The electrophysiological arm of the Section of Brain Imaging and Electrophysiology continues to make significant methodological advances in stimulus generation, control, and presentation within multiple sense modalities. Any sensory event, which can be digitally stored (including sounds, visual images, tactile patterns, etc.), can now be presented in complete synchrony with the continuous EEG acquisition. We have also written C code for dynamically updating the identity of a specified stimulus in a predefined sequence. This dynamic updating allows each pre-specified stimulus sequence to be uniquely altered based upon the response history of each individual subject. All subject responses can be logged at any point within the sequence of stimulus presentation; not just at predefined """"""""response intervals"""""""". This enables us to look at complex patterns of responding that may be useful in characterizing groups of individuals with different response profiles in tasks of varying cognitive demand. Additionally, this code is being modified for use in fMRI protocols so that we can run identical versions of tasks in the electrophysiology and fMRI/PET settings. Work has begun using the code mentioned above in a multisensory psychophysics task where the intensity of stimuli presented in different sensory modalities is being matched for each individual subject. Multisensory magnitude matching is necessary to more precisely probe the functional organization of the proposed multisensory attention system. This is done by quantitatively manipulating the perceptual salience of stimuli presented in nonattended or ignored sensory modalities. The resulting data regarding the quantitative reciprocity of processing across sensory modalities as a function of selective attention will allow us to ultimately address questions of selective processing and imperviousness to distraction in a more general way than looking within one sensory system alone. An inability to filter out distracting information is thought to be a component of behavioral impulsivity and these multisensory techniques may enable us to more precisely characterize subtypes of impulsive individuals. A multisensory analysis will also facilitate a more general understanding of brain areas that are the sites of convergence of inputs from multiple sensory pathways. These sites include the arcuate sulcus and the superior temporal gyrus. We are actively pursuing analytic strategies to co-register the electrode array data with that of structural MRI and functional blood flow data within a common coordinate system. By recording from spatially dense arrays of electrodes on the surface of the head, the fine temporal information obtained from EEG/ERP techniques can be combined with the fine spatial information of imaging modalities such as PET and fMRI to construct true spatio-temporal models of neural networks underlying cognitive phenomena. It is necessary to augment the electrophysiological data that we have collected using multisensory selective attention tasks with imaging data in order to more precisely visualize and characterize the multisensory processing areas mentioned above. The use of imaging modalities will allow us to verify the activation of these multisensory areas of the brain and the use of EEG/ERP techniques enables us to determine when these areas become activated and produce a model of the spatio-temporal dynamics of the neural network which underlies selective processing of stimuli across sensory modalities. Once a model of normal multisensory selective processing has been validated we can look at different patterns of disruptions in individuals who exhibit impulse control problems to aid in identifying the source of these disruptions.
