Neural synchrony and selective attention
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Desimone, R. “Neural synchrony and selective attention.” Neural
Networks, 2009. IJCNN 2009. International Joint Conference on.
2009. 683-684. © 2009 IEEE
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http://dx.doi.org/10.1109/IJCNN.2009.5179097
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Proceedings of International Joint Conference on Neural Networks, Atlanta, Georgia, USA, June 14-19, 2009
Neural Synchrony and Selective Attention
Robert Desimone
Abstract- A complex visual scene will typically contain
many different objects, few of which are currently relevant to
behavior. Thus, attentional mechanisms are needed to select
the relevant objects from the scene and to reject the irrelevant
ones. Neurophysiological studies in monkeys have identified
some of the neural mechanisms of attentional selection within
the ventral, "object recognition", stream of the cortex, which
begins with area VI and continues through areas V2, V4, and
IT cortex. At each stage along this stream, attended, or
behaviorally relevant, stim uli are processed preferentially
compared to irrelevant distracters. The source of the
attentional feedback to visual cortex seems to originate in
parietal and prefrontal cortex. We proposed some years ago
that this attentional feedback biased competitive interactions
among neurons in visual cortex, in favor of neuronal responses
to the most behaviorally relevant stimulus. More recent work
indicates that these competitive interactions are one aspect of a
more general visual mechanism for contrast normalization,
which is present in most or all visual areas. By providing the
appropriate input to this normalization mechanism, feedback
from parietal and prefrontal cortex appears to shift the balance
of visual cortical responses towards the attended stimulus.
I. NEURAL SYNCHRONY AND SELECTIVE ATTENTION
A
complex visual scene will typically contain many
different objects, few of which are currently relevant to
behavior. Thus, attentional mechanisms are needed to
select the relevant objects from the scene and to reject the
irrelevant ones.
Neurophysiological studies in monkeys
have identified some of the neural mechanisms of attentional
selection within the ventral, "object recognition", stream of
the cortex, which begins with area V1 and continues through
areas V2, V4, and IT cortex (Moran and Desimone 1985;
Reynolds, Pasternak et al. 2000; Chelazzi, Miller et al. 2001;
Reynolds and Desimone 2003). At each stage along this
stream, attended, or behaviorally relevant, stimuli are
processed preferentially compared to irrelevant distracters.
The source of the attentional feedback to visual cortex seems
to originate in parietal and prefrontal cortex. We proposed
some years ago that this attentional feedback biased
competitive interactions among neurons in visual cortex, in
favor of neuronal responses to the most behaviorally
relevant stimulus (Desimone and Duncan 1995). More
recent work (Reynolds and Heeger 2009) indicates that these
competitive interactions are one aspect of a more general
visual mechanism for contrast normalization, which is
present in most or all visual areas. By providing the
appropriate input to this normalization mechanism, feedback
Manuscript received March 30, 2009. Robert Desimone Ph.D., is Doris
and Don Berkey Professor of Neuroscience, Director,
McGovern
Institute for Brain Research at MIT, USA.
978-1-4244-3553-1/09/$25.00 ©2009 IEEE
from parietal and prefrontal cortex appears to shift the
balance of visual cortical responses towards the attended
stimulus.
In recent years, we have focused on the detailed
mechanisms by which the attentional feedback affects cells
in visual cortex. Our work has suggested that the attentional
bias is mediated, at least in part, in visual cortex through an
increase in high-frequency (gamma) synchronization of
neurons carrying critical information about the location or
features of the behaviorally relevant stimulus (Fries,
Reynolds et al. 2001; Liang, Bressler et al. 2003; Fries,
Womelsdorf et al. 2008). Increases in gamma synchrony
are found during both spatial attention and featural attention
engaged during visual search (Bichot, Rossi et al. 2005), and
the presence of synchrony in visual cortex predicts faster
responses in visual tasks (Womelsdorf, Fries et al. 2006).
Recent evidence shows that inputs from the frontal eye
fields (FEF) in prefrontal cortex initiates coupled gammafrequency oscillations between FEF and area V4 in the
ventral stream during attention, and these oscillations are
phase, or time-shifted to allow for conduction and synaptic
delays between the two areas, thereby achieving maximally
effective communication(Gregoriou, Gotts et al. 2009).
Attentional effects in V2 and VI, which are earlier stages in
the ventral stream, occur later in V4, suggesting that
attentional feedback works in a "backwards", step by step
through the ventral stream.
Our unpublished human
experiments using magnetoencephalograpy (MEG) show
results that are remarkably similar to that found in animals.
Specifically, with attention, neural activity in visual cortex
becomes synchronized with that in the prefrontal and
parietal cortex, which a phase shift that seems to allow for
the necessary conduction and synaptic delays. Cross-area
synchrony may be a general mechanism for regulating
information flow through the brain (Buschman and Miller
2007; Saalmann, Pigarev et al. 2007; Lakatos, Karmos et al.
2008) and for regulating spike-timing dependent plasticity.
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