synchronous activity within and between areas v4 and fef in attention steve gotts laboratory of...
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Synchronous activity within and between areas V4 and FEF in attention
Steve GottsLaboratory of Brain and Cognition
NIMH, NIH
with: Georgia Gregoriou, Hui Hui Zhou,and Bob Desimone
Visual Selective Attention:
The ability to monitor an object or location selectively in a crowded visual scene
CueBiased Competition Theory (Desimone & Duncan, 1995):
Multiple visual stimuli activate competing populations of neurons in visual cortex ("bottom up") Attention biases this competition in favor of the attended stimulus ("top down")
V1
PG
TE
PFC
V4
TE
V1
PFC
Attention and Extrastriate Cortex:
Attentional modulation of neural responses is observed in extrastriate cortical regions such as V4 (e.g. Moran & Desimone, 1985; Fries, Reynolds, Rorie, & Desimone, 2001)
Extrastriate lesions produce attentional deficits when salient distractors are present (e.g. De Weerd, Peralta, Desimone, & Ungerleider, 1999)
Good Stimulus
Pair
Time (ms)
RFFixation
Good Stimulus Poor Stimulus Pair
Spi
kes
per
seco
nd
100 200 3000
80
0
20
40
60
Sp
ike
s p
er s
eco
nd
Poor Stimulus
Reynolds et al., 1999
Good Stimulus
Pair
Time (ms)
RFFixation
Good Stimulus Poor Stimulus Attend Good
Spi
kes
per
seco
nd
100 200 3000
80
0
20
40
60
Sp
ike
s p
er s
eco
nd
Poor Stimulus
Reynolds et al., 1999
Attend Good
Good Stimulus
Pair
Time (ms)
RFFixation
Good Stimulus Poor Stimulus Attend Poor
Spi
kes
per
seco
nd
100 200 3000
80
0
20
40
60
Sp
ike
s p
er s
eco
nd
Poor Stimulus
Reynolds et al., 1999
Attend Poor
Fries, Reynolds, Rorie, and Desimone (Science, 2001)
Attentional Modulation of Neural Synchrony in Area V4
What is the source of the "top down" attentional bias inextrastriate neurons ?
One possibility (among several) is prefrontal cortex (PFC), whichis thought to play a central role in cognitive control, executive function,and working memory:
• Feedback to temporal and parietal regions, which in turn feedback to extrastriate• Imaging studies of selective attention in humans commonly show PFC activation• Lesions of PFC in humans result in a variety of attentional deficits
• Rossi et al.: lesions to PFC in monkeys produces an impairment in switching top-down control
Stimulation of FEF influences activity in V4:
Moore & Armstrong (2003) Moore & Fallah (2004)
Interaction between areas FEF and V4 in attention
Record from V4 and FEF simultaneously during visual selection
Measure time course of changes in firing rate and synchrony both within and between regions
V4
TE
V1
FEF
FEF implicated in visual attention in monkeys and humans:
Corbetta & Shulman (2002) Moore & Fallah (2001) Schall (2004)
Task:
Monitor stimulus that matches cue for a color change, ignoring changes in distractors
Stimuli: Oriented, drifting, sinusoidal gratings (R,G,B) at 50 eccentricity
Cue: Random cue onset, ranging from 1 sec before stimulus onset to 1 sec after Cue color chosen randomly for each trial
Targets: change between 250 ms and 3 sec post-cue (or post-stim)
Distractors: 0, 1, or 2 might change
Fixation: 0 – 500 ms
Cue before stimuli:
Cue on: 500 – 1500 ms Stimuli on: 1500 msTarget change:
250-3000 ms post-stimuli
Fixation: 0 – 1500 ms
Stimuli before cue:
Stimuli on: 1500 msTarget change:
250-3000 ms post-cueCue on: 1500 – 2500 ms
Effect of attention on firing rates
FEF (N=30 MUs)
V4 (N=31 MUs)
Cue before stim Cue after stim
Distribution of FR separation times (targets vs distractors)
Cue before stim
Cue after stim
Effect of attention on spike-LFP coherence
Spikes in V4, LFP in V4 (different electrodes)
Effect of attention on spike-LFP coherence (cont.)
Spikes in FEF, LFP in FEF (different electrodes)
Effect of attention on coherence across regions
Spikes in FEF, LFP in V4
Spikes in V4, LFP in FEF
Effect of attention on coherence across regions (cont.)
Effect of attention on V4-FEF phase relationshipsWithin-region Between-region
Spike-triggered average (STA) of LFP
STAs band-pass filtered 35-80 Hz
Results:
~ Synchrony within regions
Phase-shift of 10 ms between regions
Distribution of gamma phase across electrode pairs
Within-region Between-region
Time course of coherence: spikes in FEF, LFP in FEF
Time course of coherence: spikes in V4, LFP in V4
Time course of coherence: spikes in FEF, LFP in V4
Time course of coherence: spikes in V4, LFP in FEF