Nucleus subputaminalis (Ayala): The still disregarded magnocellular component of the basal forebrain may be human specific and connected with the cortical speech area

The small magnocellular group located within the rostrolateral extension of the basal forebrain was named and described as the nucleus subputaminalis in the human and chimpanzee brain by Ayala. Analysis of cytoarchitectonic a nd cytochemical characteristics of this cell group has been largely disrega rded in both classical and more current studies. We examined the nucleus su bputaminalis in 33 neurologically normal subjects (ranging from 15 weeks of gestation to 71 years-of-age) by using Nissl staining, choline acetyltrans ferase immunohistochemistry, acetyl cholinesterase histochemistry and nerve growth factor receptor immunocytochemistry. In addition, we applied reduce d nicotinamide adenine dinucleotide phosphate-diaphorase histochemistry and calbindin-D28k immunocytochemistry in three neurologically normal subjects . At the most rostrolateral levels we describe the previously poorly charac terized component of the lateral (periputaminal) subdivision of the subputa minal nucleus, which may be human specific since it is not described in non -human primates. Moreover, we find the human subputaminal nucleus best deve loped at the anterointermediate level, which is the part of the basal nucle us that is usually much smaller or missing in monkeys. The location of subp utaminal cholinergic neurons within the frontal lobe, the ascension of thei r fibers through the external capsule towards the inferior frontal gyrus, t he larger size of the subputaminal nucleus on the left side at the most ros tral and anterointermediate levels and the most protracted development amon g all magnocellular aggregations within the basal forebrain strongly sugges t that they may be connected with the cortical speech area.