Evaluation of time resolution of primary visual cortex using a single paradigm: sequence design employing a stimulation system

Abstract

The characteristics of fMRI include high-resolution, non-invasiveness, and ease of use, making it increasingly popular for brain imaging. However, imaging by the block paradigm is limited in time resolution from stimulus presentation to the subject to image acquisition. Therefore, it is not necessarily adequate for the evaluation of early (initial) brain activity. To evaluate this activity, real-time resolution during stimulation is required. We considered a single paradigm to be the most suitable for this purpose. To obtain real-time information at stimulation, it is necessary to utilize the sequence design of a single paradigm that synchronizes with an external trigger. By so doing, we found that it was possible to evaluate brain activity in the early stage in the primary visual cortex. The relative decrease of PO(2) ("sank") that was generated in the initial stage of BOLD, that is, the initial dip, was captured as a transitory change in signal by using a stimulation presentation of about two seconds in the single paradigm. Results showed that the single design provided time resolution with a high time to activation. Moreover, it is thought that imaging by a single paradigm that synchronizes with stimulation is indispensable for the time and spatial elucidation of detailed brain activity. Therefore, brain activity at the early stage in primary visual cortex was clarified by using a single paradigm that synchronized with stimulation from single-shot EPI.