Effects of stimulus presentation rate on the activity of primary somatosensory cortex: A functional magnetic resonance imaging study in humans

To investigate the effect of stimulus presentation rate on the activity of primary somatosensory cortex, we performed echo-planar functional magnetic resonance imaging using a 1.5-tesla magnetic resonance system. Eight right- handed normal volunteers underwent functional magnetic resonance imaging du ring somatosensory stimulation with a 0.2 ms electrical square wave to the left index finger at 1, 4, 8, 16, and 32 Hz at constant intensity. Activate d areas were located mainly around 'the hand area' of the right postcentral gyrus. Between 4 and 16 Hz, almost all subjects showed significant activat ion, but at 1 Hz and 32 Hz, five of eight subjects showed no activation. Th e average number of activated pixels in this area between 4 and 16 Hz were significantly greater than those at 1 Hz and 32 Hz, and the average percent signal increase had its activation peak at 8 Hz. Our results suggest that the existence of the optimal stimulation rate range may be a common phenome non to a variety of sensory modalities. The electrical somatosensory stimul ation rates from 4 Hr to 16 Hz are advisable to investigate the activation of the primary somatosensory cortex in human subjects, (C) 2001 Elsevier Sc ience Inc.