Donald Olding Hebb

Figure 1: Donald O. Hebb

Donald Olding (D. O.) Hebb (1904-1985) was, during his lifetime, an extraordinarily influential figure for the disciplines of psychology and behavioral and computational neuroscience. Since his death, Hebb's seminal ideas exert an ever-growing influence on those interested in the mind -- natural minds (cognitive science) and artificial minds (computer science) -- as well as the brain (neuroscience) and how the brain implements the natural mind (cognitive neuroscience).

[edit] Donald Hebb - the person

Donald Olding (D. O.) Hebb was raised by his physician parents in Chester, Nova Scotia, Canada. He graduated from Dalhousie University in 1925 aspiring to write novels, but chose instead the more practical field of education, becoming, shortly after graduation, a school principal in the Province of Quebec. The writings of James, Freud, and Watson stimulated an interest in psychology that encouraged him to become a graduate student at McGill University. On the recommendation of his Master’s supervisor, the physiologist Boris Babkin, Hebb joined the laboratory of Karl Lashley (then North America’s leading Physiological Psychologist) at the U. of Chicago, and began work on his PhD, which was about spatial learning and behavior. He moved with Lashley to Harvard where, in 1936, he completed a dissertation on the effects of early visual deprivation upon size and brightness perception in the rat. Hebb published 5 papers that were based on research he conducted at U. of Chicago and Harvard (Hebb, 1937a,b; Hebb, 1938a,b,c)

In 1937 Hebb accepted the first of two formative post-doctoral positions when Wilder Penfield offered him of a fellowship at the Montreal Neurological Institute (MNI). At the MNI Hebb explored the effects of brain injury and surgery (particularly frontal lobe lesions) on human intelligence and behavior. Observing that removal of large amounts of tissue seemed to have little impact on memory and intelligence, Hebb concluded (as had Lashley, 1929, from animal lesion studies) that much of the neural substrate for learning and memory must be widely distributed in the brain, rather than strictly localized. This experience also gave him an appreciation of both the value and the challenge of clinical data for psychological theorizing.

Following his work at the MNI, Hebb served as a professor at Queens University (Kingston, Ontario) for 3 years. At Queens, Hebb developed human and animal intelligence tests, including the "Hebb-Williams" maze (Hebb & Williams, 1946), which has since been used to investigate the intelligence of many different species in hundreds of studies (Brown & Stanford, 1997; Shore et al., 2001), making it the "Stanford-Binet" of comparative intelligence. Hebb's studies of intelligence led him to the conclusion that experience played a much greater role in determining intelligence than was typically assumed (Hebb, 1942). He would later point out that every bit of behavior is jointly determined by heredity and environment, just as the area of a field is jointly determined by its length and its width (Hebb, 1953). His simple analogy has often been used since then in Psychology textbooks to illustrate the (sometimes unequal) contributions of both nature and nurture to the organization of behavior.

In 1942, Hebb took up his second formative post-doctoral position when he rejoined Lashley, who had become director of the Yerkes Laboratory of Primate Biology. At the Yerkes Laboratory Hebb explored fear, anger, and other emotional processes in the chimpanzee through careful observation. He would later write that he: “...learned more about human beings during that time than during any other five year period of my life except the first” (Hebb, 1980, p. 293). Apart from the influence of the chimpanzees themselves, Hebb was much stimulated by the intellectual climate at the Yerkes Laboratory, the bright and knowledgeable scholars there, and the regular seminars that provided an opportunity to put forward bold new ideas and receive invaluable feedback on them. While at the Yerkes, Hebb began writing a book that synthesized different lines of research into a "general theory of behavior that attempts to bridge the gap between neurophysiology and psychology (Hebb, 1949, vii)." Hebb returned to McGill as Professor of Psychology and in 1948 was appointed chair.

When the book he drafted at the Yerkes, "The Organization of Behavior: A Neuropsychological Theory," appeared in 1949, it was greeted enthusiastically as “a breath of fresh air.” Since then it has become a landmark work that has recently been described (along with Darwin’s “Origin of Species”) as one of the two most important books in Biology (Adams, 1998).

When Hebb's book was published there was a growing movement in psychology to reject cognitive constructs and undervalue links to the physiological bases of behavior (Skinner, 1938). "The Organization of Behavior" marked a turning point away from this trend. In it Hebb insisted that "the problem of understanding behavior is the problem of understanding the total action of the nervous system, and vice versa" (1949, p. xiv) and he presented a theory, with three key postulates, that laid the foundation for an integrative solution to this problem.

[edit] Three postulates of Hebb’s theory

[edit] Hebbian learning

Hebbian Learning: Connections between neurons increase in efficacy in proportion to the degree of correlation between pre- and post-synaptic activity.

In one of the most often quoted passages in Neuroscience Hebb boldly postulated: "When an axon of cell A is near enough to excite B and repeatedly or persistently takes part in firing it, some growth process or metabolic change takes place in one or both cells such that A's efficiency, as one of the cells firing B, is increased" (p. 62). In Neuroscience, this proposal is referred to the "Hebb synapse", the first instances of which were later discovered in long term potentiation (Bliss & Lømo, 1973) and kindling (Goddard, McIntyre & Leech, 1969). In Cognitive Science and Computational Neuroscience this proposal is referred to as the "Hebb rule" which provides a basic learning algorithm for adjusting connection weights in neural and artificial network models (Trappenberg, 2002).

[edit] Cell assemblies

Cell-Assembly: Group of neurons which tend to fire together.

The brain basis of mental representation (images, ideas) is groups or assemblies of neurons that tend to be active at the same time because of Hebbian learning. The firing of neurons in a cell-assembly can persist after the triggering event and this persistence is a form of memory (see Hebb’s illustration in Figure 2). Some consider the cell-assembly proposal, to be Hebb's most important conceptual contribution (Milner, 1986).

Figure 2: Schematic of Hebb’s “cell-assembly” hypothesis. “Arrows represent a simple “assembly” of neural pathways or open multiple chains firing according to the numbers on each (the pathway ”1,4” fires first and fourth, and so on), illustrating the possibility of an alternating reverberation which would not extinguish as readily as that in a simple closed circuit.” Redrawn from Hebb, 1949, Figure 10, p. 73.

[edit] Phase sequence

Phase Sequence: Thinking is the sequential activation of sets of cell-assemblies.

The following is an elaboration, from "The Organization of Behavior," of these postulates into a theory:

"Any frequently repeated, particular stimulation will lead to the slow development of a "cell-assembly," a diffuse structure comprising cells in the cortex and diencephalon (and also, perhaps, in the basal ganglia of the cerebrum), capable of acting briefly as a closed system, delivering facilitation to other such systems and usually having a specific motor facilitation. A series of such events constitutes a "phase sequence" - the thought process. Each assembly action may be aroused by a preceding assembly, by a sensory event, or—normally—by both. The central facilitation from one of these activities on the next is the prototype of ‘attention.’ ... The theory is evidently a form of connectionism... though it does not deal in direct connections between afferent and efferent pathways: not an S-R psychology, if R means muscular response... It does not, further, make any single nerve cell or pathway essential to any habit or perception." (p. xix)

Entire new fields of study on the role of early experience in perceptual development (Hunt, 1979), sensory deprivation (Zubek, 1969), self-stimulation (Olds & Milner, 1954), the stopped retinal image (Pritchard, Heron, & Hebb, 1960), synaptic modifiability (Goddard, 1980), and learning without awareness (McKelvie, 1987), were launched to test or validate Hebb’s neuropsychological theory and to explore its consequences.

Hebb knew that the details of his theory would be superseded (e.g. Milner, 1957). But he believed it was the right kind of theory, one that sought to explain what went on between stimulus and response using neuroscientific principles. The ideas at the core of Hebb’s Neuropsychological Theory – the Hebbian synapse, the Hebbian cell-assembly, and the proposal that thinking is the sequential activation of assemblies of neurons – seem to have captured fundamental truths about how the nervous system generates and organizes of behavior.

Hebb won many honours and awards and held many positions of leadership. He was a Fellow of the Royal Society of Canada and of the Royal Society (London); he won the APA Award for Distinguished Scientific Contribution. He served as President of the Canadian and American Psychological Associations. His specific contributions and his influences have been recognized in many review articles, symposia and books, and in professorships and prizes which bear his name. In Canada, for example, both the Canadian Psychological Association and the Canadian Society for Brain, Behavior and Cognitive Science award prizes for outstanding contributions to psychological science that are named in Hebb's honour.

For the reader interested in learning more about Hebb's life and the evolution of his ideas, his own articles (Hebb, 1959, 1980) as well as those by Brown & Milner (2003), Glickman (1996), Klein (1980), Milner (1986) are interesting and informative.

[edit] References

Adams, P. (1998) Hebb and Darwin. Journal of Theoretical Biology, 195, 419–438
Bliss, T. V. P., & Lømo, T. (1973). Long lasting potentiation of synaptic transmission in the dentate area of the anaesthetized rabbit following stimulation of the perforant path. Journal of Physiology, 232, 331-356.
Brown, R. E. & Milner, P. M. (2003) The legacy of Donald O. Hebb: More than the Hebb Synapse. Nature Reviews Neuroscience, 4, 1013-1019.
Brown, R. E., & Stanford, L. (1997). The Hebb-Williams Maze: 50 years of research (1946-1996). Society for Neuroscience Abstracts (#110.15), 23, 278.
Goddard, G. V. (1980). Component properties of the memory machine: Hebb revisited. In P. W. Jusczyk & R. M. Klein (Eds.), The Nature of Thought: Essays in Honor of D. O. Hebb (pp. 231-247). Hillsdale, N. J.: Erlbaum.
Goddard, G. V., McIntyre, D. C., & Leech, C. K. (1969). A permanent change in brain function resulting from daily electrical stimulation. Experimental Neurology, 25, 295-330.
Hebb, D. O. (1937a). The innate organization of visual activity: I. Perception of figures by rats reared in total darkness. Journal of Genetic Psychology 51: 101-126.
Hebb, D. O. (1937a). The innate organization of visual activity. II. Transfer of response in the discrimination of brightness and size by rats reared in total darkness. Journal of Comparative Psychology 24: 277-299.
Hebb, D. O. (1938a). The innate organization of visual activity. III. Discrimination of brightness after removal of the striate cortex in the rat. Journal of Comparative Psychology 25: 427-437.
Hebb, D. O. (1938b). Studies of the organization of behavior. I. Behavior of the rat in a field orientation. Journal of Comparative Psychology 25: 333-353.
Hebb, D. O. (1938c). Studies of the organization of behavior. II. Changes in the field orientation of the rat after cortical destruction. Journal of Comparative Psychology 26: 427-441.
Hebb, D. O. (1942). The effects of early and late brain injury upon test scores, and the nature of normal adult intelligence. Proceedings of the American Philosophical Society, 85, 275-292.
Hebb, D. O. (1949). The Organization of Behavior: A neuropsychological theory. New York: Wiley.
Hebb, D. O. (1953). Heredity and environment in mammalian behavior. British Journal of Animal Behavior, 1, 43-47.
Hebb, D. O. (1959). A neuropsychological theory. In S. Koch (Ed.), Psychology: A Study of a Science (Vol. 1). New York: McGraw-Hill.
Hebb, D. O. (1980). D. O. Hebb. In G. Lindzey (Ed.), A history of psychology in autobiography Vol. VII. San Francisco: W. H. Freeman.
Hebb, D. O. & Williams, K. (1946). A method of rating animal intelligence. Journal of General Psychology, 34, 59–65.
Hunt, J. M. (1979). Psychological development: Early experience. Annual Review of Psychology, 30, 103-143.
Lashley, K. S. (1929) Brain Mechanisms and Intelligence. A quantitative study of injuries to the brain. Chicago: U. of Chicago Press.
McKelvie, S. (1987). Learning and awareness in the Hebb digits task. Journal of General Psychology, 114, 75-88.
Milner, P. M. (1957). The cell assembly: Mark II. Psychological Review, 64, 242-252.
Olds, J., & Milner, P. M. (1954). Positive reinforcement produced by electrical stimulation of the septal area and other regions of the rat brain. Journal of Comparative and Physiological Psychology, 47, 419-427.
Pritchard, R. M., Heron, W., & Hebb, D. O. (1960). Visual perception approached by the method of stabilized images. Canadian Journal of Psychology, 14, 67-77.
Shore, D. I., Stanford, L., MacInnes, W. J., Klein. R. M. & Brown, R. E. (2001) Of mice and men: Using virtual Hebb-Williams mazes to compare learning across gender and species. Cognitive, Affective and Behavioral Neuroscience, 1, 83-89.
Skinner, B. F. (1938). The Behavior of Organisms: An Experimental Analysis New York: Appleton-Century.
Trappenberg, T. P. (2002) Fundamental of computational neuroscience. Oxford: Oxford University Press.
Zubek, P. (1969). Sensory Deprivation: 15 years of Research. New York: Meredith.

[edit] Recommended reading

Brown, R. E. & Milner, P. M. (2003) The legacy of Donald O. Hebb: More than the Hebb Synapse. Nature Reviews Neuroscience, 4, 1013-1019.
Glickman, S. (1996). Donald Olding Hebb: Returning the nervous system to psychology. In G. Kimble, C. Boneau, & M. Wertheimer (Eds.), Portraits of pioneers in psychology Vol 2. Hillsdale, N. J.: Erlbaum.
Harnad, S. (1985) D.O. Hebb: Father of Cognitive Psychobiology (1904-1985) Behavioral and Brain Sciences 8(4) 765.
Klein, R. M. (1980). D. O. Hebb: An appreciation. In P. W. Jusczyk & R. M. Klein (Eds.), The Nature of Thought: Essays in Honor of D. O. Hebb (pp.1-18). Hillsdale, N. J.: Erlbaum.
Milner, P. M. (1986). The mind and Donald O. Hebb. Scientific American, 268, 124-129.

[edit] External links

Raymond Klein's webpage

[edit] See also

Cell assembly, Synaptic plasticity