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Blindsight: A case study and implications
The Rat Brain in Stereotaxic Coordinates (2nd edn) by George Paxinos and Charles Watson, Academic Press, 1986. £40.00/ $80.00 (264 pages) ISBN 012 547 6213
The second editon of Paxinos and Watson's rat stereotaxic atlas is, like the first, a detailed and definitive resource for stereotaxic surgery, brain dissection and neuroanatomical instruction. It offers accurate and detailed stereotaxic coordinates in three planes of section (coronal, horizontal and sagittal), and is presented in a clear, coherent manner. The photomicrographs included are well-reproduced and informative and the corresponding linedrawings detailed and thoroughly annotated. The nomenclature employed is clear and useful. As such, it is, like the first edition, an indispensable commodity for neuroscientists utilizing rodent models for research as well as for students learning basic fundamentals of rat brain neuroanatomy.
However, the second edition is far more than a mere recapitulation or update of the first. Most notably, the authors have approximately doubled the number of plates and line drawings, yielding a greater sampling density through the brain (roughly every 0.25 mm in coronal and horizontal sections, as opposed to about 0.40 to 0.50 mm in the first edition). It is clear from the added plate's and drawings that changes in brain nuclear and subnuclear structure can be quite dramatic within 0.50 mm and that the increase in illustrations were sorely needed; indeed, sampling density was one of the few criticisms of the first edition. The authors have also included a more detailed analysis of the cytoarchitecture of brain structures, a product of both extensive consultation with numerous authorities on neuroanatomical organization of brain nuclei and careful analysis of their own material. The criteria used to make these changes were wellannotated in the introduction to
the second edition, and were based on cytoarchitectonic distinctions and, perhaps more importantly, on distinctions derived from contemporary histochemical techniques. The latter improvement clearly represents a successful attempt on the authors' part to incorporate information derived from modern chemical neuroanatomy in determining their coordinate system, and represents one strong point of this second edition. In sum, the second edition of Paxinos and Watson is every bit as indispensable to the neuroscientist and neuroscience student as was the first. In preparing this second edition, the authors have answered some of the limited criticisms of the first (for example, see Swanson's comments in the February 1984 issue of TINS) and have taken into consideration state-of-the-art neuroanatomy. The Rat Brain in Stereotaxic Coordinates (2nd edn) stands alone as a research
and instructional resource for the neuroscientist of the 1980s.
sight' research followed experi- does the finding in monkey reflect mental observations in animals. the greater importance of subcorAfter the complete removal of tical pathways in less advanced visual cortex, monkeys are not species? by L. Weiskrantz, Oxford University 'Blindsight' is the selfPress, 1986. £19.50 (viii + 187 pages) rendered blind. Although they can no longer recognize other contradictory term that has come ISBN 9 18 852129 4 monkeys or discriminate patterns to describe the residual visual and colors, they can still reach for behavior in humans that is comEver since Gordon Holmes descri- peripheral objects and avoid parable to the findings in pribed a consistent topographic rela- obstacles better than by sheer mates. Aided by nature, neurotionship between visual field chance. Assuming that the abla- surgery, and a familiarity with the defects and wounds of the occipi- tions were complete (this has work of Ernst Poppel, Weiskrantz tal lobe, geniculostriate proces- been disputed), the only way to and his colleague Elizabeth Warsing has been considered indis- explain the remaining ability is to rington sought to test the pensable to vision. In this book, postulate the function of visual blindsight hypothesis. Since 1974 Professor Larry Weiskrantz ad- areas untouched by the experi- they have collaborated in the vances a challenging hypothesis ments. The best candidate for the experimental study of human that predicts residual vision role is the phylogenetically older subject D. B., who had a portion despite striate cortex lesions. In 'second' visual system, previously of his visual cortex removed durPart I of his monograph, he theor- delegated to a vestigial role in ing surgery for the removal of a izes that non-geniculostriate pro- primates. This system has major vascular malformation. 'From the jections through the diencepha- subcortical relays from the retina surgical notes it was estimated Ion do more than merely serve to the pulvinar and superior collic- that the incision extended from reflex functions such as eye blink. ulus, whence it projects secon- the occipital pole forward by This substantial network may darily to prestriate visual cortex. approximately 6cm and was possess additional properties that Layer IV of Brodmann's area 17, thought to include a major porpermit useful visual discrimina- the recipient of geniculostriate tion of the calcarine cortex - in tions even without our aware- impulses, is avoided altogether. which the striate cortex is situated ness. Do humans also have such an - i n the right hemisphere.' The original impetus for 'blind- alternative visual pathway, or Immediately after surgery,
Blindsight: A Case Study and Implications
TINS, Vol. 10, No. 10, 1987
James P. Herman and Stanley J. Watson MentalHealth ResearchInstitute, Universityof Michigan,Ann Arbor, M148109,USA.
Matthew Rizzo Divisionof Behavioral Neurology, Departmentof Neurology,The Universityof lowa Collegeof Medicine, IowaCity,1,452242, USA.
439
D. B. was unable to detect light in the left half of both eyes. Although his defect improved considerably, he was left with a chronic scotoma that occupied mainly the left lower quadrant. It was in this visual field that Weiskrantz performed experiments, described in Part II, which led him to advocate blindsight. Subjects like D. B. deny the ability to see in a 'destriated' field, and are diagnosed as blind in that region according to classical prejudice. However, according to Weiskrantz, only awareness but not detection of visual inputs depends on striate function. The key to demonstrating preserved visual ability in blindsight subjects is an experimental design that incorporates forced-choice pardigms. It is: not sufficient to ask 'do you see it?' because the answer is always 'no'. Statistical analysis of forcedchoice responses (especially on tasks of visuospatial localization)
reveals a performance above chance that can only result from covert discrimination in our ancient mammalian visual brain. The main criticisms of blindsight reviewed in Part III have concerned psychophysical methodology and anatomical verification. In 1983, Campion and colleagues made the psychophysical argument that artifactual light scatter can lead to detection, localization or discrimination of stimuli that are actually mediated by normal vision. A stray light hypothesis, however, does not include blindsight. Similarly, it is important to verify true fixation as objectively as possible during blindsight experiments (e.g. by using electro-oculography) to minimize the potential that the good field does not 'cheat' for the bad. Anatomical documentation of visual system lesions is crucial to the argument of blindsight. The
best opportunity for in-vivo verification of occipital lesions currently demands computerized tomography and magnetic resonance imaging with threedimensional reconstructions. These modern techniques are. more accurate than estimations obtained from the bloody field of surgery, but they have not been possible in D. B. Also, it is important to consider that D. B. suffered with a vascular malformation. Since these are often congenital, it is possible that the underlying visual brain in D.B. never developed normally and that his results do not reflect a standard visual organization. Blindsight is a comprehensive review of an intriguing topic by a leading investigator in the field. While the debate continues, Blindsight is a convenient sourcebook for multidisciplinary investigators and students with open minds.
the basal ganglia in members of each vertebrate class. This is clearly a major undertaking, since the field of basal ganglia research has grown enormously in recent years, resulting in a large MI48109, USA. A great deal of progress has been body of information for an author made over the last 20 years in to digest and summarize. A further understanding the organization challenge in this endeavor is that it of the basal ganglia. This research requires an understanding of brain has led to greater insight into the organization in many different circuitry and neurochemical fea- mammalian and non-mammalian tures of the basal ganglia and has species. Although many basic greatly advanced, though not yet features of basal ganglia organizaentirely clarified, the understand- tion are similar across vertebrates, ing of its functions. In addition, cytoarchitectonic and terminomuch has been revealed about logical differences can pose diffithe organization of the basal culties in mastering the literature ganglia (in fact, of the entire on the diverse vertebrate species. telencephalon) in non-mammals, Parent is, however, well-suited to which has fundamentally invali- be the author of a book such as dated the classical ideas about the this. Early in his career he used evolution of these structures catecholamine histofluorescence (such as those presented in The procedures and pathway tracing Comparative Anatomy of the techniques to study brain organiNervous System of Vertebrates, zation in a wide variety of nonincluding Man by Ariens- Kappers, mammalian vertebrates. With this Huber and Crosby). Although work, he (and Harvey Karten, who many books and review articles independently carried out similar have been published on the basal studies) played a major role in ganglia in mammals and there helping to identify correctly the have been a few reviews on the location of the basal ganglia in organization of the basal ganglia birds, reptiles and amphibians. in some groups of non-mammal- More recently, Parent has been ian vertebrates, this is the first investigating the histochemistry modern work (that I know of) that and connectivity of the basal attempts to present a thorough ganglia in a number of different overview of what is known about mammalian groups, including rats,
cats and monkeys. Thus, he is in a position to speak authoritatively about basal ganglia organization in a wide variety of vertebrates. It is therefore not surprising to see that the scholarship and clarity of the book reflect this expertise. Parent has marshalled a vast amo.unt of information into a very readable book. The book is divided into two parts. First, after a brief chapter describing basal ganglia terminology, vertebrate phylogeny and the older ideas on basal ganglia evolution, the four succeeding chapters describe what is known about basal ganglia organization in fish, amphibians, reptiles and birds, respectively. Each of these chapters details current findings on the locations, connections, histochemistry and (less thoroughly) the functions of the basal ganglia and its family of related cell groups such as the substantia nigra, the subthalamic nucleus, etc. Included among the histochemical data is information on the neurotransmitters and neuropeptides in the basal ganglia in these non-mammalian groups. Although the presentation shows that there are gaps in our knowledge, particularly for fish, it is nonetheless obvious that substantial progress has been made (particularly in birds and reptiles),
Anton Reiner
Comparative Neurobiology
Departmentof of the Basal Ganglia AnatomyandCell Biology,The by Andr~ Parent, John Wiley & Sons, Universityof 1986. £57.50 (xiv + 335 pages)*lSBN Michigan,AnnArbor, 0 471 80348 0
440
TINS, VoL 10, No. 10, 1987
The second editon of Paxinos and Watson's rat stereotaxic atlas is, like the first, a detailed and definitive resource for stereotaxic surgery, brain dissection and neuroanatomical instruction. It offers accurate and detailed stereotaxic coordinates in three planes of section (coronal, horizontal and sagittal), and is presented in a clear, coherent manner. The photomicrographs included are well-reproduced and informative and the corresponding linedrawings detailed and thoroughly annotated. The nomenclature employed is clear and useful. As such, it is, like the first edition, an indispensable commodity for neuroscientists utilizing rodent models for research as well as for students learning basic fundamentals of rat brain neuroanatomy.
However, the second edition is far more than a mere recapitulation or update of the first. Most notably, the authors have approximately doubled the number of plates and line drawings, yielding a greater sampling density through the brain (roughly every 0.25 mm in coronal and horizontal sections, as opposed to about 0.40 to 0.50 mm in the first edition). It is clear from the added plate's and drawings that changes in brain nuclear and subnuclear structure can be quite dramatic within 0.50 mm and that the increase in illustrations were sorely needed; indeed, sampling density was one of the few criticisms of the first edition. The authors have also included a more detailed analysis of the cytoarchitecture of brain structures, a product of both extensive consultation with numerous authorities on neuroanatomical organization of brain nuclei and careful analysis of their own material. The criteria used to make these changes were wellannotated in the introduction to
the second edition, and were based on cytoarchitectonic distinctions and, perhaps more importantly, on distinctions derived from contemporary histochemical techniques. The latter improvement clearly represents a successful attempt on the authors' part to incorporate information derived from modern chemical neuroanatomy in determining their coordinate system, and represents one strong point of this second edition. In sum, the second edition of Paxinos and Watson is every bit as indispensable to the neuroscientist and neuroscience student as was the first. In preparing this second edition, the authors have answered some of the limited criticisms of the first (for example, see Swanson's comments in the February 1984 issue of TINS) and have taken into consideration state-of-the-art neuroanatomy. The Rat Brain in Stereotaxic Coordinates (2nd edn) stands alone as a research
and instructional resource for the neuroscientist of the 1980s.
sight' research followed experi- does the finding in monkey reflect mental observations in animals. the greater importance of subcorAfter the complete removal of tical pathways in less advanced visual cortex, monkeys are not species? by L. Weiskrantz, Oxford University 'Blindsight' is the selfPress, 1986. £19.50 (viii + 187 pages) rendered blind. Although they can no longer recognize other contradictory term that has come ISBN 9 18 852129 4 monkeys or discriminate patterns to describe the residual visual and colors, they can still reach for behavior in humans that is comEver since Gordon Holmes descri- peripheral objects and avoid parable to the findings in pribed a consistent topographic rela- obstacles better than by sheer mates. Aided by nature, neurotionship between visual field chance. Assuming that the abla- surgery, and a familiarity with the defects and wounds of the occipi- tions were complete (this has work of Ernst Poppel, Weiskrantz tal lobe, geniculostriate proces- been disputed), the only way to and his colleague Elizabeth Warsing has been considered indis- explain the remaining ability is to rington sought to test the pensable to vision. In this book, postulate the function of visual blindsight hypothesis. Since 1974 Professor Larry Weiskrantz ad- areas untouched by the experi- they have collaborated in the vances a challenging hypothesis ments. The best candidate for the experimental study of human that predicts residual vision role is the phylogenetically older subject D. B., who had a portion despite striate cortex lesions. In 'second' visual system, previously of his visual cortex removed durPart I of his monograph, he theor- delegated to a vestigial role in ing surgery for the removal of a izes that non-geniculostriate pro- primates. This system has major vascular malformation. 'From the jections through the diencepha- subcortical relays from the retina surgical notes it was estimated Ion do more than merely serve to the pulvinar and superior collic- that the incision extended from reflex functions such as eye blink. ulus, whence it projects secon- the occipital pole forward by This substantial network may darily to prestriate visual cortex. approximately 6cm and was possess additional properties that Layer IV of Brodmann's area 17, thought to include a major porpermit useful visual discrimina- the recipient of geniculostriate tion of the calcarine cortex - in tions even without our aware- impulses, is avoided altogether. which the striate cortex is situated ness. Do humans also have such an - i n the right hemisphere.' The original impetus for 'blind- alternative visual pathway, or Immediately after surgery,
Blindsight: A Case Study and Implications
TINS, Vol. 10, No. 10, 1987
James P. Herman and Stanley J. Watson MentalHealth ResearchInstitute, Universityof Michigan,Ann Arbor, M148109,USA.
Matthew Rizzo Divisionof Behavioral Neurology, Departmentof Neurology,The Universityof lowa Collegeof Medicine, IowaCity,1,452242, USA.
439
D. B. was unable to detect light in the left half of both eyes. Although his defect improved considerably, he was left with a chronic scotoma that occupied mainly the left lower quadrant. It was in this visual field that Weiskrantz performed experiments, described in Part II, which led him to advocate blindsight. Subjects like D. B. deny the ability to see in a 'destriated' field, and are diagnosed as blind in that region according to classical prejudice. However, according to Weiskrantz, only awareness but not detection of visual inputs depends on striate function. The key to demonstrating preserved visual ability in blindsight subjects is an experimental design that incorporates forced-choice pardigms. It is: not sufficient to ask 'do you see it?' because the answer is always 'no'. Statistical analysis of forcedchoice responses (especially on tasks of visuospatial localization)
reveals a performance above chance that can only result from covert discrimination in our ancient mammalian visual brain. The main criticisms of blindsight reviewed in Part III have concerned psychophysical methodology and anatomical verification. In 1983, Campion and colleagues made the psychophysical argument that artifactual light scatter can lead to detection, localization or discrimination of stimuli that are actually mediated by normal vision. A stray light hypothesis, however, does not include blindsight. Similarly, it is important to verify true fixation as objectively as possible during blindsight experiments (e.g. by using electro-oculography) to minimize the potential that the good field does not 'cheat' for the bad. Anatomical documentation of visual system lesions is crucial to the argument of blindsight. The
best opportunity for in-vivo verification of occipital lesions currently demands computerized tomography and magnetic resonance imaging with threedimensional reconstructions. These modern techniques are. more accurate than estimations obtained from the bloody field of surgery, but they have not been possible in D. B. Also, it is important to consider that D. B. suffered with a vascular malformation. Since these are often congenital, it is possible that the underlying visual brain in D.B. never developed normally and that his results do not reflect a standard visual organization. Blindsight is a comprehensive review of an intriguing topic by a leading investigator in the field. While the debate continues, Blindsight is a convenient sourcebook for multidisciplinary investigators and students with open minds.
the basal ganglia in members of each vertebrate class. This is clearly a major undertaking, since the field of basal ganglia research has grown enormously in recent years, resulting in a large MI48109, USA. A great deal of progress has been body of information for an author made over the last 20 years in to digest and summarize. A further understanding the organization challenge in this endeavor is that it of the basal ganglia. This research requires an understanding of brain has led to greater insight into the organization in many different circuitry and neurochemical fea- mammalian and non-mammalian tures of the basal ganglia and has species. Although many basic greatly advanced, though not yet features of basal ganglia organizaentirely clarified, the understand- tion are similar across vertebrates, ing of its functions. In addition, cytoarchitectonic and terminomuch has been revealed about logical differences can pose diffithe organization of the basal culties in mastering the literature ganglia (in fact, of the entire on the diverse vertebrate species. telencephalon) in non-mammals, Parent is, however, well-suited to which has fundamentally invali- be the author of a book such as dated the classical ideas about the this. Early in his career he used evolution of these structures catecholamine histofluorescence (such as those presented in The procedures and pathway tracing Comparative Anatomy of the techniques to study brain organiNervous System of Vertebrates, zation in a wide variety of nonincluding Man by Ariens- Kappers, mammalian vertebrates. With this Huber and Crosby). Although work, he (and Harvey Karten, who many books and review articles independently carried out similar have been published on the basal studies) played a major role in ganglia in mammals and there helping to identify correctly the have been a few reviews on the location of the basal ganglia in organization of the basal ganglia birds, reptiles and amphibians. in some groups of non-mammal- More recently, Parent has been ian vertebrates, this is the first investigating the histochemistry modern work (that I know of) that and connectivity of the basal attempts to present a thorough ganglia in a number of different overview of what is known about mammalian groups, including rats,
cats and monkeys. Thus, he is in a position to speak authoritatively about basal ganglia organization in a wide variety of vertebrates. It is therefore not surprising to see that the scholarship and clarity of the book reflect this expertise. Parent has marshalled a vast amo.unt of information into a very readable book. The book is divided into two parts. First, after a brief chapter describing basal ganglia terminology, vertebrate phylogeny and the older ideas on basal ganglia evolution, the four succeeding chapters describe what is known about basal ganglia organization in fish, amphibians, reptiles and birds, respectively. Each of these chapters details current findings on the locations, connections, histochemistry and (less thoroughly) the functions of the basal ganglia and its family of related cell groups such as the substantia nigra, the subthalamic nucleus, etc. Included among the histochemical data is information on the neurotransmitters and neuropeptides in the basal ganglia in these non-mammalian groups. Although the presentation shows that there are gaps in our knowledge, particularly for fish, it is nonetheless obvious that substantial progress has been made (particularly in birds and reptiles),
Anton Reiner
Comparative Neurobiology
Departmentof of the Basal Ganglia AnatomyandCell Biology,The by Andr~ Parent, John Wiley & Sons, Universityof 1986. £57.50 (xiv + 335 pages)*lSBN Michigan,AnnArbor, 0 471 80348 0
440
TINS, VoL 10, No. 10, 1987