topics: |  neuro-science | brain | language

neural darwinism

I. The brain has a huge diversity of interconnections which allow a vast
   repertoire of actions both mental and physical which may or may not be
   useful.

II. When activities occur which prove successful, the corresponding
   connections are re-inforced (through chemical change in the synapses
   between successive neurons) which are more likely to repeat a similar
   action on a future occasion.

III. These functions operate on groups of neurons which become hugely
   interconnected within groups and between groups including re-entrant
   linkages within a group and dual linkages between groups that allow them
   to work as units in co-operation.

In the lifetime of the individual, this leads to a process akin to natural
selection developing facilities appropriate for successful survival.

	- from David Tall


Edelman ( Nobel, 1992, for work on how the body immuno-system clones
itself when facing a foreign antigen), has been writing for some
decades from the brain-as-mind position (as opposed to other biologists
like Eccles Evolution of the Brain (1989), for instance).

    Here he attempts to present a revolution in neuroscience "as significant
as the Galilean revolution in physics or the Darwinian revolution in
biology", but to my mind (perhaps I belong to the converted), it reads more
like a long diatribe against dualism.

    Part 1 is a direct critique of cartesian dualism, though arguments
against it appear all over the book.  Part 2 looks at the evolutionary
origins of the brain, and also roles certain behaviours (e.g. recognizing
friends / enemies) play as adaptations beneficiary in evolution.  Part 3,
which contains the main meat of his proposals, outlines Edelman's views on
how these connections arise in the brain.  The theory that the brain
structures reflect evolutionary advantages he calls "neural darwinism" (ch.9),
originally proposed in 1978 and elaborated further in a book of that title in
1999.  Patterns of brain connections that are evolutionarily beneficial are
programmed genetically, but also epigenetically (i.e. in terms of
cell-division and other processes beyond the genetic program).  Yet other
structures form postnatally.

    Particularly focuses on the role of "re-entrant" mechanisms that code for
spatiotemporal similarity.  Different groups of neurons may be sampling the
same stimulus, and recognition involves combining them, with latency playing
a role; this results in robustness.  This, together with a mechanism for
memory, leads to categorization and then to concepts (ch.10).

    "Consciousness: the remembered present" (ch.11) outlines a theory that is
largely focused on distinguishing collections of personal, subjective
experiences (qualia or phenomenal experience, that are deeply personal), from
external experiences that can be shared.  Proposes a way out by suggesting
that we realize that other humans also share similar qualia, though we have
no direct way of knowing it.  This presents a model where we can
conceptualize a self as distinct from a non-self.   Possibly the discovery of
mirror neurons in the 1990s provides added justification for such a structure.

    Language is viewed as a mechanism for "breaking the tyranny of the
remembered present", through a socially-constructed self (ch.12).  Constructs
like  the subject-predicate distinction may be present in the chimpanzee,
which has concepts, and is also self-aware.  Makes a case for the state of
the brain prior to evolution of language, from which speech was a natural
evolutionary step, during which specialized structures (Brocas and Wernickes
areas, etc.) evolved to allow "more sophisticated sensorimmotor ordering that
is the basis of true syntax." (p.127)

    The chapter on Attention and the Unconscious (ch.13) focuses on the
process of forming conscious experience.  "Consciousness reigns, but does not
govern" (quote from Paul Valery).  The chapter presents a list of what is
reasonably understood about the brain (neural centers and their functions,
classical neurophysiology; patterns of animal behaviour, descriptive
psychology; socially transmitted behaviour - eg. social imprinting); and what
is less known (longer list).

    The last part of the book attacks other aspects in which philosophers
have gone wrong, and finally outlines some steps whereby one may eventually
construct a "conscious artifact".  - AM

Opening Quotation

	And going on, we come to things like evil, and beauty, and hope...
            Which end is nearer to God, if I may use a religious metaphor,
	beauty and hope, or the fundamental laws? I think that the right way,
	of course, is to say that what we have to look at is the whole
	structural interconnection of the thing; and that all the sciences,
	and not just the sciences but all the efforts of intellectual kinds,
	are an endeavor to see the connections of the hierarchies, to connect
	beauty to history, to connect history to man's psychology, man's
	psychology to the working of the brain, the brain to the neural
	impulse, the neural impulse to the chemistry, and so forth, up and
	down, both ways. And today we cannot, and it is no use making believe
	that we can, draw carefully a line all the way from one end of this
	thing to the other, because we have only just begun to see that there
	is this relative hierarchy.

            And I do not think either end is nearer to God.

		- Feynman, The Character of Physical Law, ch. 5 [Context: F
		is presenting a hierarchy from the laws of physics, to the
		properties of substances (water has surface tension) to
		effects like waves, or a storm; to nerve impulses; concepts
		like "man", or "history" or "political expediency", and then
		to evil, beauty and hope]

Brain structure: not the computer metaphor

The notion that we can think about how mental matters occur in the
absence of reference to the structure, function, development, and
evolution of the brain is intellectually hazardous. The likelihood of
guessing how the brain works without looking at its structure seems
slim. Certainly, if one agrees with the ethologists that mental states
are a product of evolution, we must at least study how the brain
evolved. Our obligation is to complete Darwin's program.

When we make even our first halting efforts to do so, we come upon a
series of intriguing and baffling findings. We see that the development
of brains in enormously dynamic and statistical. Developmental analysis
suggests that the way genes regulate the intricate anatomy of the brain
is through epigenetic interactions- particular developmental events
must occur before others can occur. Certain adhesion molecules regulate
collectives of cells and their migration, but do not do so cell by cell
in a prescribed or prearranged pattern. And to some extent, cell
migration and cell death are stochastic- they have unpredictable
consequences at the level of individual cells. These statistical
processes oblige individual brains, unlike computers, to be
individual. The somatic diversity necessarily generated by these means
is so large that it cannot be dismissed as "noise," as one would
dismiss the noise in an electronic circuit at normal operating
temperatures. (The hiss from your hi-fi amplifier is an example.)

Indeed, the circuits of the brain look like no others we have seen
before. The neurons have treelike arbors that overlap and ramify in
myriad ways. Their signaling is not like that in a computer or a
telephone exchange; it is more like the vast aggregate of interactive
events in a jungle. And yet despite this, brains give rise to maps and
circuits that automatically adapt their boundaries to changing
signals. Brains contain multiple maps interacting without any
supervisors, yet bring unity and cohesiveness to perceptual
scenes. And they let their possessors (pigeons, for example)
categorize as similar a large if not endless set of diverse objects,
such as pictures of different fish, after seeing only a few such
pictures.

If you consider these extraordinary brain properties in conjunction
with the dilemmas created by the machine or the computer view of the
mind, it is fair to say that we have a scientific crisis. The question
then arises as to how to resolve it. For a possible way out, let us
look to biology itself rather than to physics, mathematics, or
computer science.

Contents

Part 1 Problems

    1.  Mind:
	the defect of Descartes' Discourse on Method lies in his resolution
	to empty himself of himself, of Descartes, of the real man, the man
	of flesh and bone, the man who does not want to die, in order that he
	might be a mere thinker--that is, an abstraction.  But the real man
	returned and thrust himself into his philosophy...

	    The truth is sum, ergo cogito--I am, therefore I think, although
	not everything that is thinks.  Is not conscious thinking above all
	consciousness of being?  Is pure thought possible, without
	consciousness of self, without personality?
	      - Miguel de Unamuno, Tragic Sense of Life, trans. C.J.  Flitch

	"Don't think of an elephant."
	Of course, you did, and so did I.  But where is the elephant?  In
	your mind, and certainly not in the room.  p.3

    2.  Putting the Mind back into nature
Part 2 Origins:
    4.  Putting psychology on a biological basis
    5.  Morphology and mind - completing Darwin's programme
    6.  Topobiology - lessons from the embryo
    7.  The problems reconsidered.
Part 3 Proposals:
    8.  The sciences of recognition
    9.  Neural Darwinism
    10. Memory and concepts - building a bridge to consciousness
    11. Consciousness - the rembered present
    12. Language and higher-order consciousness
    13. Attention and the unconscious
    14. Layers and loops - a summary.
Part 4 Harmonies:
    15. A graveyard of isms - philosophy and its claims
    16. Memory and the individual soul - against silly reductionism
    17. Higher products - thoughts, judgments, emotions
    18. Diseases of the mind - the reintegrated self
    19. Is it possible to construct a conscious artifact?
    20. Symmetry and memory - on the ultimate origins of mind.

other reviews: Summary

Owen Flannagan, Consciousness Reconsidered, chapter 3, section 3:
[In reference to Daniel Dennett's Consciousness Explained, 1991), :

The theory of "neural Darwinism" or "neuronal group selection" helps
bring together and extend some of the insights about brain
composition, structure, function, and evolution discussed so far
(Edelman 1987, 1989; also see Changeux 1985). Five ideas are
especially important.

First, it is mathematically inconceivable that the human genome
specifies the entire wiring diagram of the brain. The genome,
powerful as it is, contains too few instructions by several orders
of magnitiude to build a fully funcitonal brain. The synaptic
connections that evolve in the brain over time are the complex
causal outcome of genotypic instructions, endogenous biochemical
processes, plus vast amounts of individually unique interactions
between organism and environment (Edelman 1989, 30 Hundert 1989,
237). It follows that talk of the brain as hard-wired is
misleading. To be sure, the overall structure of the brain is fixed
by our genes and certain neuronal paths, and certain specific areas
are designed to serve certain dedicated functions. But the "wires"
in the brain are soft, even those built during fetal development
and those serving specific functions. Furthermore, all the wires
are capable of being drawn into novel and complex connections with
indefinitely many other segments of the neural network. The key to
our magnificent abilities as anticipation machines involves fixing
gross architecture while leaving the development of connections at
the microstructural level undedicated and adaptable.

Second and relatedly, individual brains are extraordinarily diverse
in terms of structure ond connectivity. Identity theory has some
credibility in the domain of sensory experience. Certain
characteristic neural patterns subserve similar cross-personal
sensory experiences. But by and large most mental states probably
do no involve strict identites between types of mental and neural
states. Thus one and the same conscious mental state, for example,
believing that a speeding fire engine is coming from behind, is
almost certainly subserved by compositionally distinct neural
states in all the different drivers who have that thought. Once
massive connectivity is added in, it is no surprise that this
thought kicks off a series of other, different thoughts for each of
us. Once person worries about the victims and their property, and
another that he will be delayed. A third is thrown into a Proustian
reminiscence of summer nights in his childhood spent with
grandfather, the fire chief, at the station. He feels the humid
summer breeze on his face as he rides to a fire, and the smells of
burning embers and pictures of lonely stone chimneys well up in
him. Neural connectivity is the mother of "meaning holism" and the
"drift of thought" the way the meaning of each term connects
idiosyncratically with the meaning of many others. We are good at
keeping attention focused, but certain events send thought reeling
to unanticipated places, some welcome, others not. Neural
connectivity helps explain why this happens so easily.

The third, fourth, and fifth theses of neural Darwinism further
clarify the prospect for a complex form of mind-brain identity
theory and indicate some of the problems such a theory will
face. The third thesis is that neuronal ensembles projecting
through many levels are selected during experiences to map and
thereby to represent certain saliencies. Which ensembles represent
what is jointly determined by the genetically specified
receptivities of different neural locaitons (so visual processing
takes place in areas dedicated to vision and not to audition) and
by the neuronal groups available for selection and strengthening at
the time a stimulus is presented. But the jobs of all ensembles are
not assigned in advance, as they are, for example, on the view that
the mind contains all concepts innately. On such a view, experience
merely acts to trigger what is there (Fodor 1975, 1981). On the
neural-selctionist view, the brain is a vast territory with
contours roughed out by nature and more than enough room for all
comers. Experiences come looking for squatter's rights, for room to
make a life. The brain makes room in various ways. Sometimes it
simply gives over unclaimed terrain; other times it sets up
time-sharing and multiple-tenancy arrangements. Selection is
involved in that the world plays an important part in determining
which neuronal groups are activated for what roles. It does not
simply trigger neuronal groups preset to work for a particular
boss, should he turn up, and give the marching orders they
passively await. Nonetheless, once a neuronal group is assigned to
a task, that group shows up regularly for the job.

Fourth and relatedly, the neuronal network retains representations,
but not in permanently coded files. It retains representations as
dispositions to reactivate distributed activation patterns selected
during previous experience. Once a particular distributed
activation pattern has reached an equilibrial state so that it is
activated by a certain type of stimulus pattern, it frames novel
occurent stimulation with that activation pattern. This leads to
quick and easy identification of the stimulation and, depending on
its connections to other neuronal groups, to the right motor
repsponse. The neuronal groups are selected to detect certain
constellations of features. The groups are extremely sensitive but
not overly fussy. This explains why we are so quick to identify
degraded stimuli, for example, letters written in new and obscure
handwriting. The right pattern of activation is turned on by any
stimulus that possesses a sufficient number, or some adquately
patterned configuration, of the relevant features. The stimuli need
not be exactly the same as the stimuli that the neuronal group was
initially trained to detect. Indeed, a system that could only
recognize duplicates of previous stimuli would be of no use at all
in our fluid ecological surround. Recognition and recall do not
involve permanent storage, and thus lost space each time a
particular pattern becomes recognizable. Rather, neuronal groups
play multiple roles. My red detectors are activated whenever red is
before me. But when red things are not before me, my red detectors
are available for other recongitional labor- purple and orange
detection, for example.

Fifth, a neuronal system functioning according to principles of
ontogenic (lifespan) selection, as opposed to phylogenic
(species-level) selection, is fluid in several repects: (1) It can
gain, retain, revise, and abandon all sorts of thoughts, ideas,
desires, and intentions in the course of a life. (2) The system can
lose certain neurons to death, or in a labor dispute, one function
can lose neurons to some other function, without any loss in
functional capacity. If the capacity to recognize a banana as
edible is subserved by parallel activity in numerous recurrent
layers of neuronal groups, then all manner of degradation and loss
of members is compatible with continuous high performance. Neuronal
destruction can, of course, reach a point where the amount of
neuronal degradation is great enough to lead to functional
incapacitation in certain domains, as it does, for example, in
Alzheimer's patients. (3) Neuronal dedication to a task is not
fixed for all time once the neuronal group subserving the
recognitional or motor task in question is well honed. For example,
the neuronal group responsible for pressure detection on two
adjacent fingers wil "segregate into groups that at any one time
are nonoverlapping and have sharp boundaries" (Edelman 1989,
52). But these dedicated groups can shift boundaries over time
because of differential experience, or possibly even
randomly. Imagine the boundary between the United States and Canada
shifting several miles one way or the other each day along its
entire expanse (Calvin 1990, 175).

author bio

Edelman, Gerald Maurice (1929- )
 http://userwww.sfsu.edu/%7Ersauzier/Edelman.html

[Biochemist, born in New York City. He studied at Pennsylvania and
Rockefeller universities, and became professor of biochemistry at
Rockefeller in 1966. His special interest was in the chemical
structure and mode of action of the antibodies which form part of a
vertebrate animal's defence against infection. He shared the nobel
prize for Physiology or Medicine in 1972.]