Alpes and ELyPsEs.
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Redding, G.M., & Wallace, B. (1995). Contributions of motor control andspatial alignment to prism adaptation. In Bardy, Bootsma, & Guiard (Eds.),Studies in Perception and Action. (pp. 277-280). Mahwah, NJ: LawrenceErlbaum Associates.
Redding, G.M., & Wallace, B. (1996). Adaptive spatial alignment andstrategic perceptual-motor control. J Exp Psychol Hum Percept Perform,22(2), 379-394.
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Rossetti, Y., Rode, G., Pisella, L., Farnè, A., Li, L., Boisson, D. &Perenin M-T.(1998) Prism adaptation to a rightward optical deviationrehabilitates left hemispatial neglect. Nature, 98, 395, 166-169.
