- 一般社団法人 日本霊長類学会
- 霊長類研究 (ISSN:09124047)
- vol.19, no.1, pp.107-113, 2003 (Released:2005-03-24)
The anterior cingulate cortex (Brodman’s areas 24 and 25) has been shown to participate in various functions: emotion, pain, visceromotor, skeletomotor control, and attention. Moreover, the area is involved in vocalization, singing and word processing, suggesting that it is of particular importance for higher brain functions such as communication and language. Anatomical studies have indicated that an unusual type of neurons (spindle neuron) is present in the layer Vb of the anterior cingulate cortex. The spindle neurons are characterized by large vertical fusiform morphology and are a type of projection neuron. They have a large apical dendrite extending toward the pial surface and a single large basal dendrite extending toward the white matter. The neurons have been demonstrated only in humans and the great apes; bonobos, common chimpanzees, gorillas and orangutans. The neurons are absent in the gibbon, as well as in New and Old World monkeys. The density of the spindle neurons in layer V and the volume of the cell body vary as a function of relative brain size (encephalization) across humans and great apes. We recently observed the existence of the spindle neurons in a chimpanzee fetus (embryonic day 224), which was stillborn. About 5% of neuronal cells in layer Vb were spindle neurons. No spindle neurons were observed in layer V of the prefrontal cortex. These findings suggest that the existence of the spindle neurons in the anterior cingulate cortex is intrinsically characterized during the embryonic stage of the chimpanzee. The relationship between this unique neuron and the physiological functions of the anterior cingulate cortex such as communication and language remains to be clarified.