From: L' Ermit (lhermit@hotmail.com)
Date: Sat Mar 02 2002 - 10:41:51 MST
Nature Reviews Neuroscience 3, 215 -229 (2002) March 2002 Vol 3 No 3
CONTROL OF GOAL-DIRECTED AND STIMULUS-DRIVEN ATTENTION IN THE BRAIN
Maurizio Corbetta & Gordon L. Shulman
Preface
We review evidence for partially segregated networks of brain areas that
carry out different attentional functions. One system, which includes parts
of the intraparietal cortex and superior frontal cortex, is involved in
preparing and applying goal-directed (top-down) selection for stimuli and
responses. This system is also modulated by the detection of stimuli. The
other system, which includes the temporoparietal cortex and inferior frontal
cortex, and is largely lateralized to the right hemisphere, is not involved
in top-down selection. Instead, this system is specialized for the detection
of behaviourally relevant stimuli, particularly when they are salient or
unexpected. This ventral frontoparietal network works as a 'circuit breaker'
for the dorsal system, directing attention to salient events. Both
attentional systems interact during normal vision, and both are disrupted in
unilateral spatial neglect.
Summary
This review proposes that two networks of brain areas are involved in
controlling attention. One network is primarily responsible for applying
cognitive, top-down selection for stimuli and responses, whereas the other
detects behaviourally relevant stimuli and might act as a 'circuit breaker'
for the first system.
Humans use cognitive information to direct attention to relevant objects
(targets) in a visual scene. Information such as the target's colour or
location is represented as a 'perceptual set'. Similarly, advance
information about the required response to a target is represented as a
'motor set'. These can be considered together as an 'attentional set', which
aids the detection of and response to targets.
Such top-down control of attentional processes activates dorsal posterior
parietal and frontal regions of the brain bilaterally in both monkeys and
humans. This dorsal frontoparietal system is responsible for the generation
of attentional sets.
Attention can also be driven by stimulus properties rather than cognitive
processes. This 'bottom-up' control of attention explains why we find
ourselves drawn to 'oddball' stimuli that are very different from the
background, or to salient stimuli that share some sensory features, such as
colour, with the target for which we are searching. The dorsal
frontoparietal system seems to maintain a 'salience map' that combines
bottom-up with top-down information during visual search.
Potentially important sensory stimuli, such as loud alarms or sudden
movement, can attract our attention regardless of the ongoing task. This
sensory orienting process seems to be mediated by the second attentional
network, which is mainly lateralized to the right side of the brain and
includes the temporoparietal junction and the ventral frontal cortex. This
network seems to interrupt ongoing cognitive activity when a stimulus that
might be behaviourally important is detected.
These two networks could interact in humans to control attention. It is
possible that damage to these networks is responsible for the syndrome of
neglect, in which patients that have suffered damage to the right side of
the brain tend to ignore stimuli on the left side of space. The authors
suggest that neglect results from damage to the ventral network that also
'functionally inactivates' the dorsal network.
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