Parsing auditory neural code into maximum-entropy packets

Deciphering the neural code requires identifying its fundamental symbols or code-words. Neural activity is usually interpreted either as a rate code – based on average spike counts – or as a temporal code, which distinguishes patterns with identical counts. Yet, the symbols of the code remain undefined. Here we show that the symbols can be clearly defined by parsing auditory spike trains into variable-duration “packets”, within which precise spike timing is irrelevant. Because packets vary in duration, this is not a rate code. A single neuron could encode very different stimuli depending on the number of spikes it produced per packet. The packet-based code enables real-time readout upon packet completion due to its instantaneous code structure and maximizes information capacity at both single-neuron and population levels.