DIRECTION SELECTIVITY AND PHYSIOLOGICAL COMPENSATION IN THE SUPERIOR COLLICULUS FOLLOWING REMOVAL OF AREAS 17 AND 18

Previous studies indicate that cortical areas 17 and 18 play a promine nt role in generating the direction selectivities of neurons in the su perior colliculus of the cat. This hypothesis was tested by quantifyin g the activities of neurons in the superficial collicular layers in in tact cats and cats which incurred ablation of areas 17 and 18 and part of area 19. In addition, since behavioral and anatomical studies sugg est a functional adjustment in the superior colliculus following remov al of inputs from areas 17, 18, and 19 in the neonatal cat, we include d a group of neonatally lesioned cats. Computation of an index of dire ctionality indicated that the majority of neurons in intact cats prefe rred movement in one direction, thus confirming reports of others. Fol lowing ablation of areas 17 and 18 and part of area 19 in both groups of lesioned cats, only modest changes in the population indices were d etected when poorly responsive neurons were eliminated from the analys es. Based upon levels of visually evoked neuronal activity, our data s uggest a physiological compensation by neurons in stratum griseum supe rficiale following removal of areas 17, 18, and 19 inputs. In the inta ct and neonatally operated groups, activity in stratum griseum superfi ciale is high, whereas in the adult lesioned group activity is low. In stratum opticum, neuronal activity was similar in all three groups of cats. These results show that neurons in stratum griseum superficiale undergo a physiological compensation following removal of immature ar eas 17 and 18.