PARTIAL REMISSION OF HEMIPLEGIA AND SOMATOPARAPHRENIA THROUGH VESTIBULAR STIMULATION IN A CASE OF UNILATERAL NEGLECT G. Rodet, N. Charles 1, M.-T. Perenin1 , A. Vighetto 1, M. Trillet 1 and G. Aimard 1 eclinique Universitaire de Neurologie, H8pital Neurologique, Lyon; 2Vision et Motricite, INSERM U94, Bron, France)
INTRODUCTION
Recent studies have shown that vestibular stimulation may produce a tem porary remission of unilateral neglect phenomena. Improvement concerns not only extrapersonal and personal neglect, but also representational neglect (as when a mental representation is required to describe from memory a given pla ce) and anosognosia (Rubens, 1985; Cappa et al., 1987, Vallar et al., 1990, Rode and Perenin, 1990). Even more striking, somatoparaphrenic delusions may also disappear under vestibular stimulation, as observed recently in one patient (Bis iach et al., 1991). The fact that a sensory manipulation acts on these different aspects of the neglect syndrome has important implications. First, it argues for a unitary conception of the syndrome, even if its manifestations may be disso ciated; second, it opens the way to neurophysiological explanations, whatever psychological theory, attentional or representational, is adopted (reviewed in Jeannerod, 1987). . Unilateral neglect is frequently associated with neurological sensory and motor deficits. In fact, Vallar et al. (1990) have shown that at least part of the somato-sensory deficits may be a manifestation of the neglect syndrome, as they decrease substantially under vestibular stimulation. However, in their three pa tients, the severe motor deficit remained unaffected by the stimulation. In the present note, we report on a case of long lasting neglect, in which the vestibular stimulation produced a temporary reduction of the motor deficit and also disappearance of the somatoparaphrenic delusion, in addition to the pre viously reported improvement of extrapersonal and personal neglect and ano sognosia. CASE REPORT
TS, a 69-year-old woman, sustained a right-hemisphere stroke on January 15th, 1990 and was admitted to an emergency department. She was referred to us 6 months later for per sistence of a complete hemiplegia and delusions concerning her left hemibody. The CT-scan, performed 2 months post-onset, showed a large cortico-subcortical hypodensity in the ter ritory of the middle cerebral artery including the parieto-temporo-occipital carrefour. On neurological examination, the motor deficit was shown to be still complete on both upper and lower limbs, as well as the left hemianesthesia. There was an apparently total left hemianopia on confrontation. Head and gaze were permanently deviated to the right and Cortex, (1992) 28, 203-208
204
G. Rode and Others
could never cross the midline in response to verbal command or during visual pursuit. The patient showed a severe extrapersonal and personal neglect. She failed to orient toward au ditory and visual stimuli produced on her left hemispace and when asked to count people or objects she omitted those located on the left. On a line-crossing test (Albert, 1973), only lines of the rightmost column were crossed. Left-sided omissions were also noted in copying drawings and in reading isolated words. When required to touch her left hand with the right, she did not even start any movement (score= 3, according to the four-point scale of Bisiach et al., 1986, for personal neglect). The patient was quite alert and well oriented in time and space. She had no problem for recognizing people from the hospital staff and her intellectual status, although not scaled, appeared normal on informal questioning. But strikingly, she could not stop talking when somebody was next to her. This logorrhea with delusional speech (see below) had remained unchanged for 6 months as well as the complete anosognosia (score= 3 for both the motor and visual deficits, according to the four-point scale of Bisiach et al., 1986). In addition to denying hemiplegia, the patient claimed that she was able to walk without any problem and did not understand why she was in a hospital. She even accused her husband for having brought her there and asked over and over to go home. Finally, she repeatedly affirmed that her left upper limb was not hers but the examiner's. When the latter (GR) brought the patient's left arm in her good visual field and asked whose it was, she answered: "It's not mine. I found it in the bathroom, when I fell. It's not mine because it's too heavy; it should be yours. It can move and do everything; when I feel it too heavy, I put it on my stomach. It does'nt hurt me, it's kind". When asked where her own arm was, she answered: "Behind the door". On the dichotic test, there was a total left ear extinction. METHODS
The vestibular stimulation was performed by using a cold left ear caloric stimulation. The external ear canal was irrigated with 60 cc of cold (20 oq water for 1 min. During stimula tion the room illumination was decreased; the patient laid down in her bed and her head was tilted approximatively 30° forward. This vestibular activation produced a clear horizontal nystagmus with a leftward slow phase of about 3 min duration. Two identical caloric stimulations were performed at 48 hours interval. Different aspects of neglect were assessed immediately after each stimulation: extrapersonal and personal neg lect, anosognosia and somatoparaphrenia on the first time, extrapersonal neglect and hem iplegia on the second time. The patient was also tested during the interval between the 2 sti mulations and during the 2 days following the second one. Further explorations could not be done, as the patient left the hospital to go back to Spain one week following her admission. RESULTS
First Stimulation Extrapersonal neglect: head and gaze deviation were reduced from 45° to 20° to the right. On verbal request, the patient was able to move her head and to orient her gaze to the left from the midline. In most cases she was then able to detect visual or auditory stimuli produced on her left. Personal neglect: the })ll:tient was able to reach her left hand with her right without hesitation (score~ 0). Anosognosia and soniatoparaphrenia: the patient was totally aware of her hemiplegia. When asked if she could move her arm, she answered: "No" (sco re= 0) and when asked why, she said: "Because I have suffered from a hemi plegia". When asked when and where this appeared, she answered: "In Janu
Vestibular stimulation and neglect syndrome
205
ary, I was in my bathroom and I fell. I called my niece and I was taken to the hospital". When the examiner brought her left arm in her good field, she re cognized it as hers and no longer claimed it was the examiner's. Strikingly, the logorrhea also disappeared immediately after stimulation.
Second Stimulation Extrapersonal neglect: this was assessed this time through the line-crossing test. Although the patient still omitted a few lines and showed a marked trend to repeatedly cross some of the same lines, the pattern of line-crossing was very similar on the two halves of the sheet, thus indicating a marked improvement in the visual explorationn of the left side of space. Hemiplegia: the patient did not move her left limbs spontaneously. But when asked to, she was able to flex and stretch her left leg. The effect did not extend to the upper limb which remained motionless. On a rapid examination, left hemianesthesia and hemianopia remained un changed. Although the stimulations produced some local discomfort, due to irriga tion of the ear with cold water, neither of them caused any sensation of self-dis placement or displacement of the environment. Neither was there any vegeta tive sign, like nausea.
Delayed Post-stimulation State Although this could not be assessed in a formal way for every item men tioned above, the following observations were made. In the interval between the two stimulations and on the day following the second one, the patient again showed a marked deviation of head and gaze to the right and did not orient when called from her left. Anosognosia remained less severe, as she admitted that "she could not walk like everybody"; she added: "Why? I don't know, it could be because I have one leg longer than the other, it's the thing that has to be reeducated". But later, when asked if she could walk, she answered: "If you give me my shoes, you will see how well I can walk". The logorrhea remained attenuated, but the patient again produced delu sional speech concerning her left upper limb. When shown it by the examiner, she did not recognize her arm as hers. She did not know whose arm it was but said that hers was behind the door. The leg motor improvement was no longer manifest, even after verbal en couragement repeated on three successive days. DISCUSSION
Our study has confirmed previous findings on the reversibility of neglect and some of associated disorders through vestibular stimulation (Rubens, 1985; · Cappa et al., 1987; Vallar et al., 1990). In addition, it has shown that the tem porary remission of symptoms is not only possible a few days post-onset as in the previous studies, but may also be obtained much later, as in our case of long
206
G. Rode and Others
lasting neglect and anosognosia. This provides an additional argument to eli minate an aspecific effect of the vestibular stimulation on hypoarousal or con fusion phenomena, as these are no longer present in the later condition. A new and striking finding is the temporary remission of the motor deficit. Before stimulation the patient was considered to be totally hemiplegic. The transient improvement of lower limb motor capacities under vestibular activa tion argues for a motor neglect component in the motor deficit. This result seems very similar to that reported by Vallar et al. (1990) on the temporary re mission of the somato-sensory deficits in neglect patients. If confirmed, the motor neglect component may provide an explanation of the poor motor re covery of left compared to right hemiplegia (Held et al., 1975), especially in cases with associated left hemineglect (Denes et al., 1982). It might also open new perspectives in the rehabilitation of left hemiplegia. Another interesting finding lies in the temporary remission of our patient's delusions concerning her left hemibody. This kind of disorder, called "soma toparaphrenia" by Gertsmann (1942), is most often seen during the acute phase of right hemisphere strokes. In the present case it has taken an exceptionally long lasting form and one may wonder if its regression through caloric stimu lation had not coincided with, or had favored a spontaneous evolution. Al though this was tested only once, the fact that the delusions reappeared a few hours following stimulation rules out such an hypothesis. Thus we have con firmed the recent result by Bisiach et al. (1991) showing in one neglect patient a temporary remission of somatoparaphrenia consistently observed on four ca loric tests. When considering previous results from the literature as well as the present ones, it appears that vestibular activation not only improves the neglect phen omena but also affects a series of disorders often associated to it, even in the same patient, as illustrated in our study. This reinforces the view, recently ar gued by Bisiach and Berti (1987), of a unitary syndrome whose multiple mani festations, although often dissociated, would rely on a common basic disturb ance. The authors have done justice to a largely omitted work by Zingerle at the beginning of this century, whose merit has been both to coin the appropriate term of "dyschiria" to designate this multiform syndrome and to propose the still up-to-date interpretation of a disordered awareness or representation of one side (of the body and/or extracorporeal space). The fact that neglect and related symptoms can be amended through a sen sory manipulation such as vestibular stimulation opens the way to neurophy siological explanations of these symptoms, including false beliefs on the left hemibody. In humans, most cases of neglect are related to a lesion including the right posterior parierallobe and carrefour (Vallar and Perani, 1986); moreover the complete syndrome with anosogriosia and delusions appears to require a le sion in this area (De Renzi, 1982; Kinsbourne, 1987), which is thus seen as crit ically involved in the representation of both corporeal and extracorporeal ego centric space. Accordingly, patients with posterior parietal lesions show an ips ilesional shift of their egocentric reference (i.e. midsagittal plane representa tion), which is significantly larger than in patients with other cortical lesions (Perenin et al., in preparation). Interestingly, the parietal lobe is also the site of
Vestibular stimulation and neglect syndrome
207
vestibular projections as shown by a regional blood-flow study (Friberg et al., 1985) as well as by an early PET-scan work (Tuohimaa et al., 1983): both have disclosed a cortical activation in the temporo-parietal region in response to a unilateral vestibular stimulation, although they do not allow a definitive con clusion about the more activated side. In our opinion, this vestibular input takes part, as do other (mainly sensory) types of inputs, in building up and updating the representation of egocentric space. This might account for the shift of the egocentric reference observed in normal people following vestibular stimula tion as well as the shift reversal of this reference produced in neglect patients after the same stimulation (Rode, 1990). However, this only represents a small step in understanding the neural mechanisms by which vestibular stimulation improves the neglect syndrome and restores awareness and correct representa tion of the left hemibody and surrounding space. As animal work concerning the functional relationships between the vestibular nuclei and the parietal cor tex are still at a preliminary stage, further hypotheses are speculative. For rea sons already developed by Cappa et al. (1987) the vestibular stimulation in neg lect patients will more likely activate the left intact hemisphere than the right damaged one. In fact this might reinforce the vestibular imbalance previously shown following posterior parietal lesions in the monkey and which appears to oppose the ipsilesional orientation bias (Ventre and Faugier-Grimaud, 1986). Further neurophysiological work in the monkey as well as metabolic studies in humans will bring a better understanding of the effect of vestibular activation on neglect as well as of the organization of the parietal lobe, which must har bour multiple functional modules involved in space representation. ABSTRACT
In a case of long lasting severe neglect resulting from a large right parieto-temporo-oc cipital infarct, vestibular stimulation produced a temporary reduction of the motor deficit and disappearance of the somatoparaphrenic delusion, in addition to the already reported improvement of extrapersonal and personal neglect and anosognosia. These data open new perspectives in the understanding of the neglect syndrome and of functional involvement of the parietal lobe in space representation.
Acknowledgements. We are particularly grateful to Edoardo Bisiach for his valuable comments on this paper. We also thank Jerry Nelson who kindly revised the manuscript. REFERENCES ALBERT, M.L. A simple test of visual neglect. Neurology, 23: 658-654, 1990. BISIACH, E., and BERTI, A. Dyschiria. An attempt at its systemic explanation. In M. Jeannerod (Ed.), Neurophysiological and Neuropsychological Aspects of Spatial Neglect. Amsterdam: North Hol land, 1987, pp. 183-201. BISIACH, E., PERANI, D., VALLAR, G., and BERTI, A. Unilateral neglect: personal and extrapersonal. Neuropsychologia, 24: 759-767, 1986. BISIACH, E., RuscoNI, M.L., and VALLAR, G. Remission of somatoparaphrenic delusion through vesti bular stimulation. Neuropsychologia, 29: 1029-1031, 1991. CAPPA, S., STERZI, R., VALLAR, G., and BISIACH, E. Remission of hemineglect and anosognosia during vestibular stimulation. Neuropsychologia, 25: 775-782, 1987. DENES, G., SEMENZA, C., STOPPA, E., and Lis, A. Unilateral spatial neglect and recovery from hemiple
208
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gia. A follow-up study. Brain, 105: 543-552, 1982. DE RENZI, E. Disorders ofSpace Exploration and Cognition. Chicester: Wiley, 1982. FRIBERG, L., OLSEN, T.S., RoLAND, P.E., PAULSON, O.B., and LASSEN, N.A. Focal increase ofblciod flow in the cerebral cortex of man during vestibular stimulation. Brain, 108: 609-623, 1985. GERTSMANN, J. Problem of imperception of disease and of impaired body territories with organic lesions. Relation to body scheme and its disorders. Archives ofNeurology and Psychiatry, 48: 890-913, 1942. HELD, J.P., PIERROT-DESSELLIONY, E., BuSSEL, B., PERRIGOT, M., and MALlER, M. Devenir des hemi p!egies vasculaires par atteinte sylvienne en fonction du ci>te de Ia lesion. Annates de Medecine Phy sique, 18: 592-604, 1975. JEANNEROD, M. Neurophysiological and Neuropsychological Aspects of Spatial Neglect. Amsterdam: North-Holland, 1987. KINSBOURNE, M. Mechanisms of unilateral neglect. In M. Jeannerod (Ed.), Neurophysiological and Neu ropsychological Aspects ofSpatial Neglect. Amsterdam: North-Holland, 1987, pp. 69-86. RODE, G. Referentiel egocentrique et negligence unilaterale. Influence de Ia stimulation vestibulaire ca lorique et applications therapeutiques. Medical thesis, Universite Claude Bernard, Lyon, 1990. RODE, G., and PERENIN, M.-T. Caloric stimulation and representational hemineglect. Poster presented at the symposium "Consciouness and Cognition: Neuropsychological Perspectives", St. Andrews, 1990. RuBENS, A.B. Caloric stimulation and unilateral visual neglect. Neurology, 35: 1019-1024, 1985. TuOHIMAA, P., AANTAA, E., TOUKONIITTY, K., and MAKELA, P. Studies of vestibular cortical areas with short-living "02 isotopes. O.R.L., 45: 315-321, 1983. VALLAR, G., and PERANI, D. The anatomy of unilateral neglect after right-hemisphere stroke lesions. A clinical CT/Scan study in man. Neuropsychologia, 24: 609-622, 1986. VALLAR, G., STERZI, R., BoTTINI, G., CAPPA, S., and RUSCONI, M.L. Temporary remission of left hemi anesthesia after vestibular stimulation. A sensory neglect phenomenon. Cortex, 26: 123-131, 1990. VENTRE, J ., and FAUGJER-GRIMAUD, S. Effects of posterior parietal lesions (area 7) on VOR in monkeys. Experimental Brain Research, 62: 654-658, 1986. ZINGERLE, H. Ober Storungen der Wahrnemung des eigen Korpers bei organischen Gehirnkrankungen. Monatschriftfi.ir Psychiatrie und Neurologie, 34: 13-36, 1913. Marie-Therese Perenin, Vision et
Motricit~,
INSERM U94, 16 Avenue du Doyen Upine, 69500 Bron, France.
INTRODUCTION
Recent studies have shown that vestibular stimulation may produce a tem porary remission of unilateral neglect phenomena. Improvement concerns not only extrapersonal and personal neglect, but also representational neglect (as when a mental representation is required to describe from memory a given pla ce) and anosognosia (Rubens, 1985; Cappa et al., 1987, Vallar et al., 1990, Rode and Perenin, 1990). Even more striking, somatoparaphrenic delusions may also disappear under vestibular stimulation, as observed recently in one patient (Bis iach et al., 1991). The fact that a sensory manipulation acts on these different aspects of the neglect syndrome has important implications. First, it argues for a unitary conception of the syndrome, even if its manifestations may be disso ciated; second, it opens the way to neurophysiological explanations, whatever psychological theory, attentional or representational, is adopted (reviewed in Jeannerod, 1987). . Unilateral neglect is frequently associated with neurological sensory and motor deficits. In fact, Vallar et al. (1990) have shown that at least part of the somato-sensory deficits may be a manifestation of the neglect syndrome, as they decrease substantially under vestibular stimulation. However, in their three pa tients, the severe motor deficit remained unaffected by the stimulation. In the present note, we report on a case of long lasting neglect, in which the vestibular stimulation produced a temporary reduction of the motor deficit and also disappearance of the somatoparaphrenic delusion, in addition to the pre viously reported improvement of extrapersonal and personal neglect and ano sognosia. CASE REPORT
TS, a 69-year-old woman, sustained a right-hemisphere stroke on January 15th, 1990 and was admitted to an emergency department. She was referred to us 6 months later for per sistence of a complete hemiplegia and delusions concerning her left hemibody. The CT-scan, performed 2 months post-onset, showed a large cortico-subcortical hypodensity in the ter ritory of the middle cerebral artery including the parieto-temporo-occipital carrefour. On neurological examination, the motor deficit was shown to be still complete on both upper and lower limbs, as well as the left hemianesthesia. There was an apparently total left hemianopia on confrontation. Head and gaze were permanently deviated to the right and Cortex, (1992) 28, 203-208
204
G. Rode and Others
could never cross the midline in response to verbal command or during visual pursuit. The patient showed a severe extrapersonal and personal neglect. She failed to orient toward au ditory and visual stimuli produced on her left hemispace and when asked to count people or objects she omitted those located on the left. On a line-crossing test (Albert, 1973), only lines of the rightmost column were crossed. Left-sided omissions were also noted in copying drawings and in reading isolated words. When required to touch her left hand with the right, she did not even start any movement (score= 3, according to the four-point scale of Bisiach et al., 1986, for personal neglect). The patient was quite alert and well oriented in time and space. She had no problem for recognizing people from the hospital staff and her intellectual status, although not scaled, appeared normal on informal questioning. But strikingly, she could not stop talking when somebody was next to her. This logorrhea with delusional speech (see below) had remained unchanged for 6 months as well as the complete anosognosia (score= 3 for both the motor and visual deficits, according to the four-point scale of Bisiach et al., 1986). In addition to denying hemiplegia, the patient claimed that she was able to walk without any problem and did not understand why she was in a hospital. She even accused her husband for having brought her there and asked over and over to go home. Finally, she repeatedly affirmed that her left upper limb was not hers but the examiner's. When the latter (GR) brought the patient's left arm in her good visual field and asked whose it was, she answered: "It's not mine. I found it in the bathroom, when I fell. It's not mine because it's too heavy; it should be yours. It can move and do everything; when I feel it too heavy, I put it on my stomach. It does'nt hurt me, it's kind". When asked where her own arm was, she answered: "Behind the door". On the dichotic test, there was a total left ear extinction. METHODS
The vestibular stimulation was performed by using a cold left ear caloric stimulation. The external ear canal was irrigated with 60 cc of cold (20 oq water for 1 min. During stimula tion the room illumination was decreased; the patient laid down in her bed and her head was tilted approximatively 30° forward. This vestibular activation produced a clear horizontal nystagmus with a leftward slow phase of about 3 min duration. Two identical caloric stimulations were performed at 48 hours interval. Different aspects of neglect were assessed immediately after each stimulation: extrapersonal and personal neg lect, anosognosia and somatoparaphrenia on the first time, extrapersonal neglect and hem iplegia on the second time. The patient was also tested during the interval between the 2 sti mulations and during the 2 days following the second one. Further explorations could not be done, as the patient left the hospital to go back to Spain one week following her admission. RESULTS
First Stimulation Extrapersonal neglect: head and gaze deviation were reduced from 45° to 20° to the right. On verbal request, the patient was able to move her head and to orient her gaze to the left from the midline. In most cases she was then able to detect visual or auditory stimuli produced on her left. Personal neglect: the })ll:tient was able to reach her left hand with her right without hesitation (score~ 0). Anosognosia and soniatoparaphrenia: the patient was totally aware of her hemiplegia. When asked if she could move her arm, she answered: "No" (sco re= 0) and when asked why, she said: "Because I have suffered from a hemi plegia". When asked when and where this appeared, she answered: "In Janu
Vestibular stimulation and neglect syndrome
205
ary, I was in my bathroom and I fell. I called my niece and I was taken to the hospital". When the examiner brought her left arm in her good field, she re cognized it as hers and no longer claimed it was the examiner's. Strikingly, the logorrhea also disappeared immediately after stimulation.
Second Stimulation Extrapersonal neglect: this was assessed this time through the line-crossing test. Although the patient still omitted a few lines and showed a marked trend to repeatedly cross some of the same lines, the pattern of line-crossing was very similar on the two halves of the sheet, thus indicating a marked improvement in the visual explorationn of the left side of space. Hemiplegia: the patient did not move her left limbs spontaneously. But when asked to, she was able to flex and stretch her left leg. The effect did not extend to the upper limb which remained motionless. On a rapid examination, left hemianesthesia and hemianopia remained un changed. Although the stimulations produced some local discomfort, due to irriga tion of the ear with cold water, neither of them caused any sensation of self-dis placement or displacement of the environment. Neither was there any vegeta tive sign, like nausea.
Delayed Post-stimulation State Although this could not be assessed in a formal way for every item men tioned above, the following observations were made. In the interval between the two stimulations and on the day following the second one, the patient again showed a marked deviation of head and gaze to the right and did not orient when called from her left. Anosognosia remained less severe, as she admitted that "she could not walk like everybody"; she added: "Why? I don't know, it could be because I have one leg longer than the other, it's the thing that has to be reeducated". But later, when asked if she could walk, she answered: "If you give me my shoes, you will see how well I can walk". The logorrhea remained attenuated, but the patient again produced delu sional speech concerning her left upper limb. When shown it by the examiner, she did not recognize her arm as hers. She did not know whose arm it was but said that hers was behind the door. The leg motor improvement was no longer manifest, even after verbal en couragement repeated on three successive days. DISCUSSION
Our study has confirmed previous findings on the reversibility of neglect and some of associated disorders through vestibular stimulation (Rubens, 1985; · Cappa et al., 1987; Vallar et al., 1990). In addition, it has shown that the tem porary remission of symptoms is not only possible a few days post-onset as in the previous studies, but may also be obtained much later, as in our case of long
206
G. Rode and Others
lasting neglect and anosognosia. This provides an additional argument to eli minate an aspecific effect of the vestibular stimulation on hypoarousal or con fusion phenomena, as these are no longer present in the later condition. A new and striking finding is the temporary remission of the motor deficit. Before stimulation the patient was considered to be totally hemiplegic. The transient improvement of lower limb motor capacities under vestibular activa tion argues for a motor neglect component in the motor deficit. This result seems very similar to that reported by Vallar et al. (1990) on the temporary re mission of the somato-sensory deficits in neglect patients. If confirmed, the motor neglect component may provide an explanation of the poor motor re covery of left compared to right hemiplegia (Held et al., 1975), especially in cases with associated left hemineglect (Denes et al., 1982). It might also open new perspectives in the rehabilitation of left hemiplegia. Another interesting finding lies in the temporary remission of our patient's delusions concerning her left hemibody. This kind of disorder, called "soma toparaphrenia" by Gertsmann (1942), is most often seen during the acute phase of right hemisphere strokes. In the present case it has taken an exceptionally long lasting form and one may wonder if its regression through caloric stimu lation had not coincided with, or had favored a spontaneous evolution. Al though this was tested only once, the fact that the delusions reappeared a few hours following stimulation rules out such an hypothesis. Thus we have con firmed the recent result by Bisiach et al. (1991) showing in one neglect patient a temporary remission of somatoparaphrenia consistently observed on four ca loric tests. When considering previous results from the literature as well as the present ones, it appears that vestibular activation not only improves the neglect phen omena but also affects a series of disorders often associated to it, even in the same patient, as illustrated in our study. This reinforces the view, recently ar gued by Bisiach and Berti (1987), of a unitary syndrome whose multiple mani festations, although often dissociated, would rely on a common basic disturb ance. The authors have done justice to a largely omitted work by Zingerle at the beginning of this century, whose merit has been both to coin the appropriate term of "dyschiria" to designate this multiform syndrome and to propose the still up-to-date interpretation of a disordered awareness or representation of one side (of the body and/or extracorporeal space). The fact that neglect and related symptoms can be amended through a sen sory manipulation such as vestibular stimulation opens the way to neurophy siological explanations of these symptoms, including false beliefs on the left hemibody. In humans, most cases of neglect are related to a lesion including the right posterior parierallobe and carrefour (Vallar and Perani, 1986); moreover the complete syndrome with anosogriosia and delusions appears to require a le sion in this area (De Renzi, 1982; Kinsbourne, 1987), which is thus seen as crit ically involved in the representation of both corporeal and extracorporeal ego centric space. Accordingly, patients with posterior parietal lesions show an ips ilesional shift of their egocentric reference (i.e. midsagittal plane representa tion), which is significantly larger than in patients with other cortical lesions (Perenin et al., in preparation). Interestingly, the parietal lobe is also the site of
Vestibular stimulation and neglect syndrome
207
vestibular projections as shown by a regional blood-flow study (Friberg et al., 1985) as well as by an early PET-scan work (Tuohimaa et al., 1983): both have disclosed a cortical activation in the temporo-parietal region in response to a unilateral vestibular stimulation, although they do not allow a definitive con clusion about the more activated side. In our opinion, this vestibular input takes part, as do other (mainly sensory) types of inputs, in building up and updating the representation of egocentric space. This might account for the shift of the egocentric reference observed in normal people following vestibular stimula tion as well as the shift reversal of this reference produced in neglect patients after the same stimulation (Rode, 1990). However, this only represents a small step in understanding the neural mechanisms by which vestibular stimulation improves the neglect syndrome and restores awareness and correct representa tion of the left hemibody and surrounding space. As animal work concerning the functional relationships between the vestibular nuclei and the parietal cor tex are still at a preliminary stage, further hypotheses are speculative. For rea sons already developed by Cappa et al. (1987) the vestibular stimulation in neg lect patients will more likely activate the left intact hemisphere than the right damaged one. In fact this might reinforce the vestibular imbalance previously shown following posterior parietal lesions in the monkey and which appears to oppose the ipsilesional orientation bias (Ventre and Faugier-Grimaud, 1986). Further neurophysiological work in the monkey as well as metabolic studies in humans will bring a better understanding of the effect of vestibular activation on neglect as well as of the organization of the parietal lobe, which must har bour multiple functional modules involved in space representation. ABSTRACT
In a case of long lasting severe neglect resulting from a large right parieto-temporo-oc cipital infarct, vestibular stimulation produced a temporary reduction of the motor deficit and disappearance of the somatoparaphrenic delusion, in addition to the already reported improvement of extrapersonal and personal neglect and anosognosia. These data open new perspectives in the understanding of the neglect syndrome and of functional involvement of the parietal lobe in space representation.
Acknowledgements. We are particularly grateful to Edoardo Bisiach for his valuable comments on this paper. We also thank Jerry Nelson who kindly revised the manuscript. REFERENCES ALBERT, M.L. A simple test of visual neglect. Neurology, 23: 658-654, 1990. BISIACH, E., and BERTI, A. Dyschiria. An attempt at its systemic explanation. In M. Jeannerod (Ed.), Neurophysiological and Neuropsychological Aspects of Spatial Neglect. Amsterdam: North Hol land, 1987, pp. 183-201. BISIACH, E., PERANI, D., VALLAR, G., and BERTI, A. Unilateral neglect: personal and extrapersonal. Neuropsychologia, 24: 759-767, 1986. BISIACH, E., RuscoNI, M.L., and VALLAR, G. Remission of somatoparaphrenic delusion through vesti bular stimulation. Neuropsychologia, 29: 1029-1031, 1991. CAPPA, S., STERZI, R., VALLAR, G., and BISIACH, E. Remission of hemineglect and anosognosia during vestibular stimulation. Neuropsychologia, 25: 775-782, 1987. DENES, G., SEMENZA, C., STOPPA, E., and Lis, A. Unilateral spatial neglect and recovery from hemiple
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