Brigitte Lipschutz

Attention-Dependent Changes of Activation and Connectivity in Dichotic Listening

Functional studies of auditory spatial attention generally report enhanced neural responses in auditory cortical regions. However, activity in regions of the spatial attentional network as described in the visual modality is not consistently observed. Data analysis limitations due to oppositely lateralized activity depending on the side of attentional orientation and heterogeneity of paradigms makes it hard to untangle the possible causes of these various activation patterns. In the present article we present a PET study of auditory spatial attention in which we manipulated orientation of attention, attentional load, and difficulty of the task by means of the dichotic listening paradigm. Moreover, we designed a systematic, voxel-specific, method in order to deal with oppositely lateralized activity. The results show that when listeners are involved in auditory spatial attention tasks an interacting network of frontal, temporal, and parietal regions is activated. Selective orientation toward one side mostly yields activity and connectivity modulations in the hemisphere contralateral to the attended side while in divided attention activity is mostly bilateral. Taken together, our observations are consistent with the idea of a multimodal large-scale attentional network.

Assessing study-specific regional variations in fMRI signal.

In this paper, we present a post hoc method for identifying regions where functional MRI data are subject to signal reduction that may compromise sensitivity to activations. The motivation for developing this technique derives from recent language studies that showed responses in the inferior temporal lobe that could be detected by PET but not by fMRI. Reduced signal is due mostly to susceptibility artifacts and can be identified by comparing the T2* images (which are subject to susceptibility artifacts) with T2 images (which are not). However, T2 images are not usually acquired in fMRI studies. Therefore, we propose that areas with reduced signal can be identified by comparing T2* images that are corrected for nonuniformity with the original uncorrected images. The technique provides a voxel-wise characterization of signal reduction that pertains to the particular data that enter into a statistical model. It requires only the functional data and can thus be applied post hoc and without any additional scans.

Attention-dependent changes of activation and connectivity in dichotic listening: Evidence from two studies

Functional studies of auditory spatial attention generally report enhanced neural responses in auditory cortical regions. However, activity in regions of the spatial attentional network as described in the visual modality is not consistently observed. Data analysis limitations due to oppositely lateralized activity depending on the side of attentional orientation and heterogeneity of paradigms makes it hard to untangle the possible causes of these various activation patterns. In the present article we present a PET study of auditory spatial attention in which we manipulated orientation of attention, attentional load, and difficulty of the task by means of the dichotic listening paradigm. Moreover, we designed a systematic, voxel-specific, method in order to deal with oppositely lateralized activity. The results show that when listeners are involved in auditory spatial attention tasks an interacting network of frontal, temporal, and parietal regions is activated. Selective orientation toward one side mostly yields activity and connectivity modulations in the hemisphere contralateral to the attended side while in divided attention activity is mostly bilateral. Taken together, our observations are consistent with the idea of a multimodal large-scale attentional network.