Lulu L. C. D. Bursztyn

Neural correlates of internal-model loading.

Skilled object manipulation requires knowledge, or internal models, of object dynamics relating applied force to motion , and our ability to handle myriad objects indicates that the brain maintains multiple models . Recent behavioral studies have shown that once learned, an internal model of an object with novel dynamics can be rapidly recruited and derecruited as the object is grasped and released . We used event-related fMRI to investigate neural activity linked to grasping an object with recently learned dynamics in preparation for moving it after a delay. Subjects also performed two control tasks in which they either moved without the object in hand or applied isometric forces to the object. In all trials, subjects received a cue indicating which task to perform in response to a go signal delivered 5-10 s later. We examined BOLD responses during the interval between the cue and go and assessed the conjunction of the two contrasts formed by comparing the primary task to each control. The analysis revealed significant activity in the ipsilateral cerebellum and the contralateral and supplementary motor areas. We propose that these regions are involved in internal-model recruitment in preparation for movement execution.

Sensorimotor memory of weight asymmetry in object manipulation

Using a precision grip-lifting task, we examined how sensorimotor memory for weight asymmetry transfers across changes in hand and object configuration. We measured object tilt when participants lifted a visually symmetric box with an offset centre of mass. Transfer was assessed after participants lifted the box 10 times, during which the large tilt observed in the first lift was reduced. Consistent with previous work of Salimi et al. (J Neurophysiol 84:2390–2397, 2000), we found that when the object was rotated 180°, participants failed to update their sensorimotor memory appropriately. Instead, participants acted as if the object did not rotate and negative transfer was observed. However, when the hand was rotated 180° around the object, participants were able to correctly update sensorimotor memory and positive transfer was observed. This finding argues against the hypothesis that sensorimotor memory is digit-specific because the rotation of the hand (like rotation of the object) changes the forces that each digit must generate to prevent tilt. Positive transfer was also observed when both the hand and object were rotated. This suggests that the rotation of the hand may facilitate rotation of an internal representation of the object. Finally, we found positive transfer of weight asymmetry across the two hands but only when the second hand was rotated such that homologous digits of each hand gripped the same contact surfaces. We suggest that good transfer is observed under these conditions because, when we pass objects from hand to hand, we typically place homologous digits of the two hands in similar locations on the object.

Has rising pediatric obesity increased the incidence of idiopathic intracranial hypertension in children

OBJECTIVE Idiopathic intracranial hypertension (IIH) in children is an uncommon but significant cause of morbidity, including permanent visual loss. It is important to understand if, like obesity, IIH in children is on the rise and is related to that increase. The aim of this study is to compare the recent incidence rate of pediatric IIH in a tertiary care hospital with earlier data published from that same hospital. DESIGN Retrospective chart review. PARTICIPANTS All children aged 2 to 16 years diagnosed with IIH at the IWK Health Centre in Halifax between 1997 and 2007. METHODS Charts of eligible patients were reviewed to ensure all diagnostic criteria for IIH were met. Incidence and obesity rates were calculated based on data from Statistics Canada. RESULTS Twelve cases (5 males, 7 females) fulfilling the diagnostic criteria for IIH were identified, for an annual incidence of 0.6 cases per 100,000 children with no sex predilection (p = 0.51). Obesity was noted in 75% of patients examined (9/12). Children older than 12 years were more likely to be obese (6/6, 100%) compared with those younger than 12 years (3/6, 50%). CONCLUSIONS The calculated incidence is lower than that found in an earlier study for the same geographic region (0.9 cases per 100,000 children) despite increasing obesity rates. This decrease may be a reflection of improved diagnostic techniques or may indicate that factors other than obesity govern IIH predilection in younger children.

Simple Approach for Quantifying the Thermodynamic Potential of Polymer–Polymer Adhesion

ABSTRACT The free energies of mixing a series of water-soluble polymers with cellulose were calculated using the UNIFAC (universal functional group activity coefficients) algorithm, and the results were correlated with measurements of polymer/cellulose adhesion. The more negative the minimum free energy of mixing, the greater the measured adhesion. Adhesion was quantified by single-lap shear test in which regenerated cellulose films were laminated with aqueous polymer. The results are relevant to the use of adsorbed water-borne polymers to strengthen cellulose fiber–fiber bonds in paper. The calculations did not anticipate the exceptional strength-enhancing properties of carboxymethyl cellulose, nor did they predict molecular-weight effects. Nevertheless, the approach may have utility as a general tool to relate polymer chemistry to adhesion performance.

The Optic Disc Drusen Studies Consortium Recommendations for Diagnosis of Optic Disc Drusen Using Optical Coherence Tomography

Background: Making an accurate diagnosis of optic disc drusen (ODD) is important as part of the work-up for possible life-threatening optic disc edema. It also is important to follow the slowly progressive visual field defects many patients with ODD experience. The introduction of enhanced depth imaging optical coherence tomography (EDI-OCT) has improved the visualization of more deeply buried ODD. There is, however, no consensus regarding the diagnosis of ODD using OCT. The purpose of this study was to develop a consensus recommendation for diagnosing ODD using OCT. Methods: The members of the Optic Disc Drusen Studies (ODDS) Consortium are either fellowship trained neuro-ophthalmologists with an interest in ODD, or researchers with an interest in ODD. Four standardization steps were performed by the consortium members with a focus on both image acquisition and diagnosis of ODD. Results: Based on prior knowledge and experiences from the standardization steps, the ODDS Consortium reached a consensus regarding OCT acquisition and diagnosis of ODD. The recommendations from the ODDS Consortium include scanning protocol, data selection, data analysis, and nomenclature. Conclusions: The ODDS Consortium recommendations are important in the process of establishing a reliable and consistent diagnosis of ODD using OCT for both clinicians and researchers.

Vision loss caused by retinal and lateral geniculate nucleus infarction in H1N1 influenza

A 13-year-old girl developed encephalopathy and severe bilateral vision loss to the level of light perception within 24 hours of having fever and myalgias heralding H1N1 influenza A. Ophthalmoscopy demonstrated findings of confluent ischemic retinopathy. Brain MRI disclosed lateral geniculate body signal abnormalities indicative of hemorrhagic infarction. Despite aggressive treatment with intravenous corticosteroids, intravenous immunoglobulin, and plasmapheresis, vision did not substantially improve. This case demonstrates that H1N1 can cause simultaneous retinal and lateral geniculate body infarctions, a combination of findings not previously described in any condition. We postulate an immunologic response to the virus marked by occlusive damage to arteriolar endothelium.

Congenital trochlear-oculomotor synkinesis.

Synkinesis of the extraocular muscles forms a subset of congenital ocular motility abnormalities termed congenital cranial dysinnervation disorders. Synkinesis most frequently involves the abducens or oculomotor nerves and rarely the trochlear nerve. Only 3 such patients have been described in the literature. We report an isolated case of trochlear-oculomotor synkinesis in a healthy 6-year-old boy and discuss the proposed pathophysiology of this disorder.

Multiple Cranial Nerve Palsies in Giant Cell Arteritis

Giant cell arteritis (GCA) is a systemic vasculitis of medium and large arteries often with ophthalmic involvement, including ischemic optic neuropathy, retinal artery occlusion, and ocular motor cranial nerve palsies. This last complication occurs in 2%-15% of patients, but typically involves only 1 cranial nerve. We present 2 patients with biopsy-proven GCA associated with multiple cranial nerve palsies.

Comparison of intraocular pressure post penetrating keratoplasty vs Descemet's stripping endothelial keratoplasty.

OBJECTIVE To compare the effect of Descemets stripping endothelial keratoplasty (DSEK) with penetrating keratoplasty (PKP) on intraocular pressure (IOP) and use of ocular antihypertensives. DESIGN Retrospective cohort study. PARTICIPANTS Thirty-five eyes in 33 patients undergoing PKP and 43 eyes in 38 patients undergoing DSEK were included in the analysis. Fifteen eyes undergoing PKP and 12 undergoing DSEK had diagnosed glaucoma. Patients undergoing corneal transplant because of trauma, keratoconus, pellucid marginal degeneration, or prior failed transplant were excluded. METHODS Charts were obtained for all patients who underwent PKP or DSEK by a single surgeon at the Ivey Eye Institute between 2003 and 2010. IOP and all IOP-lowering medications were recorded preoperatively and at 1, 4, 8, 12, and 24 weeks postoperatively. Complications, graft survival, and glaucoma surgeries were noted. RESULTS There was no significant difference in preoperative IOP between the 2 groups (p = 0.30). Postoperatively, IOP was significantly higher in the PKP group at 1 week (p < 0.01), 4 weeks (p < 0.01), and 8 and 12 weeks (p < 0.05), but not at 24 weeks (p = 0.62). Mean IOP increased significantly post-transplant in all groups (p < 0.05). In patients without glaucoma, postoperative IOP elevation requiring treatment occurred in 68% of PKP eyes and 23% of DSEK eyes. In patients with prior glaucoma, an increased requirement for ocular antihypertensives occurred in 60% of PKP eyes and 20% of DSEK eyes. Three trabeculectomies and 1 tube shunt were performed in the cohort with glaucoma undergoing PKP. No glaucoma surgery was required in the DSEK cohort. CONCLUSIONS Elevation of IOP requiring treatment occurred at a lower rate after DSEK compared with PKP. This difference was significant during the early postoperative course but nonsignificant at 24 weeks. Additional long-term studies on the effect of DSEK on glaucoma and IOP control are warranted.

Positive Apraclonidine Test in Horner Syndrome Caused by Thalamic Hemorrhage.

Reversal of anisocoria following instillation of apraclonidine 0.5% has been reported in Horner syndrome caused by lesions of the central and peripheral nervous system. The shortest documented latency between symptom onset and a positive apraclonidine test is 36 hours, occurring in a patient with a pontomedullary infarct. We present the case of a 69-year-old man with Horner syndrome due to thalamic hemorrhage in whom apraclonidine testing demonstrated reversal of anisocoria 4 days after symptom onset. This is the first reported case of a positive apraclonidine test in a Horner syndrome caused by a lesion at this site. It suggests that apraclonidine testing is useful in confirming the diagnosis within days of onset even in a lesion located at the most proximal portion of the oculosympathetic pathway.