High-resolution mapping of discrete representational areas in rat somatosensory cortex using blood volume-dependent functional MRI

The present study documents the use of an iron oxide-based blood-pool contr ast agent in functional magnetic resonance imaging to monitor activity-rela ted changes in cerebral blood volume (CBV) resulting from peripheral sensor y stimulation and the application of this technique to generate high-resolu tion functional maps. Rats, anesthetized with alpha-chloralose, were imaged during electrical stimulation (3 ms, 3 Hz, 3 V) of forelimb or hindlimb. A ctivation maps were generated by cross-correlation of the measured signal r esponse and a square-wave function representative of the stimulus for each image pixel. Multislice imaging produced functional maps consistent with th e known functional anatomy of rat primary somatosensory (S-I) cortex. Imagi ng with improved temporal resolution demonstrated rapid (<6 s) CBV increase s which were sustained and relatively stable (coefficient of variation = 0. 17 +/- 0.02) for forelimb stimulation periods of up to 5 min. Enabled by th is sustained response we generated high-resolution (approximately 100 mu m inplane) functional maps showing discrete forelimb and hindlimb activation. This technique offers many advantages over other methods for the study of brain activity in the rat and has resolution sufficient to be useful in reo rganization studies. (C) 1999 Academic Press.