Impact of neuronal dynamics on anatomical organization of the cerebral cortex.
J.J. Wright, D.M. Alexander and
9th Tamagawa Dynamic Brain Forum - DBF, Nov 2005
Action potential and local field activity in the gamma frequency range plays a
major part in information processing in the alert state, and synchronous oscillation at
gamma frequencies is believed to bind transient assemblies of neurones together in
functional coalitions. The interaction of âspike-and-waveâ dynamics with
synaptic dynamics has been little considered.
Analytic and simulation considerations show that synchronous oscillation can act in
concert with Hebbian synaptic modification to give rise to anatomically realistic
features of the visual cortex (V1). From random lateral connections which decline in
synaptic density with distance from the soma of origin, and which are distributed with
terminal arborizations of approximately 300 micron dimension, evolution of synaptic
strengths under organization by synchronous oscillation proceeds to a stable state in
which all synapses are either saturated, or have minimum pre/post-synaptic coincidence.
The most stable configuration gives rise to âlocal mapsâ, each of macro-columnar
size, and each organised as Mobius projections of retinotopic space. A tiling of V1,
constructed of approximately mirror-image reflections of each local map by its
neighbours is formed, accounting for orientation-preference singularities, linear
zones and saddle points - with each map linked by connections between sites of
common orientation preference. Ocular dominance columns are partly explained as a
special case of the same process. The occurrence of direction preference fractures
always in odd numbers around singularities, and effects of stimulus velocity,
orientation relative to direction of motion, and extension, upon orientation
preference are thus explained.
This model appears applicable outside the context of V1.