Subcortical neglect as a consequence of a remote parieto-temporal dysfunction. A quantitative EEG study.

In patients with a right-sided deep-seated lesion, a causal relationship between a cortical dysfunction in the right temporo-parietal region and the occurrence of neglect has been suggested. In the present study we tried to correlate clinical and quantitative EEG data from a sample of 33 right stroke patients divided into two subgroups according to the presence or absence of neglect. A 20-channel EEG cartography system was used for EEG mapping. Delta and theta activities were calculated in sixteen regions of interest. The analysis of raw values stressed the importance of the right parieto-temporal cortex to discriminate between the two subgroups of patients. These results suggest that in patients with right subcortical damage, a remote cortical parieto-temporal dysfunction within an intra-hemispheric network is necessary to provoke neglect.

Quantitative EEG in subcortical neglect.

Right-sided capsulo-lenticular strokes may cause left visuo-spatial neglect. The neural mechanism most frequently evoked to account for the occurrence of related cognitive disorders is remote cortical dysfunction in the posterior part of the right hemisphere. We studied 33 patients with capsulo-lenticular stroke, with (n = 16) or without (n = 17) associated subcortical neglect. A 20-channel EEG cartography system was used. Four regions of interest were delineated on the topographic map. Absolute delta and thêta amplitude peaks were obtained, as well as left-to-right ratios between activities in homologous regions of interest. The population was subdivided into two groups according to the presence or absence of neglect. Delta activity was higher in neglect patients than in patients without neglect, but the magnitude of delta activity differences between the two groups of patients did not depend on the site. The left-to-right ratio of delta activity between posterior homologous regions was lower in neglect patients, suggesting that right posterior dysfunction producing an imbalance between these regions might contribute to the emergence of the attention disorder.

Pathogenesis of subcortical visuo-spatial neglect. A HMPAO SPECT study.

The pathophysiology of neuropsychological disorders due to right deep-seated hemispheric lesions remains a debated point. We undertook this study to check the hypothesis according to which remote cortical dysfunction could be responsible for the occurrence of neglect. Twenty-eight patients presenting with a right-sided subcortical stroke were studied. A neuropsychological battery of tests suitable for assessment of possible visuo-spatial neglect was performed as well as HMPAO SPECT. Neglect was observed in 15 cases out of 28. The lesion's site (at CT and/or MRI) did not allow discrimination between patients without neglect and patients with neglect. The latter however could be distinguished from the former by the presence of a remote decrease in cortical blood flow in the right temporo-parietal region. By suggesting that cortical involvement is necessary for the occurrence of neglect, the results were interpreted according to a network approach in which subcortical neglect is attributed to a cortical deprivation from afferent input in the posterior part of the brain.

Remote cortical dysfunction as a possible cause of subcortical neglect? A regional cerebral blood flow study.

Cortical remote effects of right deep-seated lesions were studied with two cerebral blood flow measurement methods (two-dimensional xenon-133 inhalation and 99mTc HMPAO SPECT) in a population of 13 right-handed stroke patients. A neuropsychological battery of tests suitable for assessment of possible visual neglect was performed. Neglect was present in 7 cases. A regional cortical hypoperfusion was observed in all patients. However, in neglect patients it was more extended and involved the right inferior parietal region suggesting a causal relationship between cortical dysfunction and neuropsychological deficit. This finding supports the model attributing neglect to a unilateral attention-arousal defect in a cortico-limbic-reticular loop.

Functional dissociations following bilateral lesions of auditory cortex.

We present two patients with bilateral lesions of the superior temporal cortex who manifested a number of functional dissociations in the auditory domain. The perception of speech and environmental sounds were preserved; yet, the perception of tunes, prosody and voice was impaired. As the processing of melodic but not rhythmic variations in musical sequences was selectively disturbed, the deficit cannot be attributed to a general impairment in auditory memory or sequential processing. These findings suggest that melody processing is not mediated by a general-purpose auditory architecture but by specialized cortical subsystems residing within the lesioned areas. Current taxonomies of auditory agnosia and models of normal music cognition are evaluated in light of the functional dissociations manifested by these patients.

Pure topographical disorientation due to a deep-seated lesion with cortical remote effects.

Lesions producing pure topographical disorientation syndromes are classically located either in the right parietal region either in the right parahippocampal gyrus. The patient described in the present study was admitted to hospital after sudden onset of a left hemiparesis. The lesion at CT scan was located in the posterior limb of the right internal capsule. Neuropsychological assessment was normal except for the presence of a major topographical disorientation and of mnestic disturbances for visuo-spatial material leading us to attribute topographical disorientation to a specific loss of topographical memory. Regional cerebral blood flow measurements disclosed a right parietal hypoperfusion. This remote cortical effect could account for the presence of the neuropsychological disorders.

[Cerebral crossed diaschisis caused by cerebellar lesion: role of the cerebellum in mental functions]. / Diaschisis cérébral croisé par lésion cérébelleuse: rôle du cervelet dans les fonctions mentales.

In 3 patients with a stroke limited to the posterior fossa, regional cerebral blood Flows were measured by the 133 Xe inhalation method (the first two cases) or by the SPECT with HMPAO method (the third case). The first patient had a median and paramedian hematoma of the left cerebellar hemisphere and the left dorsolateral portion of the pons. Remote cerebral hypoperfusion, measured 3 months later, was observed in both frontal premotor regions (but more marked in the right hemisphere) and in a circumscribed area of the right temporal region. The second patient had a right-sided ischaemic lesion of the anterior cerebellar lobe and the mesencephalic tectum. Contralateral parietal and rolandic hypoperfusion, measured 7 weeks after the stroke, was observed. The third patient had on old infarct of the right cerebellar hemisphere. The SPECT, measured 17 years later, showed a left fronto-parieto-temporal hypoperfusion and the absence of perfusion in the right cerebellar hemisphere. Preliminary data of neuropsychological assessment in our patients disclosed impairment in visuo-spatial and constructive organization, memory and learning compatible with the published findings in some patients and animals with predominantly cerebellar damage. These interesting findings should be confirmed in a large number of patients with age, sex, and sociocultural matched controls. In the absence of supratentorial insult, and during the hemodynamical stable phase, crossed cerebello-cerebral diaschisis is suggested in our 3 patients. Although it is too early to draw definite conclusions, our findings may: (1) confirm the functional interconnections between the cerebellum and the cerebrum in man and (2) provide functional basis for the behavioral function impairment reported in patients with cerebellar insult. Further rCBF, metabolism, and pathologic studies on this subject are required to elucidate this issue.

Spatial constraints on attention to speech in the blind.

When sighted persons try to identify one of two speech utterances coming from different directions, they display both a frontal position advantage, i.e., better recognition of inputs from the front than of those from the rear, and a right-side advantage, better recognition of inputs from the right than of those from the left. The present study demonstrates a dissociation of the two effects in blind subjects (N = 10) who showed no frontal position advantage together with a right-side advantage superior to that of control sighted subjects (N = 16). There was no systematic difference between congenitally blind subjects and noncongenitals. The absence of frontal position advantage in the blind is consistent with the notion that this effect originates in the habit of sighted listeners to orient toward the source of heard speech. The occurrence of at least normal right-side advantage in the blind does not support recent suggestions of reduced lateralization of language functions in such subjects.

Assessment of hemispheric dominance for language in crossed aphasia by two atraumatic methods.

In a right handed patient with crossed aphasia, two atraumatic techniques (regional cerebral blood flow measurements during the performance of a linguistic task and dichotic listening test) were used to assess language lateralization. The prominence of rCBF activation patterns in the right hemisphere and the presence of a clear-cut right ear extinction on the dichotic listening test provide evidence that, is this case, the right hemisphere was dominant for language.

[Agraphia, cortical anarthria and planning disorders as a result of a lesion of the right hemisphere in a right-handed patient]. / Agraphie, anarthrie corticale et troubles de la programmation par lésion hémisphérique droite chez un droitier manuel.

A right-hemisphere premotor cerebral infarct in a right-handed man from a largely left-handed family caused cortical anarthria and constructional agraphia. The effect of programming difficulties on impaired oral and written expression was demonstrated by the clinical picture of pure agraphia, which could thus be attributed to a primary disorder of programming. Measurements of cerebral blood flow three months after the accident showed that language representation was ambilateral.

Spatial effects in speech perception in the absence of spatial competition.

Two synthetic speech syllables, differing in pitch, were presented over one loudspeaker situated at one of the following azimuths: 0 degrees (in from of the subject); 45 degrees, 90 degrees, and 135 degrees to the left or to the right; and 180 degrees. The subject's task was to report the high-pitch syllable. The pattern of performance can be described in terms of two component effects: a decreasing anterior-posterior gradient, and right-side advantage. Competition between messages from one direction only appears to be as effective in determining auditory spatial effects as competition between spatially distinct sources.

Spatial constraints on focused attention: beyond the right-side advantage.

The subjects listened to one of two simulataneous synthetic speech syllables delivered independently over two loudspeakers. When the loudspeakers were situated at 90 degrees to the left and to the right, right-side advantage was found. When one loudspeaker was situated in front of the subject in the median plane, and the other at one of several azimuthal positions around him an advantage of the frontal position was observed in all cases. On the other hand, performance on the nonfrontal message was affected significantly by its position. The pattern of performance which is presumably to cerebral dominance, an advantage of sources situated in front of the subject over those at his back, and possibly an advantage of sources near the median plane over more remote ones.