Address for correspondence: Max Planck Institute for Brain Research, Deutschordenstr. 46, 60528 Frankfurt am Main, Germany. Voice: ++49-(0)69-96769-218.
singer{at}mpih-frankfurt.mpg.de
It is proposed that phenomenal awareness, the ability to be
aware of one's sensations and feelings, emerges from the capacity
of evolved brains to analyze their own cognitive processes by
iterating and reapplying on themselves the very same cortical
operations that they use for the interpretation of signals from
the outer world. Search for the neuronal substrate of awareness
therefore converges with the search for the cognitive mechanisms
through which brains analyze their environment. The hypothesis
is put forward that the mammalian brain generates continuously
highly dynamic states that, when modulated by input signals,
rapidly converge towards points of transient stability that
correspond to the respective input constellation. It is proposed
that these states are characterized by the dynamic binding of
feature-specific cells into functionally coherent cell assemblies
which as a whole represent the constellation of features defining
a particular perceptual object. Arguments are presented that
favor the notion that the cognitive operations supporting awareness
consist of an iteration of such dynamic binding processes which
then lead to the formation of higher-order assemblies that correspond
to the contents of conscious awareness. Experimental data are
reviewed relating to the questions of how assemblies are formed
and which signatures define the relations among the responses
of distributed neurons. It is argued that assemblies self-organize
through reciprocal interactions of neurons coupled by reentrant
loops and that the signature of relatedness consists of the
transient synchronization of the discharges of the respective
neurons. Evidence is presented that these synchronization phenomena
depend on the same state variables as awareness: Both require
for their manifestation activated brain states characterized
by desynchronized EEGs. It is concluded that phenomenal awareness
is amenable to neurobiological reductionism; but it is also
proposed that self-consciousness requires a different explanatory
approach because it emerges from the dialogue between different
brains and hence has the quality of a cultural construct.
