CONSCIOUSNESS

2. Neuroscience 115
2.15 Specific brain areas
145 Two Legs, Two Arms, One Head. Who am I? H. Henrik Ehrsson (Department of Neuroscience, Karolinska Institutet, Stockholm, Sweden)
Ask any child if his hands belong to him and the answer will be “Of course!” But how
does the brain actually identify its own body? In this talk I will describe how cognitive neuroscientists
have recently begun to address this fundamental question. It has been known for
some time that patients with damage to their premotor or parietal lobes can fail to recognize
their own limbs (e.g. after stroke). This suggests that these brain regions are involved in
generating a sense of body ownership, but says nothing about how this is achieved. In my
presentation I will present experiments that suggest that multisensory mechanisms are crucial
for how we come to experience that we own our body. The hypothesis is that parts of the
body are distinguished from the external world by the patterns they produce of correlated
information from different sensory modalities (vision, touch and muscle sense). These correlations
are hypothesized to be detected by neuronal populations that integrate multisensory
information from the space near the body. We have recently used a combination of functional
magnetic resonance imaging and human behavioral experiments to test these predictions. To
change the feeling of body ownership, perceptual illusions were used where healthy individuals
experienced that a rubber hand was their own, that a mannequin was their body, or, that
they are outside their physical body and inside the body of other individual. Our behavioral
results demonstrate that ownership of limbs and entire bodies depend on the temporal and
spatial congruency of visual, tactile and proprioceptive signals in body-centered reference
frames, and that the visual information from first person perspective plays a crucial role. Our
imaging data show that neuronal populations in the premotor and intraparietal cortex are active
when humans sense they own limbs, which supports the hypothesis that the integration of
multisensory information in body-centered coordinates is crucial for ownership. These results
are of fundamental importance because they identify the brain mechanisms that produce the
feeling of ownership of one’s entire body. By clarifying how the normal brain produces a
sense of body ownership, we can learn to project ownership onto artificial bodies and simulated
virtual ones; and even make two people have the experience of swapping bodies with
one another. This could have ground-breaking applications in the fields of virtual reality and
neuro-prosthetics. PL3
2.16 Miscellaneous
146 A Systems Model for Selectivity Between Default and Task Modes Kevin Brown,
Jonathan Smallwood; Jonathan W. Schooler; Jean M. Carlson
(Physics, University of California Santa Barbara, Santa Barbara, CA)
Neuroimaging data suggests that the human brain has at least two attentional states - a
task-focused mode in which attention is focused externally on the task at hand and a less
constrained internal mode dubbed the default state. An essential step to understanding the
distinct processes governed by these different states is to understand the way in which the
brain divides finite cognitive resources and selects among externally- and internally-driven
goal states. We present a coarse-grained, systems-level dynamical model which explores the
temporal nature of the interaction between these different modes, in which we examine the
role of the locus coeruleus in modulating between external events and internally generated
signals. We discuss the implications of the model for understanding mindwandering and attentional
failures, which we characterize as partitioning of cognitive effort away from externallydriven
tasks to internally-generated ones. We also discuss the potential of directly fitting the
dynamical model to multimodal dynamical measurements (surface EEG, BOLD fMRI and
pupillometry data). C3