Cortical activation during color discrimination task in macaques as revealed by positron emission tomography

Physiological and lesion studies have shown that the anterior inferior temporal (IT) cortex (aITC) is involved in the color vision of macaque monkeys. However, some functional imaging studies using awake monkeys contradicted the involvement of aITC in color vision. Thus, in most of the imaging studies, cortical activation has been observed during a fixation task. However, because the neuronal activity of aITC is highly affected by the behavioral task, it is desirable to investigate cortical activity during a color discrimination task to determine the functional role of aITC in the color vision of macaque monkeys. In this study, we investigated the cortical activity of aITC of macaque monkeys during color discrimination by positron emission tomography. Two monkeys were trained in a color discrimination task. Cortical areas involved in color processing were investigated by comparing activities during the color discrimination and lever release tasks. In addition to area V4 and the posterior IT cortex (pITC), we found color-related activities in the anterior IT gyrus. Consistent activation was observed in the region posterior to the anterior medial temporal sulcus (AMTS), although the exact location and the size of activations differed between monkeys and hemispheres. We also found color-related activities in the anterior portion of the superior temporal sulcus (STS), suggesting its involvement in the color vision. The present results revealed that aITC is involved in the color vision of macaque monkeys by a functional imaging technique.