The dorsal diencephalic conduction system: a review of the anatomy and functions of the habenular complex.

The first part of this paper is an attempt to sketch an outline of the anatomy of the dorsal diencephalic conduction system by reviewing experimental evidence establishing the afferent and efferent connections of the habenular complex. This system provides an alternative to the descending medial forebrain bundle for the conduction of information from the limbic forebrain to limbic midbrain areas. The second part is a critical examination of experiments using ablation or electrical and chemical stimulation techniques which are concerned with the behavioural functions of the habenular complex. The habenula has been shown to play an important role in a diverse set of behavioural systems, which include olfaction, ingestion, mating, endocrine function, aversive motivation, and brain stimulation. Anatomical and behavioural support is presented for the view that the dorsal diencephalic conduction system provides an opportunity for interaction of activity in motivational systems with movement systems in the striatum and midbrain.