Figure 5. Effects of inactivation of area 21a on the magnitude of responses of collicular neurones vs. effects of inactivation of area 17.

A, the PSTHs of a collicular neurone before and during cooling and after rewarming of area 21a. Each PSTH was constructed on the basis of responses to 10 presentations of a 1.6 × 0.6 deg light bar moving across the cell's RF at 5 deg s⁻¹ parallel to the horizontal meridian. Other conventions as in Fig. 3. Note that cooling the Peltier probe located over area 21a to 10 °C resulted in a dramatic reduction (over 70 %) in the magnitude of responses and 30 min after rewarming area 21a to 36 °C the magnitude of the response was largely restored (over 84 % of the original response). B, the PSTHs of responses of the same cell before and during cooling and after rewarming of area 17. Note that the response was almost abolished (94 % reduction) during cooling the Peltier probe located over area 17 to 10 °C and 30 min after rewarming area 17 to 36 °C partially recovered (over 56 % of the pre-cooling magnitude). C, the standardised decrease in the magnitude of response of 10 collicular cells in the preferred direction during inactivation of area 21a vs. decrease in the magnitude of responses of the same cells following sequential inactivation of area 17. The cells were recorded in three animals. The laminar location (see Fig. 1) of all but one cell (Not det) is indicated. Note that inactivation of area 17 resulted in a more profound decrease in the magnitude of response of the collicular neurones than inactivation of area 21a. This difference was highly significant (P < 0.001; Wilcoxon test). D, in three of our population cells (two of them recorded in one animal), inactivation of areas 21a and 17 had opposite effects; detailed description in the text.