Brain : a journal of neurology
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Precise knowledge about limb position and orientation is essential for the ability of the nervous system to plan and control voluntary movement. While it is well established that proprioceptive signals from peripheral receptors are necessary for sensing limb position and motion, it is less clear which supraspinal structures mediate the signals that ultimately lead to the conscious awareness of limb position (kinaesthesia). Recent functional imaging studies have revealed that the cerebellum, but not the basal ganglia, are involved in sensory processing of proprioceptive information induced by passive and active movements. ⋯ This kinaesthetic impairment significantly correlated with the severity of disease in Parkinson's disease patients, as determined by the Unified Parkinson's Disease Rating Scale (r = -0.7, P = 0.03) and duration of disease (r = -0.7, P = 0.05). In contrast, there was no significant correlation between performance and the daily levodopa equivalent dose. These results imply that an intact cerebro-basal ganglia loop is essential for awareness of limb position and suggest a selective role of the basal ganglia but not the cerebellum in kinaesthesia.
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Comparative Study
Autobiographical memory and autonoetic consciousness: triple dissociation in neurodegenerative diseases.
Few studies have investigated autobiographical amnesia in neurodegenerative diseases and yet these pathologies are particularly relevant when addressing the issue of theories of long-term memory consolidation. According to the standard model, the medial temporal lobe (MTL) is involved in the storage and retrieval of episodic and semantic memories during a limited period of years. An alternative model, the multiple trace theory (MTT), suggests that the capacity of the MTL to recollect episodic memories is of a more permanent nature. ⋯ A deficit of autonoetic consciousness emerged in Alzheimer's disease and fv-FTD, but not in semantic dementia, though beyond the most recent 12-month period, the latter group could not justify their subjective sense of remembering to the same extent as the controls, in terms of the actual contextual information retrieved-phenomenological, spatial or temporal details. Our results demonstrate that autobiographical amnesia varies according to the nature of the memories under consideration and the locus of cerebral dysfunction. They are discussed in the light of the two competing models of long-term memory consolidation and recent conceptions of autobiographical recollection: new insights based on current concepts of episodic memories challenge the standard model and tend to support the MTT instead.
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Laser pulses excite superficial free nerve endings innervated by small-myelinated (Adelta) and unmyelinated (C) fibres. Whereas laser-evoked scalp potentials (LEPs) are now reliably used to assess function of the Adelta-fibre nociceptive pathways in patients with peripheral or central lesions, the selective activation of C-fibre receptors and recording of the related brain potentials remain difficult. To investigate trigeminal C-fibre function, we directed laser pulses to the facial skin and studied sensory perception and scalp evoked potentials related to Adelta- or C-fibre activation in healthy humans and patients--one having a bilateral facial palsy, two a trigeminal neuropathy, and two a Wallenberg syndrome. ⋯ The trigeminal territory yields rewarding LEP findings owing to the high density of thermal receptors and, because the short conduction distance, minimizes the problem of signal dispersion along slow-conducting unmyelinated afferents. The opercular-insular region and the cingulate gyrus are involved in the processing of C-fibre trigeminal inputs. The method we describe may prove useful in patients with lesions affecting the trigeminal thermal pain pathways.
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Case Reports
Clinical correlates with anti-MuSK antibodies in generalized seronegative myasthenia gravis.
The term seronegative myasthenia gravis (SNMG) refers to the generalized disease without detectable anti-acetylcholine receptor (anti-AChR) antibodies. In these patients, IgG antibodies against the muscle-specific kinase (MuSK) have been described, which reduced agrin-induced AChR clustering in vitro. We have assayed anti-MuSK antibodies in 78 patients with SNMG, who have been followed for many years in our Institution. ⋯ At the end of the observation period, most patients, although improved, were still symptomatic, having developed permanent facial and pharyngeal weakness together with some atrophy of facial muscles. MuSK-negative disease was comparatively more heterogeneous. Most patients were affected with mild to moderate symptoms and responded well to pharmacological treatment; however, a few subjects in this group had severe refractory disease, poorly responsive to both acetylcholinesterase inhibitors and immunosuppressants.
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Migraineurs are characterized interictally by lack of habituation, or even potentiation, of cortical evoked potentials during repetitive stimulation and by a strong intensity dependence of auditory evoked potentials (IDAP). To determine whether these two features of sensory processing are interrelated, we have studied them simultaneously on the same recordings of auditory evoked potentials (AEPs). AEPs were obtained at four different stimulation intensities in 14 patients suffering from migraine without aura (MO) and 14 healthy volunteers (HV). ⋯ The negative correlation found between IDAP and habituation suggests that the latter is able to have a strong influence on the former and perhaps even lead to it. In migraine, the habituation deficit amplifies the IDAP and may thus be the causal functional abnormality. We propose that it is due to a decreased pre-activation level of sensory cortices, a hypothesis also supported in this study by the lower amplitude of first AEP blocks in patients.