As many cortical ares are more developed in human brain than in other organisms, no effective animal model exists.
Here
come the Ratbots : desire drives remote-controlled rodents
The Philosophy of Psychiatry: A Companion by Ed Jennifer Radden,
Oxford University Press, ISBN 0 19 514953 X
In the chapter called "Desire" one issue is how homosexuality got removed
from official diagnostic manuals, once doctors had "decided" that it should
no longer be regarded a disease. However, when this medical decision is
exposed to the hard edged precision of philosophical analysis, some rather
painful politically incorrect problems begin to surface. Whatever the reason
brought to bear for not classing homosexuals as diseased and in need of
medical attention, there are difficult implications, because exactly the
same set of arguments could be used for removing a host of paraphilias
or perversions from the diagnostic manuals as well. Perversions and paraphilias
range from the familiar, such as sexual masochism and fetishism, to the
more exotic, such as klismaphilia, sexual enjoyment derived from enemas.
Many of these do not cause distress to other people, and any upset caused
to the "patient" often seems to be largely exogenous—in other words, if
wider society accepted the behaviour and didn't condemn or discriminate
against it then personal suffering supposedly engendered by the condition
might disappear altogether. Another flaw with the medical definition and
diagnosis of perversions lies in the words "Usually the fetish is required
or strongly preferred for sexual excitement, and in its absence there may
be erectile dysfunction," which comes from the definition in the Diagnostic
and Statistical Manual of Mental Disorders, fourth edition, the bible of
North American psychiatry. But the stubbornly flaccid husband who no longer
finds his wife arousing is not necessarily impaired. The stimulus is inadequate;
or a stimulus that would work for him—another woman—is missing. The chapter
on emotion raises another uncomfortable question: that there could be innumerable
other common states of being that we doctors mess with in the cause of
pure consistency that might better be left alone, in particular mood problems
such as depression. Some forms of depression may be understandable reactions
to genuine quandaries, a form of "existential alienation"—a reasonable
and even desirable response to calling into question one's own values.
This isn't a new idea. Aristotle asked, "Why is it that all men who have
become outstanding in philosophy, statesmanship, poetry, or the arts are
melancholic, and some to such an extent that they are infected by the diseases
arising from black bile?" It might be that the reduction of depression
to faulty wiring in the brain or chemical imbalance is actually an impoverished
understanding of the breadth and depth of the human predicament. The New
Yorker magazine, in a tongue-in-cheek take on the medicalisation of life,
began publishing a series of cartoons entitled, "If they had Prozac in
the Nineteenth Century," featuring figures such as Karl Marx remarking,
"Sure! Capitalism can work out its kinks!" and Friedrich Nietzsche saying
to his mother after church, "Me, too, Mom. I really liked what the priest
said about the little people." The implication is clear: if stress and
dysfunction are "natural" reactions to difficulties, and if Immanuel Kant
is even partly right that melancholia is a result of the mind's imagination
run riot, then what might we have lost as a culture if psychopharmacology
had prevailed in earlier times? The boundary between suffering that requires
the ministrations of the medical profession and distress that should be
coped with without professional intervention has become blurred, with massive
implications in terms of cost and stress on the profession. It is in the
attempt to bring some focus in this area that philosophy is desperately
needed. Indeed, with the remorseless advance of medical technology it is
likely that our ability to interfere with states of being that are statistically
extremely common is always going to be on the increase, meaning that philosophy
will become ever more relevant. This erudite volume, with its numerous
practical examples, reminds us that philosophy and its tools of pitiless
precision and brutal clarity are as vital a weapon against disease as brain
scanners and multidisciplinary teams in the armament of modern medicine—perhaps
even more so. What might we have lost as a culture if psychopharmacology
had prevailed in earlier times? ref
Neuroscientists today are peering into the brain to understand the drive
of romantic love, and they are finding evidence backing the 19th-century
philosopher's observation: Love has a striking neural kinship with drug
addiction. As they probe love's neurochemistry, researchers are also finding
that its neural substrates are conserved among species. Human romantic
love evolved from the same brain system that mediates attraction in animals.
But despite agreeing on the fact that animal experience love and some other
points, researchers differ as to what and where the brain's love system
exactly is. On the one hand is a growing stack of simple, elegant findings
– a pleasing convergence of human and animal studies – that suggest the
basic outlines of the answer have been laid out. But quarrels remain on
some points, such as whether studies to date on animals are applicable
to human love. Some note a study that has linked a single genetic change
to a complex behavioral adjustment as particularly elegant. Boosting the
expression of one gene switched meadow voles, a type of rodent, from a
promiscuous to a monogamous lifestyleref.
For a new behavior to evolve, you might think a lot of different genes
would have to evolve in concert, but I don't think it works that way. It's
possible that this gene, which encodes the V1a receptor, lies in a pathway
homologous to one underlying human love. fMRI scans of couples who professed
to be deeply in love, as they viewed photographs of their belovedsref
show significant activations in brain networks rich in receptors for the
hormones vasopressin and oxytocin. These are the hormones identified as
crucial for pair bonding in a series of animal studiesref,
suggesting the pathways are homologous. Researchers have found that vasopressin
and oxytocin have largely similar effects in facilitating pair bonding,
although each has different additional functions. Some have suggested vasopressin
is more important in male pair bonding, and oxytocin in female pair bonding,
but this remains obscureref.
An observation that may lead to greater clarity is that brain regions rich
in oxytocin and vasopressin receptors overlap strongly with those rich
in dopamine, the neurotransmitter classically associated with the brain's
reward system. Long-term partner preference occurs when the vasopressin
circuits, which are also known to mediate individual recognition, somehow
connect with the dopamine pathway, causing an animal to associate a specific
individual with a sense of reward. In key dopamine-rich brain regions,
V1a is expressed more highly in monogamous than in promiscuous mammals.
Its upregulation might be the evolutionary event or events that caused
the pathways to connectref.
The mechanism of attachment preference uses the dopamine pathway to make
attachment a rewarding experience. No one has pinpointed how, chemically,
the vasopressin and dopamine pathways might link in this proposed system.
But while a molecular explanation is lacking for that part of the story,
it might already be partially worked out in others. As the hypothesis of
a vasopressin-dopamine linkage suggests, and as scientists have found,
dopamine is another substance crucial for long-term pair bonding in animals
that pair bond. Dopamine seems to achieve this effect by cutting levels
of cAMP, a common intracellular signaling molecule, in the brain's nucleus
accumbensref.
This region is thought to be a key pleasure center. The lower cAMP levels
may in turn reduce levels of the enzyme protein kinase A. Although further
details haven't been worked out, similar events are believed to underlie
the pleasure involved in drug and alcohol use. In love-smitten people,
not only these detailed neurochemical events, but also overall brain activation
patterns are similar to what you would see when you take a drug like cocaine.
The images show brain regions that are deactivated when subjects viewed
pictures of their friends compared to when they viewed pictures of loved
partners. Deactivations are right lateralized within the prefrontal cortex,
the middle temporal gyrus and the parietal cortex as is apparent in (A),
the projections onto cortical surfaces and in (B), the glassbrain projections.
In (C), the sagittal section (X = 4 mm) shows deactivations in the posterior
cingulate gyrus (pc) and the medial prefrontal cortex (mp). In (D), the
coronal section (y = -8 mm) shows deactivation in the left amygdaloid region.
To some researchers, the combination of rodent and human studies presents
a tidy picture. "The prairie vole story ... strips away cognitive clutter
and allows you to see some of the components of love without the human
version of cognition lying on top of it. But others question this neat
portrayal. The vole findings may be pretty remote from anything having
to do with love. For instance, he suggests, increased vasopressin in voles
might facilitate pair bonding not by directly creating a partner preference
(a mechanism conceivably related to human love), but by reducing their
odor sensitivity, a scenario of little apparent human relevance. Lowering
odor sensitivity might facilitate long-term bonds by stifling the normally
solitary voles' tendency to avoid each anotherref.
Animals experience love, at least somewhat, and that their love is homologous
with human love, but vole pair-bonding is not love: it's attachment. Attachment
is what in humans is sometimes called "companionate love". It's what's
left after the fire of romantic attraction dies down; it's the relationship
necessary to raise young together and share chores. Attachment is one of
3 neural systems Fisher distinguishes in connection with reproductionref.
The other 2 are romantic love, characterized by increased energy and focused
attention on a preferred partner, and lust. Each can operate independently
and is associated with a different neurochemistry: attachment with vasopressin
and oxytocin, love with dopamine and norepinephrine, and lust with testosterone.
Neuroimaging studies of lovers as they view photographs of their belovedsref
highlighted brain areas associated with dopamine and norepinephrine, in
patterns similar, though not identical, to voles. Fisher's studies required
that participants had just fallen in love, whereas Bartel's studies didn't
impose this requirement. Thus Bartels could have picked up more signs of
what Fisher calls attachment. If Fisher is correct about attachment being
separate from love, it would seem, she says, that scientists haven't gotten
very far beyond fMRI studies in examining love's chemistry. But other researchers
don't use Fisher's distinctions; some make different ones. Love is a concept.
Concepts are not such solid, real things in the brain. Social attachment,
that is a very solid, real thing. Surely that has implications for our
understanding of love." Bartels, for his part, tends to unify his subject
of study with a larger theme: love in general, not just the romantic type.
"It boils down to the biological function of bonding individuals together.
Many of the same regions were activated in mothers' brains as they viewed
pictures of their babies as in the romantic typeref.
The zones of overlap, including the oxytocin and vasopressin areas, evidently
represent a core attachment system. In humans, one might even call them
the neural substrates of "pure love." The challenge remains to clarify
how this circuitry works, and whether it really is related to simpler animals'
pair-bonding systems. Human love has all kinds of emotional components,
cognitive components, in which if the other partner doesn't happen to be
there, we can still talk about the feelings. It's unclear the extent to
which mate preference in voles really resembles what we see in humans.
Copyright © 2001-2005 Daniele Focosi.
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