Abstract
The cortical column has been an invaluable concept to explain the functional organization of the neocortex. While this idea was born out of experiments that cleverly combined electrophysiological recordings with anatomy, no one has ‘seen’ the anatomy of a column. All we know is that when we record through the cortex of primates, ungulates, and carnivores in a trajectory perpendicular to its surface there is a remarkable constancy in the receptive field properties of the neurons regarding one set of stimulus features. There is no obvious morphological analog for this functional architecture, in fact much of the anatomical data seems to challenge it. Here we describe historically the origins of the concept of the cortical column and the struggles of the pioneers to define the columnar architecture. We suggest that in the concept of a ‘canonical circuit’ we may find the means to reconcile the structure of neocortex with its functional architecture. The canonical microcircuit respects the known connectivity of the neocortex, and it is flexible enough to change transiently the architecture of its network in order to perform the required computations.
Highlights
The cortical column has been an invaluable concept to explain the functional organization of the neocortex
We suggest that in the concept of a ‘canonical circuit’ we may find the means to reconcile the structure of neocortex with its functional architecture.The canonical microcircuit respects the known connectivity of the neocortex, and it is flexible enough to change transiently the architecture of its network in order to perform the required computations
NEURAL ECONOMIES In the visual cortex of whisking rodents, single unit recording provided no indication of columns, orientation or otherwise (Girman et al, 1999), dendritic bundles are present (Peters and Kara, 1987).The imaging with calcium indicators confirmed the single unit results in showing an apparently random, column-less distribution of orientation preferences (Ohki et al, 2005), so that in the false color representations it looked like a spilled box of Smarties (“M ‘n M’s” in the USA)
Summary
Peering down a microscope, squinting at a computer monitor, or listening to the activity at the tip of a microelectrode, one no longer needs the eye or ear of faith to see columns almost everywhere It was not always : Mountcastle (2003), reminiscing about his work in the 1950s, wrote, ‘When in 1955–1959 I described the columnar organization of the somatic sensory cortex on the basis of observations made in single neuron recording experiments in cats and monkeys (Mountcastle et al, 1955; Mountcastle, 1957; Powell and Mountcastle, 1959a), the report was met with disbelief by many neuroanatomists.’.
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