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. 2007 Apr;28(4):355-62.
doi: 10.1002/hbm.20282.

Spatiotemporal cortical dynamics underlying abstract and concrete word reading

Rupali P Dhond  1 , Thomas Witzel, Anders M Dale, Eric Halgren
Affiliations

Spatiotemporal cortical dynamics underlying abstract and concrete word reading

Rupali P Dhond et al. Hum Brain Mapp. 2007 Apr.

Abstract

The current study used whole-head anatomically constrained magnetoencephalography (aMEG) to spatiotemporally map brain responses while subjects made abstract/concrete judgments on visually presented words. Both word types evoked a similar posterior-to-anterior sequence of cortical recruitment involving occipital, temporal, parietal, and frontal areas from approximately 100 to 900 ms poststimulus. A prominent left temporofrontal N400m was smaller to abstract words, while the right temporal N400m was smaller to concrete words, suggesting that differences may exist in their semantic representation. The left temporofrontal decrease for abstract words is consistent with EEG studies, indicating a smaller N400 for abstract words based on a more extensive or accessible lexicosemantic network. Furthermore, the N400m peaked at approximately 420 ms and was followed by a large right hemisphere medial occipitoparietal as well as lateral parietal response to concrete words peaking at approximately 550 ms, perhaps embodying imagistic processing. These data suggest that words may be initially understood using a left-lateralized (frontotemporal) verbal-linguistic system that for concrete words is supplemented after a short delay by a right parietal and medial occipital imagistic network.

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Figures

Figure 1
Figure 1
Main sequence of cortical response during abstract and concrete word reading: both word conditions demonstrated similar cortical response patterns beginning with the bilateral visual response at ∼90 ms within occipital cortex (yellow arrow). By ∼135 ms, response moved anteriorly to occipitotemporal regions (left > right, green arrow), and at ∼200 ms was strongest within posterior and lateral temporal cortex (purple arrow). At ∼400 ms, response was strong within ventral and lateral prefrontal regions (left > right) as well as anterolateral temporal cortex (blue arrows) similar to that seen for the N400m [Halgren et al., 2002]. During this time, there was also strong bilateral response within anterior and posterior cingulate areas. Activity was also prominent in bilateral medial occipital cortex. At ∼700 ms, activity remained prominent within anterior frontotemporal and medial occipitoparietal (orange arrows) cortical areas. In the current figure, threshold values are the same for both abstract and concrete words with a minimum significance for response of P < 10−7 and full red indicating a minimum of P < 10−9.
Figure 2
Figure 2
Estimated cortical sources of differential responses to abstract vs. concrete words: significant differences are first seen at ∼ 330 ms poststimulus within left prefrontal, right lateral parietal, medial parietal areas, and right ventral temporal cortex. Differential responses continue to increase (465 ms) and by ∼ 550 ms are strongest within left lateral prefrontal (yellow arrow), left ventral prefrontal (purple arrow), left and right anterior temporal (green arrows), right medial parietal (lower blue arrow), and right lateral parietotemporal areas (upper blue arrow). It is possible that response modulations reflect interhemispheric cooperation between frontotemporal (semantic integration) and right medial/lateral parietal (imagery) networks. In the current figure, the significance threshold for response is P < 10−7 with full red indicating a significance of P < 10−9.
Figure 3
Figure 3
Time courses for selected locations, estimated for concrete (red) and abstract (black) words: the initial response peak at ∼ 135 ms in lateral occipital, ∼ 180 ms in parietal, ∼ 210 ms in temporal, and ∼ 230 ms in frontal cortices (purple arrows), is equal to concrete and abstract words, and is followed by sustained distributed procession in all brain areas. Four phases of differential response are then observed: left frontotemporal peak at ∼ 400 ms, larger to concrete (red arrows, a typical N400m); right anterior temporal, slightly later and with opposite modulation (i.e., larger to abstract words, orange arrow); right parietal, both medial and lateral, as well as medial occipital, later and stronger to concrete words (blue arrows); and a reversed modulation after ∼ 650 ms of the left frontotemporal N400m (green arrows). The scale bars indicate a significance level of P < 10−9.
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