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

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per

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nd

100 200 3000

80

0

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Sp

ike

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Poor Stimulus

Reynolds et al., 1999

Good Stimulus

Pair

Time (ms)

RFFixation

Good Stimulus Poor Stimulus Attend Good

Spi

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per

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100 200 3000

80

0

20

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Sp

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Poor Stimulus

Reynolds et al., 1999

Attend Good

Good Stimulus

Pair

Time (ms)

RFFixation

Good Stimulus Poor Stimulus Attend Poor

Spi

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per

seco

nd

100 200 3000

80

0

20

40

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Sp

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s p

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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