Browse all publications by topic
Browse all publications by year
- K. Wimmer, M. Stimberg,
R. Martin, J. Schummers, M. Sur, and K. Obermayer. Dependence of
orientation tuning dynamics on map location in a network model of V1.
.
In Society for Neuroscience Abstracts, 2008.
Neurons in primary visual cortex are embedded in an orientation
preference map. The lateral inputs that a cell receives are thus determined
(1) by its position in the orientation map and (2) by the way that synaptic
inputs are pooled across the map. While the synaptic pooling radius is
constrained by experimental measurements the strength of lateral connections
is unknown. Here, we use recent experimental data from reverse correlation
experiments to constrain a Hodgkin-Huxley network model and to pin down the
relative strength of lateral excitatory and inhibitory
connections.Single-unit recordings from cat primary visual cortex showed that
neurons close to pinwheel centers and neurons in orientation domains exhibit
a similar time course in their averaged responses, but differences in their
inter-cell variability. The mean responses of orientation domain cells are
more similar to one another than those of pinwheel cells. We investigated how
the temporal characteristics in pinwheel and orientation domain neurons vary
with different parameterization of the Hodgkin-Huxley network. We find that
in an excitation dominated regime the responses of orientation domain cells
are markedly longer than those of cells close to pinwheel centers. The
response curves of pinwheel and orientation domain cells are relatively
similar for a relatively wide range of feed-forward, recurrent, and
moderately inhibition dominated regimes. The difference in the variance of
the temporal responses between pinwheel and orientation domain cells observed
in vivo can only be observed in the excitatory-dominated and the balanced
recurrent regime of the network model. We show that the differential
variability can be attributed to the variability present in the afferent
input provided by neurons with different temporal characteristics. The
recurrent connectivity removes some of this variability, but the degree of
'smoothing' differs between orientation domains and pinwheel centers. In sum,
we find that the in-vivo responses are not compatible with either excitatory
or inhibitory dominated regimes, but can only be reproduced in a balanced
recurrent regime. Interestingly, this regime is close in phase space to a
'line of instability' beyond which the network settles into a state of high,
self-sustained activity.
|
