A self-organising model is proposed to explain the criticality
in cortical networks deduced from recent observations of neuronal
avalanches. Prevailing understanding of self-organised criticality (SOC)
dictates that conservation of energy is essential to its emergence.
Neuronal networks however are inherently non-conservative as demonstrated
by microelectrode recordings. The model presented here shows that SOC can
arise in non-conservative systems as well, if driven internally. Evidence
suggests that synaptic background activity provides the internal drive for non-conservative
cortical networks to achieve and maintain a critical state. SOC is robust to
any degree η∈(0,1] of background activity when the network size N
is large enough such that ηN∼103. For small networks, a strong background
leads to epileptiform activity, consistent with neurophysiological knowledge
about epilepsy