Living Rat SSVEP Mapping With Acoustoelectric Brain Imaging

Objective: Acoustoelectric Brain Imaging (ABI) is a potential method for mapping brain electrical activity with high spatial resolution (millimeter). To resolve the key issue for eventual realization of ABI, testing that recorded acoustoelectric (AE) signal can be used to decode intrinsic brain electrical activity, the experiment of living rat SSVEP measurement with ABI is implemented. Method: A 1-MHz ultrasound transducer is focused on the visual cortex of anesthetized rat. With visual stimulus, the electroencephalogram and AE signal are simultaneously recorded with Pt electrode. Besides, with FUS transducer scanning at the visual cortex, corresponding AE signals at different spatial positions are decoded and imaged. Results: Consistent with the directly measured SSVEP, decoded AE signal presents a clear event-related spectral perturbation (ERSP). And, decoded AE signal is of high amplitude response at the base and harmonics of the visual stimulus frequency. What's more, for timing signal, a significant positive amplitude correlation is observed between decoded AE signal and simultaneously measured SSVEP. In addition, the mean SNRs of SSVEP and decoded AE signal are both significantly higher than that of background EEG. Finally, with one fixed recording electrode, the active area with an inner diameter of 1mm is located within the 4 mm×4 mm measurement region. Conclusion: Experimental results demonstrate that the millimeter-level spatial resolution SSVEP measurement of living rat is achieved through ABI for the first time. Significance: This study confirms that ABI should shed light on high spatiotemporal resolution neuroimaging.

I. Introduction

Brain functional imaging is an important technology to study brain function, which is of great significance in both clinical application and brain computer interface (BCI). The widely used noninvasive brain functional imaging techniques include EEG, functional magnetic resonance imaging (fMRI) and functional near-infrared spectroscopy (fNIRS) [1]–[3]. EEG, fMRI and fNIRS are poor either in temporal resolution or spatial resolution. EEG, the most used method, is adopted to detect electrophysiological signal and has particularly good temporal resolution (millisecond). Due to the effect of volume conductor, it is limited in poor spatial resolution (centimeter). fMRI and fNIRS are used to detect the metabolism of substances in the blood and are of moderate spatial resolution. But they are of low temporal resolution (second). Therefore, multi-modal imaging technique has been investigated, for example fNIRS-EEG and fMRI-EEG [4], [5]. However, due to different data types, it is difficult to achieve effective data fusion. And noninvasive brain functional imaging with high spatiotemporal resolution remains an open quest in biomedical imaging.