We recorded activity of the hand-manipulation-task-related neurons in the posterolateral bank of the anterior intraparietal sulcus (area AIP) of the monkey parietal cortex during a delayed hand manipulation task. 2. We examined mainly the object-type visual-dominant and visual-and-motor neurons that responded to the sight of objects for manipulation. The majority of these neurons (32 of 48) showed sustained activity during the delay period in the dark before manipulation of preferred objects. 3. Six visual-and-motor neurons showed set-related activity before the hand manipulation in the dark, so that their delay period activity was likely to be related to motor preparation. 4. The delay period activity of 18 visual-dominant and visual-and-motor neurons without set-related activity was likely to represent spatial features of objects, because the majority of the neurons showed the same selectivity in the shape and/or orientation during object fixation and the delay period. 5. Of these 18 neurons, 10 showed sustained activity in the dark after brief illumination of objects during a light-interrupted fixation task, suggesting that they store the short-term memory of objects without the intention to remember. 6. The results suggest that the visual memory of three-dimensional features of objects is likely to be incorporated in area AIP and to be used for the guidance of hand manipulation.
