Where is the human nucleus basalis of Meynert?

Abstract

Introduction: The nucleus basalis of Meynert (nbM) is generally defined as the collection of cholinergic neurons located ventral to the anterior commissure. However, detailed anatomical studies on the basal forebrain of the rhesus monkey, using retrograde tracers and cholinergic markers, have revealed a number of different sub-regions that innervate the cortex topographically. It is not known whether this topography translates to the human brain directly and there is a lack of consistency between different studies with regards to the sub-regional anatomy within the human basal forebrain. Therefore, our aim was to simplify and standardise the anatomy of the basal forebrain with a focus on defining the sub-regions of the nbM based on the general consensus in the existing literature. Material and methods: Published literature which included description of the nbM subdivisions was reviewed and 222 basal forebrain sections were obtained from the Parkinson’s UK Tissue bank. Tissues were stained with H&E and immunohistochemistry with choline-acetyltransferase (ChAT) for the identification of cholinergic neurons. Key anatomical landmarks were noted and matched with stained tissue sections. Results: Based on the published literature and our own findings, the nbM can be divided into three clear divisions: the anterior nbM is defined by the level of anterior commissure decussation; Intermediate nbM by the splitting of globus pallidus and anterior commissure located ventral to the globus pallidus externa and putamen; and posterior nbM by the level of mammillary body and anterior commissure located ventral/ventrolateral to the putamen. Conclusion: We have established a simplified classification system of the human nbM. This should facilitate further research into clinico-pathological correlations between sub-regional nbM pathology and cognitive deficits found in different neurological disorders.