The Emergence Of A Sense Of Orientation - Scientists Have Developed A Theoretical Model That Shows How An Orientation Map Develops In The Brain

To orient ourselves, we mainly need two pieces of information: where am I
and in which direction am I heading? Experiments in the rat have shown
that
these types of information are directly accessible and independently coded
in the brain. When the rat explores a new territory, so-called place cells
and head direction cells form within only a few minutes. Place cells are
active when the rat visits a particular area, no matter which direction it
is
facing. In contrast, head direction cells code the direction the rat is
heading, independent of where it is. Also humans presumably have these and
other types of cells which specifically instruct its sense of orientation.
Scientists around Mathias Franzius and Laurenz Wiskott from the
Humboldt-University and Bernstein Center for Computational Neuroscience
Berlin (Germany) have now developed a theoretical model that can explain
the
emergence of all orientation-specific cells that are known in rats and
primates to date. The work will be published on August 31, 2007, in the
scientific journal PLoS Computational Biology.



The model analyzes realistic image data that reflect the visual input a
rat would perceive when exploring a new environment. The core of their
model
is a mathematical algorithm called "slow feature analysis", which extracts
information relevant to orientation from the image data. On the basis of
this algorithm, the model generates place cells and head direction cells -
without this being an a priori requirement.



Every receptor in the eye only captures a very small section of the
perceived image. When shifting the gaze just a little, the information
that every
single receptor transmits will be quite different than before. While
sensors deliver constantly changing data, the information important for
orientation varies far more slowly - the overall impression in the example
above remains almost constant. Features that vary slowly can be obtained
from image data by slow feature analysis.



With their model, the scientists could show that slow feature analysis
allows the emergence of what one could call a "cognitive map" from the
linear
sequence of visual data a rat receives when moving through a new
environment. In this map, positions are coded by place cells, whereas a
directional
reference frame is given by head direction cells. It is only after this
learning process that disparate visual impressions can activate the same
set
of place- or head direction cells. If, for example, the rat is located in
the northern corner of its cage, the same place cells will show activity,
no
matter if it is heading east or west.





CITATION: Franzius M, Sprekeler H, Wiskott L (2007) Slowness and
sparseness lead to place, head-direction, and spatial-view cells. PLoS
Comput Biol
3(8): e166. doi:10.1371/journal.pcbi.0030166

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