An Investigation Of Human Brain Areas Related To Attentional Modulation Of Sensory Processing Using Functional MRI

Background and Objective:Attention refers to a person's mental activity to focus on something and eliminate distractions.Although it is known that sensory processing in the brain can be modulated by attention,a consensus on which brain areas are involved in such attentional modulation of sensory processing has not been reached.Previous functional brain imaging studies have shown that,by attending to some sensory input of a particular modality,the neural activity of the corresponding unimodal sensory cortex elicited by this sensory input can be enhanced,suggesting that the unimodal sensory cortex corresponding to the particular sensory input being attended is involved in attentional modulation.However,sensory processing in the brain also engages multimodal areas which are not solely responsible for processing information of a single sensory modality,and thus these multimodal areas might also be involved in attentional modulation of sensory processing.Most of previous studies only examined attentional modulation of sensory processing of a particular modality in a single study,and thus evidence involving multiple sensory modalities is still lacking.To this end,we used functional Magnetic Resonance Imaging(fMRI)to sample brain responses to tactile,visual and auditory stimuli while attention was being directed to either tactile or visual stimuli.We first identified the brain areas whose responses to tactile stimuli were modulated by attention and the brain areas whose responses to visual stimuli were modulated by attention.Then we identified the multimodal areas involved in attentional modulation by identifying the common areas whose responses to both tactile and visual stimuli were modulated by attention.Materials and Methods:Twenty-three healthy subjects underwent fMRI scan while receiving sensory stimulation from three different modalities including touch,vision and audition.The subjects were instructed to attend to either tactile stimuli or visual stimuli at different periods of the experiment.FMRI data were preprocessed and analyzed using the software package SPM8.In brief,first,the brain responses to tactile stimuli were compared between two different attentional conditions(contrast analysis 1);second,the brain responses to visual stimuli were compared between two different attentional conditions(contrast analysis 2);and finally,the conjunction of the brain areas identified from the above two contrast analyses were obtained(conjunction analysis).Statistical results were corrected(P<0.05)for multiple comparisons using family-wise error(FWE)correction at cluster level(cluster defining threshold P<0.001).Result:When attention was directed to tactile stimulation compared with to visual stimulation,neural responses elicited by tactile stimuli were enhanced in the following areas: the bilateral supplementary motor area,the bilateral anterior/mid cingulate cortex,bilateral insula,bilateral middle frontal gyrus,bilateral inferior frontal gyrus,the right inferior parietal lobule,the left caudate nucleus and the left cerebellum.When attention was directed to visual stimulation compared with to tactile stimulation,brain responses elicited by visual stimuli were enhanced in the following areas: the bilateral supplementary motor area,the bilateral anterior/mid cingulate cortex,the left precentral gyrus,bilateral insula,bilateral middle frontal gyrus,the right inferior frontal gyrus,the bilateral inferior parietal lobule,the left caudate nucleus and bilateral cerebellum.The common areas involved in attentional modulation of both tactile and visual processing were found in the following areas:bilateral middle frontal gyrus,the right inferior frontal gyrus,the right inferior parietal lobule,the bilateral anterior/mid cingulate cortex,bilateral insula,the bilateral supplementary motor area,the left caudate nucleus and the left cerebellum.Conclusion:Our results showed that several areas located in the frontal and parietal lobes,the cingulate cortex and the insula were involved in attentional modulation of sensory processing of multiple modalities,suggesting that these areas plays an important role in attentional modulation.These results can help us better understand the brain mechanisms of attentional modulation of sensory processing,and provide basis for further studying neurological and psychiatric diseases associated with attentional deficits.