Multiple-domain dissociation between impaired visual perception and preserved mental imagery in a patient with bilateral extrastriate lesions.

A brain-damaged patient is described whose pattern of performance provides insight into both the functional mechanisms and the neural structures involved in visual mental imagery. The patient became severely agnosic, alexic, achromatopsic and prosopagnosic following bilateral brain lesions in the temporo-occipital cortex. However, her mental imagery for the same visual entities that she could not perceive was perfectly preserved. This clear-cut dissociation held across all the major domains of high-level vision: object recognition, reading, colour and face processing. Our findings, together with other reports on domain-specific dissociations and functional brain imaging studies, provide evidence to support the view that visual perception and visual mental imagery are subserved by independent functional mechanisms, which do not share the same cortical implementation. In particular, our results suggest that mental imagery abilities need not be mediated by early visual cortices.

Improvement of severe postural cerebellar tremor in multiple sclerosis by chronic thalamic stimulation.

Tremor can be particularly disabling in patients with multiple sclerosis (MS) and is mildly improved by drug treatment. The efficiency of stereotactic thalamotomy has been reported in a small number of patients but was counterbalanced by severe postoperative complications. Stimulation of the thalamic ventral intermediate nucleus, which is a less aggressive surgical method, is efficient in essential and in parkinsonian tremors. We report here the results of thalamic stimulation in 13 patients with MS with tremor. All patients were subjected to clinical examination, videorecording, and quantification of the functional disability before surgery and 3 months postoperatively. The surgical intervention was well tolerated in all cases. A clear improvement of the tremor was observed in 69.2% of the patients. Functional improvement was more varied and depended on the severity of tremor and coexistence of other neurological symptoms. Of the eight most severely affected patients, seven recovered the possibility to easily catch an object and use it. The results indicate that thalamic stimulation may be useful in the treatment of severe postural cerebellar tremor in MS.

Rest tremor and extrapyramidal symptoms after midbrain haemorrhage: clinical and 18F-dopa PET evaluation.

A 25 year old man had an acute subarachnoid haemorrhage due to the rupture of a right peduncular subthalamic arteriovenous malformation. Seven months later he developed a left rest tremor associated with mild bilateral extrapyramidal symptoms and responsive to levodopa treatment. Surface EMG recording showed synchronous activity of agonist and antagonist muscles in the left limbs. A PET 18F-dopa study showed a large decrease of the Ki value in the right striatum. One year after the stroke a persistent postural component developed in the tremor.

Thalamic stimulation and proximal tremor. A specific target in the nucleus ventrointermedius thalami.

The severe proximal cerebellar postural tremor (also called action or intention or hyperkinetic tremor) is barely influenced by thalamotomy or stimulation of the thalamus at the classic target in the lower part of the nucleus ventrointermedius thalami (VIM). In four patients with a severe postural distal and proximal tremor, an electrode fitted with four points of contact was introduced within the entire height of the VIM. In each patient, stimulation of the lower part of the VIM was most effective in the distal component of the tremor, whereas its proximal component was specifically reduced by stimulation of its upper part. These results indicate that (1) proximal postural tremors can be as much affected by stimulation of the VIM as distal tremors, (2) there is a somatotopy in the VIM that is similar to that in the nucleus ventralis posterolateralis thalami, and (3) it is possible with this technique to adjust the VIM stimulation site so as to obtain the maximum efficacy according to the locale of the tremor.

[Treatment of tremor by stereotactic surgery]. / Traitement du tremblement par chirurgie stéréotaxique.

Thalamotomy in the ventrolateral thalamic nucleus is a common treatment of severe parkinsonian or essential tremor. Although results are often satisfactory, complications may occur and alter the success of the operation. High frequency stimulation of the target before thalamotomy leads to transitory abolition of the tremor. Therefore, a chronic stimulation device was developed and its use produced results similar to those of thalamotomy for parkinsonian tremor. Unwanted side-effect can be reduced by changing the parameters of the stimulation. Improvements in multiple sclerosis and post-traumatic tremors may be expected. We present a review of the indications and results of both technics.

Brain energy metabolism in bilateral paramedian thalamic infarcts. A positron emission tomography study.

Positron emission tomography (PET) studies of the cerebral metabolic rate of oxygen (CMRO2) were performed in seven consecutive patients with bilateral paramedian thalamic infarcts (BPTI), selected on neuroradiological and clinical criteria. The latter consisted of sudden onset of coma or confusion followed by a persistent amnesia of varying severity, with or without language impairment and frontal lobe signs. There was a highly significant decrease of CMRO2 for the whole cortex as well as for all the regions analysed: medial-frontal, latero-frontal, temporal, sensorimotor and posterior associative cortex. The mean regional metabolic ratios (region/whole cortex CMRO2) were not significantly different from controls, indicating an essentially uniform effect in the cortex, except the sensorimotor ratio which was significantly increased. Diffuse cortical hypometabolism most likely reflects thalamo-cortical deafferentation secondary to damage to the 'non-specific' thalamic nuclei, while sparing of the latero-ventral thalamus presumably explains the relative preservation of the sensorimotor cortex metabolism. Although no clear-cut individual relationship was found between magnitude of cortical hypometabolism and the severity and pattern of neuropsychological impairment, the data suggest that the former underlies and/or reflects the latter. Further studies with higher resolution PET devices might shed more light on the relationships between distinct cognitive patterns and specific topography of cortical hypometabolism in BPTI patients.

[Non-dominant hemisphere syndrome as a result of a right thalamic infarct: an anatomoclinical case]. / Syndrome de l'hémisphère mineur par infarctus thalamique droit: un cas anatomoclinique.

A 71 year old man had a massive left sensory deficit and hemiplegia, with left heminanopia, visual neglect and constructional apraxia. Moreover he experienced an extra-left arm and illusions of movements. 3 weeks later he suffered "thalamic" pain on left side; he died suddenly 6 weeks after the stroke. Post-mortem examination revealed: a) a right inner temporal and occipital infarction; b) a right thalamic infarction in the thalamogeniculate and paramedian territories; c) an infarction in the adjacent right internal capsule. Considering this case and pertinent literature on clinicopathological studies of right thalamic infarction, the authors suggest that a simultaneous ischaemia of thalamogeniculate and paramedian territories should be necessary to induce somatognosic and visuospatial disturbances.

Motor neglect.

Motor neglect is characterised by an underutilisation of one side, without defects of strength, reflexes or sensibility. Twenty cases of frontal, parietal and thalamic lesions causing motor neglect, but all without sensory neglect, are reported. It is proposed that the cerebral structures involved in motor neglect are the same as those for sensory neglect and for the preparation of movement. As in sensory neglect, the multiplicity of the structures concerned suggests that this interconnection is necessary to maintain a sufficient level of activity. Predominance of left sided neglect by right sided lesions suggests that the left hemisphere is dominant for deliberate activity; hemispheric dominance could be applied to sensory neglect where conscious awareness would play the role of deliberate activity.

[Motor neglect of thalamic origin: report on two cases (author's transl)]. / La négligence motrice d'origine thalamique. A propos de deux cas.

Two cases of thalamic lesions with motor neglect are presented. The syndrome of motor neglect was complete in those cases with a) underutilization of left limbs, but good utilization upon verbal orders, b) loss of placement reaction, c) weakness of movement when hand was approaching the target, d) weakness of motor reaction to nociceptive stimuli. Those cases confirm that motor neglect exists after thalamic lesions and bring pathologic clues for topographic discussion. Motor neglect seems to be a particular case of partial unilateral neglect throwing some doubt on the hypothesis of a global trouble of hemispheric activation. Prevalence of left motor neglects suggests some linkage between propositional motility and language. One may suppose that in the right hemisphere language is able to have a vicarious action when spontaneous activation is lost; at the opposite, in the left hemisphere language and motility would be too linked to let this dissociation be generally possible.

[Amnesia from bilateral ischemic lesions of the thalamus (author's transl)]. / Amnésie par lésion ischémique bi-thalamique.

A 43-year-old woman developed during post-partum an axial amnesia of ischemic origin. Stereotactic correlations were obtained by matching CT scan images with the true reference plane of the examination, according to an original method. This led to the diagnosis of infarction in the territory of a paramedian thalamomesencephalic artery. The amnesia probably resulted from bilateral lesions of Vicq d'Azyr's bundle. Atypical features in this case were the absence of disorder of vigilance and oculomotor disorders. This striking fact in this patient was recovery of some recognition capability contrasting with the persistence of a major evocation disorder.