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J Neurosci. 2015 Jun 10;35(23):8768-76. doi: 10.1523/JNEUROSCI.4888-14.2015.

Time-varying effective connectivity during visual object naming as a function of semantic demands.

Author information

1
Department of Biological and Health Psychology, Autonoma University of Madrid, 28049 Madrid, Spain.
2
Centre for Advanced Imaging, Queensland Brain Institute, and Australian Research Centre of Excellence for Integrative Brain Function, The University of Queensland, Brisbane, Queensland 4072 Australia.
3
Department of Basic Psychology, Autonoma University of Madrid, Madrid, Spain.
4
Hospital Ruber Internacional, Epilepsy Unit, Neurology Department, 28034 Madrid, Spain, and University Hospital of San Carlos, Epilepsy Unit, Neurology Department, 28040 Madrid, Spain.
5
Department of Basic Psychology, Autonoma University of Madrid, Madrid, Spain, pablo.campo@uam.es.

Abstract

Accumulating evidence suggests that visual object understanding involves a rapid feedforward sweep, after which subsequent recurrent interactions are necessary. The extent to which recurrence plays a critical role in object processing remains to be determined. Recent studies have demonstrated that recurrent processing is modulated by increasing semantic demands. Differentially from previous studies, we used dynamic causal modeling to model neural activity recorded with magnetoencephalography while 14 healthy humans named two sets of visual objects that differed in the degree of semantic accessing demands, operationalized in terms of the values of basic psycholinguistic variables associated with the presented objects (age of acquisition, frequency, and familiarity). This approach allowed us to estimate the directionality of the causal interactions among brain regions and their associated connectivity strengths. Furthermore, to understand the dynamic nature of connectivity (i.e., the chronnectome; Calhoun et al., 2014) we explored the time-dependent changes of effective connectivity during a period (200-400 ms) where adding semantic-feature information improves modeling and classifying visual objects, at 50 ms increments. First, we observed a graded involvement of backward connections, that became active beyond 200 ms. Second, we found that semantic demands caused a suppressive effect in the backward connection from inferior frontal cortex (IFC) to occipitotemporal cortex over time. These results complement those from previous studies underscoring the role of IFC as a common source of top-down modulation, which drives recurrent interactions with more posterior regions during visual object recognition. Crucially, our study revealed the inhibitory modulation of this interaction in situations that place greater demands on the conceptual system.

KEYWORDS:

dynamic causal modeling; effective connectivity; recurrent interactions; top-down modulation; visual object naming

PMID:
26063911
PMCID:
PMC6605208
DOI:
10.1523/JNEUROSCI.4888-14.2015
[Indexed for MEDLINE]
Free PMC Article

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