BRAIN IMAGING · Investigation of auditory plasticity using MEG and f MRI

Final Activity Report Summary - BRAIN IMAGING (Investigation of auditory plasticity using MEG and f MRI)

The allocation of attention affects brain activity in response to concurrent auditory and visual information. Focussed attention to one modality increases activation intensity in the corresponding sensory cortex relative to when attention is focussed on another modality, as mentioned by Laurienti et al. in 2001. Dividing attention between concurrent auditory and visual information reduces activation intensity in early sensory cortices relative to selective attention (Loose et al., 2003) and may recruit the dorsolateral prefrontal cortex (PFC), as noted by Johnson and Zatorre in 2006. The recruitment of the PFC has been interpreted as reflecting the involvement of the central executive system which is in charge of the allocation and coordination of attentional resources, as described in the Baddeley's model of working memory in 1986. Using positron emission tomography, single, either auditory or visual, and dual, i.e. audiovisual, working memory tasks were found to recruit overlapping brain regions in the right PFC, bilateral inferior parietal cortex (IPC) and anterior cingulate cortex (AC) (Klingberg 1998). In this project, we used 3 T functional Magnetic resonance imaging (fMRI) to investigate the role of focussed and divided attention during a working memory task. We hypothesised that divided compared to focussed attention would increase activations in PFC areas as well as reduce activations in early sensory cortices. The 18 examined subjects performed a delayed-match-to-sample task with simultaneous auditory and visual stimuli in three active conditions, i.e. focussed auditory, focussed visual and divided audiovisual. Subjects indicated whether or not pairs of stimuli in the attended modality or modalities, separated by a 1.2 s delay, were identical. Audio and visual stimuli were 400 ms frequency modulated tones and non-nameable line figures, respectively. Analysis was limited to brain regions that were hypothesised to be involved both in working memory and attention tasks. Compared to passively viewing and listening, all tasks activated sensory cortices, PFC, insula, IPC, thalamus and AC bilaterally. Divided memory was associated with decreased activation in auditory cortices compared to focussed auditory memory. Recruitment of visual areas was most prominent in the focussed visual condition. The highest intensity of activation in the PFC was observed for the divided attention condition. The results showed that, while focussed and divided attention in short-term memory tasks activated overlapping brain networks, the status of attention was reflected by differences in activation intensity within the network. This might reflect the central role of top-down influences in early sensory processing.

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