The Cognitive Neuroscience of Action

As I sit now at my computer to write this book review, I can easily find words to describe the general topic of this book (“the neuroscience of intentional motor behavior”), words to describe the things I liked about the book (“clearly written, comprehensive, provocative”), and words to tell you about some of the ideas the book has inspired in me (“the role of the failure of representations for action in disorders such as schizophrenia”). And you probably are able to get a pretty clear picture of what I am trying to communicate to you, even though these are complex and highly abstract concepts.

So why is it so much more difficult for me to find the words to describe the concrete and simple actions that my eyes and fingers and hands are carrying out at this very same moment? Imagine that you aren’t familiar with computer keyboards and typing—would you really be able to comprehend this laborious description of “my brain directs my eyes to scan the computer screen and the target letters on the keyboard underneath my fingers while simultaneously giving commands to my hands and fingers to move above the target letters as it is forming a word in consciousness so that as the word is formed the fingers can flex and move downward to strike the keys for each letter of the word in the correct succession”?

This paradox—that it is inherently difficult to describe even the simplest motor behavior in any accurate and detailed way, that it is in fact much easier to show someone a motor sequence and have them imitate it rather than try to use words to explain what you are doing—is related to one of the core themes explored in The Cognitive Neuroscience of Action by Marc Jeannerod. The paradox results from the way our brains carry out the task of instructing our motor system to perform actions.

As the author states at the outset, his book aims “to investigate the main aspects of representations for actions. It explores in detail the contribution of cerebral structures, particularly that of the cerebral cortex, to the various aspects of movement preparation and execution” (p. 7). After a brief introduction, Dr. Jeannerod discusses the neural substrates for object-oriented actions (chapter 2) and then moves to the question of task-dependent representations for action (chapter 3). For those of you who are new to the field of cognitive neuroscience, an example of an object-oriented action might be the act of my finger moving to strike the keyboard; the task-dependent representation would then be all of the things my brain is doing as it has me execute the movement.

Early in the book, Dr. Jeannerod provides an overview of the two diverging corticocortical vision pathways: the ventral “perception” system for salient objects in our visual field (what is it?) and the dorsal “action” system for such objects (where is it?). He presents a thorough examination of the data relating to these systems and to their role in motor behavior, explores experimental findings on the brain mechanisms involved in reaching and grasping movements, and notes that the ensemble of the research data suggests that “actions are driven by implicit ‘knowledge’ of object attributes, such that stable and decomposable motor patterns arise to cope with external reality” (p. 51).

From here, Jeannerod introduces his own more general distinction between a pragmatic and a semantic representation for action. Pragmatic representation refers to the rapid transformation by the brain of sensory input about an object into motor commands (visuomotor transformation—where I see and then hit a letter key—being but one example). As in my opening example about typing on a keyboard, it is not easy to describe these operations, even though we often perform them easily and automatically. In contrast, semantic representation in the brain refers to the use of cognitive cues for generating actions. In this series of operations, the brain binds together all of the elementary visual features of an object (color, contrast, depth) into higher-order properties (volume, form) and then finally performs supraordinate processing, where the semantic and contextual properties of the object are understood and the many separate attributes become a coherent and meaningful entity (so that, for instance, I am able to search for and then strike the specific letter key “I” as I begin to recount a personal anecdote).

In other words, “the same object has to be simultaneously represented in multiple ways, simply because the environment asks different questions to the nervous system and because the answer to each of these questions requires accessing different types of representations” (p. 79). To paraphrase work by Dr. Jeannerod and others, my pragmatic system, which directs my finger to type the letter “I” quickly and efficiently, has chosen a letter that is simultaneously experienced and chosen in my semantic system, with all its attendant meaning structures.

From this point, Dr. Jeannerod goes on to discuss the contribution of mental imagery to understanding motor representations (chapter 4), then covers action planning (chapter 5), and concludes with a chapter proposing a design for motor representation. Along the way, his far-reaching coverage of the literature touches on the research of C.D. Frith and colleagues on schizophrenia and the work of Patricia Goldman-Rakic on executive function and the frontal cortex. Neurodevelopmental issues pertinent to motor representations and action are not presented in this book, however.

The Cognitive Neuroscience of Action is clearly Dr. Jeannerod’s synthesis and integration of his own research and the research of others in his field, but experimental data are presented and reviewed in detail throughout the book, there are ample citations of the literature, and the discussions appear well balanced. For the reader who might feel overwhelmed by the sheer complexity of the material to be assimilated, each chapter contains a succinct summary of its major points and conclusions.

Although this book aims to cover only the fundamentals and is written as a general overview of the brain’s role in motor action, the level of the exposition is detailed, and Dr. Jeannerod assumes that his readers are familiar with basic aspects of experimental neuroscience, brain neuroanatomy, and current concepts in cognitive science. It is fascinating and useful reading for any research psychiatrist whose work is grounded in the principles of systems neuroscience and in the underlying brain mechanisms of mental activity and behavior. It is not for the general psychiatrist or the clinician, unless she or he has developed a strong interest in the field and is willing to engage her or his own semantic and memory systems in some heavy autodidactic activity.

This book is part of a series titled Fundamentals of Cognitive Neuroscience, edited by Martha J. Farah and Mark H. Johnson. This series proposes to produce “concise, readable and up-to-date reviews of a particular problem area by a leading scientist” and is designed to help foster the “growing rapprochement among cognitive scientists, specialists in artifical intelligence, neuropsychologists and brain scientists in their various efforts to understand human mental activity.” This rapprochement represents the future of psychiatry. On the basis of the high quality of Dr. Jeannerod’s book, I am eager to see others in the series.