Fig. 2.

High-amplitude positive spike (HAPS). This HAPS (solid lines) was recorded as the pipette was moved progressively over a distance of 90 μm (depths below cortical surface are indicated). Identification as a single unit is based on a stable and well-defined response to a preferred stimulus orientation. During recording at the last location, the unit abruptly lost amplitude and then stopped spiking altogether. It appears qualitatively similar to an AP recorded intracellularly, but it has about 1/60 the amplitude and is sped up by a factor of 2 to 3.