The amplitude of the somatosensory evoked field (SEF) decreases with increasing rate of stimulation in human primary (S1) and secondary (S2) somatosensory cortex (e.g. Zhu et al, SFN 2004). Our goal is to compare the rate effect observed in the MEG signal to underlying electrophysiology. As a first step we have developed a non-human primate model to examine somatosensory cortex while varying the tactile stimulation rate. We also compare these data with our findings from humans. SEFs were recorded from anaesthetized macaque monkeys (3-5 mg/kg/hr Ketamine and 0.18-0.36 mg/kg/hr Midazolam, IV) using whole-head magnetoencephalography (MEG; Omega 2000 Whole-Cortex MEG System; CTF Systems Inc.). Pneumatically driven pulses (25 PSI, 30ms) were applied simultaneously to the tips of D1 and D2 with three inter-stimulus intervals (ISI): 330ms, 1s and 2s, with a jitter of 50ms. Blocks of 512 trials were presented in random order. Data were collected at a sample rate of 1200 Hz. The filtering passband for data analysis...