Canonical computations of cerebral cortex

•Cortical circuits specialize but may share fundamental properties and computations.•We suggest canonical computations by which cortical areas compute selectivity, gain.•Hierarchical arrangements of such local computations may allow invariant recognition.•Motor/frontal cortex may self-generate activity through enhanced excitation.•Lack of columnar organization in rodent cortex could reflect deeper differences.

The idea that there is a fundamental cortical circuit that performs canonical computations remains compelling though far from proven. Here we review evidence for two canonical operations within sensory cortical areas: a feedforward computation of selectivity; and a recurrent computation of gain in which, given sufficiently strong external input, perhaps from multiple sources, intracortical input largely, but not completely, cancels this external input. This operation leads to many characteristic cortical nonlinearities in integrating multiple stimuli. The cortical computation must combine such local processing with hierarchical processing across areas. We point to important changes in moving from sensory cortex to motor and frontal cortex and the possibility of substantial differences between cortex in rodents vs. species with columnar organization of selectivity.