Figure 6. Effect of inactivation of area 21a on the direction selectivity indices (DI) of collicular neurones.

A, the PSTHs illustrating the direction selectivity of a collicular unit before and during cooling as well as after rewarming of area 21a. Each PSTH was constructed on the basis of responses to 10 presentations of a 3.3 × 0.8 deg light bar moving across the cell's RF at 5 deg s⁻¹ parallel to the horizontal meridian. The neurone exhibited DIs of 0.2 and 0.73 before and during inactivation of area 21a, respectively. After rewarming area 21a, the DI was reduced to 0.38. B, DIs of collicular neurones with significant change in the magnitude of response before and during cooling area 21a. Inactivation of area 21a resulted in some change in DI in almost all of the cells (42/43; 98 % of sample). The filled symbols indicate cells which changed their preferred direction of response during cooling (10/43; 23 % of sample). The parallel dashed lines separate the cells with a DI change greater than 20 % from those with smaller changes. Thus, in a majority of cells (26/43; 60.5 %) the change in their DIs was 20 % or more.