The Great Awakening: “My Brain Is PLASTIC”
How the scientist writing this account finally saw the light
- An annotated autobiography including an abbreviated description of my University of California laboratory’s studies on brain plasticity has been recently published; see History of Neuroscience in Autobiography, Volume 7, Chapter 10 (2012). The majority of the main claims about research from my laboratory are referenced in that published summary.
- For a description of “classical” studies of the development of the visual system arguing that brain plasticity was limited to an early childhood epoch (a “critical” or “sensitive period”), see: Visual Perception: The Story of a 25-Year Collaboration by Hubel D and Wiesel T (2004); or Eye, Brain, and Vision by Hubel DH (1995)
- For an introduction to the complex world of binocular vision, begin with reviews (two of many) by an old comrade Gian Poggio, Mechanisms of stereopsis in monkey visual cortex. Cerebral Cortex 5:193 (1995); or for a more contemporary perspective, Fang L and Grossberg S, From stereogram to surface: How the brain sees the world in depth. Spat Vis 22:45 (2009).
- The arguments that the brain was aplastic after a “critical period” limited to the first epoch of life strongly influenced the way scientists imagined how the brain created neurological “representations” of the things of the world. Each neuron was imagined to have a permanent information-processing assignment. The brain was imagined to encode information with progressively more complex integration across progressively “higher” system levels, with “real” objects represented by object-specific neurons at the top (highest level) of brain systems. This notion was termed the “grandmother cell hypothesis” because neurons “at the top” were imagined to selectively represent things in their “complete” forms at that level.OF COURSE, neurons do encode incoming information in greatest detail at lowest system levels, and DO combine more complexly coded resultants over longer slices of time and over greater representational “distances” to get closer to the representation of “real” objects at each higher system level. HOWEVER, in contradistinction to the “grandmother cell” model: a) the neurons and their locations representing the things of the world are subject to change over time—which means that every aspect of these neurological representations must, by their nature, be relational, and NOT permanently location- or neuron-specific; and b) very widely distributed populations of very large numbers (think millions to hundreds of millions) of neurons activated together “represent” grannie. No neuron ever receives a “permanent assignment”; and every neuron is a member of MANY representational “teams”. In short, every neuron has lots of jobs to do.For a contemporary perspective and a lead-in to references related to the “grandmother cell hypothesis”, see Gross CG (2002) Genealogy of the “Grandmother Cell” Hist of Neuroci 8:512. I recommend the posthumous book Vision, by David Marr (1982) if you’re interesting in reading an intelligent, broad (but, of course, dated) perspective about experimental and theoretical concepts of visual representation/recognition processes in the first decade of my own research career.The development of these ideas arose at the apogee of strict “locationism”, by which scientists believed that all brain activities representing all things in the world arose from specific, aplastic brain loci. Perhaps one reason for the ascendance of this view stemmed from the unacceptably extreme perspective posited by the primary contrarian in mid-20th Century science, Karl Lashley, who held that the brain was broadly “equipotential” for the representation of the things of the world, or for the complex behaviors that were controlled by the brain. The Russian neuropsychologist Alexander Luria also compellingly argued that the very different consequences of brain injury in different individuals, and the different progressions and limitations in recovery, argued strongly against a strict locationist view. The apparent balance of these perspectives: Brains have broadly localized functions; but in detail, are highly plastic. As Lashley understood, the representations of the things in the world and the control of our actions within the brain and within the world must be relational, and must be expressed by different neuronal populations at different moments in time. Or put another way, very general locationism applies. Strict locationism does not.
Interestingly, Lashley originally defined “equipotentiality” in appropriately limited terms (see his brilliant description, for example, in Lashley K, 1923, Temporal variation in the function of the gyrus precentralis in primates. Amer J Physiol 65:585, or his Studies of cerebral function in learning, seven seminal scientific reports published between 1920 and 1926), but ultimately exaggerated it at a level in which he absurdly denied almost all location of function for complex cognitive aspects of behavior.Lashley’s perspective was originally strongly influenced by a strong early-20th Century mentorship at St. Elizabeth’s Hospital in Washington with a clinician-scientist had earlier compellingly argued that the brain must be plastic, Shepherd Ivory Franz. I encourage the more historically minded amongst you to seek out what he had to say about this subject in the 1910’s and 20’s. In a sense, Karl Lashley confirmed Shepherd Ivory Franz’ then-more-speculative conclusions.
- References to the studies of Norman Weinberger, E. Roy Johns, John Disterhoft, Marion Diamond, Charles Woody and the other scientists identified as being fore-runners in elucidating plasticity in studies in mammalian brains [note that many other individuals could have been cited as well; you can get to them through reading the manuscripts and reviews of these leaders] can be easily located at www.pubmed.gov or at www.psychinfo.org. Norman Weinberger, Richard Thompson, Charles Woody and Marion Diamond have all written important reviews and/or books summarizing their research over the past 30-40 years. For a broader more-historical perspective, see the wonderful account by the late E. Roy Johns and Robert Thatcher of early brain plasticity studies dating back to the 1870’s: Functional Neuroscience (Ehrlbaum; 1977; ISBN 0470989262). If you can’t find this book (it’s out of print), we’ve referenced some of the best of those seminal older studies in Nudo RJ et al (1990) Repetitive microstimulation alters the cortical representation of movements in adult rats. Somatosen Mot Res 7:463. Note that several thousand other scientists, not cited here, have contributed to this scientific sub-discipline over the past 60-70 years.
- To read about “classical conditioning” and its origins, see Pavlov I P, Conditioned Reflexes: An Investigation of the Physiological Activity of the Cerebral Cortex (1927). A student of the history of psychology might smell a revival, in my book, of the “behaviorist” arguments of Pavlov, and most strongly outside Russia, by the American psychologist B.F. Skinner. One of their shared notions: Every child/individual can be shaped by “classical” forms of behavioral conditioning to be a superior human being. The Soviet Union invested heavily in helping Pavlov achieve that “dream”, because for Russian Communism improvement of human individuals and societies was a central authoritarian goal.
While he accepted the support of the Soviet government for his research, Pavlov bluntly condemned their broader “social experiment”. Because of his international eminence, he was perhaps the strongest anti-government voice allowed to operate within the Soviet Union across the decades of the ‘20s and ‘30s.
Especially strongly before the Second World War, Skinner argued compellingly for reforming human societies by using behavioral approaches to create a more effective generation of children. Both efforts fell flat, in part because one-size-fits-all behavioral modification is a lousy idea, because the behaviorist perspective taken alone was extremist and neurologically incomplete and unrealistic—but also because the underlying science AND the technology required to deliver the goods were both immature, and not up to achieving the (for its proponents) utopian goals of this movement.
But, on the other hand, isn’t improving human lives by helping our fellow human beings get the most out of their brains in ways that empower individuals and societies what real progress IS all about? To that extent, the dreams of the pre-WWII behaviorists (sans the Soviet baggage or the limited focus in training on Pavlovian or related associative conditioning) were (in the author’s view) “right on”!
- Finally, I comment at the end of this Chapter that scientists were painfully slow to accept our brain plasticity studies as valid. Early reviews of our scientific reports demonstrating adult brain plasticity commonly came back with skeptical or sarcastic commentaries, although the work was undeniably conducted to high standards and was always (albeit sometimes grudgingly) accepted for publication. On a number of occasions, comments at scientific meetings in which we presented our findings were sharply critical. Scientists who were invested in critical period research in visual neuroscience were especially skeptical, and did not always hold back on what could be very personal insults.This did not bother me for long, as a scientist. The truth always wins out. It only irritated me to the extent to which it slowed down the application of this science for human good. I initially imagined that neuroplasticity science would be carried into the clinic for human benefit at high speed. In fact, it has been a >20 year slog for this perspective to predominate, and there are still clinical domains (perhaps most importantly in pediatrics, psychiatry, neurology, and educational and child psychology), where ignorance about this subject is often still rather astonishing.