Book Review, Neuroscience

1. v 70 The American Acupuncturist 31
Sense and Sensitivities: A Book Review of David Linden’s
Touch: The Science of Hand, Heart, and Mind
Author of a half-dozen books on the
subject of neuroscience that have
crossed over into the popular realm,
David Linden has repeated his pub-
lishing success one more time. With
Touch: The Science of Hand, Heart, and
Mind, the Johns Hopkins neuroscientist who wrote The New York
Times best-seller The Compass of Pleasure is back to explain how
our sense of touch has been molded over millions of years by the
continuously evolving features of the human nervous system. He
passionately presents and discusses curiously-shaped skin receptors,
synaptic functions, neural activity, and signals coursing to the
brain and back again to sites of injury, and all of this mingled with
additional sensory input from the human vision center, auditory
clues, and the senses of smell and taste. Together, the five senses are
interpreted by the brain’s higher functions in the context of cogni-
tion, emotion, and the instinctive expectation of physical action.
Linden, who is a top-notch neuroscience scholar, also wants
the reader to know he is no nerdy professor sporting a plastic
pocket protector: chapter two’s title was originally a line from a
late 19th century children’s rhyme that became the popular 1986
Stan Ridgway hit, “Pick It Up and Put It in Your Pocket,” and
was later featured prominently in a Miami Vice episode. He also
borrows chapter seven’s title, “The Itchy and Scratchy Show,” from
the long-running off-beat TV cartoon series The Simpsons. While
Linden, then, promises to entertain as much as to provide insight
into the workings of the sensory perception of touch, he is first and
foremost a neuroscientist. That is made quite clear in his enthusias-
tic discussions of the structural minutiae of glabrous and hairy skin,
Merkel disks, Meissner’s corpuscles, Schwann cells, and Ruffini
endings, which are located deep in the dermis.
Just when the reader borders on neurological overload, Linden
shifts his narration from empirical annotation to speculation, and
he ponders how the various receptors with which Homo sapiens
is endowed contribute to fine grip control. Without the latter, of
course, our evolutionary ancestors would not have been able to
develop tool use. Then, in a most astonishing chronological vault,
Linden jumps from the springboard of tool use by the earliest
hominids to “human culture as we know it” (p 44). This is certainly
a historical leap of unprecedented magnitude and the reader is left
to consider the implications of Linden’s assumptions, the most
obvious being that evolution is a linear event uninterrupted by
catastrophic natural events, climate changes, the Black Plague,
and other such phenomena that have wreaked havoc on our
planet Earth.
In switching perspectives from neurological minutiae to philo-
sophical speculation, Linden’s ever-increasing accomplishment as
a writer with a repertoire of expository techniques is quite clear.
Happily, the author is also adept at this technique, so he can pre-
vent the reader from drowning in scientific detail. In this respect,
Linden’s skill is analogous to Bill Bryson’s literary dexterity. Author
of The Mother Tongue: English and How It Got That Way, among a
plethora of cross-over intellectual, popular tomes just like Linden’s,
Bryson can sense when he is overwhelming the reader with detail,
and shifts the reader’s view to a larger, roaming, synthetic perspec-
tive, sometimes by way of injecting broad speculation, sometimes
by slotting in personally meaningful anecdotes, another technique
that Linden uses with aplomb.
Touch contains 37 pages of heavily annotated references as well
as a host of detailed illustrations from sources as diverse as CNN,
the journals Science and Biological Psychiatry, J.K. McNeely’s Holy
Wind in Navajo Philosophy, Shakespeare’s Macbeth, Horace’s poetry,
Dante’s Inferno, Henry Fuseli’s psychologically fascinating painting
“The Nightmare,”19th century German physician and pioneering
psychologist Ernst Weber, and French novelist Andre Gide, known
equally well for his odd homosexual characters and for dreaming
up the acte gratuit, or a senseless act of freedom that one of his
characters expresses by throwing a perfect stranger off a speeding
train to his death. Now, we must ask, is Linden really the new
Renaissance Man he appears to be, or simply trying to impress the
reader with these multidisciplinary and often obscure references?
Only the editors at Viking Press and possibly a bevy of Hopkins’s
Reviewed by Susanne Thomas, PhD, Associate Editor, The American Acupuncturist
Viking
$28.95
ISBN 978-0-670-01487-3
Also available as an e-book
272 pages
“In switching perspectives from neurological
minutiae to philosophical speculation,
Linden’s ever-increasing accomplishment
as a writer with a repertoire of expository
techniques is quite clear. Happily, the
author is also adept at this technique,
so he can prevent the reader from
drowning in scientific detail.”

2. 32 The American Acupuncturist Spring 2015
graduate research assistants know for certain. Linden’s photo on
Amazon.com (1) features a balding man with a curly ponytail and
rimless spectacles, grinning in a positively mischievous way that
leaves the viewer guessing.
Research methods aside, this book is an intriguing read. Those
readers who dislike flipping back and forth from text to notes
would do well to read through the annotations and pause to
examine the illustrations as well before beginning the book proper.
Linden’s references often serve up half-page long commentaries as
fascinating as the main text of the book itself while the illustrations,
although tied to the text, can lead the reader down some interesting
historical, literary, artistic, and philosophical byways.
In chapter 2, “The Skin Is a Social Organ,” the author probes
the origin of such metaphors as a “warm individual,” a “rough
day,” “weighty matters,” a “smooth negotiator,” and a person with
“gravitas.” Tactile and other sensory tropes abound in the text
and include emotional matters as well, such as “hurtful behavior”
and “heartbreak” (p 173). Linden documents the sensory roots of
language and the way in which our linguistic choices are informed
by reference to psychological studies. But such metaphors are by no
means a novel discovery, and indeed many examples can be found
in the Psalms of the Hebrew Bible. Much more recently, these
tropes can be traced back on this side of the Atlantic to Jonathan
Edwards, the firebrand theologian from New England who drew
on the natural world as a source for figurative language, which he
wielded so effectively in his famous sermon of 1741, “Sinners in
the Hands of an Angry God.” On the European continent, we find
sensory input expressed in figurative speech at the beginning of the
Romantic period with Jean-Jacques Rousseau’s publication of the
Confessions. This important book was composed while the author
rocked gently in a small boat on scenic Lake Geneva in 1782, and
with its publication, nature burst into the consciousness of the
West as a source of inspiration for research, creative expression, and
conversation.
Touch as a social phenomenon, we learn, is modeled in the
grooming practices of vampire bats, baboons, monkeys, and rats. It
also figures in successful NBA basketball teams, where interpersonal
touch between teammates early in the season is related to better
performance throughout the whole season (p 14). Of course, we
now know that deprivation of human touch in infants and children
can have devastating effects on the developmental psychology of
the young. “Are You Touch Deprived?” asked Psychology Today
in a June 9, 2014, article linking aggressive, criminal behavior in
adults to social isolation as children. While no one is suggesting
that more ballroom dancing lessons for children will eradicate the
serial killer phenomenon, Linden does claim that of the five senses,
touch is the primordial one and thought to be the first sense to
mature in the human fetus at about 8 weeks in its development
(p 26). Touching, of course, is significant material for the cultural
anthropologist, and the degree of touching between people engaged
in conversation can vary from 0 times per hour in London, as
Linden notes, to 110 times per hour in Paris in one study of people
in coffee shops around the world (p 31). The evolution of touching
practices, from primitive times to our own, is very clearly molded
by social practices, gender roles, and our own developmental
history from infancy to adulthood.
The story of Louis Braille as recounted by Linden is fascinating
reading and replete with information concerning the processing of
tactile information. The brain must recognize each raised braille
character within one-twentieth of a second in order to read at the
astounding rate of 200 words per minute. Illustrations are plentiful
in this chapter, as are analogies of the sort that the best science
teachers use to explain complex biological processes. It helps, too,
that Linden knows a bit about the mores of Victorian history.
Many incidents of body numbness experienced by women of that
era turned out to be caused not by Freudian neuroses, but rather by
wearing excessively tight undergarments such as corsets, drawers,
bloomers, and garters.
By reviewing bio-neurological experiments, research papers,
and meta-studies, Linden is able to extract some general principles
about touch: “Information converges from skin to brain,” (p 65)
a process that is illustrated by the wonderful image of the “touch
map” of the human being (p 64) reproduced here.
Illustration by Joan
M.K. Tycko reprinted
by permission of
the publisher from
THE ACCIDENTAL
MIND: HOW BRAIN
EVOLUTION HAS
GIVEN US LOVE,
MEMORY, DREAMS,
AND GOD by David
J. Linden, p. 85,
Cambridge, Mass.:
The Belknap Press
of Harvard University
Press, Copyright
© 2007, by the
President and Fellows
of Harvard College.
The tongue, lips, and especially hands, where most of our
sensing receptors are located, are artistically rendered as gigantic
in proportion to our legs and torso. Likewise, Linden covers the
body’s serial and parallel processing of touch information, stopping
along the way to examine the new paradigm of plasticity, by which
the brain’s wiring structure can actually be modified as a result of
“individual sensory experience” (p 69), as in the case of profes-
sional string instrument players. Gender, too, plays a role in touch
discrimination. Based on experimentation, a group of scientists has
discovered that the smaller fingertips of women are more highly
touch-discriminatory than those of men.
Book Review: Touch: The Science of Hand, Heart, and Mind

3. v 70 The American Acupuncturist 33
In the chapter “Sexual Touch,” Linden discusses something that
most of us already know: our sense of touch is utterly dependent
upon our expectations and the situational context in which we
find ourselves. One man’s torture, we might say, is another man’s
pleasure. Further, according to Linden’s study, “…when we look
at the fine branching patterns of the nerves and the distribution of
nerve endings, individual variation becomes apparent” (p 98). One
woman may have fewer nerve endings in one genital area than in
another area, and her cousin, for example, may have an opposite
pattern. The scientist in Linden ponders whether this individual
variation in genital regions may underlie preference for one type
of sexual activity over another (p 98). The author then gives the
reader an anatomical tour of nerve signals between genital areas and
the brain, noting along the way the often-used analogy between
taking pleasure in eating and taking pleasure in sexual activity. The
comparison is illustrated by graphs comparing Wanting/Liking/
Satiety as parabolic wave forms (p 106). Both of these activities, we
might say, are subject to the economic law of diminishing returns:
the more we partake of either, the less likely we are to pay for
consuming additional servings—that is, unless satiety is overcome
by some particular circumstance such as novelty (p 108). Linden
wraps up this chapter by noting gender differences in response to
various stimuli—women demonstrating response to a wider sensory
range than men—and closes by serving up a rather affected “recipe
for orgasm” based on studies of brain scanner activity in both sexes:
“…Mix together the following ingredients: Activation of touch
sense from the genitals (somatosensory cortex), Deactivation of fear
and vigilance (amygdala), Activation of the pleasure circuit (ventral
tegmental area, nucleus accumbens, dorsal striatum), Activation
of motor control center (cerebellar nuclei), Deactivation of areas
involved in slow decision making (lateral orbitofrontal cortex and
anterior temporal pole), Serves: 1” (p 120).
“Hot Chili Peppers, Cool Mint, and Vampire Bats” leads off
with a short history of the spice trade before introducing the
reader to human biological thermosensors, which Linden con-
jectures evolved first in plants as a protective response by certain
compound-producing botanical species to deter animal predators
from consuming them. This speculation appears to be an unusual
matter of plant evolution driving animal—and ultimately—human
evolution, a rather novel idea. Linden does admit, however, that the
science is still not all quite there and that there are probably more
heat-sensing molecules in human skin that have yet to be identi-
Book Review: Touch: The Science of Hand, Heart, and Mind
fied as part of the TRPV family of genes responsible for activating
our thermosensors. The next time you rub some wasabi or yellow
mustard on your sushi, or load up your home-made pasta sauce
with garlic and onion, do consider that there is a host of chemical
activating compounds that trigger different TRPV family sensors—
including the ones that make your eyes water when you chop that
onion (p 128).
One of the more entertaining features of Linden’s romp through
neuroscience is his inclusion of home remedies and references
to various types of cuisines. Figure 5.2, for example, features an
illustration of horseradish, onion, ginger, garlic, and olive oil float-
ing above an illustration of skin receptors, one of which is actually
named the “wasabi sensor.” Linden regales us, too, with home
remedy chit-chat about the “tickle-tongue tree” and the “toothache
tree,” as well as the gustatory potency of Szechuan peppercorns
(p131).
Heat sensors, also, are the subject of the author’s examination of
vampire bats, those curious and frightening little creatures whose
sole food supply consists of warm blood extracted from mammals.
The reader understands that Linden has included them for the
sheer fun of it, but the author does manage to pack an awful lot of
science into the illustrations of the ugly creatures (figure 5.3, p133)
with their infrared-sensing triangular nasal “pits,” also described less
offensively as a “nose leaf” (p 132).
Another technique that the author frequently uses to keep the
audience entertained and on their toes is the epistemological teaser:
Just when one thinks that the scientific narrative has led to its logi-
cal conclusion, Linden stops the flow of thought in its tracks and
points to a surprisingly different conclusion, making new, amusing
word coinages along the way. Speaking of the molecular heat sensor
in the TRPA family, he notes: “If we have come to think of TRPA1
as the wasabi sensor, it is only because we happened to study mam-
malian TRPA1 first. If we had a more vipercentric worldview, we’d
say that TRPA1 is a heat sensor that can also be activated by wasabi
and garlic (p 137).” “Vipercentric” worldview? Linden does have a
sly wit. When pondering how genetic factors may, in the future, be
linked to individual temperature preferences, he simply can’t resist
expressing his suspicion that his former sister-in-law “has a frog-like
TRPM8 gene, but that has yet to be confirmed” (p 142).
Turning his attention to pain-sensing, Linden presents a fascinat-
ing case in which a group of genetically-related Pakistanis who
emigrated to England was unable to sense pain from birth onward
“Another technique that the author frequently uses to keep the audience entertained
and on their toes is the epistemological teaser: just when one thinks that the scientific
narrative has led to its logical conclusion, Linden stops the flow of thought in its tracks
and points to a surprisingly different conclusion, making new, amusing word coinages
along the way.”

4. 34 The American Acupuncturist Spring 2015
Book Review: Touch: The Science of Hand, Heart, and Mind
(p 143). Because individuals in this group frequently intermarried,
their offspring carried the genetic mutation for congenital insensi-
tivity to pain, a “loss-of-function” mutation (p 145). While able to
experience emotion and sympathize with others who were in pain,
this group suffered from early mortality rates. We know that pain
is an instinctive reaction to bodily danger. Who among us hasn’t
burned her hand on a hot pot or dish and instantly recoiled? But in
the pain-insensitive Pakistani group, the life-saving voltage-sensitive
sodium channel, which propagates electrical signals in our neurons,
death came early. Apparently such banal causes such as overly tight
shoes, underwear cutting into the flesh, and burning food that
damaged the esophagus brought deadly bacterial infections in their
wake to this clan (p 145).
There are fast and slow pain fibers, Linden notes. Waves of
successive pain that reach our brain when we stub our toe are the
universally experienced example of this phenomenon. And Linden
can use hyperbole at times with the best of the literati. In this
particular case, he creatively illustrates what the time lag might be
for the second wave of pain to arrive in her brain when a ninety-
foot-long diplodorcus dinosaur whacks her tail on a floating log (p
148). Quite interestingly, the author notes that “there is no single
brain area that is responsible for registering pain” (p 153). Surely
chronic pain patients are aware of this phenomenon, though they
very well may not be able to distinguish all five of the pain path-
ways, of which Linden describes three in extraordinary detail. The
chronic pain sufferer, however, experiences his pain’s “characteristic
negative emotional tone” and is able to place pain sensations in the
context of his immediate environment. This instinctive orientation
allows the pain sufferer to determine whether he is safe or “under
threat,” whether the pain was “anticipated or a surprise,” and what
the future implications of the pain might be (p 154). Linden offers
a discussion of phantom limb pain and several anecdotal tales of
combatants who were wounded, yet nevertheless surged forward
in the heat of battle when their sense of pain was dulled either by
overwhelming emotional situations or by extraordinary “cognitive
stressors” (p 163).
Why is such detail given so much weight in Linden’s discussion?
The reader certainly must ponder what a marvelous creation the
human brain is. Its pain-transmitting neurons can travel downwards
to the source of the pain as well as receive upward signals, thus
allowing us to consciously or unconsciously “suppress or enhance
pain information” (p 164). “It [the brain] spins the media, so to
speak,” notes Linden, in one of his many popular “I’m just folks”
comments, which lend the text a great deal of its popular appeal.
Linden’s “Pain and Emotion” chapter (pp 143-174) covers
extensive territory from the function of the “spino-hypothalamic
pathway” to threat anticipation, placebo-based studies, chronic pain
reduction techniques such as yoga and Tai Chi, as well as mindful-
ness meditation practice, including Buddhist and Zen meditation.
This particular discussion makes these pages a must-read for prac-
titioners who treat chronic pain patients. His examination of the
relationship between pain and emotion is an enlightening one, and
includes examples from the universal experience of hurt, whether
from social ostracism or unrequited love. Simply thinking about
being the wallflower at a high school dance is enough to bring back
to most of us a bountiful supply of that unpleasant feeling.
“Semanza lived in the Rukungiri district of rural Uganda” (p
175). Thus begins Linden’s chapter seven. If the chapter did not
carry the amusing Simpsons-inspired subtitle, “The Itchy and
Scratchy Show,” the reader might think he had been transported
to a Shiva Naipaul novel set in sub-Saharan Africa. But that is our
author’s engaging anecdotal voice, and in this case, it leads to a
discussion of the unbearable itch that comes with river blindness,
known scientifically as “onchocerciasis” (p 175). The torment
caused by this parasitic invasion appears to often lead to suicide
(p 176) and the subject’s gravitas seems to compel Linden to
develop a reference to Dante’s Inferno, in which the falsifiers of the
eighth circle are doomed to an eternity of perpetual itch. Itching
is yet another disagreeable tactile phenomenon with its very own
metaphors that Linden draws from the likes of Woodie Guthrie’s
music (“Well I know that you are itching to get married/Nora Lee”)
(p 185) and Ogden Nash’s poetry (“Happiness is having a scratch
for every itch”) (p 184).
While Linden presents multiple theories for the presence of itch
receptors, in this case as in that of all other sensory phenomena
that he discusses, our author is clearly a staunch proponent of
evolutionary theory. Along with the correlated phenomenon of
human genetic mutation and the theoretical existence of a link
between plant and animal evolution, our humanity is expressed by
Linden in the micro-phenomenology of the human central nervous
system. Evolution and biology form the basis for his insights and
observations, and so he appears quite awkward using the term
“transcendent,” which he does in the final chapter of this book,
titled “Illusion and Transcendence.”
Wherever he may venture—whether it be the realm of personal
anecdote, classical literature, music, or popular culture—Linden
always comes back to roost on “the fundamental power of biology”
(p 194). Ever since the 17th century, when Descartes’s cogito ergo
sum replaced God with human knowledge as the seat of our very
being, there has been no turning back in the application of science
to the empirical world, to the human mind, to human emotions,
and yes, even to human creativity. While our bodily sensations
and our reactions (as in the placebo effect) can sometimes be the
result of illusion, expectation, or anticipation, we do live in a
post-transcendent age. This seemingly compulsorily-written ending
to his work in which he gratuitously alludes to the phenomenon
of transcendence, just doesn’t jibe with the scientific weight of his
book, and Linden has done far too good a job as an evolutionary
neurobiologist to convince the reader otherwise.
References
1. Amazon [Internet]. [place unknown]: Amazon.com Inc.; c1996-2015. David J. Linden;
[cited 2015 Apr 11]; [about 6 screens]. Available from: http://www.amazon.com/
David-J.-Linden/e/B001IGM008