[Neurons in monkey parietal association cortex sensitive to axis orientation]

Patients with parietal lesions may fail to adjust the orientation of the hand to that of the target object or may make errors in judging the orientation of the bar. This suggests that the parietal cortex functions to discriminate the orientation of objects. Therefore, we studied orientation selectivity of the visual neurons of the posterior parietal association cortex of alert behaving monkeys. We recorded 23 neurons that showed selectivity in the axis orientation of visual stimulus in the lateral bank and fundus of the caudal part of the intraparietal sulcus (IPS). Almost all the neurons tested with a slit on the screen responded better to a longer or narrower stimulus. There were also neurons which responded only to three dimensional objects, such as a bar presented in the sagittal orientation tilted forward or backward. The majority of these neurons had wide receptive fields and their responses were position-invariant. These results suggest that the axis orientation selective neurons of the parietal cortex represent orientation of the longitudinal axis of objects in 3-dimensional space.