  The brain did not develop a dedicated device for reasoning. This fact bears
dramatic consequences. While for perceptuo-motor functions neural activity is
shaped by the input's statistical properties, and processing is carried out at
high speed in hardwired spatially segregated modules, in reasoning, neural
activity is driven by internal dynamics, and processing times, stages, and
functional brain geometry are largely unconstrained a priori. Here, it is shown
that the complex properties of spontaneous activity, which can be ignored in a
short-lived event-related world, become prominent at the long time scales of
certain forms of reasoning which stretch over sufficiently long periods of
time. It is argued that the neural correlates of reasoning should in fact be
defined in terms of non-trivial generic properties of spontaneous brain
activity, and that this implies resorting to concepts, analytical tools, and
ways of designing experiments that are as yet non-standard in cognitive
neuroscience. The implications in terms of models of brain activity, shape of
the neural correlates, methods of data analysis, observability of the
phenomenon and experimental designs are discussed.
