Spike Train Statistics from Empirical Facts to Theory: The Case of the Retina - Modeling in Computational Biology and Biomedicine - page 257

Fig. 8.5 Multi-electrode arrays. ( Left ) “Multichannelsystems MEA” from http://www.

multichannelsystems.com ; Right ) Schematic view of the implementantion of a MEA on

the retina (not scaled)

When in contact with a small piece of neural tissue, a MEA is able to record the
simultaneous activity (spike and/or field potential) from, e.g., 10-150 G cells. The
final goal is to produce from the MEA signal a raster plot of G cells activity, namely
a graph with time in abscissa and a neuron labeling in ordinate such that a vertical
bar is drawn each “time” a neuron emits a spike. This poses an important challenge
for signal processing: to sort out from a complex (spatial and temporal) neural
signal superposition recording the contribution of each cell. With the recent increase
in the number of electrodes of MEA devices, the necessity of adequate spike
sorting algorithms turns out to be critical. Recently the Berry's lab at Princeton has
developed an efficient method, enabling to sort out, from a 256 MEA experiment,
about 200 different G cells (personal communication).
MEA devices constitute an excellent tool to track the physiological properties
of G cells [ 45 ] as well as their coding capacity [ 29 , 30 ]. Before the introduction of
MEA devices, the neural coding properties of single G cells was studied using intra
or extra cellular electrodes, giving a limited sense of their collective role. In that
respect, the work of Meister et al. [ 40 ] using MEA devices was pioneer. With simple
stimulus, like checkerboard random white noise, and spike sorting algorithms these
authors were able to determinate the number of spiking cells and their respective RF.
They have shown that concerted G cells are critical, not only for retina development,
but for the neural coding processing.

8.2.3 Encoding a Visual Scene

The distribution and fluctuations of visual signals in the environment can be treated
as a statistical problem [ 43 , 67 ]. Natural scenes (a digital image or movie from
a natural scenario) differ in their particular statistical structure and therefore the