Response to movement of neurons in areas 17 and 18 of the cat: direction selectivity.

Abstract

Area 17 neurons (106) and 97 area 18 neurons were recorded in paralyzed and anesthetized (N2O/O2) cats and tested for direction selectivity with a multihistogram technique. In 56% of all neurons, direction selectivity depended on stimulus velocity. Direction selectivity depended more on velocity in area 18 than in area 17 neurons. Direction selectivity was largest for velocities eliciting the strongest response in the preferred direction. Comparison of direction selectivity assessed with quantitative and qualitative techniques showed that on the plotting table about 1/4-1/3 of the cells were wrongly classified. The proportion of direction-selective cells was larger in area 18 than in area 17. In area 18 but not in area 17 the proportion of direction-selective cells decreased with eccentricity. Differences between areas 17 and 18 were clearest in the region devoted to central vision. Direction-selective cells in area 18 preferred directions away from the area centralis, those in area 17 perferred directions away and toward the area centraliis. Given the velocity sensitivity of area 18 neurons, the direction-selective output of areas 17 and 18 is strongest at medium velocities (4-64.degree./s). The results are discussed as further evidence of the functional differences between areas 17 and 18 and the influence of eccentricity on functional properties of cortical cells.