Coexistence of Attention-Based Facilitation and Inhibition in the Human Cortex

Abstract

A key function of attention is to select an appropriate subset of available information by facilitation of attended processes and/or inhibition of irrelevant processing. Functional imaging studies, using positron emission tomography, have during different experimental tasks revealed decreased neuronal activity in areas that process input from unattended sensory modalities. It has been hypothesized that these decreases reflect a selective inhibitory modulation of nonrelevant cortical processing. In this study we addressed this question using a continuous arithmetical task with and without concomitant disturbing auditory input (task-irrelevant speech). During the arithmetical task, irrelevant speech did not affect task-performance but yielded decreased activity in the auditory and midcingulate cortices and increased activity in the left posterior parietal cortex. This pattern of modulation is consistent with a top down inhibitory modulation of a nonattended input to the auditory cortex and a coexisting, attention-based facilitation of taskrelevant processing in higher order cortices. These findings suggest that task-related decreases in cortical activity may be of functional importance in the understanding of both attentional mechanisms and taskrelated information processing. Academic Press

The irrelevant speech effect: a PET study

“…Taken together, the reported activations and areas of decreased activity can be interpreted in terms of suppression of irrelevant areas consistent with previous findings (Ghatan et al, 1998). Decreases of activation were found in the bilateral (left > right) superior temporal region, the bilateral inferior/middle frontal cortices (right > left), as well as in the left inferior parietal cortex (Fig.…”

“…Conversely, decreased activity may reflect suppression of neural activity in task-irrelevant modalities (Haxby et al, 1994;Shulman et al, 1997). In keeping with this hypothesis, the decreased activity observed in the secondary auditory areas (BA 22) might reflect top-down attentional inhibitory modulation of task-irrelevant processing (Ghatan et al, 1998).…”

“…Whether the superior temporal cortex is an integral part of the core verbal working memory network can be discussed. However, following its important role in phonological processing, we suggest that the decrease of activity in the superior temporal region reflect an active top-down suppression of early phonological processing (Ghatan et al, 1998).…”

“…The PET images were realigned, spatially normalized and transformed into a common stereotactic space as defined by the SPM99 template, an approximate Talairach space (Talairach & Tournoux, 1988 , that previously have been shown to be involved in verbal working memory, that is, the superior temporal cortex (BA 22/41/42) (Ghatan et al, 1998;Paulesu et al, 1993), the inferior parietal cortex (BA 39/40) Jonides et al, 1998), the ventrolateral prefrontal cortex (BA 44/45) Burton, 2001;Schumacher et al, 1996;Smith & Jonides, 1999) as well as the premotor (BA 6) Smith & Jonides, 1999) and supplementary motor areas (medial part of BA 6) Smith & Jonides, 1999). When referring to these regions of interests, activations were thresholded at Z = 3.05 (or omnibus significance P = 0.001).…”

“…The results from the interaction contrast can be discussed in terms of attentional modulation (Ghatan et al, 1998). Functional imaging studies have shown that activity in motion sensitive areas in the human brain (V5) is enhanced when subjects attend to motion rather than view moving stimuli passively (Corbetta, Miezin, Dobmeyer, Shulman, & Petersen, 1991;Shulman et al, 1997) or even without moving stimuli (Chawla, Rees, & Friston, 1999).…”