- Email: [email protected]
Introduction
V
Preface/lntroduction
Apraxia is a term used to denote a disorder in the performance of limb, oral verbal and oral non-verbal gestures either t o command or on imitation with often preserved ability to perform these same gestures outside t h e clinical setting in t h e appropriate situation or environment. Over the past century and particularly in t h e past four decades a great deal of research has focused on understanding t h e nature of this complex disorder. Problems concerning neural substrates (e.g. association with left versus right hemisphere damage), associated disorders (e.g. agraphia and aphasia), methods of assessment (e.g. command versus imitation) and underlying mechanisms have all been addressed. Considering this current state of knowledge t h e time seems right for a comprehensive review of this work. Such a review will serve to consolidate what is currently known of apraxia; however, in order to foster a deeper understanding of t h e nature of this disorder it would seem necessary t o go beyond studies of apraxia into areas which have a bearing on praxis and action sequencing, particularly those dealing with motor control. The first section of the volume, then, is devoted to a review of t h e current state of knowledge in apraxia. Faglioni and Basso provide a historical perspective t o apraxia. Much of the early work by t h e pioneers in t h e field is meticulously reviewed. Ennio De Renzi evaluates t h e various methods for assessing apraxia as they pertain to interpreting t h e disorder. He considers aspects such as t h e nature of t h e movement (e.g., single vs. sequenced) and t h e mode of input of t h e command. D e Renzi concludes that the crucial factor in apraxia is not the quality of the movement (e.g., symbolic or meaningless, proximal or distal, transitive or intransitive, single or sequenced) but relates t o t h e patient's inability to select from among his repetoire of motor programs when his performance is not assisted by the environmental context.
Leslie Rothi and Kenneth Heilman review much of their work examining t h e basis of ideomotor apraxia. They apply paradigms used in examining memory in t h e verbal domain t o the study of memory in apraxia. New insights into t h e nature of this disorder are revealed in this chapter. Henri Hecaen and Pierre Rondot view apraxia as a disorder t o a system of signs. A brief historical review is followed by a consideration of neurophysiological and neuropsychological factors important in uderstanding apraxia. A system for classifying signs is then developed and discussed as it pertains to apraxia. In his chapter Klaus Poeck continues t h e discussion pertaining t o understanding apraxia by reviewing his extensive work. Both qualitative and quantitative studies are described. Ideational and ideomotor apraxia are considered as to their underlying nature and their relation to aphasia. Eric Roy and Paula Square examine t h e commonalities between verbal, oral and limb apraxia using a framework developed by Roy in which praxis is thought t o involve the operation of conceptual and production systems. Comparisons include types of errors observed, stimulus and response variables which influence t h e errors observed and t h e environmental conditions under which t h e observed errors occur. The approach in this chapter argues that control of praxis involves both t o p d o w n and bottom-up influences which operate in parallel. A f u l l understanding of t h e neurobehavioural basis for apraxia will arise only when t h e delicate balance between these influences is focused on in studying these disruptions. The relationship between apraxia and aphasia is carefully reviewed in t h e next chapter by Andrew Kertesz. Investigations establish a significant relationship
vi
Preface/lntroduction
between the two disorders, but dissociations occur in substantial numbers. Aphasia and apraxia coexist either because of anatomical proximity of t h e mechanisms of language and praxis or because of a sharing of their fundamental mechanisms. Kertesz discusses extensive research, much of it his own, in evaluating t h e basis of this association. He finds that impairment in comprehension correlates best with apraxia, although comprehension is not t h e cause of apraxia. The disruption to a n underlying general factor of cognitive processing common t o both language comprehension and praxis may explain this association. Anna Basso and her colleagues provide a comprehensive review of advantages and limitations of the various neuroradiological methods currently used to examine brain-behaviour relationships. The focus of the chapter, however, is on t h e neurobehavioural correlates of apraxia as revealed through CT studies. Large lesions are associated with apraxia more frequently than small ones, while deep lesions alone d o not frequently result in apraxia. The importance of t h e parietal and, to a lesser extent, the frontal regions is confirmed.
The role of cross species studies in understanding apraxia in humans is convincingly presented by Bryan Kolb and Ian Whishaw. The organization of descending motor pathways is considered as it relates t o t h e nature of apraxia. Kolb and Whishaw argue that much additional research is necessary before it will be possible t o delineate t h e anatomical origin of apractic syndromes in either human or nonhuman subjects. The problems of what behaviours t o measure and how to quantify t h e severity of the apractic deficit are also considered as they pertain t o studying apraxia in both animals and man. They argue that in order to fully comprehend t h e nature of apraxia much more consideration must go into what movements are t o be examined and how the performance of these movements will be measured. These points a r e also made by De Renzi in the preceding chapter and by Todor and Smiley and MacKenzie and Marteniuk in subsequent chapters. In a final section Kolb and Whishaw discuss what needs t o be considered in making cross species comparisons. One fundamental issue is whether t h e cerebral hemispheres are equivalent in t h e non human species t o that in humans. Another concern is what behaviour in t h e animal selected would be appropriate and possibly comparable to t h a t studied in humans. Sharon Cermak examines t h e nature of disruptions t o praxis in children. The neurobehavioural bases of this disorder are considered in depth. Of particular interest is whether the disorder is a unitary one, a question which has relevance for t h e study of adult onset apraxia. The relationship between this disorder in children and that in adults is evaluated. Finally, Cermak presents some interesting ideas on how t o remediate this disorder. These chapters in the first section in the book a r e meant t o provide a rather broad perspective on apraxia: the historical roots of apraxia, various views of t h e nature of apraxia, methods used in assessing the disorder, t h e relationship of various forms of apraxia with one another and with disorders of speech and language, and the implications of studies of apraxia in animals and children for understanding this disorder in t h e human adult. While this first section provides a rather complete view of apraxia, a consideration of aspects of motor control provided in t h e next section complements this one and provides information necessary t o gain further insight with the study of this disorder. The first chapter by Gary Goldberg reviews t h e evolutionary development of the premotor area, a region of t h e cortex which has been thought t o play an important role in the control of limb praxis. His hypothesis is that the brain has evolved t o enable the organization of action across two poles: one pole involving projective action (extrapolating from the current s t a t e t o a future desired state), and the other
Preface/ln troduction
vi i
pole involving responsive action (adaptation to current specific external inputs). Goldberg proposes t h a t t h e medial premotor region (supplementary motor area) provides t h e neural basis for t h e first pole, while the lateral prernotor area subserves the second pole. The implications of these poles of action for t h e study of apraxia as well as for learning motor skills are discussed. Donald MacKay in t h e next chapter presents a theory of t h e representation, organization and timing of action. A consideration of these issues is important t o an understanding of disruptions t o t h e sequential organization of action in apraxia. Adapting concepts he used in describing organizational principles in speech production MacKay has presented a theory relevant to t h e production of limb actions. Under t h e theory several types of nodes are thought to be organized into independently controllable systems which provide a basis for producing actions. MacKay discusses t h e implications of this theory for understanding t h e nature of errors made by both normals and apractics. The basis of manual asymmetries is discussed in t h e next chapter by John Todor and Anne Smiley. A consideration of these asymmetries is important a s comparisons of right and left hand performance are often made in apractic patients. As well, i t is not uncommon t o compare performance of t h e left hand of apractic patients who frequently have left hemisphere damage to the right hand of right-hemispheredamaged non-apractic patients as t h e other hand in each group of patients being contralateral t o the damaged hemisphere is often hemiparetic. Todor and Smiley present work which examines asymmetries in several tasks, notably those involving visually aimed movements, and movements requiring fine motor control. Studies using t h e dual task paradigm are also considered. The implication of this work for understanding manual and hemispheric asymmetries in motor control as well as for the study of apraxia are discussed. The final chapter by Christine MacKenzie and Ronald Marteniuk focusses on bimanual coordination. Many limb praxis tasks require t h e coordination of t h e two limbs, thus, it is important to have some perspective on variables which influence bimanual coordination. In their chapter bimanual coordination and t h e coordination of movements of a single limb are viewed as special cases of multimovement coordination. They identify a number of dimensions on which bimanual tasks might be classified. Research suggests a n intrinsic relationship between t h e two limbs providing internal constraints on bimanual movements t h a t give rise t o preferred, stable modes of control. The implications of this view for understanding motor impairments in apraxia are discussed. Together t h e chapters in this volume provide a n overview of research into apraxia, examine t h e relationship of this disorder to other related deficits and review areas in motor control which bear upon a n understanding of apraxia. While t h e volume reviews a bulk of t h e research on apraxia and related disorders, t h e work of several scholars, particularly t h a t of Doreen Kimura, Norman Geschwind, Kathleen Haaland, and Edith Kaplan, is not adequately represented here. Unfortunately, these people were unable t o contribute chapters due t o conflicting commitments. I would urge t h e serious student to read their fine work referenced throughout the volume.
***** There are many people t o acknowledge in t h e preparation of this volume. Lori Whippler, Joan Pache and Sherrie Bieman Copland all provided invaluable assistance in preparing t h e manuscript. Bruce Uttley and Carol Vogt of the Computer Science Centre of t h e University of Waterloo provided much needed advice as t o the prepa-
viii
Preface/lntroduction
ration of t h e manuscript on t h e General Markup Language computer system. I would like to thank Dr. George Stelmach, one of t h e series editors, f o r encouraging me t o prepare this volume and Dr. K. Michielsen, Editor, for his patience during the process of preparing t h e volume. Finally, I must express my deepest appreciation to my wife and family for their support throughout this project.
***** I would like t o dedicate this volume t o t h e memory of t h e late Professor Henri Hecaen who made a n immense contribution to t h e study of apraxia and, indeed, t o neuropsychology in general. He kindly accepted my invitation to contribute a chapter t o t h e volume and encouraged m e in preparing it, but, unfortunately, was unable to see t h e finished product.
Eric A. Roy Toronto and Waterloo Ontario
Preface/lntroduction
Apraxia is a term used to denote a disorder in the performance of limb, oral verbal and oral non-verbal gestures either t o command or on imitation with often preserved ability to perform these same gestures outside t h e clinical setting in t h e appropriate situation or environment. Over the past century and particularly in t h e past four decades a great deal of research has focused on understanding t h e nature of this complex disorder. Problems concerning neural substrates (e.g. association with left versus right hemisphere damage), associated disorders (e.g. agraphia and aphasia), methods of assessment (e.g. command versus imitation) and underlying mechanisms have all been addressed. Considering this current state of knowledge t h e time seems right for a comprehensive review of this work. Such a review will serve to consolidate what is currently known of apraxia; however, in order to foster a deeper understanding of t h e nature of this disorder it would seem necessary t o go beyond studies of apraxia into areas which have a bearing on praxis and action sequencing, particularly those dealing with motor control. The first section of the volume, then, is devoted to a review of t h e current state of knowledge in apraxia. Faglioni and Basso provide a historical perspective t o apraxia. Much of the early work by t h e pioneers in t h e field is meticulously reviewed. Ennio De Renzi evaluates t h e various methods for assessing apraxia as they pertain to interpreting t h e disorder. He considers aspects such as t h e nature of t h e movement (e.g., single vs. sequenced) and t h e mode of input of t h e command. D e Renzi concludes that the crucial factor in apraxia is not the quality of the movement (e.g., symbolic or meaningless, proximal or distal, transitive or intransitive, single or sequenced) but relates t o t h e patient's inability to select from among his repetoire of motor programs when his performance is not assisted by the environmental context.
Leslie Rothi and Kenneth Heilman review much of their work examining t h e basis of ideomotor apraxia. They apply paradigms used in examining memory in t h e verbal domain t o the study of memory in apraxia. New insights into t h e nature of this disorder are revealed in this chapter. Henri Hecaen and Pierre Rondot view apraxia as a disorder t o a system of signs. A brief historical review is followed by a consideration of neurophysiological and neuropsychological factors important in uderstanding apraxia. A system for classifying signs is then developed and discussed as it pertains to apraxia. In his chapter Klaus Poeck continues t h e discussion pertaining t o understanding apraxia by reviewing his extensive work. Both qualitative and quantitative studies are described. Ideational and ideomotor apraxia are considered as to their underlying nature and their relation to aphasia. Eric Roy and Paula Square examine t h e commonalities between verbal, oral and limb apraxia using a framework developed by Roy in which praxis is thought t o involve the operation of conceptual and production systems. Comparisons include types of errors observed, stimulus and response variables which influence t h e errors observed and t h e environmental conditions under which t h e observed errors occur. The approach in this chapter argues that control of praxis involves both t o p d o w n and bottom-up influences which operate in parallel. A f u l l understanding of t h e neurobehavioural basis for apraxia will arise only when t h e delicate balance between these influences is focused on in studying these disruptions. The relationship between apraxia and aphasia is carefully reviewed in t h e next chapter by Andrew Kertesz. Investigations establish a significant relationship
vi
Preface/lntroduction
between the two disorders, but dissociations occur in substantial numbers. Aphasia and apraxia coexist either because of anatomical proximity of t h e mechanisms of language and praxis or because of a sharing of their fundamental mechanisms. Kertesz discusses extensive research, much of it his own, in evaluating t h e basis of this association. He finds that impairment in comprehension correlates best with apraxia, although comprehension is not t h e cause of apraxia. The disruption to a n underlying general factor of cognitive processing common t o both language comprehension and praxis may explain this association. Anna Basso and her colleagues provide a comprehensive review of advantages and limitations of the various neuroradiological methods currently used to examine brain-behaviour relationships. The focus of the chapter, however, is on t h e neurobehavioural correlates of apraxia as revealed through CT studies. Large lesions are associated with apraxia more frequently than small ones, while deep lesions alone d o not frequently result in apraxia. The importance of t h e parietal and, to a lesser extent, the frontal regions is confirmed.
The role of cross species studies in understanding apraxia in humans is convincingly presented by Bryan Kolb and Ian Whishaw. The organization of descending motor pathways is considered as it relates t o t h e nature of apraxia. Kolb and Whishaw argue that much additional research is necessary before it will be possible t o delineate t h e anatomical origin of apractic syndromes in either human or nonhuman subjects. The problems of what behaviours t o measure and how to quantify t h e severity of the apractic deficit are also considered as they pertain t o studying apraxia in both animals and man. They argue that in order to fully comprehend t h e nature of apraxia much more consideration must go into what movements are t o be examined and how the performance of these movements will be measured. These points a r e also made by De Renzi in the preceding chapter and by Todor and Smiley and MacKenzie and Marteniuk in subsequent chapters. In a final section Kolb and Whishaw discuss what needs t o be considered in making cross species comparisons. One fundamental issue is whether t h e cerebral hemispheres are equivalent in t h e non human species t o that in humans. Another concern is what behaviour in t h e animal selected would be appropriate and possibly comparable to t h a t studied in humans. Sharon Cermak examines t h e nature of disruptions t o praxis in children. The neurobehavioural bases of this disorder are considered in depth. Of particular interest is whether the disorder is a unitary one, a question which has relevance for t h e study of adult onset apraxia. The relationship between this disorder in children and that in adults is evaluated. Finally, Cermak presents some interesting ideas on how t o remediate this disorder. These chapters in the first section in the book a r e meant t o provide a rather broad perspective on apraxia: the historical roots of apraxia, various views of t h e nature of apraxia, methods used in assessing the disorder, t h e relationship of various forms of apraxia with one another and with disorders of speech and language, and the implications of studies of apraxia in animals and children for understanding this disorder in t h e human adult. While this first section provides a rather complete view of apraxia, a consideration of aspects of motor control provided in t h e next section complements this one and provides information necessary t o gain further insight with the study of this disorder. The first chapter by Gary Goldberg reviews t h e evolutionary development of the premotor area, a region of t h e cortex which has been thought t o play an important role in the control of limb praxis. His hypothesis is that the brain has evolved t o enable the organization of action across two poles: one pole involving projective action (extrapolating from the current s t a t e t o a future desired state), and the other
Preface/ln troduction
vi i
pole involving responsive action (adaptation to current specific external inputs). Goldberg proposes t h a t t h e medial premotor region (supplementary motor area) provides t h e neural basis for t h e first pole, while the lateral prernotor area subserves the second pole. The implications of these poles of action for t h e study of apraxia as well as for learning motor skills are discussed. Donald MacKay in t h e next chapter presents a theory of t h e representation, organization and timing of action. A consideration of these issues is important t o an understanding of disruptions t o t h e sequential organization of action in apraxia. Adapting concepts he used in describing organizational principles in speech production MacKay has presented a theory relevant to t h e production of limb actions. Under t h e theory several types of nodes are thought to be organized into independently controllable systems which provide a basis for producing actions. MacKay discusses t h e implications of this theory for understanding t h e nature of errors made by both normals and apractics. The basis of manual asymmetries is discussed in t h e next chapter by John Todor and Anne Smiley. A consideration of these asymmetries is important a s comparisons of right and left hand performance are often made in apractic patients. As well, i t is not uncommon t o compare performance of t h e left hand of apractic patients who frequently have left hemisphere damage to the right hand of right-hemispheredamaged non-apractic patients as t h e other hand in each group of patients being contralateral t o the damaged hemisphere is often hemiparetic. Todor and Smiley present work which examines asymmetries in several tasks, notably those involving visually aimed movements, and movements requiring fine motor control. Studies using t h e dual task paradigm are also considered. The implication of this work for understanding manual and hemispheric asymmetries in motor control as well as for the study of apraxia are discussed. The final chapter by Christine MacKenzie and Ronald Marteniuk focusses on bimanual coordination. Many limb praxis tasks require t h e coordination of t h e two limbs, thus, it is important to have some perspective on variables which influence bimanual coordination. In their chapter bimanual coordination and t h e coordination of movements of a single limb are viewed as special cases of multimovement coordination. They identify a number of dimensions on which bimanual tasks might be classified. Research suggests a n intrinsic relationship between t h e two limbs providing internal constraints on bimanual movements t h a t give rise t o preferred, stable modes of control. The implications of this view for understanding motor impairments in apraxia are discussed. Together t h e chapters in this volume provide a n overview of research into apraxia, examine t h e relationship of this disorder to other related deficits and review areas in motor control which bear upon a n understanding of apraxia. While t h e volume reviews a bulk of t h e research on apraxia and related disorders, t h e work of several scholars, particularly t h a t of Doreen Kimura, Norman Geschwind, Kathleen Haaland, and Edith Kaplan, is not adequately represented here. Unfortunately, these people were unable t o contribute chapters due t o conflicting commitments. I would urge t h e serious student to read their fine work referenced throughout the volume.
***** There are many people t o acknowledge in t h e preparation of this volume. Lori Whippler, Joan Pache and Sherrie Bieman Copland all provided invaluable assistance in preparing t h e manuscript. Bruce Uttley and Carol Vogt of the Computer Science Centre of t h e University of Waterloo provided much needed advice as t o the prepa-
viii
Preface/lntroduction
ration of t h e manuscript on t h e General Markup Language computer system. I would like to thank Dr. George Stelmach, one of t h e series editors, f o r encouraging me t o prepare this volume and Dr. K. Michielsen, Editor, for his patience during the process of preparing t h e volume. Finally, I must express my deepest appreciation to my wife and family for their support throughout this project.
***** I would like t o dedicate this volume t o t h e memory of t h e late Professor Henri Hecaen who made a n immense contribution to t h e study of apraxia and, indeed, t o neuropsychology in general. He kindly accepted my invitation to contribute a chapter t o t h e volume and encouraged m e in preparing it, but, unfortunately, was unable to see t h e finished product.
Eric A. Roy Toronto and Waterloo Ontario