Doesburg Gamma Attention 2007

Jun 22, 2010 12:56 PM  Note;  FULL PDF is free and online!!  Link to this on my website.

Sam DOESBURG ...  Lawrence WARD  at  UBC  Vancouver

in Cereb Cortex  2007  sent to me by Bernie on April 22 2010.  Key Paper!

Read Intro...  cites all the evidence supporting gamma in binding features and

in binding the whole consc field.

(Advanced access was June 2007;  published Feb 2008)

I looked for a list of online pubs by Sam Doesburg (he is a post-doc at UBC and by

Lawrence Ward (prin investigaotr) ... no list of online pubs for either)  but

THIS paper is online and free and it is great!

(see enclosed link)

Explaining the emergence of a coherent conscious percept and an

intentional agent from the activity of distributed neurons is key to

understanding how the brain produces higher cognitive processes.

Gamma-band synchronization has been proposed to be a mechanism

for the functional integration of neural populations that together

form a transitory, large-scale, task- and/or percept-speciﬁc net-work. 

The operation of this mechanism in the context of attention orienting

entails that cortical regions representing attended locations should

show more gamma-band synchronization with other

cortical areas than would those representing unattended locations.

This increased synchronization should be apparent in the same time

frame as that of the deployment of attention to a particular location

In order to observe this effect, we made electroencephalogram

recordings while subjects attended to one side or the other of the

visual ﬁeld (which we conﬁrmed by event-related potential

analysis) and calculated phase-locking statistics between the

signals recorded at relevant electrode pairs. We observed increased

gamma-band phase synchronization between visual cortex

contralateral to the attended location and other, widespread,

cortical areas approximately 240--380 ms after the directional cue

was presented, conﬁrming the prediction of a large-scale gamma

synchronous network oriented to the cued location.

page 1 (of 11)

Performance of the myriad perceptual and cognitive processes

of which the brain is capable requires transient functional

coupling, and subsequent decoupling, of speciﬁc, task-relevant,

neural populations. Gamma-band synchronization is a plausible

mechanism for the selection and integration of such neuronal

groups (e.g., Varela et al. 2001). Direct brain recordings show

that increased gamma-band synchronization within a cortical

area occurs most strongly between columns representing

information that is being integrated, for example, between

columns representing features of a common object

(Gray and Singer 1989; Gray et al. 1989; Engel, Kreiter et al. 1991).

Stimulus-speciﬁc gamma synchronization has been observed

between monkey V1 and V2, between V1 and extrastriate

motion areas, and between left and right hemisphere V1s of cats

(Engel, Konig, and Singer 1991; Engel, Konig et al. 1991; Frein et al. 1994). 

The summation of such gamma synchronous                                CLEAR= consc, learning, expectation, attn, resonance.

activation yields increased gamma-band power in the electro-            (from Grossberg:  R= recognition or resonance)

encephalogram (EEG) and has been experimentally linked to

a wide range of cognitive processes including attention,

learning, and memory and visual and auditory perception

(Ward 2003; Kaiser and Lutzenberger 2005).

LONG_RANGE Gamma Synchrony between task-relevant brain areas is also seen

during associative learning, mental rotation, conscious recol-

lection, visual working memory, and coherent perception

(Tallon-Baudry et al. 1998; Miltner et al. 1999; Rodriguez et al.

1999; Bhattacharya et al. 2001; Burgess and Ali 2002; Gruber

et al. 2002). 

Such results support the hypothesis that gamma-

band synchronization enables the selective activation of a func-

tionally coupled ensemble of neuronal groups relevant for the

performance of a particular task and for binding the features of

an object into a uniﬁed percept (Engel and Singer 2001; Varela

the allocation of attention to one location 

results in  advantages being given to stimuli

appearing at that location, relative to unattended

locations. Speciﬁcally, attended stimuli are promoted for pro-

cessing in cortical regions responsible for higher cognition and

are biased for inclusion in consciousness, a highly integrated

yet, apparently, anatomically distributed state (Treisman 1996;

and Tononi

page 2 (of 11)

cortical areas representing attended loci must be biased for

inclusion in a large-scale functional network to support the

enhanced feature binding, higher processing, and propensity for

conscious experience that stimuli appearing at such a locus of

attention are known to receive. We hypothesized that long-

range gamma-band synchronization mediates this transient

functional network, enabling the increased communication

between cortical areas representing attended loci and other

diverse cortical regions and creating a preparatory network for

the enhanced processing of attended stimuli.

We recorded EEG while subjects were engaged in a covert attention-orienting task.

Our a priori hypothses:  attention deployed to one side of visual space,

electrodes in contralateral visual cortex would show incr. gamma sych withother

wide-spread areas,  indexing the establishment of the predicted long-range gamma synch attentional network.

METHODS

13 adults (8 males)  mean age was 19.4 years

maintain fixation on the plus sign in the middle of the screen.

An arrow would appear at the center, replacing the fixation plus to

instruct S to COVERTLY attend to a box either to the L or the R.

Arrow was there for 100 ms.  (fixation point was 1.3 degr)

targets were presented in boxes (2 degr on a side)

target was either a + or a X.

S was instructed to press the button is they detected a + but NOT an X

at the cued location and NO response if either stim appeared in the uncued loaction.

Paradigm was selected from an earlier study that showed incr local power with spatial selection attn.

EEG  59 electrodes.  scalp;

band-pas filterd btwn 0.1 and 100 hz

Synchrony analysis:

Epochs of analyssis began 400 ms before til 1200 ms after the cue.

they deleted epochs in which there were ocular or nonocular artifacts.

DISCUSSION page 6

Cue-directed deployment of attention to one side of the visual field, confirmed by ERP,

coincides with incr. in gamma pahse synchronization btwn the contralateral 

visual cortex and widespread areas.  Our results support the view that

gamma-band synch IS the MECH that implements

1) selective properties of attention (biasing certain neuronal groups for inclusion in the network

2) its integrative properties  (when neurons corresponding to attended objects' features are included in a long-range network they are MORE INTEGRATED

 with other percetpual and cognitive resp and

3) the special relation btwn attention and conscious executive processes

(inclusion is equivalent to inclusion in a 

GLOBAL CONSCIOUS WORKSPACE allowing cognitive and behavioral operations,

informed by goals and context.

(see eg  Dahaene and Naccache 2001).

Synchronously oscillating neurons can perform such integration because they communicate more effectiely than do nonsynchronous neurons.

Bursts of action potentials from a sending neuron must be consistently received during the depolarized phase

of a target neuron's membrane potential flucturation in order for those action potentials to be efficacious, 

and this happends whent he sending and receivng neuons are phase locked  (Fries 2005).

What is still mysterious is how and why synchronization in the various freq. bands plays the role it does.

Our results on relation btwn local and long-range synch in alpha, beta, gamma bands begin to address the Q. 

<<Bernie Baars highlights the following  paragraph in the copy he sent me.  Pure Dynamite!!!>>

Gamma-Band Phase Synchronization

The selection and integration of information into a large-scale complex

that extends across brain areas has been posited to BE consciousness (Tononi 2004).

We propose that the selection of certain neuronal groups

for integration into a large-scale gamma synchronous network

accounts for how selective attention

enables the increased integration of attended information,

relative to unattended information, within and across sensory

modalities and biases attended information for higher process-

ing and entry into consciousness (cf., Lamme 2003; Koch and

Tsuchiya 2006). 

In this view, the emergence of a dynamic executive consciousness

within the brain may result from

a large-scale gamma-synchronous network of task-relevant

neural populations. This IMPLEMENTS functional integration

and serves to activate a speciﬁc network from a large repertoire

of possible networks.

The REPRESENTATIONAL CONTENTS of neural groups included

in this coherently oscillating network DEFINE

the CONTENT of consciousness and are dynamically assigned

according to task demands, perceptual input, and motor output

(Varela et al. 2001).

page 7

Alpha-Band Amplitude Reduction

page (v last para)

A striking temporal correspondence is evidence between the

early, bilateral but unequal DECREASE of LOCAL  ALPHA,

the similar (page 8) but unequal INCREASE of LOCAL GAMMA

and the FIRST BURST of lateralized GAMMA phase synchronization:

all these effects were maximal about 300 ms  after cue onset.

This suggests that the activities of oscillatory mechanisms 

in multiple frequency bands interact across local and long-distance scales

to enable selective visuo-spatial attention..  Specifically we propose that

local alpha-band activity reflects suppression of a cortical area,

local gamma reflects active processing in an area, and

long range gamma synch establishes a transient network

 that promotes transfer of info appearing at attended locations. 

from the relevant modality-specific area to other regions.

(see Ward 2003)

The lateralization effect is more complex, though.

When cortical tissue is engaged in long-range gamma synch assembly,

increased columnare selection and segration occur locally, leading to relatively

lower gamma and relatively higher alpha as comparatively

restricted set of columns are engaged in active prcoessing.

so,  40 hz stimulation leades to incr focal responses (intercolumnar inhibition)  whereas

10 hz stimulatin propagates to other cortical areas (Llinas 98).

... suggests that an an alpha oscillatory mechanism involving local desynchronization and

long-range synchronization is responsible for the maintenance of selective attention.

page 8:  Beta-Band Attention Network

some evidence supports a separate beta synchronous network that is

generally relevant for attentional deployment and that it operates

in tandem with gamma oscillations.

The beta-band implements general attention preparation and the gamma networks selects

task-relevant neural populations and integrates them into a a transient functional network.

Doesburg Gamma Attention 2007

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