Nemesius of Emesa and early brain mapping
2008; Elsevier BV; Volume: 372; Issue: 9637 Linguagem: Inglês
10.1016/s0140-6736(08)61183-6
ISSN1474-547X
Autores Tópico(s)History of Medicine Studies
ResumoCurrent neuroimaging techniques offer information that is more detailed and complex than has ever been available about the involvement of parts of the brain in conscious and unconscious activities of the mind and the senses. Whether neuroimaging can increase our understanding of the perennial problem of the mind–body relation is still a question—to which the answer will partly depend on the extent to which the interpretation of the imaging data leaves room for disagreement. But the insights it provides into the mechanisms of connection and coordination of brain activities—or the lack of such connections—will be important for the diagnosis and treatment of brain disease.In this short contribution I should like to draw attention to an early stage in the history of localisation of mental functions in different regions of the brain. The oldest evidence for this idea is from a Christian text: the treatise On the Nature of Man written by a certain Nemesius, bishop of Emesa (in Syria) in the late 4th century. This work, written in classical Greek (but due to its success soon translated into Latin, Arabic, Syriac, and Armenian), sets out a comprehensive physical as well as philosophical anthropology. Nemesius describes the structure of the human body, the position and function of its constituent parts, and the relation between the body and the soul (or the mind) in complex activities such as sense perception, voluntary movement, imagination, memory, thought, desire, and the emotions. The presupposition of the work is that the human soul–body composite is as good as it possibly can be: the body and its parts serve as an “instrument” (the Greek word is organon) for the mind and its functions.But Nemesius did not just write for Christians. He lived in a world in which pre-Christian and non-Christian thinkers were very influential; and he takes account of the views of the main pagan Greek thinkers, Plato, Aristotle, and the Stoics. What is more, Nemesius tried to take on board the latest developments in the medical thought of his day. Although not himself a practising doctor, he dwells extensively on what we would call physiological functions, such as nutrition, digestion, respiration, pulsation, and reproduction. For each topic, he makes use of the medical ideas of his time, most prominently those of Galen of Pergamum, the great 2nd-century doctor and philosopher.The attraction of Galen's work to Nemesius was obvious: it offered a teleological account, based on expert knowledge, of the structure and workings of the human body and its parts, showing in detail its purposeful design and referring, in language very similar to the Christian accounts of the creation, to the design and skill of “the Craftsman”. Nemesius believed that medicine supported his argument about the careful craftsmanship that has gone into the creation and shaping of the human body and its suitability to serve as an instrument for the human soul. He reflected this belief also in his discussion of the localisation of the key functions of the human soul—sensation, imagination, thinking, and memory—in different regions of the brain.To put this in perspective, we need to realise that the role of the brain and the nervous system in human consciousness had not always been as uncontroversial as it seems to us now. In Greek medicine and philosophy, the question of which part of the body was the centre of consciousness or intelligence had long been debated. The cardiocentric view, which prevailed during much of the classical period, had strong defenders in Aristotle and the Stoics. But after the discovery of the nervous system in 3rd century BCE Alexandria by the medical scientists Herophilus and Erasistratus—who for the first time in medical history made use of vivisectory experiments on human beings—and after Galen's experiments on living animals in the 2nd century CE, the cognitive primacy of the brain was firmly established. Galen believed that the brain and the nerves formed one continuous system connecting all parts of the body. He also believed in the existence of pneuma, a delicate airy intelligent substance (comparable to our notion of oxygen) flowing through the nerves and informing and energising the various bodily parts.Galen's empirical knowledge of the structure of the brain was, by the standards of his time, extensive, even though it was mainly based on dissection of animals such as apes and oxen (systematic human dissection was considered unethical in Galen's times). Accidental knowledge of the human brain, gained from battle or sports injuries, may have been an additional source of information (Galen started his career as a surgeon for gladiators). Yet although Galen described in detail the ventricles—“cavities”, as he calls them—of the brain, the surrounding brain tissue, and the cerebral membranes, he never went so far as to assign the various functions of the mind to specific places in the brain. Indeed, Galen explicitly denied such spatial dimensions to cognitive variation.Nemesius, however, makes precisely such a spatial subdivision: he assigns sensation and imagination to what he calls the “frontal cavities”, by which he seems to refer to the two anterior cerebral ventricles of the brain, intellectual thought to the central cavity of the brain, and memory to the posterior cavity of the brain. Moreover, he provides empirical evidence for this: “If the frontal cavities are damaged in any way, the senses are impaired but thought remains unharmed. If the central cavity alone suffers, thought is overthrown but the sense-organs continue to preserve their natural power of sensation. If both the frontal and the central cavities suffer, reason is damaged together with the senses. But if the cerebellum suffers, memory alone is lost together with it, without sensation and thought being harmed in any way. But if the posterior cavity suffers together with the frontal and central ones, sense, reason and memory also are destroyed, in addition to the whole creature being in danger of perishing.”Thus, the basis for the localisation theory advanced here is provided by empirical, clinical evidence from disturbance of cognitive functions in specific cases of brain injury. Such evidence might, indeed, have been obtained on the battlefield or in the arena. But where did bishop Nemesius get this information from, if not from Galen? Interestingly, his ideas find a close parallel in the fragments of the late-4th-century medical writer Posidonius of Byzantium. Posidonius (not to be confused with the Stoic philosopher with the same name) is talking here about “phrenitis”, a kind of mental illness manifesting itself in disturbance of cognitive activities: “Phrenitis is an inflammation of the membranes surrounding the brain during acute fever, causing insanity and loss of reason… There are several different kinds of phrenitis, but the following three are most important. Either only imagination is affected and reasoning and memory are spared; or only reasoning is affected and imagination and memory are spared; or imagination and reasoning are affected and memory is spared. Furthermore, loss of memory due to febrile diseases usually destroys the faculties of reason and imagination as well. A disorder of the anterior part of the brain affects only the imagination; a disorder of the middle ventricle leads to aberration of reason; a disorder of the posterior part of the brain in the region of the occiput destroys the faculty of memory, usually together with the other two.”This passage presents striking similarities with Nemesius; it is based on the clinical observation of loss of cognitive function in cases of disorders of various parts of the brain. How such disorders were determined, the text does not tell us. Clearly, this is where only modern brain imaging would have provided the answers. But the logic of the argument is clear enough. That Nemesius was aware of it, or at least of the ideas it expresses, is likely. We seem to have a clear example here of a case where Nemesius makes use of medical ideas that go beyond Galen: he assigns to each of the three cardinal mental functions a specific region of the brain. Nemesius thus elaborates on Galen's claim that the physical structure of the brain serves as a suitable instrument for the activities of the soul, in particular the three most important cognitive functions of sensation or imagination, thought, and memory.With the benefit of hindsight, it is easy to criticise Nemesius and Posidonius for factual inaccuracy and error. For example, they seem unaware that the cerebral ventricles contain only clear cerebrospinal fluid and are not composed of brain tissue; and the clinical evidence Nemesius cites of loss of cognitive function does not include damage to the brain tissue in the vicinity of the cerebral ventricles—although in this respect, the medical writer Posidonius is less specific and, therefore, ironically, more accurate. Inevitably, their descriptions are vague and not sufficiently detailed to provide answers to the questions today's neurologists would raise. Moreover, and unfortunately, we have only textual evidence for their views, no images or drawings.Yet, conceptually, Nemesius' brain mapping is a remarkable step to take. Although the anatomy and the neuronal composition of the human brain were not to be understood for many centuries to come, Nemesius' theory was very influential in the medical thinking of late antiquity and the early middle ages—most notably in Arabic medical writers such as Avicenna, who used this and other medical evidence to update Aristotle's obsolete cardiocentrism, while maintaining the theoretical differentiation of cognitive functions for which the philosopher had laid the foundation. I am grateful to Evelyn Jaros for her comments on an earlier draft of this article from the point of view of modern neuroanatomy. All responsibility for the use I have made of her suggestions is mine. Current neuroimaging techniques offer information that is more detailed and complex than has ever been available about the involvement of parts of the brain in conscious and unconscious activities of the mind and the senses. Whether neuroimaging can increase our understanding of the perennial problem of the mind–body relation is still a question—to which the answer will partly depend on the extent to which the interpretation of the imaging data leaves room for disagreement. But the insights it provides into the mechanisms of connection and coordination of brain activities—or the lack of such connections—will be important for the diagnosis and treatment of brain disease. In this short contribution I should like to draw attention to an early stage in the history of localisation of mental functions in different regions of the brain. The oldest evidence for this idea is from a Christian text: the treatise On the Nature of Man written by a certain Nemesius, bishop of Emesa (in Syria) in the late 4th century. This work, written in classical Greek (but due to its success soon translated into Latin, Arabic, Syriac, and Armenian), sets out a comprehensive physical as well as philosophical anthropology. Nemesius describes the structure of the human body, the position and function of its constituent parts, and the relation between the body and the soul (or the mind) in complex activities such as sense perception, voluntary movement, imagination, memory, thought, desire, and the emotions. The presupposition of the work is that the human soul–body composite is as good as it possibly can be: the body and its parts serve as an “instrument” (the Greek word is organon) for the mind and its functions. But Nemesius did not just write for Christians. He lived in a world in which pre-Christian and non-Christian thinkers were very influential; and he takes account of the views of the main pagan Greek thinkers, Plato, Aristotle, and the Stoics. What is more, Nemesius tried to take on board the latest developments in the medical thought of his day. Although not himself a practising doctor, he dwells extensively on what we would call physiological functions, such as nutrition, digestion, respiration, pulsation, and reproduction. For each topic, he makes use of the medical ideas of his time, most prominently those of Galen of Pergamum, the great 2nd-century doctor and philosopher. The attraction of Galen's work to Nemesius was obvious: it offered a teleological account, based on expert knowledge, of the structure and workings of the human body and its parts, showing in detail its purposeful design and referring, in language very similar to the Christian accounts of the creation, to the design and skill of “the Craftsman”. Nemesius believed that medicine supported his argument about the careful craftsmanship that has gone into the creation and shaping of the human body and its suitability to serve as an instrument for the human soul. He reflected this belief also in his discussion of the localisation of the key functions of the human soul—sensation, imagination, thinking, and memory—in different regions of the brain. To put this in perspective, we need to realise that the role of the brain and the nervous system in human consciousness had not always been as uncontroversial as it seems to us now. In Greek medicine and philosophy, the question of which part of the body was the centre of consciousness or intelligence had long been debated. The cardiocentric view, which prevailed during much of the classical period, had strong defenders in Aristotle and the Stoics. But after the discovery of the nervous system in 3rd century BCE Alexandria by the medical scientists Herophilus and Erasistratus—who for the first time in medical history made use of vivisectory experiments on human beings—and after Galen's experiments on living animals in the 2nd century CE, the cognitive primacy of the brain was firmly established. Galen believed that the brain and the nerves formed one continuous system connecting all parts of the body. He also believed in the existence of pneuma, a delicate airy intelligent substance (comparable to our notion of oxygen) flowing through the nerves and informing and energising the various bodily parts. Galen's empirical knowledge of the structure of the brain was, by the standards of his time, extensive, even though it was mainly based on dissection of animals such as apes and oxen (systematic human dissection was considered unethical in Galen's times). Accidental knowledge of the human brain, gained from battle or sports injuries, may have been an additional source of information (Galen started his career as a surgeon for gladiators). Yet although Galen described in detail the ventricles—“cavities”, as he calls them—of the brain, the surrounding brain tissue, and the cerebral membranes, he never went so far as to assign the various functions of the mind to specific places in the brain. Indeed, Galen explicitly denied such spatial dimensions to cognitive variation. Nemesius, however, makes precisely such a spatial subdivision: he assigns sensation and imagination to what he calls the “frontal cavities”, by which he seems to refer to the two anterior cerebral ventricles of the brain, intellectual thought to the central cavity of the brain, and memory to the posterior cavity of the brain. Moreover, he provides empirical evidence for this: “If the frontal cavities are damaged in any way, the senses are impaired but thought remains unharmed. If the central cavity alone suffers, thought is overthrown but the sense-organs continue to preserve their natural power of sensation. If both the frontal and the central cavities suffer, reason is damaged together with the senses. But if the cerebellum suffers, memory alone is lost together with it, without sensation and thought being harmed in any way. But if the posterior cavity suffers together with the frontal and central ones, sense, reason and memory also are destroyed, in addition to the whole creature being in danger of perishing.” Thus, the basis for the localisation theory advanced here is provided by empirical, clinical evidence from disturbance of cognitive functions in specific cases of brain injury. Such evidence might, indeed, have been obtained on the battlefield or in the arena. But where did bishop Nemesius get this information from, if not from Galen? Interestingly, his ideas find a close parallel in the fragments of the late-4th-century medical writer Posidonius of Byzantium. Posidonius (not to be confused with the Stoic philosopher with the same name) is talking here about “phrenitis”, a kind of mental illness manifesting itself in disturbance of cognitive activities: “Phrenitis is an inflammation of the membranes surrounding the brain during acute fever, causing insanity and loss of reason… There are several different kinds of phrenitis, but the following three are most important. Either only imagination is affected and reasoning and memory are spared; or only reasoning is affected and imagination and memory are spared; or imagination and reasoning are affected and memory is spared. Furthermore, loss of memory due to febrile diseases usually destroys the faculties of reason and imagination as well. A disorder of the anterior part of the brain affects only the imagination; a disorder of the middle ventricle leads to aberration of reason; a disorder of the posterior part of the brain in the region of the occiput destroys the faculty of memory, usually together with the other two.” This passage presents striking similarities with Nemesius; it is based on the clinical observation of loss of cognitive function in cases of disorders of various parts of the brain. How such disorders were determined, the text does not tell us. Clearly, this is where only modern brain imaging would have provided the answers. But the logic of the argument is clear enough. That Nemesius was aware of it, or at least of the ideas it expresses, is likely. We seem to have a clear example here of a case where Nemesius makes use of medical ideas that go beyond Galen: he assigns to each of the three cardinal mental functions a specific region of the brain. Nemesius thus elaborates on Galen's claim that the physical structure of the brain serves as a suitable instrument for the activities of the soul, in particular the three most important cognitive functions of sensation or imagination, thought, and memory. With the benefit of hindsight, it is easy to criticise Nemesius and Posidonius for factual inaccuracy and error. For example, they seem unaware that the cerebral ventricles contain only clear cerebrospinal fluid and are not composed of brain tissue; and the clinical evidence Nemesius cites of loss of cognitive function does not include damage to the brain tissue in the vicinity of the cerebral ventricles—although in this respect, the medical writer Posidonius is less specific and, therefore, ironically, more accurate. Inevitably, their descriptions are vague and not sufficiently detailed to provide answers to the questions today's neurologists would raise. Moreover, and unfortunately, we have only textual evidence for their views, no images or drawings. Yet, conceptually, Nemesius' brain mapping is a remarkable step to take. Although the anatomy and the neuronal composition of the human brain were not to be understood for many centuries to come, Nemesius' theory was very influential in the medical thinking of late antiquity and the early middle ages—most notably in Arabic medical writers such as Avicenna, who used this and other medical evidence to update Aristotle's obsolete cardiocentrism, while maintaining the theoretical differentiation of cognitive functions for which the philosopher had laid the foundation. I am grateful to Evelyn Jaros for her comments on an earlier draft of this article from the point of view of modern neuroanatomy. All responsibility for the use I have made of her suggestions is mine. I am grateful to Evelyn Jaros for her comments on an earlier draft of this article from the point of view of modern neuroanatomy. All responsibility for the use I have made of her suggestions is mine. I am grateful to Evelyn Jaros for her comments on an earlier draft of this article from the point of view of modern neuroanatomy. All responsibility for the use I have made of her suggestions is mine.
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