GŁnther Palm (2000) From Lashley to Hebb:. Psycoloquy: 11(047) Lashley Hebb (15)

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PSYCOLOQUY (ISSN 1055-0143) is sponsored by the American Psychological Association (APA).
Psycoloquy 11(047): From Lashley to Hebb:

FROM LASHLEY TO HEBB:
THE DEVELOPMENT OF A BIOPHYSICAL THEORY OF LEARNING
Book Review of Orbach on Lashley-Hebb

GŁnther Palm
Neural Information Processing
University of Ulm
D-89069 Ulm, Germany
http://www.informatik.uni-ulm.de/ni/mitarbeiter/GPalm_e.html

palm@neuro.informatik.uni-ulm.de

Abstract

Orbach presents Lashley's ideas much more extensively and coherently than Hebb's. Most interesting is the discussion of Lashley's ideas vis-a-vis Hebb's "Organisation of Behavior".

Keywords

cell assembly, central autonomous process, engram, equipotentiality, Hebb, Hebbian learning, Lashley, localization, memory trace, nativism, reverberatory circuit, Vanuxem Lectures
1. "The Neuropsychological Theories of Lashley and Hebb" by Jack Orbach (1998, 1999) is more interesting for the historian of science than for the scientist. It is surprising how modern many of the issues of psychological brain research in the first half of the last century still appear today. This shows how small our conceptual and theoretical progress has been in spite of an explosive increase of experimental knowledge.

2. The title of the book is misleading for two reasons: the book contributes much more to the memory of Lashley than to the memory of Hebb and it does not really explain the "theories" of Lashley and Hebb. To put it bluntly, this is because Lashley had no theory and the author did not understand Hebb's.

3. The main objective of the book is to paint a picture of the eminent neurophysiologist Lashley as seen by a devoted pupil and to publish some hitherto unpublished material of Lashley's writing. The book also throws some light on the disagreement between Lashley and his scholar Hebb concerning Hebb's (1949) most influential book "On the Organisation of Behavior", which led Lashley to decline Hebb's offer of coauthorship of the book. Trying to understand the relation between these two men and in particular Lashley's (and Orbach's) opinion about Hebb's book was for me the most intriguing exercise which kept me reading (mostly between the lines). This is because I believe that the lack of understanding for Hebb's theoretical contribution revealed here is quite typical for the relation between experimentalists and theoreticians in neuroscience. The experimentalist, like Lashley, never fully commits himself to a theory because he knows that it is all too easy to falsify it experimentally. The theoretician, on the other hand, needs a strong commitment in order to work out all important consequences of a theory in increasingly complex model systems.

4. Lashley was struggling with the problem of localising memory traces. His experiments finally convinced him that the memory trace could not be localised in a particular connection between two neurons in a particular place. Hebb's answer to this conundrum was that the memory trace is distributed over many small synaptic changes in many synapses in various locations. For Lashley, this answer was both too diffuse and too simple. If it was a change in synaptic efficacy, it should be measurable and therefore localised; if not, it should be some completely different, inherently non-local physical phenomenon, like electro- magnetic waves. The latter theory was briefly adopted by Lashley only to show in a brave experiment that it was false. This attitude of avoiding a really strong theoretical commitment is characteristic of many experimentalists. It often precludes the necessary in-depth elaboration of the consequences of theoretical ideas, because it always leaves room for some mysterious entity yet to be discovered before we can fully understand the miraculous working of the brain. This lack of commitment was probably the main reason for Lashley's turning down Hebb's offer.

5. Hebb's idea was essentially to combine the older associationist notion (perhaps attributable to Pavlov) that associations between ideas or concepts are laid down in connections between corresponding neurons, with the rather modern idea of a distributed representation, i.e., that a concept is represented by a distributed cell assembly, not by a single neuron, and therefore a relation or association between concepts is laid down in a distributed set of perhaps small individual synaptic changes. Thus synaptic plasticity can still be the mechanistic substrate for the psychological phenomena of learning and memory despite Lashley's previous experiments that refuted a simple localisation. From the experimentalist point of view, the main problem with Hebb's theory was (and still is) that it is not straightforward how to falsify it experimentally, whereas it apparently makes a very strong claim about the functioning of the brain (which has even been successfully implemented and used in computer science). The real strength and courage of Hebb was not just to formulate his theory of cell assemblies, but to rest all of his psychology on the hypothesis that this is it, and nothing else is needed. This strong commitment to a theoretical hypothesis is the real reason theoreticians insist in naming Hebb synapses after him.

REFERENCES

Hebb, D.O. (1949) The Organization of Behavior. New York: Wiley.

Orbach, J. (1998) The Neuropsychological Theories of Lashley and Hebb. MD: University Press of America.

Orbach, J. (1999) Precis of: The Neuropsychological Theories of Lashley and Hebb. PSYCOLOQUY 10(029). ftp://ftp.princeton.edu/pub/harnad/Psycoloquy/1999.volume.10/ psyc.99.10.029.lashley-hebb.1.orbach http://www.cogsci.soton.ac.uk/psyc-bin/newpsy?10.029


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