When humans repeatedly use a tool, our body image alters until the tool finally becomes a part or an extension of the body. This alteration of body image perhaps results from re-integration of somatosensory and visual signals. We trained Japanese monkeys to use a rake-shaped tool to retrieve a distant food pellet, then used a novel tissue-sampling method to suction brain tissue from the anterior bank of their intraparietal sulcus, where somatosensory and visual signals converge. Examination of the messenger RNA expression levels of neurotrophins and their receptors using real-time quantitative polymerase chain reaction revealed learning-selective induction in the expression of brain-derived neurotrophic factor, its receptor trkB, and NT-3 during, but not after, the learning. These results suggest that these factors are involved in the reorganization of the somatosensory and visual signals in the anterior bank of the intraparietal sulcus when monkeys are learning the use of the tool.