Peter Calvert, Upstate Medical University
Stacy Ruvio, University of Rochester
Optogenetics is a combination of optical and genetic methods that allows for targeted, fast control of precisely defined events in biological systems in response to light. Light-sensitive microbial opsins, including the blue light-activated cation channel channelrhodopsin (ChR2) along with its red-shifted version VChR1, and also the green light-activated chloride pump halorhodopsin (NpHR), have recently been transduced into rodent brain to control neural activity. The goal of this project was to develop optogenetic tools to test the contributions of inhibitory and excitatory cortical connections to response properties of neurons in rat visual cortex. As a first step we obtained viral vectors targeting different optogenetic probes to either excitatory or inhibitory neurons and characterized the behavior of transduced neurons in acute slices of the rat hippocampus. We examined three viral vectors containing specific promoters designed to target specific types of neurons: two adeno-associated viruses (rAAV/CaMKII-ChR2 and rAAV/CaMKII-NpHR) targeted to excitatory neurons, and a herpes simplex virus (HSV/MGad67-VChR1) targeted to inhibitory neurons. We found maximal expression of transduced proteins approximately two weeks after injection in all three vectors. Surprisingly, immunocytochemical analysis revealed that all three viral vectors targeted primarily excitatory neurons despite the use of a GAD67 promoter in the HSV construct. Experiments with the AAV vectors showed no conclusive effect of light on activity within the hippocampus as assayed using intra and extracellular recordings. We are currently in the processes of determining better transduction methods that will allow for the control of neuronal activity using light in the hippocampus and visual cortex.
Jaewon Hwang, Advisor: Lizabeth Romanski, University of Rochester
Faces and voices are important stimuli for social communication and interaction. While it is known that there is a close relationship between face and voice processing, it remains unknown how faces and voices are combined at the level of a single neuron in the brain. The ventrolateral prefrontal cortex (VLPFC) is one part of a network of brain regions in which face-vocalization integration occurs. Because of its location and anatomical connections, this area has been noted as a possible homologue of human language areas in the inferior frontal gyrus. It is therefore important to understand the cellular activity in this region during vocal stimulus processing or face-vocalization integration. We investigated the neural basis of audiovisual face-vocalization processing and integration in the non-human primate VLPFC. Specifically we recorded from single neurons in VLPFC while subjects performed audiovisual discrimination tasks in which species-specific faces and vocalizations were used. Our experiments indicate that VLPFC neuronal activity is modulated by stimulus, task and contextual factors. We have also investigated the time course of auditory and visual processing in VLPFC neurons. Although auditory processing is typically faster than visual processing, the natural lag of vocal stimuli compared to the accompanying visual mouth movements results in an earlier rise time for visual information in VLPFC. Our results confirm and extend our understanding of the factors which affect how communication information is processed and integrated by single cells in primate frontal lobe.
Andrea Viczian, SUNY Upstate, Syracuse
Dr. Viczian studies why a group of seemingly similar cells in the early embryonic eye choose to become one retinal cell type and not another. In collaboration with the Zuber lab, the Viczian team discovered that one protein, Noggin, could replace the eye field transcription factors (EFTFs) in generating an entire functional eye from pluripotent cells in frog. Her group is now looking at this molecular mechanism, as well as using this and other proteins to generate specific retinal cells in culture. They are particularly interested in cone photoreceptors.
Adam Gazzaley, University of California, San Francisco
Cognitive aging is characterized by deficits that cross multiple domains, including attention, perception, working memory and long-term memory. Convergent findings from our laboratory support an emerging theory that alterations in top-down modulation occur in healthy older adults and are associated with cognitive deficits. Top-down modulation is a fundamental neural process that involves the modulation of activity in sensory cortices based on an individual's goals. It is characterized by the enhancement or suppression of neural representations, both when stimuli are encountered in the environment (e.g., perception and memory encoding), and when stimuli are absent and sensory representations are generated internally (e.g., expectation, mental imagery and working memory maintenance). I will present EEG and fMRI evidence from our lab that reveal older adults experience a diminished ability to implement both stimulus-absent and stimulus-present top-down modulation mechanisms, and this has broad consequences on their cognitive abilities.
Ben Hayden, BCS, University of Rochester
The anterior cingulate cortex sits at the interface between the reward system and the motor system and is therefore well positioned to use reward information to influence eye movements. I will present data from recent studies arguing that anterior cingulate cortex monitors diverse sources of reward and task-relevant information to generate a high-level control signal that can be used to govern eye movement decisions. I will argue that, while ACC has long been associated with tracking reward values, its activity is more consistent with computing a control signal derived from reward inputs. I will argue further that ACC carries a decision variable that reflects the current estimate of the value of switching, changing, or learning. Finally, I will discuss the implications of these results for our understanding of saccadic decision-making. (Inaugural Research Talk)
Eric Ullian, UCSF
A hallmark of mammalian neural circuit development is the refinement of initially imprecise connections by competitive activity-dependent processes. In the developing visual system retinal ganglion cell (RGC) axons from the two eyes undergo activity-dependent competition for territory in the dorsal lateral geniculate nucleus (dLGN). However, the direct contributions of synaptic transmission to this process remain unclear. We used a novel genetic approach to reduce glutamate release selectively from the axons of ipsilateral-projecting RGCs and found that the release-deficient axons failed to exclude competing axons from their territory in the dLGN. Surprisingly, the release-deficient axons consolidated and maintained their normal amount of dLGN territory in the face of fully-active competing axons. Furthermore, the release-deficient axons are still able to expand their territory in the presence of altered levels of spiking activity. These results show that during visual circuit refinement glutamatergic transmission plays a direct role in excluding competing axons from inappropriate target regions, and they argue that spiking activity may shape mammalian circuits through both synaptic transmission dependent and independent mechanisms. Further work on downstream signals required for proper refinement of ipsilateral axons has identified the beta-catenin pathway as playing a critical role in the establishment of appropriate ipsilateral territory.
James Jester, University of California, Irvine
To probe ocular tissue structure and function, we have recently developed a novel digital imaging approach to generate 3-dimensional, high-resolution macroscopic images. These images combine immunofluorescent computed tomography (ICT) with non-linear optical imaging of second harmonic generated signals (SHG) and two-photon excited fluorescence (TPEF) to respectively identify collagen and elastin. These novel methods are currently being used to study the collagen and elastin organization of the cornea and optic nerve head and determine how extracellular matrix organization controls tissue biomechanics and hence corneal shape and glaucoma susceptibility. ICT is also being used to identify protein expression patterns and determine how these patterns change in the context of the entire tissue volume.
Albert Compte, Computational Neurobiology Lab, IDIBAPS, Barcelona, Spain
Prefrontal selective persistent activity during the delay period of a visuo-spatial working memory task has been proposed as the neural substrate of memory for spatial location. Computational models based on this hypothesis have been developed, which posit that a continuous attractor in prefrontal networks could bridge the gap between cue and response periods, carrying the continuous spatial information necessary to carry out the task. However, direct evidence confirming the predictions of the continuous-attractor model in the parameters of prefrontal neuronal firing and in the quantitative aspects of behavioral responses is still lacking. I will demonstrate predictive relationships between the variability of prefrontal neural activity in the delay period and the fine details of imprecise oculomotor behavioral responses, in support of a continuous attractor model for spatial working memory maintenance. I will also discuss behavioral evidence in support of the continuous-attractor model during working memory tasks in humans required to remember several spatial locations presented simultaneously.
David Brainard, University of Pennsylvania
The human retina contains three distinct spectral classes of cone photoreceptors, the L-, M-, and S-cones, and cones of these three classes are spatially interleaved in the retina. Thus, generating a full color image requires application of a demosaicing algorithm that uses the available image data to estimate the values of the two cone/sensor classes not present at each cone/sensor location. I will review psychophysics and modeling that sheds light on the demosaicing algorithm employed by the human visual system. This algorithm requires that the visual system have knowledge of the spectral type of each of its cones. For the L and M cones, a variety of lines of evidence suggest that the class of the cone at each retinal location is learned, rather than signaled by some sort of biochemical marker. In the second part of the talk, I will present results that show that natural images contain sufficient statistical structure to support unsupervised learning of cone classes.
Brandon Bader, University of Rochester
The evolutionarily conserved Bar-class homeodomain has been shown to be important for organogenesis, particularly in the CNS. In Drosophila, BarH1 and BarH2 are critical for photoreceptor development in the retina. Our lab has identified roles for the homolog of BarH2, Barhl2, in the development of the mammalian CNS. In the retina, it was found Barhl2 is expressed in retinal ganglion (RGCs), amacrine (ACs), and horizontal cells. Functional deletion of the Barhl2 gene resulted in ganglion cell loss and an overall loss of ACs but a selective increase in cholinergic ACs at the expense of glycinergic and GABAergic ACs, suggesting a role of Barhl2 not only in maintenance of RGCs and ACs, but also in subtype specification within the retina. Barhl2 expression has also been identified in the spinal cord, diencephalon, and olfactory bulb. Loss of Barhl2 also results in improper mosaic patterning and tiling in the starburst ACs (SACs) in the ganglion cell layer (GCL). In this layer, SACs of Barhl2-null animals exhibited improperly spaced somas and clumping of dendritic arbors. Further work will be directed to elucidating the mechanism of control Barhl2 has on regulating mosaic patterning and tiling.
Dan Savage, University of Rochester
Intra-tissue refractive index shaping (IRIS) is a novel femtosecond laser micromachining technique currently being developed by the W. H. Knox and K. R. Huxlin research groups. IRIS uses multi-photon absorption to locally change the refractive index of a material below its damage threshold. Applications of IRIS include non-invasive refractive surgery without the need for tissue ablation and individualized customization of contact lenses. To date, Blue-IRIS has been successfully used to write phase structures in living cat cornea without causing cell death. Blue-IRIS uses blue, 100-fs laser pulses at 400 nm with 80 MHz repetition rate. Similarly, IR-IRIS is currently performed in ophthalmic hydrogel polymers using near-infrared laser pulses at 800 nm, also with 100-fs pulse duration at 80 MHz. With these IRIS techniques it may be possible to revolutionize vision correction and develop a new form of corneal laser refractive surgery that optimizes optical quality non-invasively.
Phil Jaekl, TBA, University of Rochester
I will present recent work regarding audiovisual integration. Namely, two projects; the first involves sound delay in audiovisual stimuli as a potentially new cue to distance. Currently I’m testing the effect of sound delay under direct manipulation of visual distance using a stereo display.
The second project moves upwards in complexity of audiovisual processing and concerns the relative roles of dynamic form vs. motion cues in audiovisual speech perception. The results imply that contrast-based motion cues are integral to the perception of visual speech information and advocate the use of global configural cues built from local motion signals, rather than direct analysis of changes in configuration over time.
Shukti Chakravarti, Johns Hopkins University
Keratoconus is a thinning disease of the cornea that manifests in the teenage and progresses over a period of one to two decades, with cornea transplantation being the most effective treatment for the most advanced forms of the disease. Riboflavin/UV A induced collagen cross linking is the only other treatment that attempts to strengthen the connective tissue and slow down progression of the disease. Keratoconus can be associated with atopy, eye rubbing, contact lens wear, connective tissue diseases and Down syndrome. Multiple genetic and environmental factors are suspected to play a role in its pathogenesis and origin. Histology of the cornea shows a thickened epithelium, breaks in the Bowman membrane. Our working hypothesis is that the tear film and the ocular microenvironment leads to specific changes in the keratocytes and stroma produced by these cells.
To gain deeper insights into its pathogenesis we are using multiple approaches to investigate the tearfilm, epithelium and the stroma of the cornea. I will present our findings on the cytokine analysis of the tear film. Proteomic studies of the corneal stroma shows specific changes in cellular and extracellular matrix proteins of the stroma. Finally, we have been successful in culturing the keratocytes from the stroma of normal donor corneas and surgical specimens from keratoconus patients. The keratoconus keratocytes shows specific deficiencies that suggest changes in signaling pathways that regulate cell growth and apoptosis.
Steve Burns, Indiana University
The vasculature of the retina is critical for the health and function of the retina. Our understanding of the interplay of the retinal vasculature with retinal function and health has previously been limited by our ability to visualize and quantify the smallest vascular structures of the eye. While global or macro level indicators of retinal-vascular health are useful, precise localized measures of both structural changes and blood velocity could test specific hypotheses or provide quantitative feedback concerning treatments of vascular disorders. In this presentation we will describe a third generation adaptive optics scanning laser ophthalmoscope (AOSLO) optimized to allow versatile, high resolution imaging over the central 30 deg of the living human retina. Hardware optimization allows imaging of the smallest capillaries within the retina as well as the motion of erythrocytes within them. This in turn allows mapping the complete vascular network over relatively large regions of the retina. Results of measurements in both normal and diabetic subjects will be presented.
Emily Grossman, UC Irvine
The recognition of human actions from point-light animations has sparked a significant body of research over the past three decades. How do we recognize complex activities from these sparse displays? Where is this achieved in the neural machinery? What is it all for? I will discuss experiments, completed and ongoing in my laboratory, that investigate contemporary issues in biological motion perception. I will present psychophysical results that demonstrate claims of biological motion perception as computed from stationary body templates to be misguided, and instead that observers attend to dynamic critical features when analyzing point-light displays. Neuroimaging experiments reveal robust activation on the human superior temporal sulcus (STS) that is highly correlated with the perception of biological motion. I will show evidence from fMRI studies that demonstrate specificity in the neural response for unique actions, and from TMS studies that demonstrate the STS to be causally linked to perception of biological motion. I will also show findings from fMRI experiments that this same brain region can be activated by non-biological stimuli that convey complex social interactions, challenging domain-specific hypotheses of STS functional specialization. Together, the results from these experiments reveal two current challenges to the field: the need to build models of biological motion perception that include domain general cognitive resources (e.g. attention), and the need to develop a unified theory of the STS that specifies how social cognitive information in these displays is computed and represented in the brain.
Eli Merriam, NYU
As the eyes move, objects in the world change position on the retina. Despite the constant displacement of retinal images, a coherent and stable visual scene is perceived. This phenomenon, termed spatial constancy, indicates that the brain constructs a stable representation of the visual world by combining information about eye movements with sensory information from the visual system. I will describe a series of fMRI studies in humans that explore how visual information is transformed from an unstable retinal input to a stable and coherent visual percept. I show that all of human visual cortex represents stimulus location in an eye-centered (retinotopic) reference frame, as opposed to a world-centered (spatiotopic) reference frame. I will present neuroimaging evidence that non-retinal eye position signals modulate visual responses in many cortical areas, producing eye position gain fields that resemble classic recordings from monkey parietal cortex. Using multivariate analysis methods, I show that eye position gain fields may be used by the brain to continually reconstruct stimulus location as the eyes move. Finally, I will show that eye movement signals have a profound effect on visual activity, even during the small ‘microsaccade’ eye movements that occur involuntarily during intended fixation. Together, these studies suggest that visual perception arises from an active process that tightly integrates information from the oculomotor system.
Mike Mustari, University of Washington
The primate visual system is specialized for central vision. To examine a moving object in detail, its image must be located on or near the fovea and kept relatively stable. This is achieved by different oculomotor subsystems that generate saccades, vestibular ocular, optokinetic, ocular following and smooth pursuit eye movements. These systems are immature at birth and require postnatal binocular visual-motor experience for calibration. Disruptions of binocular visual experience early in life lead to defective smooth pursuit and gaze-holding. Our studies are focused on smooth pursuit, which is a volitional behavior that requires a moving visual target for optimal performance. Visual target position, motion and depth are decoded in dorsal stream visual areas including middle temporal visual cortex (MT) and medial superior temporal (MST) cortex. These areas provide signals to the smooth pursuit region of the frontal eye fields (FEFsp). MT, MST and FEFsp are major components of the cortical pursuit system, which initiates and controls smooth pursuit by way of connections with the brainstem and cerebellum. Both feedforward and feedback signals are requited to maintain high quality smooth pursuit where eye speed matches target speed. Our studies compare and contrast the information carried in different cortical-brainstem channels responsible for converting sensory signals into motor commands.
Rahul Yadav , Advisor: Geunyoung Yoon, The Institute of Optics
Despite advances in optical coherence tomography (OCT) there is still demand for further improvements in axial and lateral resolution, imaging depth and speed. The objectives of this dissertation were to develop advanced OCT systems that overcome some of the current limitations of this technique and to advance our understanding of the mechanism of human accommodation and corneal diseases by imaging the anterior segment of the eye. A large scan depth OCT (imaging depth > 10 mm) was developed for improving our understanding of accommodation. Novel scanning optics, where scanning beams are incident normal to the four ocular surfaces (anterior and posterior cornea and lens surface) was used in the system, to maximize the OCT signal. In-vivo imaging was carried out in two young normal subjects and the four anterior segment ocular surfaces could be visualized. Six millimeter diameter posterior lens surface could be imaged without the need for pupil dilation. Reduction in anterior chamber depth, increase in lens thickness and decrease in radius of curvature in both lenticular surfaces was observed with accommodation.
An ultrahigh axial resolution OCT was developed to quantify structural changes in corneal diseases. The system, based on spectral domain OCT principle, used a broadband supercontinuum light source (375 nm at center wavelength of 812.5 nm) and was assembled in free space to avoid image degradation due to dispersion. A spectrometer based on modified Czerny Turner configuration was used to achieve relatively large scan depth (~1 mm). The experimentally measured axial resolution of the system was 1.1 μm in corneal tissue, which allowed for the visualization and quantification of individual corneal layers in normal and diseased corneas. The clinical viability of the system was proven through a study on structural changes in the epithelium and Bowman’s layer of keratoconic eyes.
In-vivo cellular imaging capability, using an optical coherence microscope, was demonstrated by imaging stromal keratocytes and endothelial cells in the mouse cornea. The system provided large working distance (30.5 mm) and also has the potential of achieving larger field if imaging speed could be improved. Thus creating the possibility of performing non-invasive follow up investigation on the cellular structure in the mouse eyes. These advanced OCT systems have successfully overcome the limitations of currently available OCT systems, by providing better axial and lateral resolution and imaging depth. With improved performance these systems can help us in understanding the diseases pertaining to the anterior segment of the eye.