Oxyopias Schedule
Friday December 1, noon, 489 Minor Hall
Chris Johnson
Devers Eye Institute, Portland, Oregon
Host: Marilyn Schneck
Frequency Doubling Technology Perimetry
Abstract
Frequency Doubling Technology (FDT) perimetry is a relatively new visual field test procedure designed
to detect and monitor glaucoma and other ocular disorders. It is based on the frequency doubling illusion
originally described by Dr. Don Kelly, in which a low spatial frequency sinusoidal grating (less than 2
cycles per degree) undergoing high temporal frequency counterphase flicker (greater than 15 Hz) appears
to have twice as many light and dark bars. This presentation will review the underlying basis of the test
procedure, the basic properties of the frequency doubling effect, the performance characteristics of the
clinical FDT test procedure, and recent advances in FDT perimetry (high resolution 24-2 test pattern,
liquid crystal display FDT, use of maximum likelihood test procedures, etc.).
Monday, November 20, 4pm, 489 Minor Hall
Alexander M. Sergeev
Institute of Applied Physics of the Russian Academy of Science
603600 Nizhny Novgorod, Russia
Host: Sheldon Miller
Optical Coherence Tomography
Abstract
The pace of the technological advancement of Optical Coherence Tomography (OCT) over the last several
years has been extremely rapid. The field has progressed from one-dimensional low-coherence ranging
to full three-dimensional imagining with individual two-dimensional images acquired at near video rate
in a span of less than eight years. Imaging applications have included polymers and advanced composites,
Ophthalmology, Developmental Biology, Gastroenterology, Urology, Cardiology, Neurology, and Gynecology.
Preliminary studies indicate the great potential for OCT to make a significant impact in clinical medicine.
Friday, November 17, noon, 489 Minor Hall
Christian Wehrhahn
Max-Planck-Institut für Biologische Kybernetik, Tübingen, Germany
Host: Karen DeValois
Disambiguating cone specific adaptation and simultaneous color contrast
Abstract
When a large colored area surrounds a small white test field, human observers perceive the test field as
colored. Its color is shifted in direction opposite to that of the surround color on a chromaticity
chart. The interpretation of this observation in terms of chromatic adaptation and simultaneous color
contrast is still controversial. With chromaticity diagrams discrimination between these mechanisms is
difficult. Based on detection experiments we have developed a new color metric and a set of equally
bright color stimuli. When plotted on the plane of equal brightness in cone difference space as a function
of the azimuth these colors are situated on a circle at equal angular distances. Use of these stimuli in
binocular and dichoptic infield-surround experiments enables us to discriminate between chromatic
adaptation and simultaneous color contrast. A matching and a nulling procedure were used to measure
induced shifts; both yield very similar results. While we find no evidence for chromatic adaptation when
testing our subjects in the binocular situation, we do observe local simultaneous color contrast. In the
dichoptic situation the state of adaptation can be set for each eye individually. By specifying the
stimulus on the basis of its azimuth as indicated above we quantified the relative strengths of L-and
M-cone adaptation and simultaneous red-green contrast. We identified a rather strong contribution of
global chromatic adaptation to the shift in the perceived color of the test field, but also observed a
substantial contribution of local simultaneous color contrast. Our results are relevant for color constancy.
Friday, November 3, noon 489 Minor Hall
Barbara Zenger PhD
Postdoctoral Scholar, Department of Psychology, Stanford University
Host: Stan Klein
Attention and surround interactions: Psychophysics and modeling
Abstract
I will present recent psychophysical studies on how contrast detection and discrimination of a peripheral
Gabor patch are affected by flanking Gabor patches presented in the near surround, and how these
center-surround interactions are modulated by attention. First, we studied how collinear Gabor flankers
affect contrast discrimination of a peripheral Gabor target. We found that for low-contrast targets
flankers impair target discrimination, while flankers have no effect on discrimination performance for
high-contrast targets. The transition between suppression and no-suppression occurs at a target contrast
similar to the flanker contrast. To account for the data we propose a computational model in which flanker
inhibition switches from divisive to subtractive inhibition for increasing target contrast. We also
demonstrate how this model could be implemented on the single-neuron level. In a complementary study we
tested how flanker effects are modulated by attention. We found that attentional effects were weak when
the target was salient (i.e. when the target popped out from the surround due to its higher contrast, or
due to an orientation difference). By contrast, attentional effects were very strong for non-salient targets
(which did not pop out). Together these studies suggest that attention may improve contrast detection and
discrimination performance by reducing the contrast gain control from the surround.
Friday October 27, noon, 489 Minor Hall
David Woods
Professor of Neurology, Dept. of Neurology, UC Davis,
Chief of Clinical Neurophysiology, Neurology Service, VA-NCHCS, Martinez
Peter Pebler
Chief Technology Officer (CTO) at Neurobehavioral Systems, Albany, CA
A stimulus delivery/experiment control program for neuroscience
Abstract
Presentation is a Windows 95/98/2000/ME program for stimulus delivery and experiment control that is now in
use by more than 825 researchers worldwide. Presentation delivers high-precision visual stimuli and video
animations with sub-ms temporal precision that is verified for each stimulus and response event. It provides
complete control of frame refresh, runs on standard PCs and is capable of monitoring responses from joystick,
mouse, keyboard, and voice relay or from parallel or serial response boxes. Presentation incorporates special
features for neurophysiological experiments using fMRI, evoked potentials, or single unit recordings and can
deliver auditory and multimodal stimuli. We will demonstrate Presentation and discuss new features of a
soon-to-be released and planned future version of Presentation. We are particularly interested in features
that Oxyopians may want included in future Presentation releases.
Friday, October 20, 2000, noon, 489 Minor Hall
Christopher Tyler
Associate Director, Smith-Kettlewell Eye Research Institute, San Fransisco
Host: Marty Banks
The discovery of perspective by neglected genius Masolino da Panicale and its impact on the Renaissance
Abstract
Depth representation, in both its geometric and its more generic forms, has often served as an impetus in
artistic development through the millennia. It appears that the Greek and Roman painters could evoke
astonishing levels of three-dimensionality in their murals but did so from an intuitive grasp of the
convergence concept rather than a fully accurate construction. Even by the 14th century, painters such as
Giotto and the Lorenzetti brothers were struggling with the concepts of linear perspective. The first to
have used an accurate central vanishing point seems to have been the underrated painter Masolino da Panicale,
in 1425. He followed up this breakthrough with a set of sparkling explorations of perspective composition
following the death of his younger collaborator, Masaccio. These compositions may have inspired the humanist
expansion of Renaissance art throughout the 15th century, consolidated by the convergence of artists of all
kinds on Rome for the Papal Jubilee of 1450. It is surprising, therefore, to find that almost all Renaissance
perspective relied on the simple one-point perspective scheme. By the 16th century, it appears that artists
felt straight-jacketed by this approach, and linear schemes were avoided in favor of spaces populated by powerful
figures in flowing garments, such as those of Michelangelo and Tintoretto. This radical switch, combined with
the lack of any description of two-point perspective in contemporary sources, suggests that an incomplete
understanding of full geometry of perspective was instrumental in its loss of popularity. Diverse attitudes to
linear perspective have continued to influence art movements even through the 20th century.
Friday October 13, noon, 489 Minor Hall
Jack Werner
Department of Ophthalmology & Section of Neurobiology, Physiology and Behavior, UC Davis
Host: Jay Enoch
Possible senescent reorganization of scotopic visual pathways
Abstract
Psychophysical data will be presented to address the question: What are the functional consequences of
age-related losses in human rod and ganglion cell numbers? The answer to this question may also be of
interest from a practical perspective as losses in night vision result in significant problems for many
elderly and even middle-age individuals. Results from several different types of psychophysical experiment
will be presented. Collectively, the data imply that the loss of ganglion cells is accompanied by an
increase in the area of complete spatial summation, as if there is a process to maintain a constant afferent
signal or retinal representation from ganglion cells to cortex.
Friday October 6, noon, 489 Minor Hall
Gary Martinsen
School of Optometry, UC-Berkeley
The Multifocal Electroretinogram in Age-Related Macular Degeneration
Abstract
The multifocal electroretinogram (MERG) is a new electrophysiological technique that is designed for
evaluation of central retinal function. By presenting stimuli in a pseudorandom sequence, over 100 focal
retinal responses can be obtained in a short period of time. Each response is relatively free of influences
from other stimulated retinal areas. Age-related macular degeneration (AMD) is the leading cause of legal
blindness in persons of ages 65 years and older in the U.S. AMD has two main forms, wet and dry, each of
which results in loss of photoreceptors in the macula. Age-related maculopathy (ARM) is a precursor to AMD
and is characterized by the presence of soft drusen in the macula. We used the MERG to study focal retinal
changes in patients with AMD and ARM. All 7 AMD patients showed decreased amplitudes and increased implicit
times compared to age-matched control subjects. The focal MERG abnormalities found in AMD patients were not
restricted to the retinal area with defects visible on fundus photographs. Sixteen of 18 ARM patients also
showed focal abnormalities in either implicit times or amplitudes or both. These abnormalities were greater
in retinal areas with soft drusen than in areas without soft drusen. In addition, increases in drusen area
were correlated with delays in b-wave implicit times in ARM patients. Since increases in the number and
confluence of soft drusen are known to increase the risk of conversion from ARM to AMD, these results suggest
that the MERG may be used to monitor at-risk patients.
Friday Sept 22, noon, 489 Minor Hall
John Flannery
School of Optometry, UC-Berkeley
Host: Christine Wildsoet
Gene Therapy for Retinal Degenerations
Abstract
Gene therapy is an approach to the treatment of retinal disease based on direct administration of gene
containing viruses into the eye. It is an extension of conventional medical therapy, attempting to treat
retinal disease by the administration of DNA rather than a drug. The concept that gene transfer might be
applied to retinal disease is founded on the extraordinary advances of the past two decades in our
understanding of the genetic defects in these diseases. It is now established that about one person in
2,000 has a genetically determined retinal dystrophy. Currently, there is no widely accepted or effective
preventive treatment for any retinal degeneration. Numerous gene therapeutic approaches for retinal disease
have been proposed, these fall into two main categories: gene replacement for recessive disease and gene
augmentation for autosomal dominant disease. In gene replacement, a normal copy of a gene is introduced.
For treatment of dominant disease, there are two main strategies: slowing of retinal cell death with
neurotrophins and growth factors and 'knockdown' strategies to reduce the quantity of the protein produced
by the mutant gene using ribozymes and anti-sense RNAs. These approaches have successfully slowed retinal
degeneration in animal models. Our laboratory has exploited both approaches to slow photoreceptor cell
death in retinal degeneration. We use viral vectors derived from AAV, a common non-pathogenic human virus,
to transfer genes to the retina. We evaluate the therapeutic effect in several rodent models of retinal
degeneration (light damage, RCS, opsin mutations), with the idea that the tools and strategies developed
and tested will be relevant to human retinal degenerations.
Friday Sept 15, noon, 489 Minor Hall
Michael S. Gilmore
The University of Oklahoma Health Sciences Center, Oklahoma City
Endophthalmitis: The design of new therapeutic approaches based on molecular pathogenesis studies
Abstract
Endophthalmitis invariably is a sight threatening inflammation of the posterior segment of the eye, and
usually is the result of bacterial or fungal infection. Endophthalmitis most often occurs as a complication
of cataract extraction surgery or penetrating injury to the globe; but it can be seeded endogenously, most
commonly associated with intravenous drug abuse. The interior of the eye is restricted by a number of
mechanisms in its ability to mount an immune response to infection. As a result, nonregenerative neurological
tissues of the retina are highly vulnerable to irreversible damage. Loss of vision in these infections results
both from direct damage to the retina induced by specific bacterial toxins, as well as bystander damage
associated with inflammation. Our research focuses on aggressive forms of endophthalmitis that are associated
with significant loss of vision, with the goal of identifying improved therapeutic strategies to enhance
visual outcome.
Bacillus cereus is a leading cause of posttraumatic endophthalmitis, an infection that is extremely fulminant
and usually leads to complete or near complete visual loss. Staphylococcus aureus and Enterococcus faecalis
are leading causes of postsurgical endophthalmitis, infections that are increasingly refractory to antibiotic
treatment and are associated with significant irretrievable loss of vision. Using molecular genetic tools,
we have shown that the enterococcal infection is associated with inflammatory sequelae that are treatable
using corticosteroids. However, in certain cases this inflammation is accompanied by toxin damage that can
render all treatments ineffective in salvaging vision. The enterococcal toxin responsible for this tissue
damage is structurally novel, and characterization of its maturation pathway and regulation of expression
highlight new therapeutic opportunities. The highly explosive nature of B. cereus endophthalmitis traditionally
has been attributed to ill-defined virulence. Our research has shown that the B. cereus toxins for which
important roles are most frequently ascribed (in the absence of direct experimentation), when directly tested
actually appear to make comparatively minor contributions to endophthalmitis pathogenesis. Instead, one of the
leading factors contributing to the virulence of B. cereus endophthalmitis appears to be the motility of the
organism. From a central midvitreous nidus, B. cereus appears to marginate to more highly oxygenated tissues,
including those of the retina and ciliary body. Based on the results of these studies of the molecular
pathogenesis of endophthalmitis by various agents, the design of new therapeutic approaches for limiting visual
loss can be posited.
Friday Sept 8, noon, 489 Minor Hall
Rich Kramer
Dept. Molecular & Cell Biology, UC-Berkeley
Host: John Flannery
Modulation of rod phototransduction by growth factors and tyrosine phosphorylation
Abstract
The sensitivity of rod and cone photoreceptors to light is not fixed, but rather is modulated during light
and dark adaptation. This type of modulation is intrinsic to photoreceptors; it occurs in isolated rods or
cones, and does not require signals from other cells. We are investigating the first known instance in which
phototransduction is modulated by factors extrinsic to photoreceptor cells; namely growth factors released
onto rod outer segments by neighboring pigment epithelial cells. Effects of growth factors often involve
activation of protein kinases and/or protein phosphatases that specifically act on tyrosine residues in
substrate proteins. In recent experiments we show that insulin-like growth factor (IGF-1) dramatically
alters the sensitivity of rod CNG channels to cyclic GMP, and this effect is mediated by changes in
tyrosine phosphorylation. In additional studies, we have identified some of the specific tyrosine residue(s)
in CNG channels responsible for modulation, understanding how the phosphorylation alters CNG channel activity,
and elucidating the biochemical cascade linking the IGF-1 receptor and channel phosphorylation. In addition,
ongoing experiments show that IGF-1 alters the light response of individual rods in a manner consistent with
the modulation of CNG channels. Future studies will address how and when IGF-1 is released and the consequences
of IGF-1 for the processing of visual information.
Friday Aug 4, noon, 489 Minor Hall
Josh D Silver
University of Oxford
Host: Dr Christine Wildsoet
A Simple Method for Correcting the Vision of a Billion People
Abstract
The "technology" of variable power fluid-filled lenses goes back over two hundred years and arguably derives
from the eye lens itself. There have been many schemes over the years to apply variable power fluid-filled
lens spectacles to vision correction. Until recently, however, it seems that the potential of this technology
to correct the uncorrected one-fifth of the world's population has not been explored. I will describe our
attempts to do this, and present some preliminary results from an ongoing field trial which seem reasonably
encouraging.
Friday July 28, noon, 489 Minor Hall
Steve Bierer
University of Michigan, Ann Arbor
Host: Ralph Freeman
Improved spike detection and sorting with multi-channel electrodes
Abstract
Multi-channel electrodes are attractive tools for the study of the nervous system because of their ability
to record from many neurons simultaneously. However, background noise -- produced, in part, by neurons relatively
far from the electrode array -- can often obscure action potentials of neurons close to the array, particularly in
the presence of a synchronizing stimulus. When the recording elements of the multi-channel array are spaced
closely together, the signal-to-noise ratio can be substantially improved by application of an optimal array
signal processing technique. This denoising process results in well-defined spike events, sortable via
multi-channel template or principal component methods. Based on the average spike waveform, each identified
neuron can then be assigned a position relative to the fixed electrode geometry, providing information about
the spatial relationship among the neurons.
I will discuss the basic array processing implementation as well as refinements employing adaptive and temporal
filtering concepts. I will also discuss its application to neural activity recorded in the guinea pig cochlear
nucleus, an auditory region, using a 16-channel 2-dimensional silicon electrode. In particular, I will
demonstrate the role that inhibitory interneurons may have in modulating the output of nearby fusiform cells,
the principal output neuron of the DCN.
Monday July 24, noon, 489 Minor Hall
Richard Murray
Department of Psychology, University of Toronto
Host: Michael Landy
Perceptual Organization and Perceptual Efficiency
Abstract
R. F. Murray, J. M. Gold, P. J. Bennett, & A. B. Sekuler
Department of Psychology, University of Toronto
Perceptual organization greatly affects performance in perceptual tasks, but little is known about how
visual processing changes with a stimulus' perceptual organization. We addressed this question using a noisy
cross-correlator model (Pelli and Farrell, 1999, Journal of the Optical Society of America A 16, 647-653).
We measured contrast thresholds for discrimination between two slightly warped Kanizsa squares embedded in noise.
Stimuli were modally completed Kanizsa squares (Modal condition), amodally completed Kanizsa squares (Amodal),
Kanizsa-like squares with luminance-defined edges (Real), and Kanizsa inducers arranged so as not to perceptually
complete into a square (Fragmented) (Ringach and Shapley, 1996, Vision Research 36, 3037-3050). In each condition
we determined observers' equivalent input noise, calculation efficiency,and classification images.
Classification images showed that observers used similar templates for Modal, Amodal, and Real stimuli, and a
very different template for Fragmented. This template difference was reflected in calculation efficiency:
efficiency was higher for Modal, Amodal, and Real than for Fragmented stimuli. Furthermore, efficiency was
highly correlated with the similarity of an observer's template to the ideal observer's template. Equivalent
input noise was the same in all conditions.
We conclude that perceptual organization affects shape discrimination by changing the efficiency of
observers' classification templates.
June 30, noon, 489 Minor
Ehud Kaplan
Jules and Doris Stein Research to Prevent Blindness
Depts. of Ophthalmology, Physiology & Biophysics, The Mount Sinai School of Medicine
Host: Russ DeValois
Color, size and all the rest: How do they all fit inside the visual cortex?
Abstract
The visual cortex must represent all the aspects of the visual environment, such as color, size, movement or
texture. We are using optical imaging of intrinsic signals to visualize these representations, in an attempt to
understand the nature of the computation that the cortex performs on the incoming visual information. It is well
established that cells tuned to particular orientations cluster together, but the representation of other stimulus
parameters is either controversial or unknown. Here we focus on the cortical representation of color and size
(or spatial frequency). We imaged the exposed primary visual cortex (V1) of anesthetized and paralyzed macaque
monkeys. The data were analyzed with extensions of principal component analysis. The animals viewed drifting
gratings of various chromatic and luminance combinations, spanning a range of spatial frequencies. Our results
showed that:
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Color is represented by two different systems of neuronal clusters, one for chromatic contrast and the other
for hue;
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The representation of spatial frequency is continuous and smooth;
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The spatial frequency representation consists of pinwheels, similar to but apparently unrelated to the
pinwheels seen for orientation preference.
June 16, noon, 489 Minor
Murray Sherman
Dept Neurobiology, State Univ New York, Stony Brook NY
Host: Ralph Freeman
The thalamus actually does something interesting.
June 2, 4pm, 489 Minor Hall
Stefan Treue
University of Tuebingen, Dept. of Neurobiology
Host: Marty Banks
Encoding and decoding transparent motion in the visual system
May 26, noon, 489 Minor Hall
Qasim Zaidi
State University of New York. College of Optometry
Host: Jitendra Malik
The Neural Basis of Shape from Texture
Tuesday May 9, 2000, noon, 489 Minor Hall
Nikos Logothetis
Professor of Neuroscience, Director of the Institute
Max-Planck Institute for Biological Cybernetics, Biological Cybernetics, Tuebingen
Magnetic Resonance Imaging of the Monkey Brain: Bridging functional brain mapping with single
unit activity
Monday May 8, noon, 489 Minor Hall
Nikos Logothetis
Professor of Neuroscience, Director of the Institute
Max-Planck Institute for Biological Cybernetics, Biological Cybernetics, Tuebingen
Perceptual Multistability: Pyschophysical and Physiological Experiments in Monkeys: B'inocular rivalry' may not be a binocular phenomenon
April 21, noon, 489 Minor Hall
David Ress
Stanford University
Host: Russ DeValois
FMRI Cortical Activity Predicts Pattern-Detection Performance
Abstract
Visual attention can affect human neural activity and behavioral performance. To quantify possible links
between the two, cortical activity in primary visual cortex (V1) was measured using event-related functional
magnetic resonance imaging (fMRI) while subjects performed a pattern-detection task.
We observed a large, stimulus-independent response
in V1, the base response. Sensory-evoked activity was superimposed on the base response, and increased with
stimulus contrast. The base response showed severalattributes that are characteristic of visual attention.
First, it depended on task difficulty. Second, it was spatially selective. Most significant, the trial-to-trial
variability in the base response predicted behavioral performance on the task; performance was best (more
correct judgments, largest d-prime) when the base response was large and worst when the base response
was small.
Our results lead us to hypothesize a link between attention, cortical activity, and behavior. Electrophysiological
studies in monkeys have shown that attention can cause an increase in the baseline firing rates of
visual-cortex neurons. Increasing baseline firing rates may potentiate an enhancement in the stimulus-evoked
responses, that could improve the signal-to-noise ratio in the sensory representation of the stimulus by
biasing neurons into a more sensitive segment of their operating range. We attribute the contingency between
V1 activity and performance to trial-to-trial fluctuation (e.g., lapses) in attention. We suggest that
variability in the observers' attentional state causes variability in the baseline firing rates that, in turn,
causes variability in performance.
April 14, noon, 489 Minor Hall
Peter Schiller
MIT
Host: Ralph Freeman
Look and See: How the Brain Moves Your Eyes About.
February 25, noon, 101 Life Science Addition
Robert Molday
University of British Columbia, Department of Biochemistry and Molecular Biology
Host: John Flannery
ABC's of Vision and Macular Degeneration
Hosted by DEPARTMENT OF MOLECULAR AND CELL BIOLOGY
Reception: 5:00 p.m., 177 Life Sciences Addition
March 17, Noon, 489 Minor Hall
Ted Adelson
MIT
Joint presentation of Cognitive Science and Vision Science
5th Annual Irvin Rock Memorial Lecture
Host: Steve Palmer
Perceptual organization and the hidden languages of vision.
Abstract
We now have a good understanding of the first stages of visual processing. To make further progress, we cannot
study isolated mechanisms, because perceptual organization and spatial form have pervasive importance. Small
changes in spatial configuration can lead to large changes in perceived motion or lightness, as can be
revealed with some compelling illusions. These phenomena allow us to learn about the rules and representations
the visual system is using in mid-level vision. It turns out that groups, contours, junctions, and surfaces
are of crucial importance. However, the configural rules of organization for motion are different from those
for lightness, and both are different from the classical Gestalt rules for spatial form. This makes sense when
one considers the differing problems that confront each of the subsystems. I will discuss some of the
principles of mid-level vision, and will demonstrate some powerful new illusions that illuminate these
principles.
March 10, noon, 489 Minor Hall
Todd P. Margolis
Professor of Ophthalmology
Director, F.I. Proctor Foundation, University of California at San Francisco
Host: Suzanne Fleiszig
Establishment of Latent Infection with HSV-1
Abstract
During primary infection of sensory ganglia with HSV-1 there is an early divergence of the latent and
productive pathways of viral gene transcription, with latent infection of primary sensory neurons established
as early as 2 days post inoculation. Since neither viral gene expression, viral DNA replication nor host immune
responses appear to be necessary in order for HSV to establish a latent infection, it has long been our working
hypothesis that biochemically distinct populations of primary sensory neurons are capable of differentially
regulating the outcome of infection with HSV. Recent work in our lab clearly demonstrates that although all
populations of primary sensory neurons are capable of supporting a productive infection with HSV, some neuronal
populations (e.g A5+) are much more permissive for a latent pattern of infection than others (e.g. IB4+).
Ongoing study of the A5+ and IB4+ neuronal populations of the mouse trigeminal ganglion through the use of
immunolabeling, in situ hybridization, transgenic mouse lines, functinal screening of cDNA expression libraries
and tandem hybridization screening of gene expression arrays has allowed us to begin to define differences in
the expression profiles of these neuronal populations that may be responsible for the differential regulation
of HSV gene expression in vivo. An understanding of the molecular mechanisms responsible for the establishment
and maintenance of latent HSV infection is likely to provide us with valuable insights into novel approaches
for the management of recurrent HSV infections.
February 4, Noon, 489 Minor Hall
Lamberto Maffei
Instituto di Neurofisiologia, Pisa, Italy
Host: Ralph Freeman
Do we really learn to see - the role of neurotrophins
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