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Abstract:
Integration in the head-direction system is a computation by
which horizontal angular head velocity signals from the
vestibular nuclei are integrated to yield a neural representation
of head direction. In the thalamus, the postsubiculum and the
mammillary nuclei, the head-direction representation has the form
of a place code: neurons have a preferred head direction in which
their firing is maximal [Blair and Sharp, 1995, Blair et al.,
1998, ?].
Integration is a difficult computation, given that
head-velocities can vary over a large range. Previous models of
the head-direction system relied on the assumption that the
integration is achieved in a firing-rate-based attractor network
with a ring structure. In order to correctly integrate
head-velocity signals during high-speed head rotations, very fast
synaptic dynamics had to be assumed.
Here we address the question whether integration in the
head-direction system is possible with slow synapses, for example
excitatory NMDA and inhibitory GABA(B) type synapses. For neural
networks with such slow synapses, rate-based dynamics are a good
approximation of spiking neurons [Ermentrout, 1994]. We find that
correct integration during high-speed head rotations imposes
strong constraints on possible network architectures.
References
[Blair et al., 1998] Blair, H., Cho, J., and Sharp, P. (1998).
Role of the lateral mammillarynucleus in the rat head direction
circuit: A combined single unit recording and lesion study.
Neuron
, 21:1387-1397.
[Blair and Sharp, 1995] Blair, H. and Sharp, P. (1995).
Anticipatory head direction signals in anterior thalamus:
evidence for a thalamocortical circuit that integrates angular
head motion to compute head direction.
The Journal of Neuroscience
, 15(9):6260-6270.
[Ermentrout, 1994] Ermentrout, B. (1994). Reduction of
conductance-based models withslow synapses to neural nets.
Neural Computation
, 6:679-695.
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