A combinatorial transcription factor code defines nine different postnatal populations of interneurons in laminae III–IV.

The first five columns (1–5) refer to inhibitory neuron cell types, while the last four columns (6–9) denote excitatory neurons. The different markers that were analyzed are indicated. The numbering of each column refers to the number assigned to each neuronal population and it is used in all the figures to indicate neurons representative of these columns. Annotation: +, expressed; −, not expressed; nd, not determined; “+”, inferred by indirect evidence. Fuller descriptions of the indirect evidence used for expression profiles 4,6 and 7 are provided in the results section. Asterisk indicates RORαCre; R26floxstop-Tomato expression.