[Frontiers in Bioscience 15, 681-707, January 1, 2010]

Interhemispheric synchrony in visual cortex and abnormal postnatal visual experience

Luc Foubert1, Daniel Bennequin2, Marie-Annick Thomas1, Jacques Droulez1, Chantal Milleret1

1Laboratoire de Physiologie de la Perception et de l'Action, College-de-France, CNRS UMR 7152, 11 Place Marcelin Berthelot, 75005 Paris, France, 2Institut de Mathematiques, Universite Paris 7 Denis Diderot, UMR CNRS 7586, 2 Place Jussieu, 75005 Paris, France

TABLE OF CONTENTS

1. Abstract
2. Introduction
3. Materials and methods
3.1. Anatomical study
3.1.1. Experimental groups
3.1.2. Monocular occlusion
3.1.3. Tracer injections, staining method and 3D reconstruction
3.1.4. Axonal morphology
3.1.5. Architecture of individual terminal arbors
3.2. Numerical simulation
3.2.1. Importing anatomical data to Neuron
3.2.2. Model assumptions and procedure
3.2.2.1. The continuous model of Hodgkin and Huxley (HH)
3.2.2.2. Effects of the myelin sheath on spike propagation
3.2.2.3. Transition from saltatory to continuous spike propagation
3.2.2.4. Implementation of the model on the diverse real morphologies of callosal axons
4. Results
4.1. Anatomical data
4.1.1. Location of the labeled axons in the corpus callosum
4.1.2. Global organization of the MD callosal axons
4.1.2.1. Location of the first node of the MD callosal axons
4.1.2.2. Architecture of the callosal terminal axons
4.1.3. Quantitative analysis of the MD callosal axons
4.1.3.1. Diameters of the trunks of the callosal axons
4.1.3.2. Mean numbers and mean diameters of the 1st to the 5th order branches of the callosal axons
4.1.3.3. Mean lengths of the 1st to the 5th order branches of the callosal axons
4.1.3.4. Mean number of nodes of the callosal axons
4.1.3.5. Mean number of terminals of the callosal axons
4.1.3.6. Mean number of boutons of callosal axons
4.2. Simulation of the propagation of spikes in MD callosal axons
5. Discussion
5.1. Effects of monocular occlusion on the morphology of callosal axons
5.2. Simulation of propagation of spikes along the callosal axons 5.3. Possible role of synchronized activities in the development of callosal connections after early monocular deprivation 5.4. Role of synchronized callosal activities during visual processing
6. Acknowledgments
7. References

1. ABSTRACT

The question of whether neural synchrony may be preserved in adult mammalian visual cortex despite abnormal postnatal visual experience was investigated by combining anatomical and computational approaches. Single callosal axons in visual cortex of early monocularly deprived (MD) adult cats were labeled anterogradely with biocytin in vivo and reconstructed in 3D. Spike propagation was then orthodromically simulated within each of these axons with NEURON® software. Data were systematically compared to those previously obtained in normally reared (NR) adult cats with comparable approaches (1-2). The architecture of the callosal axons in MD animals differed significantly from the NR group, with longer branches and first nodes located deeper below the cortex. But, surprisingly, simulation of spike propagation demonstrated that transmission latencies of most spikes remained inferior to 2 ms, like the NR group. These results indicate that synchrony of neural activity may be preserved in adult visual cortex despite abnormal postnatal visual experience. According to the temporal binding hypothesis, this also indicates that the necessary timing for visual perception is present despite anatomical abnormalities in visual cortex.