Might stimulate some thinking (from the same paper)

Inversion of expression. Specific gene-expression profiles map onto different discharge response types. The most striking example is a near-perfect inversion of the expression profile between cells that discharge initially with a burst onset (b-subtype) and those with a delayed onset (d-subtype)85. So, even cells that are normally classified in the same broad class, such as fast spiking, can have diametrically opposite expression profiles depending on the onset response. This finding also indicates that only a few transcription factors might control the expression of entire sets of ion-channel genes, in which case it is probable that different combinations of transcription factors would give rise to a finite number of distinct electrical classes.