Time Modulated Prefrontal and Parietal Activity during the Maintenance of Integrated Information as Revealed by Magnetoencephalography

Abstract

Using magnetoencephalography, we investigated the spatiotemporal patterns of brain magnetic activity responsible for maintaining verbal and spatial information in either an integrated or an unintegrated fashion. Considering time dimension, we noted a greater activation of a fronto-parietal network in early latencies during the maintenance of integrated information, and a different pattern during the maintenance of unintegrated material, showing a greater activation in a fronto-posterior network in late latencies. The greater activation found in certain areas which are traditionally reported as being engaged in spatial working memory (i.e. superior frontal gyri, dorsolateral prefrontal cortex, superior and inferior parietal lobes) when subjects maintained integrated information could be explained by a greater weight of the spatial dimension. It is as if words somehow acquired a spatial attribute, thus exerting a greater load in a neural network specialized in spatial working memory. Alternatively, and not mutually exclusive, we also propose that during the maintenance of integrated information the allocation of cognitive resources is less interfering than during the maintenance of unintegrated information, making it easier.

Oscillatory activity in prefrontal and posterior regions during implicit letter-location binding

“…No such binding effect was expected when location was the relevant feature, however. Similar to the results obtained in previous neuroimaging studies of visual-feature binding (Donner et al, 2002;Shafritz et al, 2002;Todd and Marois, 2004;Vogel and Machizawa, 2004;Xu and Chun, 2006), findings from functional magnetic resonance imaging (fMRI) and MEG/EEG studies highlight prefrontal and parietal regions as the neuroanatomical correlates of verbal-spatial binding Campo et al, 2005;Prabhakaran et al, 2000;Wu et al, 2007). In essence, these previous studies provide haemodynamic or evoked electrical/ magnetic correlates of binding without addressing the physiological mechanisms underlying this process.…”

“…As verbal-spatial binding was observed only in the verbal task it can be inferred that the greater oscillatory activity found in prefrontal areas might be signaling neural processes specifically involved in cross-code binding. However, it is important to highlight that the prefrontal activity in the current study was mainly observed in dorsal and medial regions corresponding to Brodmann's areas (BA) 9 and 46 (see also Campo et al, 2005), while in the study of Prabhakaran et al this activity was found in BA10. Whether this difference is related to specific mechanisms supporting implicit vs. explicit binding should explored in future studies.…”

“…In humans, greater prefrontal activity during integrated object-location processing has also been shown (Filbey et al, 2005;Mitchell et al, 2000;Simon-Thomas et al, 2003). Moreover, earlier functional neuroimaging (Prabhakaran et al, 2000) and neurophysiological studies (Campo et al, 2005;Wu et al, 2007) in humans have revealed increased activation in prefrontal areas during maintenance of integrated verbal-spatial information. As verbal-spatial binding was observed only in the verbal task it can be inferred that the greater oscillatory activity found in prefrontal areas might be signaling neural processes specifically involved in cross-code binding.…”

“…Accumulated evidence from psychophysical, functional neuroimaging and transcranial magnetic stimulation studies strongly support the crucial role of posterior parietal cortex in visual-feature integration processes (Corbetta et al, 1995;Donner et al, 2002;Lee and Chun, 2001;Shafritz et al, 2002;Simon-Thomas et al, 2003;Marois, 2004, 2005;Vogel and Machizawa, 2004;Xu and Chun, 2006) and verbal-spatial binding Campo et al, 2005;Wu et al, 2007). The prefrontal cortex has been proposed to integrate object identity and location through connections within prefrontal areas (Prabhakaran et al, 2000;Rao et al, 1997) and through converging projections from parietal and temporal regions on the prefrontal cortex (Fuster, 1995;Rao et al, 1997).…”

“…However, in real-world scenes we are faced daily with this kind of integrated information in the form of traffic signals, or tracking routes on maps, etc. Nonetheless, some progress has been made in understanding the behavioural mechanisms (Cowan et al, 2006;Elsley and Parmentier, 2009;Kahnemanetal., 1992;Mitroffand Alvarez, 2007;Morey,2009;Oberauer and Vockenberg, 2009) and the neural bases Campo et al, 2005;Prabhakaran et al, 2000;Wu et al, 2007) of verbal-spatial binding.…”