Concurrent brain-stimulation and neuroimaging for studies of cognition

doi:10.1016/j.tics.2009.04.007

Trends in Cognitive Sciences

Volume 13, Issue 7, July 2009, Pages 319-327

https://doi.org/10.1016/j.tics.2009.04.007 Get rights and content

Neuroimaging can address activity across the entire brain in relation to cognition, but is typically correlative rather than causal. Brain stimulation can target a local brain area causally, but without revealing the entire network affected. Combining brain stimulation with concurrent neuroimaging allows a new causal approach to how interplay between extended networks of brain regions can support cognition. Brain stimulation does not affect only the targeted local region but also activity in remote interconnected regions. These remote effects depend on cognitive factors (e.g. task-condition), revealing dynamic changes in interplay between brain areas. We illustrate this with examples from top-down modulation of visual cortex, response-competition, inter-hemispheric rivalry and motor tasks; but the new approach should be applicable to many domains of cognition.

Section snippets

Introduction: causal roles for specific brain regions within extended networks in support of cognition

Cognitive functions are supported by functionally specialized brain areas that each participate in extended brain networks. A new challenge is to understand the causal contributions that specific brain regions make to the networks in which they participate. Addressing this challenge will require new methods.

Traditional neuropsychological or lesion studies often attributed a single specific function to a given brain area, as if such areas operated in isolation. We call this the ‘regional’

Concurrent TMS–fMRI reveals remote effects of brain stimulation

fMRI and TMS are now routinely used separately, but typically for rather different purposes. fMRI has the virtue that extended functional networks can be visualized across the entire brain, whereas TMS can be used to target a specific region (if near enough the scalp) with an intervention. Combining these two methods concurrently can thus bring a new causal dimension into neuroimaging, allowing study of how ‘intervention’ at a targeted region (with TMS) can influence neural activity (assessed

Concurrent TMS–EEG also reveals remote effects of brain stimulation

TMS in human studies can also be combined with concurrent EEG recordings, to study possible remote effects with temporal precision. Again there are technical issues to overcome, but these are surmountable 13, 14. One illustrative study [15] again shows FEF influences on visual processing. Right FEF–TMS was found to modulate visually evoked negativities at posterior electrodes, starting from ∼200 ms after visual onset, and likely to reflect activity within occipital or parieto-occipital visual

State-dependence of remote effects in concurrent TMS–EEG

The examples so far illustrate that brain stimulation does not solely have local impacts on the targeted region, but can also affect activity in remote but interconnected regions (as for the case of visual cortex, assessed with occipital BOLD or EEG, after FEF–TMS or indeed microstimulation). We turn now to the further point that the remote effects of TMS can vary in a ‘state-dependent’ manner. ‘State’ in this context can refer to levels of wakefulness etc; or to contrasts between particular

State-dependence of remote effects in concurrent TMS–fMRI

Analogously to the aforementioned TMS–EEG work, recent concurrent TMS–fMRI studies also illustrate that remote effects of brain stimulation can be highly state-dependent. Bestmann et al.[22] found remote effects of PMd–TMS that differed qualitatively between the context of an active motor task versus rest. They tested a pre-existing hypothesis about possible ‘inter-hemispheric’ influences; namely, that left premotor cortex can have increased driving influence over motor regions in the opposite

Concluding remarks

Recent studies have established new methodological combinations of brain stimulation applied concurrently with neural measures (see Box 2 for non-concurrent combinations). This introduces a causal (i.e. interventional) dimension into non-invasive neuroimaging, thereby allowing direct study of remote influences upon interconnected regions. This opens up a new terrain for research on the brain basis of cognition, in terms of inter-regional influences within networks. Existing studies already

Acknowledgements

Our research was funded in London and Leuven by the European Commission, 7th Framework Programme (BrainSync: HEALTH-F2–2008–200728) and in London by the Wellcome Trust and the Medical Research Council.

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Trends in Cognitive Sciences

ReviewConcurrent brain-stimulation and neuroimaging for studies of cognition

Section snippets

Introduction: causal roles for specific brain regions within extended networks in support of cognition

Concurrent TMS–fMRI reveals remote effects of brain stimulation

Concurrent TMS–EEG also reveals remote effects of brain stimulation

State-dependence of remote effects in concurrent TMS–EEG

State-dependence of remote effects in concurrent TMS–fMRI

Concluding remarks

Acknowledgements

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Neuroimage

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Clin. Neurophysiol.

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Trends Neurosci.

Concurrent TMS and functional magnetic resonance imaging: methods and current advances

Control of goal-directed and stimulus-driven attention in the brain

Nat. Rev. Neurosci.

Selective gating of visual signals by microstimulation of frontal cortex

Nature

Rapid enhancement of visual cortical response discriminability by microstimulation of the frontal eye field

Proc. Natl. Acad. Sci. U. S. A.

Bottom-up dependent gating of frontal signals in early visual cortex

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Microstimulation of the frontal eye field and its effects on covert spatial attention

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Review
Concurrent brain-stimulation and neuroimaging for studies of cognition