Diego Contreras - US grants

Our long term goal is to understand information processing in visual cortex. A fundamental aspect of cortical processing is the integration of inputs from different sources by single cells and local networks. Here we will focus on the integration of inputs arising from visual activation of areas inside and outside the receptive field (RF). Surround stimuli (outside the RF) facilitate or suppress the responses of visual cortex neurons to stimuli inside their RF in a contrast and orientation dependent manner. It has been proposed that such modulatory effects depend on asymmetries in the response to stimulus contrast between regular spiking (RS) and fast spiking (FS) cells, which are the main excitatory and inhibitory neuronal cortical types, respectively. It is known that FS cells in vitro show firing rates in response to current injection that increase more steeply and reach higher and more sustained values than RS cells. In addition, little is known about the visual properties of the different electrophysiological cell classes of the neocortex. We will use intracellular recordings in vivo in anesthetized animals in concert with both standard and more innovative paradigms of visual stimulation. We will proceed along the following aims: (i) Establish the correspondence between electrophysiological and functional cell properties in the visual cortex, (ii) demonstrate asymmetries in the response to current injection and stimulus contrast between RS and FS cells, and (iii) demonstrate that the changes in surround effects due to contrast are based on a shift on the balance of synaptic inputs from excitatory to inhibitory. The prediction is that this shift will occur only in RS cells, while FS cells will show further facilitation with increases in contrast. This prediction is in complete agreement with our preliminary data and with in vitro studies showing IPSPs in response only to higher intensities of stimulation of the long range cortical connections. In order to characterize the synaptic events that underlie the modulatory actions of surround stimuli, we propose to use flashed bars with different contrasts and orientations. These bars will be flashed at different locations outside the RF and at different times with respect to the bars flashed inside the RF. This experimental approach will also allow us to study the spatiotemporal properties of the modulatory effects of surround stimuli.

PROJECT SUMMARY Image representation in primary visual cortex depends critically on the spatiotemporal pattern of convergence of lateral geniculate axons as well as on the dynamic properties of thalamocortical synapses. Thalamic input represents only a fraction of the excitatory drive to cortical cells in layer 4 ,but dominates their visual response patterns. We will use electrophysiological methods in vivo to record visual responses simultaneously from thalamorecipient neurons in primary visual cortex and several of their input cells in the lateral geniculate nucleus. In Aim 1, we will test the hypothesis that inhibition controls the temporal course of simple cells in layer 4. In Aim 2, we will characterize the properties of the postsynaptic potentials from single LGN neurons onto excitatory and inhibitory simple cells in layer 4. Finally, in Aim 3, we will use dynamic clamp in layer 4 simple cells to study convergent input from combinations of single LGN neurons (using knowledge obtained in Aims 1 and 2) without concomitant activation of cortical circuits. We will estimate the contributions of local inhibition in establishing L4 simple cell visual responses. These studies will generate critical insight into the transformation of visual information that takes place in the thalamocortical synapse.

DESCRIPTION (provided by applicant): We propose to continue a broad, interdisciplinary Vision Training Program now in its 35th year. The program includes 27 trainers in 8 departments across 4 schools and spans many areas: photo transduction (biophysics, molecular biology); retina (circuitry, computation, neurochemistry developmental genetics); eye (cataract, myopia, tears); central pathways (physiology, computation); higher processes (psychophysics, cognitive neuroscience, computation); retinal diseases and new genetic therapeutics. The purpose the Vision Training Program is to promote intellectual development of outstanding graduate students interested in the visual sciences so that they may ultimately become leaders in their chosen disciplines. Predoctoral students are selected for their excellence by a centralized office of Biomedical Graduate Studies and join a particular graduate group, mainly Neuroscience, Bioengineering and Psychology. On Penn's compact campus, graduate education is organized across departments and schools in order to foster multidisciplinary training and collaborative research. Students are trained broadly during their first two years and are attracted specifically to vision research by: (1) formal lectures and laboratory training, (2) weekly lunchtime seminars with research talks by a mix of intramural and external speakers, (3) research rotations in three different laboratories (each followed by a public talk), (4) an annual research retreat with student talks and scholar in residence program. At this point, all students are exposed to modern research methods (patch clamp, molecular biology, genetics, computation, etc...). Collectively, the relevant graduate groups admit about 260 students annually, and of these, about 40 rotate through vision labs. Currently, about 35 are doing their theses in vision labs and of these, 31 are eligible for support by the Vision Training Program. In the past 10 years, the Vision Training Program has trained or is training 21 PhD/MD or PhDs. Most have continued training in excellent labs and many have subsequently assumed positions at prominent research institutions. Through our graduates, the impact of our training program has been widespread, adding significantly to our understanding of vision in health and disease. Plans for the immediate future include continuing with our excellent active across campus program and expand the various activities including a new broad course in vision science. Based on continued interest in vision and significant growth of our faculty, we request continued support for 6 predoctoral students per year.

Imaging and Electrophysiology - Project Summary The goal of the Imaging and Electrophysiology Core Module (IECM) is to provide shared resources to the investigators of the vision research center (VRC) for imaging and electrophysiological recording. The core instruments of the IECM support imaging (confocal and two-photon) and electrophysiology (patch clamp in vitro, simultaneous with 2P imaging) as well as high density multiunit retinal recording using a multi-electrode array. The IECM also subsidizes the use of two confocal microscopes and a cSLO-OCT system for imaging of retina in vivo in canine. The IECM offers full technical assistance through trained personnel to facilitate use of the instruements. The IECM also provides hub of for collaborative work among members of the VRC by enabling multidisciplinary projects about the normal structure and function of the visual system and its pathological alterations.

PROJECT SUMMARY Image representation in primary visual cortex depends critically on the spatiotemporal pattern of activation of distributed visual cortical networks. Such activation relies on distribution of contrasts in the visual scene but also in part in the scaffolding of horizontal connections in supragranular layers 2-3 that connect cortical columns of similar orientation. For individual visual cortical cells their spatially well defined receptive field (RF) is not sufficient to explain their visual responses to visual scenes. Indeed, the context of visual stimuli falling outside of the RF is a critical component of the cell response. Such effects have been called contextual effects, they depend on the relative properties between the visual stimulus inside and outside of the RF and can be facilitatory, inhibitory or they can modulate the gain (the slope of the input-output function) of the neuron. A fundamental impediment to understanding the underlying mechanisms of contextual stimuli is the ability of manipulating inhibition at the mesoscale of the cortical column. Here, in Aim 1 we propose to implement in the cat optogenetic approaches that allow to manipulate inhibition with great temporal sensitivity. We will use a strategy developed recently based on the selective expression of the DLX homeobox gene enhancer mDlx in cortical GABAergic interneurons of all vertebrate species. We will procure (from the Penn Vector Core) and inject AAV vectors containing depolarizing (ChR2) and hyperpolarizing (ArchT) opsins under the control of mDLx. We will verify selective expression with electrophysiology and inmunohistochemistry and will calibrate the effect of blue and green light on the responses to visual stimuli and current injection of regular and fast spiking neurons recorded intracellularly in vivo. Work in Aim 1 will be done with the help of Dr. John Wolfe from the Veterinary School which is an expert in viral approaches for gene therapy. In Aim 2 we will obtain preliminary data on the role of GABAergic inhibition in surround suppression and gain modulation caused by contextual stimuli. In addition to strong preliminary data for a future R01 application this project will implement an approach that will allow addressing over 50 year old questions in a highly visual animal.

In great contrast to a digital computer, the brain is constantly active and responses to stimuli of single cells are noisy and unreliable. Instead of speed and accuracy by a single processor, brains rely on the parallel, simultaneous sampling of information by thousands of neurons. Neuronal populations, albeit noisy and slow, together generate sufficiently accurate perceptual representations of reality to conduct behavior much more efficiently and orders of magnitude faster than any computer in existence today. Key to such parallel processing is efficient communication among neural networks in the cortex of the brain. The interaction of the fluctuating activity of the brain and the ability of populations of neurons to efficiently communicate between cortical networks in order to encode information is unknown. In this project, the investigators explore and test the mechanisms and rules of cortico-cortical communication using state of the art experimental and computational tools. The work will not only address long-standing hypotheses about cortico-cortical communication and result in the development of novel computational analysis tools but also help shed light on cognitive disorders believed to be due in part to faulty information transmission between cortical areas. In addition, the project will provide opportunities for students from diverse backgrounds to participate in cutting-edge international interdisciplinary research.<br/><br/>In this project, the investigators examine how visual responses are communicated between local networks in layers 2-3 of primary visual cortex under those two well-defined network states. Specifically, the investigators will use electrophysiological, optogenetic, pharmacological and computational approaches to quantify cellular and network communication in primary visual cortex in vivo under network states that have been proposed to ideally allow corticocortical communication: gamma oscillations and non-oscillatory noisy states globally termed asynchronous irregular. The investigators are able to elicit and control those states with specific visual stimulation and will characterize the states’ neuronal background activity as well as their role in efficient transmission of information between cortical columns. The large volume and new qualitative aspects of the data will allow the investigators to generate novel analysis algorithms and theoretical approaches, as well as large-scale computational models. Ultimately, the computational models will help understand population dynamics for the transmission of information in well-defined network states. <br/><br/>This project is funded jointly by the Neural Systems Cluster in the Biological Sciences Directorate and the Division of Information and Intelligent Systems in the Computer and information Science and Engineering Directorate. A companion project is being funded by the French National Research Agency (ANR).<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.