Spatio-temporal interaction of evoked magnetic fields in primary auditory and somatosensory cortex of awake humans

Determines the primary cortical evoked magnetic field responses to brief somatosensory and auditory stimuli in awake humans. These responses comprise evoked coherent low-frequency oscillations in the range of 4-15 Hz lasting for 100-300 ms. Responses to pairs of stimuli occurring at various inter-stimulus intervals interact non-linearly. Latencies between the peaks of the evoked response were linearly related to the intervals between stimuli, reflecting the high-fidelity representation of stimulus intervals in both primary cortical areas. The sources of the different cycles of these oscillations and the sources of responses to stimulus pairs both localize to the same cortical area, indicating that the observed responses reflect changes in underlying cortical excitability. The potential origins and functional role of these oscillations in the processing and representation of temporal information on this time scale are discussed