Neural basis of higher visual cognition by using brain models

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OBJECTIVES : We studied the neural basis of higher visual cognitions by using brain models. Low-frequency repetitive transcranial magnetic stimulation (rTMS) was used to produce brain virtual lesion in healthy subjects while patients with Alzheimer disease (AD) and mild cognitive impairment (MCI) were considered as disease models. Subjects were instructed to perform cognitive tasks such as face recognition and coherent motion. Psychophysical and neurophysiological examinations (visual event-related potentials (ERPs), magnetoencehalography (MEG) and functional magnetic resonance imaging (fMRI)) were evaluated while the subjects performed cognitive tasks.RESULTS : Several new findings were observed. First, we filtered out either low or high spatial frequency components of the original grayscale faces (broadband spatial frequency) so that coarse (low spatial frequency) and fine (high spatial frequency) faces were made. For motion perception, coherent horizontal and optic flow stimuli were … More employed. Second, aging has a distinct effect on the motion perception. Interestingly, both MCI and AD showed increased motion thresholds and MCI revealed decreased sensitivity for optic flow motion. Third, topographical mapping of ERPs to face and motion perception was recorded. In the face tasks, P1 at the occipital site showed holistic processing of faces. N170 at the temporooccipital site reflects facial identification. Late slow components (N250-400) show distinct sensitivities for facial expressions. The difference between positive and negative expressions was first discriminated, then discrimination of negative expressions was achieved. P200 is indicative of optic flow perception and was delayed or absent in patients with MCI. Currently, we are recording MEG and fMRI during face and motion perception to further investigate the neural mechanisms. Finally, low-frequency rTMS was applied over V1 and V5 in healthy subjects, which resulted in increased reaction times for motion perception and this effect lasted for 40 min. Therefore, rTMS is a promising method for exploring the neural network for higher visual cognition. Less