Avian and mammalian "prefrontal cortices": limited degrees of freedom in the evolution of the neural mechanisms of goal-state maintenance.

Is it possible to produce the same cognitive function with different brain organizations? This question is approached for working memory, a cognitive entity that is equally organized in birds and mammals. The critical forebrain structure for working memory is the nidopallium caudolaterale (NCL) in birds and the prefrontal cortex (PFC) in mammals. Although both structures share a large number of neural architectural features, they are probably not homologous but represent a remarkable case of convergent evolution. In reviewing the neuronal mechanisms for working memory in birds and mammals it becomes apparent that the similarities of NCL and PFC extend from the neuronal activation patterns during memory tasks down to the biophysical mechanisms of synaptic currents. Both in mammals and birds, dopamine acts via D1-receptors to tune preactivated neurons into sustained high-frequency patterns with which goal states can be held over time until an appropriate response can be generated. The degrees of freedom to create different neural architectures to solve the problem of 'stimulus maintenance' seem to be very small.