Koch, Christof

English

Caltech Authors - Main

Introduction 
CHRISTOF KOCH 
CONSCIOUSNESS AI"D the problem of free will reside at the 
nexus of the mind-body problem. Consciousness appears as 
mysterious to twenty-first-century scholars as when humans 
first started to wonder about their minds several millennia 
ago. Nevertheless, scientists today are better positioned than 
ever to investigate the physical basis of consciousness and 
volition. 
The researchers represented in this section take the 
problem of consciousness, the first-person perspective, as 
given and assume that brain activity is both necessary and 
sufficient for biological creatures to experience something. A 
primary goal is to identify the specific nature of the activity 
of brains cells that gives rise to anyone specific conscious 
percept, the neuronal correlates of consciousness (Crick and 
Koch, 1990; Chalmers, 2000; Metzinger, 2000). An auxil-
iary goal is to determine to what extent these correlates differ 
from activity that influences behavior without engaging 
conscIOusness. 
Almost everyone has a general idea of what it means to 
be conscious. According to the philosopher John Searle, 
"Consciousness consists of those states of sentience, or 
feeling, or awareness, which begin in the morning when we 
awake from a dreamless sleep and continue throughout the 
day until we fall into a coma or die or fall asleep again or 
otherwise become unconscious" (Searle, 1997). Some form 
of attention is probably necessary, but is not sufficient. Oper-
ationally, consciousness is needed for nonroutine tasks that 
require retention of information over seconds. Although 
provisional and vague, such a definition is good enough to 
get the process started. As the science of consciousness 
advances, such definitions will need to be refined and 
expressed in more fundamental neuronal terms. Until the 
problem is understood much better, though, a more formal 
definition of consciousness is likely to be either misleading 
1107 
or overly restrictive, or both. If this seems evasive, try defin-
ing a gene (Keller, 2000; Churchland, 2002). 
The working hypothesis of brain scientists is that con-
sciousness emerges from neuronal features of the brain. 
Emergence is used here in the sense that the initiation and 
propagation of the action potential in axonal fibers, a highly 
nonlinear phenomenon, is the result of, and can be predicted 
from, the attributes of voltage-dependent ionic channels 
inserted into the neuronal membrane. Although conscious-
ness is fully compatible with the laws of physics, it is not easy 
to predict its properties from these interactions. 
Understanding the material basis of consciousness is 
unlikely to require any exotic new physics but rather a much 
deeper appreciation of how highly interconnected networks 
of a large number of heterogeneous neurons work. The abil-
ities of groups of neurons to learn from interactions with the 
environment and from their own internal activities are rou-
tinely underestimated. The individual neurons themselves 
are complex entities with unique morphologies and thou-
sands of inputs and outputs. Humans have no real exp,eri-
ence with such vast organization. Hence, even biologists 
struggle to appreciate the properties and power of the 
nervous system. 
It would be contrary to evolutionary continuity to believe 
that consciousness is unique to humans. Most brain scien-
tists assume that some species of animals-mammals, in par-
ticular-possess some, but not necessarily all, of the features 
of consciousness; that they see, hear, smell, and otherwise 
experience the world (Griffin, 2001). This is particularly true 
for monkeys and apes, whose behavior, development, and 
brain structure are remarkably similar to those of humans. 
Of cOllrse, each species has its own unique sensorium, 
matched to its ecological niche, but that is not to deny that 
animals can have feelings, subjective states. To believe other-
wise seems presumptuous and flies in the face of all experi-
mental evidence from split-brain patients, autistic children, 
evolutionary studies, and animal behavior for the continuity 
of behaviors between animals and humans. 
The focus of much of the empirical work is on sensory 
forms of consciousness-vision, in particular. More than 
other aspect of sensation, visual awareness is amenable to 
empirical investigation. This is so for a variety of reasons. 
First, humans are visual creatures. This is reflected in the 
large amount of brain tissue that is dedicated to the analy-
sis of images and in the importance of seeing in daily life. 
Second, visual percepts are vivid and rich in informa-
tion. Pictures and movies are highly structured yet easy to 
manipulate using computer-generated graphics. Third, 
many visual illusions, such as binocular rivalry, flash sup-
pression, or motion-induced blindness, directly manipulate 
visual experience while leaving the physical retinal input 
unchanged. Last, and most important, the neuronal basis of 
many visual phenomena and illusions has been investigated 
1108 CONSCIOUSNESS 
throughout the animal kingdom. Perceptual neurOSCIence 
has advanced to the point that reasonably sophisticated com-
putational models have been constructed and have proved 
their worth in guiding experimental agendas and summa-
rizing the data. It is not unlikely that all the different aspects 
of consciousness-smell, pain, vision, self-consciousness, 
the feeling of willing an action, and so on-employ one or 
perhaps a few common mechanisms. Figuring out the neu-
ronal basis for one modality, therefore, will simplifY under-
standing them all. 
Similar to the quest to understand life, discovering and 
characterizing the molecular, biophysical, and neurophysio-
logical operations that constitute the neuronal correlates of 
consciousness will likely help solve the central enigma, how 
events in certain privileged systems can be the physical basis 
of, or even be, feelings. 
With this as background, let me briefly introduce the eight 
chapters. Chalmers summarizes, from the philosopher's 
point of view, the challenges inherent in coming to grips with 
the problem of consciousness. He argues for a science that 
catalogues and quantifies both first-person and third-person 
data and perspectives and shows how one relates to the 
other. Schiff reviews the enabling factors needed for any sen-
sation to occur at all. Persistent vegetative states and minimal 
conscious states are clinical conditions in which affected 
patients are situated at the borderline between unconscious 
and consciousness and in which midline structures in the 
brainstem and thalamus are affected. The next two chap-
ters, by Crick and Koch and by Dehaene and Changeux, 
provide conceptual frameworks and empirical data for think-
ing about the neural basis of consciousness. Coming from 
different directions and traditions (primate electrophysiology 
versus global workspace theory), the two sets of authors 
arrive at broadly similar conclusions, emphasizing uncon-
scious processing, the all-or-none aspects of consciousness, 
interactions among coalitions of neurons that vie for domi-
nance, and the bias exerted on this competition by attention. 
Goodale defends the two visual streams hypothesis: the idea 
that "vision for action" is carried out by the dorsal pathway 
and is quite distinct from the "vision for perception" imple-
mented by the ventral pathway. Whereas the latter is associ-
ated with consciousness, the former can proceed without any 
sensation. This hypothesis explains a great deal of clinical 
data in neurological patients with their otherwise difficult to 
interpret patterns of deficits and retained abilities. Among 
students of the human brain, the most popular tool is 
functional magnetic resonance imaging (fM:RI). The chapter 
by Rees summarizes what has been learned about the neu-
rology of consciousness from fM:RI in normal subjects and 
in patients, with some intriguing discrepancies that need to 
be resolved between the interpretation of human imaging 
data and the results of single-cell studies in monkeys. Split-
brain patients have, historically, been of immense impor-
tance in demonstrating the brain basis of phenomenal expe-
rience, with two conscious minds living in two separate cere-
bral hemispheres within a single skull. Wolford, Miller, and 
Gazzaniga investigate the distinct nature of the sensory and 
more abstract processing in the left and right hemispheres. 
Finally, Wegner and Sparrow study the conscious perception 
of willing an action. The feeling of being responsible for 
some behavior, which forms the cognitive background to 
everything we do throughout the day, can, under laboratory 
conditions, be dissociated from its actual execution. This 
demonstrates that, at least under some conditions, free will 
is illusory. 
Collectively, these studies signal the emergence of a 
science of consciousness, of the ability to investigate how 
phenomenal feelings emerge out of excitable brain matter 
in a rigorous, reliable, and reproducible manner. Needed 
now are invasive experiments that can close the gap between 
correlation and causation. Molecular biology is develop-
ing methods for deliberately, delicately, transiently, and 
reversibly dissecting individual components of forebrain cir-
cuits in mice and monkeys. The applications of such tech-
niques, in combination with simultaneous recordings from 
hundreds and more neurons and functional imaging tech-
niques, will do much to advance toward this goaL 
REFERENCES 
CHALMERS, D. j., 2000. v"nat is a neural correlate of conscious-
ness? In Neural Correlates of Consciousness: Empirical and Conceptual 
Qyestions, T. Metzinger, ed. Cambridge, Mass.: MIT Press, pp. 
17--40. 
CHURCHLAND, P. S., 2002. Brain-Wise: Studies in Neurophilosophy. 
Cambridge, Mass.: MIT Press. 
CRICK, E C., and C. KOCH, 1990. Towards a neurobiological 
theory of consciousness, Semi. Neurosci. 2:263~275. 
GRIFF1N, D. R., 2001. Animal Afinds: Beyond Cognition to Consciousness. 
Chicago: University of Chicago Press. 
KELLER, E. E, 2002. The Century of the Gene. Cambridge, Mass.: 
Harvard University Press. 
METZINGER, ed., 2000. Neural Correlates qf ConscioUS11£ss: Empirical 
and Conceptual (}yestions. Cambridge, Mass.: MIT Press. 
SEAlU;E, J. R., 1997. The Afystcry of Consciousness. New lark Review of 
Books, New York. 
KOCH: I:\iRODUCTIOX 1109 


Introduction [for chapter on Consciousness]

Animal Afinds: Beyond Cognition to Consciousness. Chicago:

Brain-Wise: Studies in Neurophilosophy.

The Afystcry of Consciousness. New lark Review of Books,

The Century of the Gene.

Towards a neurobiological theory of consciousness,

v&quot;nat is a neural correlate of conscious ness?

v&quot;nat is a neural correlate of consciousness?

http://authors.library.caltech.edu/19262/1/Koch2004p10929Cognitive_Neurosciences_Iii_Third_Edition.pdf

Introduction [for chapter on Consciousness]

Abstract

Similar works

Full text

Available Versions

Caltech Authors - Main