Receptive field properties of cells in area 19 of the cat

We have recorded extracellularly from single cells in area 19 of the cat for the purpose of providing a quantitative description of response characteristics. A prominent feature of this area is a high incidence of cells that are end-stopped. Drifting sinusoidal gratings were used to determine spatial and temporal characteristics of the discharge region. In addition, we have conducted independent tests to characterize end zones of receptive fields. When a grating patch was used to stimulate the discharge region alone, all of the cells showed a band-pass spatial frequency tuning characteristic. The optimal spatial frequency ranged from 0.1 to 1.13 cycles/deg, and the distribution had a peak at 0.4 cycles/deg. The bandwidth at half peak amplitude ranged widely from 0.7 to 3.3 octaves (mean 2.0 octaves). When gratings were also presented to the end zones, responses to stimulation of the central region were suppressed. The surround was phase-insensitive in that the relative phase between the grating in the two regions generally did not affect the strength of the suppression. To determine spatial characteristics of the end-zone inhibition, the spatial frequency of the end-zone grating was changed while that for the central pattern was fixed. All cells showed a band-pass characteristic for end-zone inhibition, but in each case, the tuning width was broader than that for excitation. The mean spatial frequency bandwidth of end-zone inhibition was 2.7 octaves. The peak of the inhibition generally coincided with the peak of the excitatory spatial frequency tuning of the discharge center. Considered together, these results show that neurons in area 19 share common properties with those in areas 17 and 18, but they exhibit phase-insensitive end-zone inhibition more frequently.