The Abyss in the Middle of the Bridge
The long journey from the physical molecules to the non-physical mind starts with a first step. Squire and Kandel have taken that first step in a masterful attempt to bridge the certainty of their laboratory measurements of brain function with the elusive, receding, transfinite virtuality of the human mind at the other end of the bridge. Notwithstanding their announced warning that "We are not who we are simply because we think. We are who we are because we can remember what we have thought about", the authors stick to the experimental facts. Perhaps the statement was meant as a red herring bait for the reductionists or an echo of "The Remembered Present" theory of Edelman about consciousness. The book is a no nonsense abridged laboratory report. The authors start at the beginning and move up the spiralcase of complexity one step at a time in an impressive 'show and tell' scientific act. Their rendition of memory research is credible, convincing and extremely well written; a must for students of neuro-molecular biology or the cognitive sciences.
Were the authors able to reduce mind and consciousness to a molecular equation? Of course not. Nor should they; as scientists they are committed to deal with observable facts in nature or in the simulations lab, directly or aided by instruments. That, they did, in a very systematic and cogent way from Kandel's elegant Aplysia experiments to Squire's behavioral analysis of neuropsychiatric data. The language was carefully selected and the illustrations added much needed understanding for the un-initiated. The didactic value of illustrating how an investigator moves along a research protocol path mined with conceptual and experimental difficulties is a classic in basic research.
The sequential concatenation of ionic and molecular events at synaptic receptor sites offered as an explanation of short term memory is very convincing. The explanation offered for the conversion of short term memory to long term memory involving the genetic apparatus is not so clear at the molecular transcryption level but opens up a new reliable approach to behavioral genetics. In the opinion of the undersigned, the genetic basis for Lamarcquian inheritance has been given a push forward as we anticipated in "Biopsychosociology", Limusa Ed. 1987.
True to the tradition among the practitioners of the scientific methodology, the authors do not try to explain why the selective course of ionic and molecular sequences lead to the adaptive behavior of the species. If an apple falls from a tree to the ground all they need is to measure the distance from the branch to the ground, the velocity at impact, the weight of the apple or any other observable and measurable concomittants. Why the apple did not 'fall' to the clouds instead, is outside science and properly belongs to theology. The authors knew better than to try to answer "why".
A riveting book, and a quick summary of current thinking
This compact book draws a circle around the small kernelof facts neuroscientists have accumulated about memory. The book iscurrent to within the last couple of years -- a quick way to bringyourself up to date. The book has two authors, and each of them has a distinctive voice and personality. You will notice, as you read a chapter, which scientist wrote it. Squires is engaging, wide ranging and conversational. Kandel's prose is single minded and straight to the point. The book appears to be the product of a real collaboration, not just an editor's paste-together or interleaving of two separately contributed manuscripts. By passing the microphone back and forth at timely moments, the two men are able to fill in a large and remarkable picture of what we know now about memory.
What is memory? The working hypothesis is that the nervous system rewires itself as an animal acquires new information from the world. This reworking of a pre-existing nervous system is accomplished by altering the strength of synaptic connections between nerves. Novel synaptic connections establish favored conduction pathways within the complex nest of wiring in the brain. These favored pathways are believed to constitute the memory. Although this concept was elaborated by the psychologist Donald Hebb, and is often called the Hebb hypothesis, the authors point out that it has roots in the prescient thinking of the 19th century microscopist, Ramon y Cajal.
Kandel develops an explanation of how synaptic changes record memory, using the Aplysia (sea snail) as a prototype. He carries this story right down to the level of the gene. Squires presents the overarching concepts of declarative versus non-declarative memories, introduces the idea that there exist multiple memories in the brain, enumerates and explains them, and sets the stage for an explanation of how short term memory is "switched" biochemically to become long term memory. Chapters 3 and 7 offer nicely detailed descriptions of how synaptic changes occur. These two chapters belong together and you might find it helpful to read them in succession.
It is a deeply set assumption in this science, and a rhetorical short cut in this book, that synaptic changes are essentially the same thing as a memory. As A equals B. Synaptic changes do occur, and they do coincide with learning, and both processes are measurable and proved. But a skeptical reader might ask - and really should ask -- if the memory mechanism thus assumed isn't a post hoc fallacy. Maybe memory is not written by and into synapses. Maybe memory is written somewhere else and in some other way. Maybe the experimental results mean something else or something more.
The neuron is probably a multichannel device, a cable rather than a wire. This is the only reasonable way to construct a nerve that would enable us to think as fast as we do. Because nerve impulses are so very slow moving, each successive impulse must be rich in information. A multichannel nerve would have the power to convey graded information from one end of a neuron to the other. All the while appearing, to instruments, to convey only the classically blank, "all or nothing" impulse that is so confidently presented to us on the first page of every neurobiology text.
Sodium and potassium ions flow into and out of the cell via structured portals in the cell membrane called (fortuitously) sodium and potassium channels. To create a continuous longitudinal information channel running the full length of an axon membrane, one would simply link each ion portal to its next door neighbor. A conformation change in one portal induces a conformation change in the next. One can visualize many parallel tracks, a corduroy membrane. Linked receptors are commonplace. The structure of the potassium channel has been published recently, and so we are now finally working at the level where a multichannel membrane can be detected.
At a multichannel nerve's ending, the modification and multiplication of synapses -- that is, the two specific processes so beautifully documented and explained in Chapters 3 and 7 of this book -- might not be writing memory at all. Synaptic changes could simply reflect an underlying scaling or calibration process, the pioneering of a useful operating range. Or a glimpse at the workings of a control network. This is theoretical, however, and the problem of memory has always been a jungle gym for theoreticians. It still is. This is a great book about the memory, and it is also a great book about the synapse. But it does not quite win its implicit argument that the synapse makes the memory. It does succinctly report the factual findings now in hand, many of them quite surprising, and it is current and clear. END
