VARIATION OF FUNCTIONAL MRI SIGNAL IN RESPONSE TO FREQUENCY OF SOMATOSENSORY STIMULATION IN ALPHA-CHLORALOSE ANESTHETIZED RATS

The dependence of functional MRI contrast on the repetition rate (1.59 Hz) of a sensory stimulus was investigated with a T-2()-weighted gra dient echo method during forepaw stimulation of alpha-chloralose anest hetized rats (n = 5), An activation area was observed in the left or r ight somatosensory cortex dependent on the stimulation of the right or left forepaw, respectively, The activation intensity decreased for st imulation frequencies above 3 Hz, and was negligible at 9 Hz, The inte rpretation is that at low stimulation rates the neurons can respond to each stimulus, but at higher rates there is insufficient recovery tim e so that the response is progressively occluded.