A Novel Method of Direct Brain Activation for Fmri Study

Recent functional neuroimaging studies in humans have demonstrated that anterior cingulate cortex (ACC) was activated in association with pain. But no fMRI studies have yet investigated the ACC activation evoked directly by the medial thalamus (MT) stimulation of rats. Such experimental approaches are limited because the metal electrode commonly used in electrophysiological studies may affect the imaging quality. The aim of present study was to develop a stimulation method, which can activate brain directly in fMRI study. Three groups of anaesthetized rats were implanted with tungsten, stainless steel, and glass coated carbon fiber microelectrodes in the left MT respectively. Gradient echo (GE) images were obtained in sagittal plane with a FOV of 5 cm, a slice thickness of 2 mm, TR of 215 ms, TE of 30 ms, 4 average, and a flip angle of 22.5 on a Biospec BMT 47/40 4.7 T system. The acquisition matrix was 256 x 128 with a matrix of 256 x 256 after zero-filling. Only images obtained from the carbon fiber electrode were acceptable without interference and deterioration of the signal noise ratio. A series of four-slice GE images were acquired during electrical stimuli using carbon fiber electrode. Both cross correlation analysis and independent component analysis showed that signal intensities of activated areas were significantly increased in ACC during MT stimulation. The signal intensities of ACC were increased to about 10%. The results indicated that the glass coated carbon fiber electrode is suitable for fMRI study. The present study has established a new method for fMRI study to investigate ACC activation evoked directly by MT stimulation and also provided a basis for further investigation of the neurophysiological mechanism underlying the blood oxygenation level dependent effect.