HIGHLIGHTS
NATURE REVIEWS | NEUROSCIENCE VOLUME 4 | FEBRUARY 2003 | 85
HIGHLIGHT ADVISORS
NANCY ANDREASEN
UNIVERSITY OF IOWA, IA, USA
ALLAN BASBAUM
UNIVERSITY OF CALIFORNIA
SAN FRANCISCO, CA, USA
RANDY BUCKNER
WASHINGTON UNIVERSITY,
MO, USA
DAVID CLAPHAM
HARVARD MEDICAL SCHOOL,
MA, USA
PIETRO DE CAMILLI
YALE UNIVERSITY SCHOOL OF
MEDICINE, CT, USA
BARRY EVERITT
UNIVERSITY OF CAMBRIDGE,
UK
GORDON FISHELL
SKIRBALL INSTITUTE, NY, USA
MARY KENNEDY
CALIFORNIA INSTITUTE OF
TECHNOLOGY, CA, USA
LYNN NADEL
UNIVERSITY OF ARIZONA,
AZ, USA
DENNIS O'LEARY
THE SALK INSTITUTE, CA, USA
TERRY SEJNOWSKI
THE SALK INSTITUTE, CA, USA
WOLF SINGER
MAX-PLANCK-INSTITUT FÜR
HIRNFORSCHUNG, GERMANY
CLAUDIO STERN
UNIVERSITY COLLEGE LONDON,
UK
PATRICK TAM
CHILDREN'S MEDICAL
RESEARCH INSTITUTE, SYDNEY,
AUSTRALIA
RICHARD W. TSIEN
STANFORD UNIVERSITY
SCHOOL OF MEDICINE, CA, USA
RAFAEL YUSTE
COLUMBIA UNIVERSITY, NY, USA
Although functional imaging and
electrophysiology have given us a
good idea of which brain areas are
important for cross-modal binding
-- linking together information from
different sensory modalities, such
as sight and sound, that comes from
the same stimulus -- just how these
brain areas bind sensory inputs
together is unknown. A new study
from Bushara and colleagues does
not completely answer this question,
but it does use a clever trick to give us
some more clues.
One of the problems with studying
binding is that it is hard to be sure that
neural activity is associated specifically
with the process of binding rather
than arising passively as a result of the
co-occurrence of two stimuli.Bushara
et al. used a task that dissociates these
two effects. They showed subjects a
screen on which two bars are seen to
move towards each other,then to cross
and continue moving.Usually people
perceive the two bars as crossing over
each other,but on a small number of
trials the two bars will appear to col-
lide and then bounce back towards
their points of origin. If a `collision'
sound is played at the point of overlap,
the perception of a collision becomes
more likely.
The authors reasoned that,for the
sound to influence the visual percep-
tion of the two bars,the auditory and
visual stimuli must be bound in the
brain. But if the sound is played and
the subject does not see the collision,
the stimuli were probably not bound.
By asking subjects to report their
perception, Bushara and colleagues
could compare these two types of trial,
in which the presented stimuli were
identical but the perception -- and
thereforethebindingstate--differed.
Functional magnetic resonance
imaging (fMRI) showed that activity
in `multimodal' areas such as the
superior colliculus and parietal cortex
was higher when binding occurred
and the subject saw a collision. More
interestingly, activity in unimodal
areas such as the occipital (visual) and
temporal (auditory) cortex was lower
during these trials than during trials
in which binding did not occur. This
finding was unexpected, as attention
influences perception and increased
attention to a stimulus would be
expected to increase neural activity in
sensory areas of cortex.
The authors propose that there is a
reciprocal, competitive interaction
between unimodal sensory areas and
the multimodal areas that mediate
binding. According to this view, the
interaction between these areas,rather
than a top­down,one-way influence
of multimodal cortex on unimodal
cortex, would lead to stimuli being
perceived as bound or unbound.This
kind of behavioural task should allow
more insight into the processes that
are involved in binding,particularly if
it can be extended to nonhuman pri-
mates for electrophysiological studies.
Rachel Jones
References and links
ORIGINAL RESEARCH PAPER Bushara, K. O.
et al. Neural correlates of cross-modal binding.
Nature Neurosci. 23 December 2002
(doi: 10.1038/nn993)
FURTHER READING Robertson, L. C. Binding,
spatial attention and perceptual awareness.
Nature Rev. Neurosci. 4, 93­102 (2003)
WEB SITE
Hallett's lab:
http://intra.ninds.nih.gov/Lab.asp?Org_ID=72
Sight and sound collide
FU NCTIONAL N E U ROI MAG I NG