PhD thesis on the development of the retinogeniculate pathway

[Stephen Eglen]

The following PhD thesis is available from
http://www.cns.ed.ac.uk/people/stephen/pubs.html



       Modelling the development of the retinogeniculate pathway

			     Stephen Eglen


How does the visual system develop before the onset of visually-driven
activity?  By the time photoreceptors can respond to visual stimulation,
some pathways, including the retinogeniculate pathway, have already
reached a near-adult form.  This rules out visually-driven activity
guiding pathway development.  During this period however, spontaneous
waves of activity travel across the retina, correlating the activity of
neighbouring retinal cells. Activity-dependent mechanisms can exploit
these correlations to guide retinogeniculate refinement.  In this thesis
I investigate, by means of computer simulation, the role of spontaneous
retinal activity upon the development of ocular dominance and topography
in the retinogeniculate pathway.

Keesing, Stork and Shatz (1992) produced an initial model of
retinogeniculate development driven by retinal waves.  In this thesis,
in addition to replicating their initial results, several new results
are presented.  First, the importance of presynaptic normalisation is
highlighted.  This is in contrast to most previous work on ocular
dominance requiring postsynaptic normalisation.  Second, the covariance
rule is adapted so that development can occur under conditions of sparse
input activity.  Third, the model is shown to replicate development
under conditions of monocular deprivation.  Fourth, model development is
analysed using different spatio-temporal inputs including
anticorrelations between on- and off-centre retinal units.


The layered pattern of ocular dominance in the LGN is quite different to
the stripe patterns found in the cortex.  The factors controlling the
patterns of ocular dominance are investigated using a feature-based
model of map formation (Obermayer, Ritter, & Schulten, 1991).  In common
with other models, variance of the ocularity feature controls the
pattern of stripes.  The model is extended to a three-dimensional output
array to show that ocular dominance layers form in this model, and that
the retinotopic maps are organised into projection columns.  Future work
involves extending this three-dimensional model to receive
retinal-based, rather than feature-based, inputs.