MemoryIts History and our present understanding (حافظه: تاريخچه و دريافت فعلي ما از آن) سعيد عمادي گروه علوم زيستي دانشگاه تحصيلات تكميلي در علوم پايه زنجان سمينارهاي هفته اي علوم زيستي 14 آبان 1390
BrainHistorical Milestones • Roman physician Galen (AD 129 – 199): • Argued for the importance of the brain, and theorized in some depth about how it might work. • Galen traced out the anatomical relationships among brain, nerves, and muscles, demonstrating that all muscles in the body are connected to the brain through a branching network of nerves.
BrainHistorical Milestones • Galen's ideas were widely known during the Middle Ages • Not much further progress came until the Renaissance, when detailed anatomical study resumed and combined with the theoretical speculations of Rene Descartes (1596 – 1650) and those who followed him. • Descartes believed that the highest cognitive functions are carried out by a non-physical res cogitans, but that the majority of behaviors of humans, and all behaviors of animals, could be explained mechanistically
BrainHistorical Milestones • The first real progress toward a modern understanding of nervous function, though, came from the investigations of Luigi Galvani (1737 – 1798), who discovered that a shock of static electricity applied to an exposed nerve of a dead frog could cause its leg to contract. • Since that time, each major advance in understanding has followed more or less directly from the development of a new technique of investigation.
BrainHistorical Milestones • Until the early years of the 20th century, the most important advances were derived from new methods for staining cells. • Particularly critical was the invention of a staining method by Camillo Golgi (1843 – 1926), which (when correctly used) stained only a small fraction of neurons, but not in their entirety, including cell body, dendrites, and axon. • Without such a stain, brain tissue under a microscope appears as an impenetrable tangle of protoplasmic fibers, in which it is impossible to determine any structure.
BrainHistorical Milestones • In the hands of Camillo Golgi, and especially of the Spanish neuroanatomistSantiago Ramon y Cajal (1852 – 1934), the new stain revealed hundreds of distinct types of neurons, each with its own unique dendritic structure and pattern of connectivity. • Neuron Doctrine Drawing by Camillo Golgi of a hippocampus stained with the silver nitrate method Drawing by Santiago Ramon y Cajal of two types of Golgi-stained neurons from the cerebellum of a pigeon
BrainHistorical Milestones • Charles Scott Sherrington (1857 – 1952) is a scientist best known for his work on how the elements of the nervous system join together functionally. • In 1897, Sherrington introduced the term synapse. • In the first half of the 20th century, advances in electronics enabled investigation of the electrical properties of nerve cells, culminating in work by Alan Hodgkin (1914 – 1998), Andrew Huxley (1917-), and others on the biophysics of the action potential, and the work of Bernard Katz (1911 – 2003) and others on the electrochemistry of the synapse.
MemoryHistorical and Conceptual Perspective • Socrates (470-399 BC) • Human have preknowledge, certain knowledge about the world is inborn. • Middle of the 19th century: • Experimental science (chemistry and physics): Began to attract students of behavior and the mind. • Philosophical exploration gradually replaced by psychology. • First experiments by psychologists: • Sense perception, but gradually toward more complex workings of the mind.
MemoryHistorical and Conceptual Perspective • Pioneer in experimental psychology: German psychologist Hermann Ebbinghaus(1850 – 1909) • He discovered two key principles of memory storage: • Memories, some short-lived and retained for minutes, others long-lived and persist for days to months • Repetition make memories last longer • German psychologists Georg Elias Müller(1850 – 1934) &AlfonsPilzeckersuggested that this memory that lasts days and weeks becomes consolidated with time.
MemoryHistorical and Conceptual Perspective • American philosopher William James (1842 – 1910): Short term and long term memory • Short term memory: Seconds to minutes, essentially extension of the present moment • Long term memory: Weeks, months, even a lifetime. • This distinction has proven fundamental to understanding memory.
MemoryHistorical and Conceptual Perspective • Russian psychiatrist Sergei Korsakoff (1853-1900): First description of a memory disorder (Korsakoff’s syndrome). • Memory impairment provide a great deal of useful information: The study of amnesia showed that there are multiple kinds of memory. • Charles Darwin (1809-1882): • Mental characteristics have continuity across species. • Human mental capabilities have evolved from those of simpler animals. • Inspired by these ideas Russian physiologist Ivan Pavlov (1849-1936) and American psychologist Edward Thorndike (1874-1949) developed animal models for studying learning.
MemoryHistorical and Conceptual Perspective • Classical conditioning: • Association of two events (sound of a bell and the presentation of food): Animal salivate whenever the bell sounds, even in the absence of food. • The animal has learned that the bell predicts the coming of food. • Instrumental conditioning: • Association between a correct response and a reward, or an incorrect response and a punishment that follows the response, and in this way gradually modifies its behavior.
MemoryHistorical and Conceptual Perspective • Laboratory-based learning psychology: behaviorism. • Behaviorists, led by the American John B. Watson(1878-1958) • Behavior could be studied with the same rigor as other natural sciences • Studying only observable stimuli and responses: • Behaviorists lost sight of many other interesting and important questions about mental processes such as those within the brain that underlie: perception, attention, motivation, action, planning, and thinking, as well as learning and memory. • Behaviorism: Dominant in studying learning and memory early in the 20th century, especially in the US.
MemoryHistorical and Conceptual Perspective • Among researchers for whom mental processes had center stage: Feredric C. Bartlett (1886-1969) Founder of cognitive psychology • Bartlett studied memory by having people learn material like stories and pictures: • Memory: Surprisingly fragile and susceptible to distortion • Memory retrieval: Seldom highly exact • Retrieval: Not simply a replaying of passively stored information • Retrieval: A creative and reconstructive process
MemoryHistorical and Conceptual Perspective • By 1960’s, due to the work of Bartlett: • Perception and memory depend on information in the environment and on the mental structure of the perceiver • Cognitive psychology: Not only stimuli and responses but the processes that intervene between a stimulus and a behavior- precisely the domain ignored by behaviorists • Cognitive psychologists: • Flow of information from the eye to its internal representation in the brain for eventual use in memory and action • Internal representation: Take the form of a characteristic pattern of activity in particular groups of interconnectd cells in the brain
MemoryHistorical and Conceptual Perspective • Biological Revolutions in the 20th Century: • Our understanding of how cells function in molecular terms which expanded considerably after discovering of the DNA structure by James Watson(1928 - ) andFrancis Crick (1916 – 2004). • Systems component of biological revolution: instruments such as PET and functional magnetic resonance enabled scientists to study brain processes during cognitive activities. • There is now two approaches in the studying the biology of memory: • At the nerve cells level: cellular and molecular mechanisms of memory storage (neurobiology of memory) • At the level of brain structures, circuitry and behavior: neural systems
MemoryHistorical and Conceptual Perspective • Where memory is stored? • Actually the same question has historically been arisen about other mental functions too. • Two viewpoints: • There are specialized areas in the brain for functions such as language, vision, etc. • Different function are not localized, instead they are the result of global and integrated activities of the brain. • Now the first view is predominantly accepted by neuroscientists.
MemoryHistorical and Conceptual Perspective • Karl Lashley(1890-1958): • Pioneer in localizing memory. • His conclusions: • Actually no specific location in the cortex but memory impairment for the maze habit correlated with the size of cortex removed: formulated the law of mass action for memory impairment • More experimental works in the following years led scientists to arrive at different understanding of Lashley’s results: • Lashley’s maze-learning task was not suitable for the localization of memory because the task depended on different sensory and motor capabilities • He focused only on cerebral cortex and did not explored region below the cortex region (subcortical regions)
MemoryHistorical and Conceptual Perspective • Nevertheless Lashley showed that there is no single center in the brain where all memories are permanently stored: many parts of the brain must participate in representation of memory. • Early response to lashley’s challenge about the locus of memory came from Donald O. Hebb(1904-1985), a psychologist at McGill University • He suggested that assemblies of cells, distributed over large areas of cortex, work together to represent information. • This insight came to be seen as one of the key principles of information storage in the brain. • The modern view: • Memory is widely distributed but different areas store different aspects of the hole and there is little redundancy or reduplication of function
MemoryHistorical and Conceptual Perspective • Cerebral cortex divisions: • Frontal lobe: Planning and Voluntary movement • Parietal lobe: Sensations of the body surface and spatial perception • Occipital lobe: Vision • Temporal lobe: hearing, visual perception and memory
MemoryHistorical and Conceptual Perspective • First suggestions that memory might be stored in the temporal lobe: • Wilder Penfield(1891 – 1976), working on neurosurgical treatment of focal epilepsy. • During surgery, weak electrical stimulations, and determined its effects on the ability to speak and comprehend language. • Brain contains no pain receptors, patients remained fully conscious, able to report their experiences. • Responses to electrical stimulations: • “ It sounded like a voice saying words, but it was so faint I couldn’t get it” • “ I am seeing a picture of a dog and cat … the dog is chasing the cat” • These responses were elicited invariably only from the temporal lobes of the brain.
MemoryHistorical and Conceptual Perspective • Stimulated by Penfield’s experiments: William Scoville(1926 – 2008) soon obtained direct evidence that the temporal lobes are critically important for human memory. • In 1957, Scoville and Brenda Milner (1918 - ), a colleague of Penfield reported the extraordinary story of a patient H. M (Henry Gustav Molaison, 1928 - ). • At the age of about 9, H. M. was knocked down by a bicycle and sustained a head injury that led eventually to epilepsy. • H. M.’s seizures worsened over the years. • H. M.’s epilepsy was thought to have its origin within the brain’s temporal lobe.
MemoryHistorical and Conceptual Perspective • Scoville decided, as a last resort, to remove the inner surface of the temporal lobe on both sides of the brain, including a structure called the hippocampus, in an attempt to treat his epilepsy. • This experimental treatment did help his epilepsy, but it left H. M. with a devastating memory loss from which he has never recovered. • From the time of his operation in 1953 until present day, H. M. has been unable to convert a new short-term memory into a permanent long-term memory.
MemoryHistorical and Conceptual Perspective • Larry R. Squire (1941 - ) • His pioneering work in human memory helped describe for the first time the role of the hippocampus and surrounding cortex region of the brain in human memory. • He has explored fundamental issues such as whether memory is one thing or many, what brain structures are important for memory, and what happens to memory in disease.
MemoryHistorical and Conceptual Perspective • Eric Kandel(1929 - ) • His groundbreaking research revealed what happens to the brain when memories are formed. • Kandel explored how nerve cells (neurons) change during learning. • His research involving the sea slug Aplysiaand mice uncovered the basis of short and long-term memory.
MemoryHistorical and Conceptual Perspective • Using chemical techniques to produce mutations in single genes Seymour Benzer(1921 – 2007) began to examine the effects on behavior of changing one gene at a time, with the use of Drosophila as his animal model. • He first identified a number of fascinating mutants that affected courtship, visual perception, and circadian rhythems. • Benzer then turned his genetic approach to the problem of learning and memory storage. • From mutants with memory defects, Benzer was able to identify several proteins that are important for nondeclarative forms of memory storage. • It was immediately evident that some of these proteins were the same as those identified independently in molecular biological studies of nondeclarative memory in Aplysia.
MemoryHistorical and Conceptual Perspective • Conclusions: • First there was no separation between the mind and the brain. • First philosophy: Until late in 19th century. • Then psychology. • And now biology. • Experimental studies first in psychology and more recently in biology. • New millenium: Questions posed by psychology and biology have begun to converge on common ground • From psychology perspective: • How does memory works? • Are there different kinds of memory? • What is their logic?
MemoryHistorical and Conceptual Perspective • Conclusions: • From biology perspective: • Where in the brain do we learn? • Where do we store what is learned as memory? • Can memory storage be resolved at the level of individual nerve cells? • If so, what is the nature of the molecules that underlie the various processes of memory storage? • Neither psychology nor biology alone can satisfactorily address these questions. • Common program of inquiry defined by psychologists and biologists (Neuroscience): • How are the various forms of memory organized in the brain? • How is memory storage accomplished?
MemoryHistorical and Conceptual Perspective • Conclusions: • What we know now : • Many forms of memory • Different brain structures and specific jobs • Memory: Encoded in nerve cells; depends on changes in the strength of their interconnections, stabilized by the actions of genes in nerve cells • Findings about how the molecules inside nerve cells change the connection strength between nerve cells