Sub-threshold motor evoked response latency estimation by TFA

A time-frequency analysis (TFA) based on the Exponential Distribution (ED) was used to estimate the onset latency of the cortical motor evoked potential (MEP) in surface electromyographic (SEMG) records from the abductor pollicis brevis (APB) muscle recorded under conditions of voluntary isometric contraction. A concentration of spectral energy characteristic of an MEP was observed in response records collected well below levels defined as threshold by current published methods. Estimates of onset latency derived from these observed characteristic time-frequency events demonstrated consistent behavior across three possible detection algorithms, with reported bias. Linearly decreasing onset latency was noted for increasing stimulus intensity at a constant level of voluntary facilitation