Paper Announcement: Active Dendrites & Complex Cells

[Bartlett Mel]

Members of the connectionist community may be interested in the
following paper in the June issue of the Journal of Neuroscience:

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"Translation-Invariant Orientation Tuning in Visual 'Complex' Cells
Could Derive from Intradendritic Computations "

Bartlett W. Mel, Daniel L. Ruderman, and Kevin A. Archie
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Journal of Neurocience Online:
http://www.jneurosci.org/cgi/content/full/18/11/4325

Preprint, via our lab web page (click on Publications):
http://lnc.usc.edu/

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ABSTRACT

Hubel and Wiesel (1962) first distinguished ``simple'' from ``complex''
cells in visual cortex, and proposed a processing hierarchy in which
rows of LGN cells are pooled to drive oriented simple cell subunits,
which are pooled in turn to drive complex cells. Though parsimonious and
highly influential, the pure hierarchical model has since been
challenged by results indicating many complex cells receive excitatory
monosynaptic input from LGN cells, or do not depend on simple cell
input. Alternative accounts for complex cell orientation tuning remain
scant, however, and the function of monosynaptic LGN contacts onto
complex cell dendrites remains unknown. We have used a biophysically
detailed compartmental model to investigate whether nonlinear
integration of LGN synaptic inputs within the dendrites of individual
pyramidal cells could contribute to complex-cell receptive field
structure. We show that an isolated cortical neuron with ``active''
dendrites, driven only by excitatory inputs from overlapping ON- and
OFF-center LGN subfields, can produce clear phase-invariant orientation
tuning---a hallmark response characteristic of a complex cell. The
tuning is shown to depend critically upon both the spatial arrangement
of LGN synaptic contacts across the complex cell dendritic tree,
established by a Hebbian developmental principle, and on the
physiological efficacy of excitatory voltage-dependent dendritic ion
channels. We conclude that unoriented LGN inputs to a complex cell could
contribute in a significant way to its orientation tuning, acting in
concert with oriented inputs to the same cell provided by simple cells
or other complex cells. As such, our model provides a novel,
experimentally testable hypothesis regarding the basis of orientation
tuning in the complex cell population, and more generally, underscores
the potential importance of nonlinear intradendritic subunit processing
in cortical neurophysiology. 



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 Bartlett W. Mel                               (213)740-0334, -3397(lab)
 Assistant Professor of Biomedical Engineering (213)740-0343 fax
 University of Southern California, OHE 500     mel at lnc.usc.edu,
http://lnc.usc.edu
                             
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