Search

We developed an automated squint assay using both black C57BL/6J and white CD1 mice to measure the interpalpebral fissure area between the upper and lower eyelids as an objective quantification of pain. The automated software detected a squint response to the commonly used nociceptive stimulus formalin in C57BL/6J mice. After this validation, we used the automated assay to detect a dose-dependent squint response to a migraine trigger, the neuropeptide calcitonin gene-related peptide, including a response in female mice at a dose below detection by the manual grimace scale. Finally, we found that the calcitonin gene-related peptide amylin induced squinting behavior in female mice, but not males. These data demonstrate that an automated squint assay can be used as an objective, real-time, continuous-scale measure of pain that provides higher precision and real-time analysis compared with manual grimace assessments.

Purpose Traumatic brain injury (TBI) is a risk factor for developing chronic neurodegenerative conditions including Alzheimer's disease (AD). The purpose of this study was to examine chronic effects of blast TBI on retinal ganglion cells (RGC), optic nerve, and brain amyloid load in a mouse model of AD amyloidosis. Methods Transgenic (TG) double-mutant APPswePSENd19e (APP/PS1) mice and nontransgenic (Non-TG) littermates were exposed to a single blast TBI (20 psi) at age 2 to 3 months. RGC cell structure and function was evaluated 2 months later (average age at endpoint = 4.5 months) using pattern electroretinogram (PERG), optical coherence tomography (OCT), and the chromatic pupil light reflex (cPLR), followed by histologic analysis of retina, optic nerve, and brain amyloid pathology. Results APP/PS1 mice exposed to blast TBI (TG-Blast) had significantly lower PERG and cPLR responses 2 months after injury compared to preblast values and compared to sham groups of APP/PS1 (TG-Sham) and nontransgenic (Non-TG-Sham) mice as well as nontransgenic blast-exposed mice (Non-TG-Blast). The TG-Blast group also had significantly thinner RGC complex and more optic nerve damage compared to all groups. No amyloid-β (Aβ) deposits were detected in retinas of APP/PS1 mice; however, increased amyloid precursor protein (APP)/Aβ-immunoreactivity was seen in TG-Blast compared to TG-Sham mice, particularly near blood vessels. TG-Blast and TG-Sham groups exhibited high variability in pathology severity, with a strong, but not statistically significant, trend for greater cerebral cortical Aβ plaque load in the TG-Blast compared to TG-Sham group. Conclusions When combined with a genetic susceptibility for developing amyloidosis of AD, blast TBI exposure leads to earlier RGC and optic nerve damage associated with modest but detectable increase in cerebral cortical Aβ pathology. These findings suggest that genetic risk factors for AD may increase the sensitivity of the retina to blast-mediated damage.

We developed an automated squint assay using both black C57BL/6J and white CD1 mice that measured the interpalpebral fissure area between the upper and lower eyelids as an objective quantification of pain. In C57BL/6J mice, we observed a squint response to increasing doses of a migraine trigger, the neuropeptide CGRP, including a significant response in female mice at a dose below detection by the manual grimace scale. Using the automated software, both C57BL/6J and CD1 mice lacked a detectable photic blink response. The CGRP-related peptide amylin induced squinting behavior in female mice, but not males. These data demonstrate that an automated squint assay can be used as an objective, real-time continuous-scale measure of pain that provides higher precision and real-time analysis compared to manual grimace assessments.

Migraine is the third most common disease in the world (behind dental caries and tension-type headache) with an estimated global prevalence of 15%, yet its etiology remains poorly understood. Recent clinical trials have heralded the potential of therapeutic antibodies that block the actions of the neuropeptide calcitonin gene-related peptide (CGRP) or its receptor to prevent migraine. Calcitonin gene-related peptide is believed to contribute to trigeminal nerve hypersensitivity and photosensitivity in migraine, but a direct role in pain associated with migraine has not been established. In this study, we report that peripherally administered CGRP can act in a light-independent manner to produce spontaneous pain in mice that is manifested as a facial grimace. As an objective validation of the orbital tightening action unit of the grimace response, we developed a squint assay using a video-based measurement of the eyelid fissure, which confirmed a significant squint response after CGRP injection, both in complete darkness and very bright light. These indicators of discomfort were completely blocked by preadministration of a monoclonal anti-CGRP-blocking antibody. However, the nonsteroidal anti-inflammatory drug meloxicam failed to block the effect of CGRP. Interestingly, an apparent sex-specific response to treatment was observed with the antimigraine drug sumatriptan partially blocking the CGRP response in male, but not female mice. These results demonstrate that CGRP can induce spontaneous pain, even in the absence of light, and that the squint response provides an objective biomarker for CGRP-induced pain that is translatable to humans.

Purpose Diagnosis of peripheral neuropathy (PN), which affects approximately 50% of the diabetic population, is subjective, with many patients seeking a diagnosis only after presenting with symptoms. Recently, in vivo confocal microscopy of subepithelial corneal nerve density has been promoted as a surrogate marker for early detection of PN, but imaging of corneal nerves requires sophisticated instrumentation, expertise in confocal imaging, cooperative patients, and automated analysis tools to derive corneal nerve density. As an alternative, we developed a simple screening method that is based on the sensitivity of corneal nerves to cause reflex eyelid squinting in response to hyperosmolar eye drops. Methods Eyes of control and type 2 diabetic rats were given an eye drop of a 290- to 900-mOsm solution, and the ocular response was video recorded. Other neuropathic end points including nerve conduction velocity and subepithelial cornea nerve density were determined. Results Motor and sensory nerve conduction velocity and total nerve fiber length of corneal nerves in the subepithelial layer were significantly decreased in diabetic rats. Applying the hyperosmotic solutions to the ocular surface caused an osmolarity-dependent increase in squinting of the treated eye in control rats. Squinting was almost totally blocked by preapplication of proparacaine or N-(4-tertiarybutylphenyl)-4-(3-chloropyridin-2-yl)tetrahydropyrazine-1(2H)-carbox-amide, a transient receptor potential melastatin-8 channel blocker. Squinting in response to the 900-mOsm solution was significantly reduced in diabetic rats. Conclusions Preclinical studies show that evaluation of corneal sensitivity may be an alternative method for the early detection of PN and has potential for translation to clinical studies.

This paper describes the design and operation of a highly flexible electronic flash system based around an 8-bit microconroller. Each unit is capable of emitting short and intense flashes of white and infrared light, and able to operate with various user-defined timing and intensity settings. Multiple units are capable of communicating with a master on the same bus. The system was designed for application within ophthalmology and visual sciences research.

Depressive disorders lack objective physiological measurements to characterize the affected population and facilitate study of relevant mechanisms. The melanopsin-mediated light signaling pathway may contribute to seasonal variation and can be measured non-invasively by pupillometry. We prospectively studied changes in melanopsin-mediated pupillary constriction in 19 participants with major depressive disorder (MDD) and 10 control across the summer and winter solstices. The melanopsin-mediated response, as measured by the pupil's sustained constriction six s after a high intensity blue light stimulus, was marginally attenuated in those with MDD relative to controls (p=0.071). The participants with MDD unexpectedly showed a significantly reduced transient pupillary response to low intensity red (p=0.011) and blue light (p=0.013), but not high intensity red and blue light. Sustained pupillary constriction in response to high intensity blue light was more pronounced with increasing daylight hours (p=0.037) and was more strongly related to objectively measured versus estimated light exposure. Melanopsin-mediated impairments in pupil response may serve as a biological marker for vulnerability to depression in low light conditions. Assessment of these and other responses to light stimuli, such as response to low intensity light, may be useful for the study of the neurobiology of MDD and related mood disorders.

PURPOSE The purpose of this study was to assess whether clinically useful measures of fixation instability and eccentricity can be derived from retinal tracking data obtained during optical coherence tomography (OCT) in patients with optic neuropathy (ON) and to develop a method for relating fixation to the retinal ganglion cell complex (GCC) thickness. METHODS Twenty-nine patients with ON underwent macular volume OCT with 30 seconds of confocal scanning laser ophthalmoscope (cSLO)-based eye tracking during fixation. Kernel density estimation quantified fixation instability and fixation eccentricity from the distribution of fixation points on the retina. Preferred ganglion cell layer loci (PGCL) and their relationship to the GCC thickness map were derived, accounting for radial displacement of retinal ganglion cell soma from their corresponding cones. RESULTS Fixation instability was increased in ON eyes (0.21 deg2) compared with normal eyes (0.06982 deg2; P < 0.001), and fixation eccentricity was increased in ON eyes (0.48°) compared with normal eyes (0.24°; P = 0.03). Fixation instability and eccentricity each correlated moderately with logMAR acuity and were highly predictive of central visual field loss. Twenty-six of 35 ON eyes had PGCL skewed toward local maxima of the GCC thickness map. Patients with bilateral dense central scotomas had PGCL in homonymous retinal locations with respect to the fovea. CONCLUSIONS Fixation instability and eccentricity measures obtained during cSLO-OCT assess the function of perifoveal retinal elements and predict central visual field loss in patients with ON. A model relating fixation to the GCC thickness map offers a method to assess the structure-function relationship between fixation and areas of preserved GCC in patients with ON.

Purpose Precise measurements of visual fixation and its instability were recorded during optical coherence tomography (OCT) as a marker of neural network dysfunction in multiple sclerosis (MS), which could be used to monitor disease progression or response to treatment. Methods A total of 16 MS patients and 26 normal subjects underwent 30 seconds of scanning laser ophthalmoscope (SLO)-based eye tracking during OCT scanning of retinal layer thickness. Study groups consisted of normal eyes, MS eyes without prior optic neuritis (MS wo ON), and MS eyes with prior optic neuritis (MS + ON). Kernel density estimation quantified fixation instability from the distribution of fixation points on the retina. In MS wo ON eyes, fixation instability was compared to other measures of visual and neurologic function. Results Fixation instability was increased in MS wo ON eyes (0.062 deg2) compared to normal eyes (0.030 deg2, P = 0.015). A further increase was seen for MS + ON eyes (0.11 deg2) compared to MS wo ON (P = 0.04) and normal (P = 0.006) eyes. Fixation instability correlated weakly with ganglion cell layer (GCL) volume and showed no correlation with low-contrast letter acuity, EDSS score, or SDMT score. Conclusions Fixation instability reflects the integrity of a widespread neural network germane to visual processing and ocular motor control, and is disturbed in MS. Further study of visual fixation, including the contribution of microsaccades to fixation instability, may provide insight into the localization of fixation abnormalities in MS and introduce innovative and easily measured outcomes for monitoring progression and treatment response.

Objective An important goal for functional brain studies using EEG technology is to estimate the location of brain sources that produce the scalp-recorded signals. The accuracy of source estimates is dependent upon many variables, one of which is the accurate description of the scalp positions of the EEG sensors. The objective of the present research was to develop a photogrammatic method for sensor localization that is fast, accurate, and easy to use. Methods With the novel photogrammetric method, multiple cameras were arranged in a geodesic array, and images of the sensors on the subject's head were acquired allowing for the reconstruction of the 3D sensor positions. Results Data from the photogrammetric method were compared with data acquired with the conventional electromagnetic method. The accuracy of the photogrammatic method, quantified as RMS of the measured positions and the actual known positions, was similar (mean error=1.27 mm) to the electromagnetic method (mean error=1.02 mm), and both approximated the localization error of the calibration object (mean error=0.56 mm). Conclusions Accurate determination of 3D sensor positions can be accomplished with minimal demands on the time of the subject and the experimenter using the photogrammetric method.

Purpose: to test the whether photosensitivity (photophobia) after traumatic brain injury (TBI) is due to increased sensitivity of the brainstem trigeminal sensory nucleus, as revealed objectively by an exaggerated photoblink reflex (photo-electromyogram). This will be tested in humans and in a mouse strain genetically engineered to be hypersensitive to calcitonin gene related peptide (CGRP), the neurotransmitter modulating trigeminal nerve function. Scope: objective methods to quantify photo-sensitivity include 1) light evoked potentials (electromyogram) from the blinking and squinting muscles of the forehead 2) the pupil light reflex 3) light evoked changes in sympathetic nerve activity, measured by changes in skin conductance and heart rate. Major Findings (Year 4): 1) we have designed and assembled a multi-camera platform that will allow us to transition from EMG recording with surface skin electrodes to an electrode-free system that will take advantage of facial feature changes in response to light and pain which is anticipated to be useful in remote settings and home testing, utilizing smart phone devices, 2) we have configured the recording and analysis software to apply Componica's software library to multiple camera video streams simultaneously in order to analyze minute changes in facial features in real time, and 3) we have tested additional normal subjects to better match age and sex of those subjects already tested with photosensitivity in order to define the normative range of values for light induced EMG. Significance: objective testing of photosensitivity in humans and mice will provide new approaches to finding the underlying mechanisms, classification of photosensitivity, diagnosis and monitoring of new treatments.

Purpose: to develop and validate objective tests to diagnose vision deficits in patients with cognitive impairment and ensure effective monitoring of their treatment. Scope: objective methods to monitor visual function include 1) the pupil light reflex (PLR), 2) light evoked potentials (VEP) from the brain and from the eye and 3) purposeful eye movements to track moving targets that are resolved. Major Findings (year 4): i) determined that the melanopsin mediated pupil response, derived from the differential sustained pupil response to blue light vs. red light, correlates highly with retinal ganglion cell layer thickness derived from optical coherence tomography (OCT) in eyes with optic neuropathy, ii) in terms of the red-blue pupil light reflex test, showed that the resulting responses measured with our custom DynaScan-Smart Eye system correlate well with results obtained with the clinically-used Neuroptics DP-2000 system, iii) found that a patient has greater difficulty to stay fixated on a fixation target during stimulation of a diseased eye. Significance: objective tests of vision will greatly improve eye care by providing faster, lower cost testing that can be performed in remote settings and will provide a new tool for assessing innovative treatments being developed to save or restore vision.

We describe a technique for noninvasive conductivity estimation of the human head tissues in vivo. It is based on the bounded electrical impedance tomography (bEIT) measurements procedure and realistically shaped high-resolution finite difference model (FDM) of the human head geometry composed from the subject specific co-registered CT and MRI. The first experimental results with two subjects demonstrate feasibility of such technology.

We have shown that using parameterized EIT measurements procedure and realistically shaped highresolution finite difference models (FDM) of the human head based on the subject specific co-registered CT and MRI scans, it was possible to extract up to 13 head tissues conductivities in simulations with synthetic data. We have used the multi-start downhill simplex and simulated annealing algorithms depending on the number of unknowns in inverse search. The procedure describes parcellation of a skull into 10–12 anatomically relevant bone plates and provides the skull conductivity inhomogeneities information in the forward solver for the EEG inverse problem. The preliminary results of the first experiments performed on a human subject are also reported.

Modern neuroimaging technologies afford a non-invasive view into the functions of the human brain with great spatial (fMRI) and temporal resolution (EEG). However, common signal analytic methods require averaging over many trials, which limits the potential for practical application of these technologies. In this paper we advance a novel single-trial analysis method for EEG and demonstrate this approach with a target detection task. The method utilizes a framework consisting of multiple processing modules that can be applied in whole or in part, including noise mitigation, source-space transformation, discriminant analysis, and performance evaluation. The framework introduces an enhanced noise mitigation technology based on Directed Components Analysis (DCA) that improves upon existing spatial filtering techniques. Source-space transformation, utilizing a finite difference model (FDM) of the human head, estimates activity measures of the cortical sources involved in task performance. Such a source-space discrimination provides measurement invariance between training and testing sessions and holds the promise of providing a degree of classification not possible with scalp-recorded EEG. The framework's discrimination modules interface with performance evaluation modules to generate classification performance statistics. When applied to EEG acquired during performance of a target detection task, this method demonstrated that neural signatures of target recognition correctly classified up to 87% of targets in a rapid serial visual presentation (RSVP) of target/non-target images. On average, the single-trial classification method resulted in greater than 60% improvement over behavioral performance for target detection.