Is the "functional column" really a well-defined concept?

By applying mathematical analyses to the data obtained by single-unit recordings in the monkey auditory cortex, the authors demonstrated that the similarity of responses of neurons within the same frequency band can change over time and decrease to such a level that they can no longer be considered as a unit. This indicates that the "functional unit", e.g., the column, which is based on the similarity of responses of multiple neurons, is not a well-defined concept for auditory neurons.