“…Unlike BOLD studies, numerous optical studies performed using laser Doppler flowmetry (LDF) (Ngai et al, 1999;Matsuura and Kanno, 2001;Ureshi et al, 2004Ureshi et al, , 2005 and optical imaging (Devor et al, 2003;Martindale et al, 2003;Sheth et al, 2003Sheth et al, , 2004Jones et al, 2004;Hewson-Stoate et al, 2005;Martin et al, 2006) have investigated the hemodynamic responses such as CBF and deoxygenated hemoglobin changes to neuronal activity in the rat cortex with a short stimulus duration (2-5 s) (Matsuura and Kanno, 2001;Martindale et al, 2003;Sheth et al, 2003Sheth et al, , 2004Jones et al, 2004;Ureshi et al, 2004Ureshi et al, , 2005Hewson-Stoate et al, 2005;Martin et al, 2006). Thus, an animal fMRI study with short stimulus duration is expected to bridge the results of the optical studies using short stimulus durations and those of the BOLD studies using long stimulus durations.Furthermore, most of the optical studies performed using electrical stimulation varied either in frequency (Ngai et al, 1999;Matsuura and Kanno, 2001;Martindale et al, 2003; -3 - while maintaining a fixed current strength (Brinker et al, 1999;Van Camp et al, 2006;Goloshevsky et al, 2007;Huttunen et al, 2008;Sanganahalli et al, 2009), and few fMRI studies have comprehensively investigated this relationship at different stimulus frequencies and currents.Thus, the present study aimed to investigate the relationship between BOLD signals and neuronal activities in the somatosensory cortex of anesthetized rats for forepaw electrical stimulation at a short duration of 4 s by changing both frequencies (1-10 Hz) and currents (0.5-2.0 mA). BOLD signals with a spin-echo echo planar imagining (EPI) sequence at 7 T and scalp-based somatosensory evoked potentials (SEP) were obtained from individual rats.…”