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Remission of somatoparaphrenic delusion through vestibular stimulation
NOTE REMISSION
OF SOMATOPARAPHRENIC DELUSION VESTIBULAR STIMULATION
THROUGH
EDOAKW BISIACH,MARIA L~JISARUS(.ONI and GIUSEPPEVALLAK Istituto
di Clinica
Neurologica,
(Rrwiwd
13 Fuhruur~~
UniversitB 199
di Milano.
I ; uccrpted29
April
Milano, 199
Italy
I)
Abstract-The effects of vest&Jar stimulation on somatoparaphrenic delusion were investigated in a patient suffering from a fronto-temporo-parietal infarction located in the right hemisphere. Transitory remission of the patient’s delusional belief was consistently observed during unilateral vestibular activation obtained by means of cold-water irrigation of the left (contralesional) ear.
NOTHIW appears more remote from the current frontiers of neuroscience than the circuits underlying the fixation and mutation of human beliefs. Yet clues to the ncuroarchitecture of beliefs can be found in longstanding climcal knowledge about well-defined-and far from exceptional&delusions caused by focal brain damage. Furthermore. extrapolation from such knowledge, together with more recently acquired knowledge about certain surprising effects of vestibular stimulation on cognitive activities, in our view prefigured the possibility of an experimental manipulation of somatoparaphrenia --i.e. one of the best-known instances of the aforementioned delusionsthrough neurophysiological, as opposed to psychological. means. Quite recently we were offered the opportunity to test this view, with positive results: vestibular stimulation applied to a typical patient was more than once effective in inducing a temporary (partial) withdrawal of delusional symptoms. A.R., an X4-year-old woman. sustained a right-hemisphere stroke on IX November 1990. On neurological examination she showed rightward eye and head rotation, left hemiplegia, left somatosensory defect. normal visual field but neglect of the left side of egoccntrcd space. A CT-scan performed 4 days later demonstrated a wide area of marked hypodensity involving frontal, parietal and temporal regions of the right hemisphere. The patient was fairly alert and cooperative but completely anosognosic. Besides denying hemiplegia, she insisted that her left upper limb which she was able to touch and look at, if requested-~-was not her’s but her mother’s, Phenomena such as the false ascription of contralesional limbs to other people after acute damage of the right hemisphere have been well-known since the beginning of the current century and have been collectively termed “somatoparaphrenia” by GI-XSTMANN[8]. Usually they do not last more than a few hours or days. during which. however. they are lirmly rooted in the patient’s thought and resist any kind of contrary cvidcnce. They arc usually accompanied by unawareness/denial of hemiplegia and by neglect of contralcsional space, both of whichespecially the latter-may persist after the disappearance of somatoparaphrenia. An outstanding fcaturc of the delusions at ISSUC.as well as of anosognosia and unilateral neglect. is cognitive encapsulation, in the sense that, outside the alrected domain. the contents of the patients’ thought processes may appear to be farly normal In 1941, SILer.Kt+tuxlc; [I I] reported a case of temporary remission of visual hemineglect through peripheral vcstibular activation on the side ipsilateral to the brain lesion. His finding was conlirmcd by R~JHI-NS [IO] in a group of patients. More recently, CAPPA et ul. [6] demonstrated that the effect of ipsileslonal vcstibular activation on neglect symptoms was not due to the transitory cyc rotation towards the neglected side of space induced by that activation. In fact, they reported temporary remission of neglect also on tats ofspace exploration during which the patients’eycs were shut. VALLAKet al. [IZ] found that vestibular activation may in some patients cause a transitory remission of contralesional aomatosensory defects, that appeared thus to bc due, at least partly. to neglect rather than to somatosensory impairment. Ncglcct phenomena have also been known to occur at the lcvcl of mental representation. e.g. during the description from memory ofa well-known landscape from a given vantage point [3]. Even this type of contralesional neglect has been reported to Improve during vestibular activation 191. Finally, unawarcness,‘denial of left hemiplegla was found to recede during vestibular activation in two casts out of four by CAWA et ul. [6] and in one of two severely anosognosic patients tcstcd by VAI I.AKe! trl. LIZ]. 1029
1030
NOTE
So far. ipsilcsional vestihular activation in patients with neglect and anosognosia has been obtained either by activation ofthc peripheral vcstihular system on the ipsilcsional side through irrigation ofthc external car canal with warm water, or by Inhibition of the peripheral vestibular system on the contraleslonal side with cold water (see VAI.I.AK L’I ul. [S] for technical details). The latter procedure was adopted with patient A.R. The first test took place on 29 November. Prior Ex. A.R.: I%: A.R.: I+: A.R.: EX: A.R.: I%: A.R A.R.: I%: A.R.: I%: A.R.: Ex: A.R.: 13: A.R.: fix: A.R.:
A-R.:
A.R.: FX: A.R.:
A.R.:
:
to
~w~ihularsfimnlution,
the rvarninrr
(M.L.R.)
points to the patient’s
/e/t em
und usk.s the hr\t
yurution.
Whose arm is this? It’s not mine. Whose is it’! It’s my mother’s How on earth does it happen to he here? I don’t know. I found it in my bed. How long has it been there’! Since the first day. Feel, it’s warmer than mine. The other day too. when the weather was colder, it was warmer than mine. So where is hour left arm’! (Mukrs un indefinite qcsturr forwards.) It’s under there. lmmediurul~ ufier oestihu/ur stimulurion, rhe r.uamiwr asks the putwnt fo ahow her Ihe prrrwnt’s left urm. (Point\ to her own /e/f urm.) Here it is. (Raiw thr puirm’\ left arm.) Is this arm yours’! Why, ye\. Where IS your mother’s arm? (Hesitules.) It is somewhere about. Where exactly’? I don’t know. Perhaps here, under the bedclothes. (She looks to hrr right, under Ihe hedclorhes.) Two hours offer rrstdmlor srimulatior~ A.R. is yurvrionrd ayain by thr ruuminrr. (Porn/s to thr putient’\ lrfr urm.) Whose arm is this’! It’s my mother’s, It’s warmer. Where IS your left arm? .AR stures silently ut thr euuminrr. One hour and u hulf /atcv, she spontawously addrrsws thr eutrmrner. (Points IO her /e/t arm.) My mother’s arm is colder than it was this morning. Feel how cold It is. 0,~ t/w/rJ/orviny morniq (30 Nor@n&r), Ike rJ.\-uminerasks A. R. uyuin whose is A. R.‘s /e/i urn, whilr pointing to il. It‘s my mother’s, It’s pretty warm. I found It here. She forgot it when she was discharged from the hospital. ,d/lcr rwlihulnr .stirnuloiion pw/ormcvl cuordimq 10 the .scmw procrdure used the day he/ore, the exuminrr rai.w /he pcrfienl’\ /CT/~urm crud craks onw trqain whose trrm ir is. (7huc,hrs hur /t,/i urm.) It’s mint. Where is your mother’s arm’! It must he here, in the corner. (Shr /oo~s/or hrr morhcr’s urm undrr rhr hrdclothrs without findiruq ir.) It’s pretty warm. It is a strong arm; my mother was a laundress. T\r’o hour,\ lufer. A. R. hns cwmp/erc/y relapsrd in her full-blown delusion. T/w ,sum~~routirw ~vu.~rrptw/t~d I wice.on 3 rrnd 4 Dawmher. oftrr harinq rrprtrtrdly u.wwtcrinud /hat mu c~hunyr~\ 111A. R.‘s delusioas htrd .spc~nturwtwsly occ~urr-ad dwinq the i,~trr~~cwiny hours. The rrsults o/‘restihular ucfirutiou wcw ident&/ to ~hosr ohrtriwd in Ihe //rsl t\vo~e.\/.s, theonly ~uwption brim/ that the remisison oj’lhr, dr4uGontrl /w/it:/ wluriw 10 A. R.‘r lcfi urm bva.sof writ .shor/ durtrrion: trhout I5 sec. dftrr rrlupsiy in her /u/l-hiow dclusio~~ JiJlrncimq rhr show-liwd improwmrnt curr.wd hy fhr 3rd vtimulution test. A.R. a~k,~o~~lt~d~e.s/or ~hc firsf tiw -tr/ihrm~qh rtrrlwr cursorily rhc srrtrm+wrs,~ of whclf vhr c~ltrim.5to he the cazu.) Look, it’s queer, hut that’s how it is. Just fancy finding your son.5 arm in your bed!
To rccapitulatc. whereas during the whole period of observation before and between the vestibular tests A.R. would unhesitatingly attrihutc her Icft upper limb to her mother, under theeffect ofvcstibular stimulation she would unhesitatingly rccognirc that same arm as her own. Although definite. the transitory remissions of A.R.‘s delusion during vcstihular stimulation were not complete: far from being struck by the absurdity of the cxamincr’s questions about her mother’s arm. she reacted to such questions in a somewhat elusive way. It has been claimed that the selective and encapsulated character of delusions such as those found in association with unaw;~rcncss.dcnlal of neurological disorders. together with their segregation in contralcsional space when they occur as a conscquencc of unilateral brain lesion. suggests a quasi-modular structure ofsomr thought-processes and a mapping of the heliefsystcm on the analogue medium ofsensori-specific cognitive representations L?. 41. This hypothesis is now strengthened hv the fact that somatoparaphrcnic delusions. like anosognosm. appear susceptible to mampulation by ccstihular st:mulation nearly in the same way as unilateral spatial neglect. the latter being constituted by a collection ofphenomena that may he intcrpretcd as rcflectlng a spatially circumscribed disorder of copnitl\c rcprcscntntions structured in an analoguc medium [I. 51. The term ‘quasi-modular’ is admittedly
ambiguous. Its use, here, should not suggest an organization of the beliefsystem into discrete blocks. What we want to suggest is rather that there are systems that are neither sharply modular nor homogenously interconnected and isotropic. If confirmed, the effect of vestibular stimulation on somatoparaphrenic delusions opens a promising line of investigation relative to the neural correlates of an important aspect of thought processes: the fixation of beliefs about parts ofthe body. Little is yet known concerning the brain events brought about by vestibular activation. In a regional blood-flow study, however, FRIBER(; rt al. [7] have found a focus of cortical activation located in the posterior-superior region of the temporal lobe contralateral to the side of peripheral vestibular excitation. i.e. in a region that is closely related, in the human brain, to representation of both corporeal and environmental egocentred space 1131. PET techniques may offer new possibilities to push our research deeper into an area that could. at present and without exaggeration. be deemed unfathomable by neurosclentilic means. ~1~knorvledgemmfsThis CNR (G.V.).
work was supported
by grants
from the Minister0
della Pubblica
Istruzione
(E.B.) and
REFERENCES I. BISIACH. E. and Neuropsychologicul
BERTI, A. Dyschiria. Aspects
o/
Sparid
An attempt Neglect,
at its systemic explanation. In Nt,uroph~slolo(/ic,ul ad M. JEANNLROI) (Editor), pp. I83 201. North-Holland.
Amsterdam, 1987. 2. BISIACH. E. and GEMINIANI, G. Anosognosia related to hemiplegia and hemianopia. In Awurrnrs.s ofDeficit qficv Brain Injury, G. P. PKIC~ATANO and D. L. SCHACTER (Editors). pp. I7 39. Oxford University Press, New York (1991). 3. BISIACH, E. and LUZZATTI, C. Unilateral neglect of representational space. Corfex 14, 129 133, 1978. 4. BISIA~H. E., MIZRIZGALLI.S. and BERTI, A. Mechanisms of production control and belief fixation in human visuospatial processing: Clinical evidence from unilateral neglect and misrepresentation. In Qumtilutiw Analyses of Behavior, Vol. IX. M. L. COMMONS,R. J. HEKKE~STEIN,S. M. KOSSLYN and D. B. M~MFOKI) (Editors). pp. 3 21. Lawrence Erlbaum Association, Hillsdale, NJ. 1990. 5. BISIACH, E. and VALLAR. G. Hemineglect in humans. In Hundhook o/ Neurop,s~c,holoU?. F. BOLL~K and J. GRAFMAN (Editors), pp. 195 222. Elsevier, Amsterdam, 19X8. 6. CAPPA, S., ST~KZI, R.. VALLAK,G. and BISIACH, E. Remission ofhemineglect and anosognosiaduringvestibular stimulation. Neurop.sycholoyia 2.5, 775 782, 1987. 7. FRILEKG,L., OLSEY, T. S.. ROLANU. P. E., PAULSOU, 0. B. and LASXN, N. A. Focal increase of blood flow in the cerebral cortex of man during vestibular stimulation. Bruin 108, 609 623. 1985. 8. GERSTMAVN,J. Problem of imperception of disease and of impaired body territories with organic lesions. Relation to body scheme and its disorders. Arch Nrurol. Psychiut. 48. 890 913. 1942. 9. Ro~jr, G. and PEKENIN, M. T. Poster presented at the symposium C’onsc~iou.snr.w und Coynirion: Neurop.s?.c,holoUic,uI Pw\pec!itvs. St. Andrews, 1990. IO. RUHENS,A. 8. Caloric stimulation and unilateral visual ncglcct. Neuroloyy 35, 1019 1024, 1985. I I. SILHEKPFENNIG, J. Contributions to the problem of eye movements. C‘mfiniu Nrurol. 4, I 13, 1941. 12. VALLAK, G. and PTKANI. D. The anatomy of spatial neglect in humans. In Nuuroph~sioloyicul und Nuurop.\l’choloyica/ Aspects of Spurid Neglect, M. JEANNE:KOL)(Editor), pp. 235 25X. North-Holland. Amsterdam. 1987. 13. VILLAK, G., STI WI, R.. BOTTINI,G.. CAPPA, S. and RUS(.ONI, M. L. Temporary remission oflcft hcmiancsthcsia after vestibular stimulation. A sensory neglect phenomenon. C‘ortru26, 123 131, 1990.
OF SOMATOPARAPHRENIC DELUSION VESTIBULAR STIMULATION
THROUGH
EDOAKW BISIACH,MARIA L~JISARUS(.ONI and GIUSEPPEVALLAK Istituto
di Clinica
Neurologica,
(Rrwiwd
13 Fuhruur~~
UniversitB 199
di Milano.
I ; uccrpted29
April
Milano, 199
Italy
I)
Abstract-The effects of vest&Jar stimulation on somatoparaphrenic delusion were investigated in a patient suffering from a fronto-temporo-parietal infarction located in the right hemisphere. Transitory remission of the patient’s delusional belief was consistently observed during unilateral vestibular activation obtained by means of cold-water irrigation of the left (contralesional) ear.
NOTHIW appears more remote from the current frontiers of neuroscience than the circuits underlying the fixation and mutation of human beliefs. Yet clues to the ncuroarchitecture of beliefs can be found in longstanding climcal knowledge about well-defined-and far from exceptional&delusions caused by focal brain damage. Furthermore. extrapolation from such knowledge, together with more recently acquired knowledge about certain surprising effects of vestibular stimulation on cognitive activities, in our view prefigured the possibility of an experimental manipulation of somatoparaphrenia --i.e. one of the best-known instances of the aforementioned delusionsthrough neurophysiological, as opposed to psychological. means. Quite recently we were offered the opportunity to test this view, with positive results: vestibular stimulation applied to a typical patient was more than once effective in inducing a temporary (partial) withdrawal of delusional symptoms. A.R., an X4-year-old woman. sustained a right-hemisphere stroke on IX November 1990. On neurological examination she showed rightward eye and head rotation, left hemiplegia, left somatosensory defect. normal visual field but neglect of the left side of egoccntrcd space. A CT-scan performed 4 days later demonstrated a wide area of marked hypodensity involving frontal, parietal and temporal regions of the right hemisphere. The patient was fairly alert and cooperative but completely anosognosic. Besides denying hemiplegia, she insisted that her left upper limb which she was able to touch and look at, if requested-~-was not her’s but her mother’s, Phenomena such as the false ascription of contralesional limbs to other people after acute damage of the right hemisphere have been well-known since the beginning of the current century and have been collectively termed “somatoparaphrenia” by GI-XSTMANN[8]. Usually they do not last more than a few hours or days. during which. however. they are lirmly rooted in the patient’s thought and resist any kind of contrary cvidcnce. They arc usually accompanied by unawareness/denial of hemiplegia and by neglect of contralcsional space, both of whichespecially the latter-may persist after the disappearance of somatoparaphrenia. An outstanding fcaturc of the delusions at ISSUC.as well as of anosognosia and unilateral neglect. is cognitive encapsulation, in the sense that, outside the alrected domain. the contents of the patients’ thought processes may appear to be farly normal In 1941, SILer.Kt+tuxlc; [I I] reported a case of temporary remission of visual hemineglect through peripheral vcstibular activation on the side ipsilateral to the brain lesion. His finding was conlirmcd by R~JHI-NS [IO] in a group of patients. More recently, CAPPA et ul. [6] demonstrated that the effect of ipsileslonal vcstibular activation on neglect symptoms was not due to the transitory cyc rotation towards the neglected side of space induced by that activation. In fact, they reported temporary remission of neglect also on tats ofspace exploration during which the patients’eycs were shut. VALLAKet al. [IZ] found that vestibular activation may in some patients cause a transitory remission of contralesional aomatosensory defects, that appeared thus to bc due, at least partly. to neglect rather than to somatosensory impairment. Ncglcct phenomena have also been known to occur at the lcvcl of mental representation. e.g. during the description from memory ofa well-known landscape from a given vantage point [3]. Even this type of contralesional neglect has been reported to Improve during vestibular activation 191. Finally, unawarcness,‘denial of left hemiplegla was found to recede during vestibular activation in two casts out of four by CAWA et ul. [6] and in one of two severely anosognosic patients tcstcd by VAI I.AKe! trl. LIZ]. 1029
1030
NOTE
So far. ipsilcsional vestihular activation in patients with neglect and anosognosia has been obtained either by activation ofthc peripheral vcstihular system on the ipsilcsional side through irrigation ofthc external car canal with warm water, or by Inhibition of the peripheral vestibular system on the contraleslonal side with cold water (see VAI.I.AK L’I ul. [S] for technical details). The latter procedure was adopted with patient A.R. The first test took place on 29 November. Prior Ex. A.R.: I%: A.R.: I+: A.R.: EX: A.R.: I%: A.R A.R.: I%: A.R.: I%: A.R.: Ex: A.R.: 13: A.R.: fix: A.R.:
A-R.:
A.R.: FX: A.R.:
A.R.:
:
to
~w~ihularsfimnlution,
the rvarninrr
(M.L.R.)
points to the patient’s
/e/t em
und usk.s the hr\t
yurution.
Whose arm is this? It’s not mine. Whose is it’! It’s my mother’s How on earth does it happen to he here? I don’t know. I found it in my bed. How long has it been there’! Since the first day. Feel, it’s warmer than mine. The other day too. when the weather was colder, it was warmer than mine. So where is hour left arm’! (Mukrs un indefinite qcsturr forwards.) It’s under there. lmmediurul~ ufier oestihu/ur stimulurion, rhe r.uamiwr asks the putwnt fo ahow her Ihe prrrwnt’s left urm. (Point\ to her own /e/f urm.) Here it is. (Raiw thr puirm’\ left arm.) Is this arm yours’! Why, ye\. Where IS your mother’s arm? (Hesitules.) It is somewhere about. Where exactly’? I don’t know. Perhaps here, under the bedclothes. (She looks to hrr right, under Ihe hedclorhes.) Two hours offer rrstdmlor srimulatior~ A.R. is yurvrionrd ayain by thr ruuminrr. (Porn/s to thr putient’\ lrfr urm.) Whose arm is this’! It’s my mother’s, It’s warmer. Where IS your left arm? .AR stures silently ut thr euuminrr. One hour and u hulf /atcv, she spontawously addrrsws thr eutrmrner. (Points IO her /e/t arm.) My mother’s arm is colder than it was this morning. Feel how cold It is. 0,~ t/w/rJ/orviny morniq (30 Nor@n&r), Ike rJ.\-uminerasks A. R. uyuin whose is A. R.‘s /e/i urn, whilr pointing to il. It‘s my mother’s, It’s pretty warm. I found It here. She forgot it when she was discharged from the hospital. ,d/lcr rwlihulnr .stirnuloiion pw/ormcvl cuordimq 10 the .scmw procrdure used the day he/ore, the exuminrr rai.w /he pcrfienl’\ /CT/~urm crud craks onw trqain whose trrm ir is. (7huc,hrs hur /t,/i urm.) It’s mint. Where is your mother’s arm’! It must he here, in the corner. (Shr /oo~s/or hrr morhcr’s urm undrr rhr hrdclothrs without findiruq ir.) It’s pretty warm. It is a strong arm; my mother was a laundress. T\r’o hour,\ lufer. A. R. hns cwmp/erc/y relapsrd in her full-blown delusion. T/w ,sum~~routirw ~vu.~rrptw/t~d I wice.on 3 rrnd 4 Dawmher. oftrr harinq rrprtrtrdly u.wwtcrinud /hat mu c~hunyr~\ 111A. R.‘s delusioas htrd .spc~nturwtwsly occ~urr-ad dwinq the i,~trr~~cwiny hours. The rrsults o/‘restihular ucfirutiou wcw ident&/ to ~hosr ohrtriwd in Ihe //rsl t\vo~e.\/.s, theonly ~uwption brim/ that the remisison oj’lhr, dr4uGontrl /w/it:/ wluriw 10 A. R.‘r lcfi urm bva.sof writ .shor/ durtrrion: trhout I5 sec. dftrr rrlupsiy in her /u/l-hiow dclusio~~ JiJlrncimq rhr show-liwd improwmrnt curr.wd hy fhr 3rd vtimulution test. A.R. a~k,~o~~lt~d~e.s/or ~hc firsf tiw -tr/ihrm~qh rtrrlwr cursorily rhc srrtrm+wrs,~ of whclf vhr c~ltrim.5to he the cazu.) Look, it’s queer, hut that’s how it is. Just fancy finding your son.5 arm in your bed!
To rccapitulatc. whereas during the whole period of observation before and between the vestibular tests A.R. would unhesitatingly attrihutc her Icft upper limb to her mother, under theeffect ofvcstibular stimulation she would unhesitatingly rccognirc that same arm as her own. Although definite. the transitory remissions of A.R.‘s delusion during vcstihular stimulation were not complete: far from being struck by the absurdity of the cxamincr’s questions about her mother’s arm. she reacted to such questions in a somewhat elusive way. It has been claimed that the selective and encapsulated character of delusions such as those found in association with unaw;~rcncss.dcnlal of neurological disorders. together with their segregation in contralcsional space when they occur as a conscquencc of unilateral brain lesion. suggests a quasi-modular structure ofsomr thought-processes and a mapping of the heliefsystcm on the analogue medium ofsensori-specific cognitive representations L?. 41. This hypothesis is now strengthened hv the fact that somatoparaphrcnic delusions. like anosognosm. appear susceptible to mampulation by ccstihular st:mulation nearly in the same way as unilateral spatial neglect. the latter being constituted by a collection ofphenomena that may he intcrpretcd as rcflectlng a spatially circumscribed disorder of copnitl\c rcprcscntntions structured in an analoguc medium [I. 51. The term ‘quasi-modular’ is admittedly
ambiguous. Its use, here, should not suggest an organization of the beliefsystem into discrete blocks. What we want to suggest is rather that there are systems that are neither sharply modular nor homogenously interconnected and isotropic. If confirmed, the effect of vestibular stimulation on somatoparaphrenic delusions opens a promising line of investigation relative to the neural correlates of an important aspect of thought processes: the fixation of beliefs about parts ofthe body. Little is yet known concerning the brain events brought about by vestibular activation. In a regional blood-flow study, however, FRIBER(; rt al. [7] have found a focus of cortical activation located in the posterior-superior region of the temporal lobe contralateral to the side of peripheral vestibular excitation. i.e. in a region that is closely related, in the human brain, to representation of both corporeal and environmental egocentred space 1131. PET techniques may offer new possibilities to push our research deeper into an area that could. at present and without exaggeration. be deemed unfathomable by neurosclentilic means. ~1~knorvledgemmfsThis CNR (G.V.).
work was supported
by grants
from the Minister0
della Pubblica
Istruzione
(E.B.) and
REFERENCES I. BISIACH. E. and Neuropsychologicul
BERTI, A. Dyschiria. Aspects
o/
Sparid
An attempt Neglect,
at its systemic explanation. In Nt,uroph~slolo(/ic,ul ad M. JEANNLROI) (Editor), pp. I83 201. North-Holland.
Amsterdam, 1987. 2. BISIACH. E. and GEMINIANI, G. Anosognosia related to hemiplegia and hemianopia. In Awurrnrs.s ofDeficit qficv Brain Injury, G. P. PKIC~ATANO and D. L. SCHACTER (Editors). pp. I7 39. Oxford University Press, New York (1991). 3. BISIACH, E. and LUZZATTI, C. Unilateral neglect of representational space. Corfex 14, 129 133, 1978. 4. BISIA~H. E., MIZRIZGALLI.S. and BERTI, A. Mechanisms of production control and belief fixation in human visuospatial processing: Clinical evidence from unilateral neglect and misrepresentation. In Qumtilutiw Analyses of Behavior, Vol. IX. M. L. COMMONS,R. J. HEKKE~STEIN,S. M. KOSSLYN and D. B. M~MFOKI) (Editors). pp. 3 21. Lawrence Erlbaum Association, Hillsdale, NJ. 1990. 5. BISIACH, E. and VALLAR. G. Hemineglect in humans. In Hundhook o/ Neurop,s~c,holoU?. F. BOLL~K and J. GRAFMAN (Editors), pp. 195 222. Elsevier, Amsterdam, 19X8. 6. CAPPA, S., ST~KZI, R.. VALLAK,G. and BISIACH, E. Remission ofhemineglect and anosognosiaduringvestibular stimulation. Neurop.sycholoyia 2.5, 775 782, 1987. 7. FRILEKG,L., OLSEY, T. S.. ROLANU. P. E., PAULSOU, 0. B. and LASXN, N. A. Focal increase of blood flow in the cerebral cortex of man during vestibular stimulation. Bruin 108, 609 623. 1985. 8. GERSTMAVN,J. Problem of imperception of disease and of impaired body territories with organic lesions. Relation to body scheme and its disorders. Arch Nrurol. Psychiut. 48. 890 913. 1942. 9. Ro~jr, G. and PEKENIN, M. T. Poster presented at the symposium C’onsc~iou.snr.w und Coynirion: Neurop.s?.c,holoUic,uI Pw\pec!itvs. St. Andrews, 1990. IO. RUHENS,A. 8. Caloric stimulation and unilateral visual ncglcct. Neuroloyy 35, 1019 1024, 1985. I I. SILHEKPFENNIG, J. Contributions to the problem of eye movements. C‘mfiniu Nrurol. 4, I 13, 1941. 12. VALLAK, G. and PTKANI. D. The anatomy of spatial neglect in humans. In Nuuroph~sioloyicul und Nuurop.\l’choloyica/ Aspects of Spurid Neglect, M. JEANNE:KOL)(Editor), pp. 235 25X. North-Holland. Amsterdam. 1987. 13. VILLAK, G., STI WI, R.. BOTTINI,G.. CAPPA, S. and RUS(.ONI, M. L. Temporary remission oflcft hcmiancsthcsia after vestibular stimulation. A sensory neglect phenomenon. C‘ortru26, 123 131, 1990.