Brain, Vol. 123, No. 3, 650-651,
March 2000
© 2000 Oxford University Press
Book reviews |
RIGHT HEMISPHERE DAMAGE.
.
Dipartimento di Psicologia, Universitá di Bologna, Bologna, Italy
This book explores the mysteries of the right hemisphere (RH) by showing that what was once thought to be the minor hemisphere plays co-operative roles in many cognitive functions and is dominant for certain cognitive abilities. The author synthesizes information available from clinical experience and from experimental and clinical research into a picture showing the relevance of right hemisphere damage (RHD) on attention, affective and communicative disorders. The book is intended for clinicians, either trained or in training, who have to manage people with neurological disorders in the context of the hospital and their normal daily activities. It provides clinically relevant information for conceptualizing the deficits associated with RHD, as well as useful suggestions about the assessment of the deficits and their treatment. Moreover, there is an attempt to provide a link between theory-driven assessment, symptom-driven assessment and treatment strategies. In this way, it might inspire the reader with new treatment models and promote research that is sensitive to the clinical realities of the disorders following RHD.
The book consists of 10 chapters. Chapter 1 provides an historical overview of the role of the right hemisphere in cognitive functions and gives a behavioural portrait of a patient with RHD. Chapter 2 takes the reader into the rapidly moving and increasingly interesting area of neglect, which is one of the most common consequences of RHD. Estimates of the incidence of neglect range from 31 to 66% in RHD. The chapter is written clearly and the reader's level of knowledge is rarely taken for granted. Important clinical perspectives are not forgotten, e.g. the practical and theoretical difficulties in the assessment of such a complex deficit. The various frames of reference, modalities, and input and output channels in which neglect can occur are explored, and different behavioural evidence are provided to support the idea that neglect is not a single entity, but it is the expression of a deficit of multiple spatial maps which cooperate to offer the subject an unitary representation of the external world.
This is a useful review of the current state of knowledge on neglect, and my only slight reservation is that it might have been helpful to stress the relevance of the unconscious perception shown by neglect patients. The studies of implicit processing in neglect patients have challenged the traditional assumption of what it means to be aware of something. Patients who are not aware of stimuli, or of some of their characteristics, can nonetheless use, under certain conditions, the same stimuli for purposeful behaviour (giving, for instance, correct same/different judgements). It has been assumed very often that behaviour at this level of sophistication implies subject awareness and that if a subject can systematically give correct answers to the same/different tasks then s/he must have a full experience of the stimulus. This has turned out not to be the case in patients with neglect. Therefore, the study of implicit processing in neglect, not only has induced a re-thinking of the idea of awareness, but has also stimulated the proposal of new models of space coding, dealing with the counterintuitive aspects of patients' behaviour.
Chapter 3 outlines deficits in various attentional operations that might occur subsequent to RHD. In this chapter, the author provides evidence from neurochemical, autonomic nervous system, neuroimaging and behavioural studies suggesting that the RH plays a role in maintaining attention in states of vigilance and that frontal areas in the RH are more active than comparable LH areas when selective attention and vigilance are required. Moreover, the author suggests that the most fundamental attentional deficit that can occur subsequent to RHD is a reduced arousal (hypoarousal), which may result in an impairment of other components of attention, such as sustained attention and vigilance. In other words, she suggests that various attentional mechanisms are interdependent and all of them have a significant impact on all cognitive performance.
Chapter 4 provides a very helpful and succinct overview of the deficits in prosodic production and comprehension that occur following RHD. The speech of RHD patients may sound flat and monotonous, and they may have problems using prosody to decode linguistic messages. Moreover, some patients show problems in matching prosodic contour to emotional content and a reduced reliance on pitch variation to signal emotions. The author also addresses an important issue about the relationship between the emotional prosodic deficit and the internal emotional states of these patients (i.e. depression). She presents evidence showing that the two deficits might be dissociated: patients might be frustrated with the discrepancy between the emotional experience and the ability to convey it through prosody.
Chapters 5 and 6, on linguistic deficits, are less clear than the previous chapters and the arguments put forward for semantic linguistic deficit after RHD are rather feeble; in particular, when they are compared with the literature on linguistic capacity of the RH in split-brain patients. In this respect, the conclusion that the RH has a linguistic semantic representation appears more suggestive than conclusive. The RH of commisurotomy patients has neither control of speech mechanisms nor access to the speech mechanisms in the LH: as a consequence it can be tested only in comprehension tasks. Linguistic comprehension as measured by the ability to match written words with pictures appears to be accurate, although there are exceptions. However, when the picture decoys in the multiple-choice arrays are all semantically associated with the target, the RH makes many errors. In other words, when a semantic task requires more than a simple decision about which of two broad super ordinate categories a word is in, like the case in which the semantic connection requires an inference about common semantic features, then performance is very poor. On the other hand, the conclusion that the RH has a linguistic semantic representation appears very weak when evaluated with studies in which a semantic priming was used. Complete commisurotomy patients do not show priming effect when the stimuli are presented to the RH.
Chapter 7, on affective deficits, provides an overview of the clinical findings showing that damage to the RH can alter emotional experience and affective behaviour. The author documents affective changes subsequent to RHD, including signs of apathy, indifference, denial of illness and anosognosia, problems in the verbal and non-verbal expression of emotions, and a reduced sensitivity to emotions expressed by others. In this chapter, a right-hemisphere dominance for emotion has been explained with the relative dominance of the right hemisphere for regulating emotional arousal, which is an important component of any emotional response and by the critical role of the right hemisphere in non-verbal (emotional) communication. In the first interpretation, the hemispheric specialization is attributed to the ability to regulate the emotional arousal, whereas in the second to perceiving or expressing affective stimuli. Unfortunately, the chapter lacks an interpretation of the deficits in which the disorders of emotional behaviour lies more at the interface between the emotional experience, intimately linked with the autonomic arousal level, and the cognitive or communicative aspects of emotions.
Chapter 9 is very useful for people interested in the assessment of the deficits following RHD, and clearly presents what should be the goal of the assessment and what are the instruments for achieving the goal. In this respect, the appendices, in which the author reviews the most important tests for the assessment of attentional and communicative deficits as well as for the assessment of neglect, are very useful.
Chapter 10 is related to the treatment of the cognitive and communicative disorders with RHD, a relatively new and unexplored field in neuroscience. Treatments presented in this chapter follow logically from research described in the previous chapters, and, when possible, from theories about the mechanisms that may underlie those deficits.
In summary, this is a useful clinical text for every clinician involved in the management of patients with RHD, but it also carries up-to-date reviews and references for those who may have more research-oriented interest in this field.
Notes
1999. San Diego: Singular Publishing Group.
Price not stated. Pp. 280. ISBN 1-56593-224-2.
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