Figure 1.
Responsive and unresponsive cells. We used in vivo whole-cell methods to record subthreshold responses of single neurons in auditory cortex A1. Action potentials were blocked pharmacologically. A, B, Responses of two cells to conventional pure-tone stimuli. Evoked membrane potentials are shown for an array of frequencies and intensities (the loudest tones are on the top row). Both cells exhibited robust responses to pure tones, with typical V-shaped tuning, and had similar characteristic frequencies (CFs) of 3.2 kHz (A) and 4 kHz (B). C, D, Spectrogram of a 5 sec segment of the call of a Knudsen's Frog (stimulus KF). E, F, Responses of these two cells to this sound were strikingly different. In E, this stimulus evoked robust and reliable responses, whereas in F, after a transient onset response, the cell was completely unresponsive. The cell in F was similarly unresponsive to all six natural stimuli tested (data not shown). G, This stimulus contained power at the CFs of both cells (arrows show CFs; colors match traces in A, B, E, and F). In fact, stimulus power was greater at the CF of the unresponsive cell. H, Most cells in our sample had CFs of 1–5 kHz. Arrows show CFs of the two cells in A, B, E, and F. I, Responsiveness to natural stimuli varied across cells. Here, responsiveness is quantified by the SD of the membrane potential evoked by natural stimuli (note that nonstimulus-evoked activity also contributes to this measure). Arrows show the different responsiveness of the two cells in E and F.