Measuring the coding efficiency of sensory neurons

All of an organism’s knowledge about the sensory world comes from observation of the spike trains in its own sensory cells. How much information is carried in these spike trains Nand how efficient is the coding? We have recently developed an approach to neural coding which allows us to measure the information a spike train carries about a sensory stimulus without assumptions about how the information is coded[1]Comparing this measured information with an upper bound to the information rate determined by the spiking statistics results in a direct measure of the efficiency of coding. For two different mechanoreceptors from the cricket cercal system and from the bullfrog sacculus we find information rates close to 3 bits per spike (corresponding to 300 bits per sec in the cricket 160 bits per sec in the frog) and coding efficiencies greater than 50%.