Normative data on scalp responses evoked by infraorbital nerve stimulation

Normative data concerning the waves W1, W2, W3, P4, N5, P6 and N7 recorded from the scalp after stimulation of the infraorbital nerve have been collected from 96 healthy subjects, selected according to age and sex. Peak latency, inter-peak intervals, side-to-side asymmetry of inter-peak intervals, amplitude, amplitude ratio of some components versus W1 and side-to-side asymmetry of such ratio have been analysed as functions of age and sex. None of these parameters appeared to be affected by sex; computation of the correlation coefficient showed a significant (P less than 0.01), though slight, increase of value of the inter-peak intervals W1-W2 and W1-W3 with age. This increase was partially confirmed by analysis of variance. However, such differences are too small to be useful for practical applications, so only a single normative value is proposed for each parameter. The influence of stimulus strength on the amplitude of the W1 component has been studied in 10 more subjects; amplitude saturation of this wave has been found to take place at intensities between 4 and 6 times the sensory threshold. Increasing the stimulus rate from 1 to 3 pulses/sec did not affect any of the components. It is remarked that components W1, W2, W3 and, to a lesser extent, P4 are the ones to be considered useful in clinical practice.