Multi-color flow cytometer with PIC-based structured illumination.

We demonstrate a flow cytometer in which structured light illumination is used to attribute fluorescent and scattering signals to their excitation wavelength. A suitable multi-color light source emitting structured illumination patterns at 405, 488, 561 and 640 nm is developed based on a silicon nitride photonic integrated circuit and cytometry experiments are conducted with calibration beads. Performance metrics of the novel cytometer are compared with those of a mature, commercial device. While the experimental device still features a slightly higher sensitivity floor than the commercial one, all but the most weakly stained beads can be categorized. These promising results validate the feasibility of the proposed concept.

Atypical prosopagnosia following right hemispheric stroke: A 23-year follow-up study with M.T.

Most findings on prosopagnosia to date suggest preserved voice recognition in prosopagnosia (except in cases with bilateral lesions). Here we report a follow-up examination on M.T., suffering from acquired prosopagnosia following a large unilateral right-hemispheric lesion in frontal, parietal, and anterior temporal areas excluding core ventral occipitotemporal face areas. Twenty-three years after initial testing we reassessed face and object recognition skills [Henke, K., Schweinberger, S. R., Grigo, A., Klos, T., & Sommer, W. (1998). Specificity of face recognition: Recognition of exemplars of non-face objects in prosopagnosia. Cortex, 34(2), 289-296]; [Schweinberger, S. R., Klos, T., & Sommer, W. (1995). Covert face recognition in prosopagnosia - A dissociable function? Cortex, 31(3), 517-529] and additionally studied voice recognition. Confirming the persistence of deficits, M.T. exhibited substantial impairments in famous face recognition and memory for learned faces, but preserved face matching and object recognition skills. Critically, he showed substantially impaired voice recognition skills. These findings are congruent with the ideas that (i) prosopagnosia after right anterior temporal lesions can persist over long periods > 20 years, and that (ii) such lesions can be associated with both facial and vocal deficits in person recognition.

Silicon nitride PIC-based multi-color laser engines for life science applications.

We implement a multi-color laser engine with silicon nitride photonic integrated circuit technology, that combines four fluorophore excitation wavelengths (405 nm, 488 nm, 561 nm, 640 nm) and splits them with variable attenuation among two output fibers used for different microscope imaging modalities. With the help of photonic integrated circuit technology, the volume of the multi-color laser engine's optics is reduced by two orders of magnitude compared to its commercially available discrete optics counterpart. Light multiplexing is implemented by means of a directional coupler based device and variable optical attenuation as well as fiber switching with thermally actuated Mach-Zehnder interferometers. Total insertion losses from lasers to output fibers are in the order of 6 dB at 488 nm, 561 nm, and 640 nm. Higher insertion losses at 405 nm can be further improved on. In addition to the system level results, spectrally resolved performance has been characterized for each of the developed devices.

Visual feedback explains why propointing is better than antipointing in spatial neglect.

Rossit et al. (2011) showed that neglect patients perform normally in a propointing task but not in an antipointing task which requires pointing towards the mirrored position of a target. It is assumed that antipointing relies on information from the perceptual pathway of our visual brain. Therefore, this finding supports the notion that neglect is a disorder that primarily affects perceptual spatial representations within the brain leaving spatial maps used for visuomotor guidance intact. Alternatively, performance of patients might be compromised in both tasks, but only obviously so in tasks in which online corrections are made more difficult. It can be argued that online-corrections via visual feedback are less effective in antipointing because a direct comparison between hand and target is not possible in this condition. Secondly, it is also known that neglect patients have a pronounced egocentric bias which is assumed to be associated with a deviation of the perceived body midline. Since the midline is used to compute the end-position in the antipointing task this could also explain why patients are worse in antipointing. We investigated the influence of visual feedback on pro- and antipointing and the effect of providing a visual reference line for the antipointing task in right-brain damaged patients with neglect (n = 20), right-brain damaged patients without neglect (n = 23) and in a group of healthy participants (n = 22). The withdrawal of visual feedback had a stronger effect on propointing compared to antipointing. This effect was stronger in neglect patients than in patients without neglect or healthy controls. The introduction of a reference line reduced errors in antipointing performance, particularly in neglect patients with a strong egocentric bias. The results support our alternative account and challenge the hypothesis that the spatial disorder in neglect affects primarily perceptual maps within the visual system.

Neglect and prism adaptation: a new therapeutic tool for spatial cognition disorders.

PURPOSE: A large proportion of right-hemisphere stroke patients show unilateral neglect, a neurological deficit of perception, attention, representation, and/or performing actions within their left-sided space, inducing many functional debilitating effects on everyday life, and responsible for poor functional recovery and ability to benefit from treatment. This spatial cognition disorder affects the orientation of behaviour with a shift of proprioceptive representations toward the lesion side. METHODS: This shift can be reduced after a prism adaptation period to a right lateral displacement of visual field (induced by a simple target-pointing task with base-left wedge prisms). The modification of visuo-motor or sensory-motor correspondences induced by prism adaptation involves improvement of different symptoms of neglect. RESULTS: Classical visuo-motor tests could be improved for at least 2h after adaptation, but also non-motor and non-visual tasks. In addition, cross-modal effects have been described (tactile extinction and dichotic listening), mental imagery tasks (geographic map, number bisection) and even visuo-constructive disorders. These cognitive effects are shown to result from indirect bottom-up effects of the deeper, adaptive realignment component of the reaction to prisms. Lesion studies and functional imaging data evoke a cerebello-cortical network in which each structure plays a specific role and not all structures are crucial for adaptation ability. CONCLUSIONS: These cognitive effects of prism adaptation suggest that prism adaptation does not act specifically on the ipsilesional bias characteristic of unilateral neglect but rehabilitates more generally the visuo-spatial functions attributed to the right cortical hemisphere. These results reinforce the idea that the process of prism adaptation may activate brain functions related to multisensory integration and higher spatial representations and show a generalization at a functional level. Prism adaptation therefore appears as a new powerful therapeutic tool for spatial cognition disorders.