The Limbic Brain

The fascination many psychiatrists and cognitive neuroscientists share with respect to the structure and function of the limbic brain may be explained by the broadly accepted assumption that limbic structures represent the neuronal basis for emotional awareness. Accordingly, it has been postulated (and partly substantiated by recent empirical data) that a dysfunction of limbic structures and circuits is crucially involved in the etiology of a variety of neuropsychiatric diseases, including schizophrenia, depression, and posttraumatic stress disorder. Thus, a sound knowledge of the neuroanatomical basis and functional connections of the limbic brain represents an important prerequisite not only for the understanding of normal and abnormal human experience and behavior but also for the proper interpretation of data derived from modern structural and functional neuroimaging studies. The Limbic Brain offers both a concise introduction to limbic brain anatomy and a comprehensive historical review of the evolution of current concepts of one of the most intriguing functional networks of the human brain.

The book is divided into five chapters that follow a chronological order, starting from the early description of the “great limbic lobe” by Paul Broca (1878). The first chapter (titled “Broca’s Lobe”) provides an overview of several classical (19th century) descriptions related to the limbic brain concept, including Rolando’s processo cristato, Gerdy’s circonvolution annulaire, and the already mentioned great limbic lobe of Broca. This chapter also includes an exploration of the hippocampal area (using more modern illustrations and current terminology) and surveys a variety of introductory approaches to the topic of limbic brain anatomy.

Having digested chapter 1, the reader is familiar with some of the most important anatomical details of the limbic brain and is thus well prepared for the study of chapter 2 (“Papez’s Circuit”). While the first chapter deals mainly with structural aspects of the topic, chapter 2 describes the classical model of limbic function, which was first introduced in 1937 and is known to us nowadays as Papez’s circuit. It was in 1937 that Papez, an American neuroanatomist, published a paper titled “A Proposed Mechanism of Emotion.” He proposed that a circulatory consortium of neural components and their connections participate in concert harmoniously to elaborate emotional awareness. Although the main elements of Papez’s circuit largely conformed to Broca’s great limbic lobe, Broca’s early speculations regarding an emotive function for this structure did not contribute in any direct way to the development of Papez’s concept. Rather, Papez was influenced by new data derived from brain transection and stimulation experiments, developments in comparative neuroanatomy, clinical observations, and an evolving neuroanatomical philosophy (postulating reciprocating cortical to subcortical circuits as central processes elaborating consciousness).

The third chapter (“MacLean’s Limbic System”) deals with the transformation and extension of Papez’s circuit into a more complex and dispersed limbic system. In particular, this chapter examines Paul MacLean’s contribution in 1952 to two aspects of limbic brain anatomy and function: 1) his efforts at expanding the confines of the limbic brain to include a consortium of neural structures extending rostral to the limbic fissure (frontotemporal association cortex and perihippocampal areas) and 2) his endeavor to place the mammalian limbic brain into an evolutionary context, including the introduction of the so-called triune brain concept.

Only 6 years after MacLean expanded the limbic domain into the frontotemporal domain, Walle Nauta published a paper extending the limbic system even farther. Chapter 4 (“Nauta’s Limbic Midbrain”) deals with the structural and neurobehavioral implications of this further “growth” of the limbic system both caudally and rostrally, with a particular emphasis on Nauta’s limbic midbrain.

The final chapter (“Heimer’s Limbic Striatum”) is centered on an examination of a 1975 publication by Heimer and Wilson. By introducing a concept of limbic striatal integration, Heimer and Wilson provided a model for the functional interface between the limbic and motor systems and further de-emphasized the idea of a strictly independent limbic brain domain.

The Limbic Brain is clearly written, the style is narrative, and the text is enriched by many illustrations, tables, and historical quotations. Thus, although dealing with a highly complex matter, it makes highly stimulating reading. In particular, I liked the historical approach that enables the reader to recapitulate the scientific process of exploration, discovery, and understanding as it relates to one of the principal hemispheric domains. Inevitably this leaves the reader with a much deeper understanding of the topic than could be provided by any plain presentation of the scientific “state of the art.” In conclusion, this is an excellent and convincing introduction into the field of limbic brain anatomy, covering structural as well as functional aspects of the topic. Accordingly, the book should be of interest not only for students of neuroanatomy but equally for advanced researchers in the field of cognitive neuroscience and neuropsychiatry.