Thesis and articles on thalamocortical information processing

[Ulrich Hillenbrand]

Dear colleagues,

you can find my doctoral thesis

Spatiotemporal Adaptation in the Corticogeniculate Loop
Ulrich Hillenbrand
Technical University of Munich (2001)

(see abstract below) for download at

http://tumb1.biblio.tu-muenchen.de/publ/diss/ph/2001/hillenbrand.pdf


You may also be interested in two related articles,

Spatiotemporal adaptation through corticothalamic loops: A hypothesis
Ulrich Hillenbrand and J. Leo van Hemmen
Visual Neuroscience 17, 107-118 (2000)

http://www.journals.cup.org/bin/bladerunner?REQUNIQ=989495926&REQSESS=156885&118200REQEVENT=&REQINT1=40136&REQAUTH=0

and

Does Corticothalamic Feedback Control Cortical Velocity Tuning?
Ulrich Hillenbrand and J. Leo van Hemmen
Neural Computation 13, 327-355 (2001)

http://neco.mitpress.org/cgi/content/full/13/2/327

Reprints are available upon request (by e-mail or to the address below).



Please feel free to comment.

Regards,

Ulrich Hillenbrand

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      Spatiotemporal Adaptation in the Corticogeniculate Loop

                            Abstract

The thalamus is the major gate to the cortex for almost all sensory
signals, for input from various subcortical sources such as the
cerebellum and the mammillary bodies, and for reentrant cortical
information. Thalamic nuclei do not merely relay information to the
cortex but perform some operation on it while being modulated by
various transmitter systems and in continuous interplay with their
cortical target areas. Indeed, cortical feedback to the thalamus is
the anatomically dominant input to relay cells even in those thalamic
nuclei that are directly driven by sensory systems. While it is
well-established that the receptive fields of cortical neurons are
strongly influenced by convergent thalamic inputs of different types,
the modulation effected by cortical feedback in thalamic response has
been difficult to interpret. Experiments and theoretical
considerations have pointed to a variety of operations of the visual
cortex on the visual thalamus, the lateral geniculate nucleus (LGN),
such as control of binocular disparity for stereopsis (Schmielau &
Singer, 1977), attention-related gating of relay cells (Sherman &
Koch, 1986), gain control of relay cells (Koch, 1987), synchronizing
firing of neighboring relay cells (Sillito et al., 1994; Singer 1994),
increasing visual information in relay cells' output (McClurkin et
al., 1994), and switching relay cells from a detection to an analyzing
mode (Godwin et al., 1996; Sherman, 1996; Sherman & Guillery,
1996). Nonetheless, the evidence for any particular function is still
sparse and rather indirect to date.

Clearly, detailed concepts of the interdependency of thalamic and
cortical operation could greatly advance our knowledge about complex
sensory, and ultimately cognitive, processing. Here we present a novel
view on the corticothalamic puzzle by proposing that control of
velocity tuning of visual cortical neurons may be an eminent function
of corticogeniculate processing.

The hypothesis is advanced by studying a model of the primary visual
pathway in extensive computer simulations. At the heart of the model
is a biophysical account of the electrical membrane properties of
thalamic relay neurons (Huguenard & McCormick, 1992; McCormick &
Huguenard, 1992) that includes 12 ionic conductances. Among the
different effects that corticogeniculate feedback may have on relay
cells, we focus on the modulation of their relay mode (between tonic
and burst mode) by control of their resting membrane potential.
Employing two distinct temporal-response types of geniculate relay
neurons (lagged and nonlagged), we find that shifts in membrane
potential affect the temporal response properties of relay cells in a
way that alters the tuning of cortical cells for speed.

Given the loop of information from the LGN to cortical layer 4, via a
variable number of synapses to layer 6, and back to the LGN, the
question arises, what are likely implications of adaptive speed tuning
for visual information processing? Based on some fairly general
considerations concerning the nature of motion information, we devise
a simple model of the corticogeniculate loop that utilizes adaptive
speed tuning for the fundamental task of segmentation of objects in
motion. A detailed mathematical analysis of the model's behavior is
presented. Treating visual stimulation as a stochastic process that
drives the adaptation dynamics, we prove the model's
object-segmentation capabilities and reveal some non-intended
properties, such as oscillatory responses, that are consequences of
its basic design. Several aspects of the dynamics in the loop are
discussed in relation to experimental data.

--
Dr. Ulrich Hillenbrand
Institute of Robotics and Mechatronics
German Aerospace Center/DLR
Postfach 1116
82230 Wessling
Germany

Phone: +49-8153-28-3501
Fax:   +49-8153-28-1134