Figure 5. Petilla terminology: types of firing patterns.

Cortical GABAergic interneurons display a vast repertoire of discharge responses. These samples are representative of the most common responses to standardized intrasomatic step-current injections in the rat neocortex. The features of firing patterns in response to step-onset, organized in columns, include bursts, delays and continuous firing, which is neither burst nor delayed. Steady-state patterns, displayed in rows, can be fast spiking, non-adapting non-fast spiking, adapting, irregular spiking, intrinsic burst firing or accelerating. Fast spiking neurons can also display a stuttering or ‘Morse-code-like’ discharge that is characterized by high-frequency spike clusters that are intermingled with unpredictable periods of silence for a wide range of long, sustained, somatic-current injections. Blank areas of the table and boxes containing only scale bars correspond to firing patterns that have not yet been characterized in neocortical interneurons. The scale bar at the top left refers to the traces in the first four rows; the scale bars in the fifth and sixth rows refers to the traces in the fifth and sixth rows, respectively.