Canonical cortical circuits: current evidence and theoretical implications

Abstract

Neurophysiological and neuroanatomical studies have found that the same basic structural and functional organization of neuronal circuits exists throughout the cortex. This kind of cortical organization, termed canonical circuit, has been functionally demonstrated primarily by studies involving visual striate cortex, and then, the concept has been extended to different cortical areas. In brief, the canonical circuit is composed of superficial pyramidal neurons of layers II/III receiving different inputs and deep pyramidal neurons of layer V that are responsible for cortex output. Superficial and deep pyramidal neurons are reciprocally connected, and inhibitory interneurons participate in modulating the activity of the circuit. The main intuition of this model is that the entire cortical network could be modeled as the repetition of relatively simple modules composed of relatively few types of excitatory and inhibitory, highly interconnected neurons. We will review the origin and the application of the canonical cortical circuit model in the six sections of this paper. The first section (The origins of the concept of canonical circuit: the cat visual cortex) reviews the experiments performed in the cat visual cortex, from the origin of the concept of canonical circuit to the most recent developments in the modelization of cortex. The second (The canonical circuit in neocortex) and third (Toward a canonical circuit in agranular cortex) sections try to extend the concept of canonical circuit to other cortical areas, providing some significant examples of circuit functioning in different cytoarchitectonic contexts. The fourth section (Extending the concept of canonical circuit to economic decisions circuits) reviews the experiments conducted in humans by using transcranial magnetic stimulation to demonstrate the validity of the canonical cortical circuit model. The fifth section (Extending the concept of canonical circuit to economic decisions circuits) explores the hypothesis that also complex human behaviors such as economic decision-making could also be explained in terms of canonical cortical circuit. The final section (Conclusion) provides a critical point of view, evidencing the limits of the available data and tracking directions for future research.