Making the brain plastic: early neuroanatomical staining techniques and the pursuit of structural plasticity, 1910-1970

The evolution of plasticity in the neuroscientific literature during the second half of the twentieth century to the present

In the neurosciences, concepts play an important role in the conception and direction of research. Among the theoretical notions and direction of research, plasticity stands out because of the multiple ways in which scientists use it to describe and interpret how the nervous system changes and adapts to different requirements. The occurrence of different conceptualizations of plasticity in the scientific literature during the second half of the twentieth century and up to the present was investigated using bibliometric methods. Throughout the period analyzed, synaptic plasticity has remained the dominant conceptualization of plasticity. However, scientists have continued to introduce novel plasticity concepts reflecting the scientific advances they have made in understanding the dynamic nature of the nervous system. The conceptual evolution of plasticity documents that the view of the adult nervous system as immutable has been replaced by an understanding of the nervous system as capable of lifelong change and adaptation.

Lampreys and spinal cord regeneration: "a very special claim on the interest of zoologists," 1830s-present

Employing history of science methods, including analyses of the scientific literature, archival documents, and interviews with scientists, this paper presents a history of lampreys in neurobiology from the 1830s to the present. We emphasize the lamprey's roles in helping to elucidate spinal cord regeneration mechanisms. Two attributes have long perpetuated studies of lampreys in neurobiology. First, they possess large neurons, including multiple classes of stereotypically located, 'identified' giant neurons in the brain, which project their large axons into the spinal cord. These giant neurons and their axonal fibers have facilitated electrophysiological recordings and imaging across biological scales, ranging from molecular to circuit-level analyses of nervous system structures and functions and including their roles in behavioral output. Second, lampreys have long been considered amongst the most basal extant vertebrates on the planet, so they have facilitated comparative studies pointing to conserved and derived characteristics of vertebrate nervous systems. These features attracted neurologists and zoologists to studies of lampreys between the 1830s and 1930s. But, the same two attributes also facilitated the rise of the lamprey in neural regeneration research after 1959, when biologists first wrote about the spontaneous, robust regeneration of some identified CNS axons in larvae after spinal cord injuries, coupled with recovery of normal swimming. Not only did large neurons promote fresh insights in the field, enabling studies incorporating multiple scales with existing and new technologies. But investigators also were able to attach a broad scope of relevance to their studies, interpreting them as suggesting conserved features of successful, and sometimes even unsuccessful, CNS regeneration. Lamprey research demonstrated that functional recovery takes place without the reformation of the original neuronal connections, for instance, by way of imperfect axonal regrowth and compensatory plasticity. Moreover, research performed in the lamprey model revealed that factors intrinsic to neurons are integral in promoting or hindering regeneration. As this work has helped illuminate why basal vertebrates accomplish CNS regeneration so well, whereas mammals do it so poorly, this history presents a case study in how biological and medical value have been, and could continue to be, gleaned from a non-traditional model organism for which molecular tools have been developed only relatively recently.

Dendritic Spines in Learning and Memory: From First Discoveries to Current Insights

The central nervous system is composed of neural ensembles, and their activity patterns are neural correlates of cognitive functions. Those ensembles are networks of neurons connected to each other by synapses. Most neurons integrate synaptic signal through a remarkable subcellular structure called spine. Dendritic spines are protrusions whose diverse shapes make them appear as a specific neuronal compartment, and they have been the focus of studies for more than a century. Soon after their first description by Ramón y Cajal, it has been hypothesized that spine morphological changes could modify neuronal connectivity and sustain cognitive abilities. Later studies demonstrated that changes in spine density and morphology occurred in experience-dependent plasticity during development, and in clinical cases of mental retardation. This gave ground for the assumption that dendritic spines are the particular locus of cerebral plasticity. With the discovery of synaptic long-term potentiation, a research program emerged with the aim to establish whether dendritic spine plasticity could explain learning and memory. The development of live imaging methods revealed on the one hand that dendritic spine remodeling is compatible with learning process and, on the other hand, that their long-term stability is compatible with lifelong memories. Furthermore, the study of the mechanisms of spine growth and maintenance shed new light on the rules of plasticity. In behavioral paradigms of memory, spine formation or elimination and morphological changes were found to correlate with learning. In a last critical step, recent experiments have provided evidence that dendritic spines play a causal role in learning and memory.

A Century of Brain Regeneration Phenomena and Neuromorphological Research Advances, 1890s-1990s-Examining the Practical Implications of Theory Dynamics in Modern Biomedicine

The modern thesis regarding the "structural plastic" properties of the brain, as reactions to injuries, to tissue damage, and to degenerative cell apoptosis, can hardly be seen as expendable in clinical neurology and its allied disciplines (including internal medicine, psychiatry, neurosurgery, radiology, etc.). It extends for instance to wider research areas of clinical physiology and neuropsychology which almost one hundred years ago had been described as a critically important area for the brain sciences and psychology alike. Yet the mounting evidence concerning the range of structural neuroplastic phenomena beyond the significant early 3 years of childhood has shown that there is a progressive building up and refining of neural circuits in adaptation to the surrounding environment. This review essay explores the history behind multiple biological phenomena that were studied and became theoretically connected with the thesis of brain regeneration from Santiago Ramón y Cajal's pioneering work since the 1890s to the beginning of the American "Decade of the Brain" in the 1990s. It particularly analyzes the neuroanatomical perspectives on the adaptive capacities of the Central Nervous System (CNS) as well as model-like phenomena in the Peripheral Nervous System (PNS), which were seen as displaying major central regenerative processes. Structural plastic phenomena have assumed large implications for the burgeoning field of regenerative or restorative medicine, while they also pose significant epistemological challenges for related experimental and theoretical research endeavors. Hereafter, early historical research precursors are examined, which investigated brain regeneration phenomena in non-vertebrates at the beginning of the 20th century, such as in light microscopic studies and later in electron microscopic findings that substantiated the presence of structural neuroplastic phenomena in higher cortical substrates. Furthermore, Experimental physiological research in hippocampal in vivo models of regeneration further confirmed and corroborated clinical physiological views, according to which "structural plasticity" could be interpreted as a positive regenerative CNS response to brain damage and degeneration. Yet the underlying neuroanatomical mechanisms remained to be established and the respective pathway effects were only conveyed through the discovery of neural stem cells in in adult mammalian brains in the early 1990s. Experimental results have since emphasized the genuine existence of adult neurogenesis phenomena in the CNS. The focus in this essay will be laid here on questions of the structure and function of scientific concepts, the development of research schools among biomedical investigators, as well as the impact of new data and phenomena through innovative methodologies and laboratory instruments in the neuroscientific endeavors of the 20th century.

Catalyzing Neurophysiology: Jacques Loeb, the Stazione Zoologica di Napoli, and a Growing Network of Brain Scientists, 1900s-1930s

Even before the completion of his medical studies at the universities of Berlin, Munich, and Strasburg, as well as his M.D.-graduation - in 1884 - under Friedrich Goltz (1834-1902), experimental biologist Jacques Loeb (1859-1924) became interested in degenerative and regenerative problems of brain anatomy and general problems of neurophysiology. It can be supposed that he addressed these questions out of a growing dissatisfaction with leading perceptions about cerebral localization, as they had been advocated by the Berlin experimental neurophysiologists at the time. Instead, he followed Goltz and later Gustav Theodor Fechner (1801-1887) in elaborating a dynamic model of brain functioning vis-à-vis human perception and coordinated motion. To further pursue his scientific aims, Loeb moved to the Naples Zoological Station between 1889 and 1890, where he conducted a row of experimental series on regenerative phenomena in sea animals. He deeply admired the Italian marine research station for its overwhelming scientific liberalism along with the provision of considerable technical and intellectual support. In Naples, Loeb hoped to advance his research investigations on 'tropisms' further to develop a reliable basis not only regarding the behavior of lower animals, but also concerning perception and general neural capacities. He thought that he could demonstrate the existence of center interdependence in the cerebral cortex of higher animals and humans, and was convinced that regenerative phenomena existed as plastic mechanisms influencing animal as well as human behavioral qualities. This new perspective on the organization of brain functioning and Loeb's astonishing successes in experimental research with hydrozoa and echinoidea brought him in close contact with many biologists working on the nervous system during the early twentieth century. Yet, it is impossible to conceive of Loeb's ground-breaking experiments without also taking his contemporary scientific network of teachers, colleagues, and local research milieus into account. All of these exerted a strong influence on a growing network of physiology, anatomy, and neurology peers and research trainees, who went on to interact in early brain research centers in Central Europe and North America. This article explores some intellectual and organizational influences that developed out of Loeb's early experiences at the Naples Zoological Station in Italy. The main focus is laid here on questions of the structure and organization of scientific institutions, the development of research networks among biologists of the nervous system, as well as the emergence of an interdisciplinary research style during the early decades of the twentieth century. This innovative style of laboratory investigations later influenced the make-up of a number of research units, for example at the Kaiser Wilhelm Society in Germany and the Rockefeller Institute for Medical Research in the United States.

A brain worth keeping? Waste, value and time in contemporary brain banking

If a temporal rather than spatial concept of waste is adopted, novel categories emerge which are useful for identifying and understanding logics of temporality at play in determining what is kept in contemporary brain banks, and reveal that brain banks are constituted by more than stored materials. First, I apply the categories analytically on a recent UK brain banking discussion among professionals. This analysis highlights the importance of data in brain banks, as well as the centrality of ideas about pasts and futures in the discussions. Secondly, I investigate the case of a seven decades old, Danish brain bank which had been reduced to its physically stored material for 24 years, before being reinstituted in 2006. This case demonstrates the importance of material and conceptual infrastructures that co-constitute a collection, as they make up an experimental system that is crucial to maintaining the collection's continued relevance and usefulness as a scientific institution.

Engaging cognitive circuits to promote motor recovery in degenerative disorders. exercise as a learning modality

Exercise and physical activity are fundamental components of a lifestyle essential in maintaining a healthy brain. This is primarily due to the fact that the adult brain maintains a high degree of plasticity and activity is essential for homeostasis throughout life. Plasticity is not lost even in the context of a neurodegenerative disorder, but could be maladaptive thus promoting disease onset and progression. A major breakthrough in treating brain disorders such as Parkinson's disease is to drive neuroplasticity in a direction to improve motor and cognitive dysfunction. The purpose of this short review is to present the evidence from our laboratories that supports neuroplasticity as a potential therapeutic target in treating brain disorders. We consider that the enhancement of motor recovery in both animal models of dopamine depletion and in patients with Parkinson's disease is optimized when cognitive circuits are engaged; in other words, the brain is engaged in a learning modality. Therefore, we propose that to be effective in treating Parkinson's disease, physical therapy must employ both skill-based exercise (to drive specific circuits) and aerobic exercise (to drive the expression of molecules required to strengthen synaptic connections) components to select those neuronal circuits, such as the corticostriatal pathway, necessary to restore proper motor and cognitive behaviors. In the wide spectrum of different forms of exercise, learning as the fundamental modality likely links interventions used to treat patients with Parkinson's disease and may be necessary to drive beneficial neuroplasticity resulting in symptomatic improvement and possible disease modification.

From 'Nerve Fiber Regeneration' to 'Functional Changes' in the Human Brain-On the Paradigm-Shifting Work of the Experimental Physiologist Albrecht Bethe (1872-1954) in Frankfurt am Main

Until the beginning 1930's the traditional dogma that the human central nervous system (CNS) did not possess any abilities to adapt functionally to degenerative processes and external injuries loomed large in the field of the brain sciences (Hirnforschung). Cutting-edge neuroanatomists, such as the luminary Wilhelm Waldeyer (1836-1921) in Germany or the Nobel Prize laureate Santiago Ramón y Cajal (1852-1934) in Spain, debated any regenerative and thus "plastic" properties in the human brain. A renewed interest arose in the scientific community to investigate the pathologies and the healing processes in the human CNS after the return of the high number of brain injured war veterans from the fronts during and after the First World War (1914-1918). A leading research center in this area was the "Institute for the Scientific Study of the Effects of Brain Injuries," which the neurologist Ludwig Edinger (1855-1918) had founded shortly before the war. This article specifically deals with the physiological research on nerve fiber plasticity by Albrecht Bethe (1872-1954) at the respective institute of the University of Frankfurt am Main. Bethe conducted here his paradigmatic experimental studies on the pathophysiological and clinical phenomena of peripheral and CNS regeneration.

Neither Physicians Nor Surgeons: Whither Neuropathological Skill in Post-war England?

Neuropathologists constituted a small field in post-war England, perched between neurology, psychiatry, neurosurgery and pathology, but recognised as a discrete field of expertise. Despite this recognition, the success of the neighbouring fields of neurosurgery, psychosurgery and neurobiology, and the consultant status granted to pathologists in the National Health Service, neuropathologists struggled to stabilise their field. A discourse of skills, acquired and acquirable, became central to their attempts to situate the field in relation to surgeons' handicraft, physicians' diagnostic acumen and the technologies of the biological sciences.

O sujeito cerebral e o movimento da neurodiversidade

Este artigo analisa o movimento da neurodiversidade organizado basicamente por autistas chamados de alto funcionamento que consideram que o autismo não é uma doença a ser tratada, mas uma diferença humana, a qual deve ser respeitada como outras diferenças. O movimento da "neurodiversidade" deve ser inserido em um marco sociocultural e histórico mais amplo que incorpore o impacto crescente no imaginário cultural dos saberes e das práticas neurocientíficas com o paradigma do sujeito cerebral e a expansão da neurocultura. No contexto do sujeito cerebral, o cérebro responde por tudo o que outrora costumávamos atribuir à pessoa e vem se tornando um critério biossocial de agrupamento fundamental. O artigo mostra como uma ideologia solipsista, reducionista e cientificista - o sujeito cerebral - pode servir de base para a formação de identidade e de redes de sociabilidade e comunidade.

Brain plasticity and mental processes: Cajal again

The year 2006 marks the 100th anniversary of the first Nobel Prize for Physiology or Medicine for studies in the field of the Neurosciences jointly awarded to Camillo Golgi and Santiago Ramón y Cajal for their key contributions to the study of the nervous system. This award represented the beginning of the modern era of neuroscience. Using the Golgi method, Cajal made fundamental, but often unappreciated, contributions to the study of the relationship between brain plasticity and mental processes. Here, I focus on some of these early experiments and how they continue to influence studies of brain plasticity.