Linear ensemble-coding in midbrain superior colliculus specifies the saccade kinematics

Recently, we proposed an ensemble-coding scheme of the midbrain superior colliculus (SC) in which, during a saccade, each spike emitted by each recruited SC neuron contributes a fixed minivector to the gaze-control motor output. The size and direction of this ‘spike vector’ depend exclusively on a cell’s location within the SC motor map (Goossens and Van Opstal, in J Neurophysiol 95: 2326–2341, 2006). According to this simple scheme, the planned saccade trajectory results from instantaneous linear summation of all spike vectors across the motor map. In our simulations with this model, the brainstem saccade generator was simplified by a linear feedback system, rendering the total model (which has only three free parameters) essentially linear. Interestingly, when this scheme was applied to actually recorded spike trains from 139 saccade-related SC neurons, measured during thousands of eye movements to single visual targets, straight saccades resulted with the correct velocity profiles and nonlinear kinematic relations (‘main sequence properties– and ‘component stretching’) Hence, we concluded that the kinematic nonlinearity of saccades resides in the spatial-temporal distribution of SC activity, rather than in the brainstem burst generator. The latter is generally assumed in models of the saccadic system. Here we analyze how this behaviour might emerge from this simple scheme. In addition, we will show new experimental evidence in support of the proposed mechanism

Niemann-Pick disease type C

Niemann-Pick C disease (NP-C) is a neurovisceral atypical lysosomal lipid storage disorder with an estimated minimal incidence of 1/120 000 live births. The broad clinical spectrum ranges from a neonatal rapidly fatal disorder to an adult-onset chronic neurodegenerative disease. The neurological involvement defines the disease severity in most patients but is typically preceded by systemic signs (cholestatic jaundice in the neonatal period or isolated spleno- or hepatosplenomegaly in infancy or childhood). The first neurological symptoms vary with age of onset: delay in developmental motor milestones (early infantile period), gait problems, falls, clumsiness, cataplexy, school problems (late infantile and juvenile period), and ataxia not unfrequently following initial psychiatric disturbances (adult form). The most characteristic sign is vertical supranuclear gaze palsy. The neurological disorder consists mainly of cerebellar ataxia, dysarthria, dysphagia, and progressive dementia. Cataplexy, seizures and dystonia are other common features. NP-C is transmitted in an autosomal recessive manner and is caused by mutations of either the NPC1 (95% of families) or the NPC2 genes. The exact functions of the NPC1 and NPC2 proteins are still unclear. NP-C is currently described as a cellular cholesterol trafficking defect but in the brain, the prominently stored lipids are gangliosides. Clinical examination should include comprehensive neurological and ophthalmological evaluations. The primary laboratory diagnosis requires living skin fibroblasts to demonstrate accumulation of unesterified cholesterol in perinuclear vesicles (lysosomes) after staining with filipin. Pronounced abnormalities are observed in about 80% of the cases, mild to moderate alterations in the remainder ("variant" biochemical phenotype). Genotyping of patients is useful to confirm the diagnosis in the latter patients and essential for future prenatal diagnosis. The differential diagnosis may include other lipidoses; idiopathic neonatal hepatitis and other causes of cholestatic icterus should be considered in neonates, and conditions with cerebellar ataxia, dystonia, cataplexy and supranuclear gaze palsy in older children and adults. Symptomatic management of patients is crucial. A first product, miglustat, has been granted marketing authorization in Europe and several other countries for specific treatment of the neurological manifestations. The prognosis largely correlates with the age at onset of the neurological manifestations

Blink perturbation effects on saccades evoked by microstimulation of the superior colliculus

Contains fulltext : 103911.pdf (publisher's version ) (Open Access

Prevalence of restless legs syndrome among psychiatric patients who are under antidepressant or antipsychotic monotherapy

WOS: 000383390400009Objective: Several groups of medications, such as dopamine blockers, analgesics and antihistaminergics were associated with restless legs syndrome (RLS). Although case reports showed some significant relations, they have many methodological limitations such as co-medications or medical co-morbidities. The aim of this study was to investigate the prevalence and severity of RLS in patients on antidepressant (AD) or antipsychotic (AP) monotherapy. Methods: One hundred and ninety-seven patients and 150 healthy controls were included in the study. RLS was diagnosed according to the International Restless Legs Syndrome Study Group (IRLSSG) criteria. The severity of RLS was evaluated according to IRLSSG rating scale. Participants diagnosed with RLS went under further neurological and psychiatric investigation for excluding secondary causes. Results: One hundred and twenty patients (60.9%) were on AD therapy, while 77 patients (39.1%) were on AP monotherapy. Thirty-two patients (16.2%) and seven controls (4.7%) were diagnosed with RLS according to IRLSSG criteria. The most frequent cause of RLS was quetiapine (28.5%) in the antipsychotic group and paroxetine (22.2%) in the antidepressant group. There was no statistically significant correlation between drug usage duration and RLS severity. Conclusion: AD or AP induced RLS is a common condition. ADs and APs should be considered as a cause for RLS when assesing RLS in psychiatric patients who are under treatment either of these medications