The 40 Hertz auditory event-related potential: normal values and effects of lesions

A model of the 40 Hz auditory event-related potential (40 Hz AERP) was developed and evaluated in a group of normal subjects and two patient groups. The model views the 40 Hz AERP as a combination of the brain-stem auditory evoked potential (BAEP) and a sinusoidal component presumed to arise from structures rostral to the brain-stem. Fourier analysis techniques were used to quantify changes in the sinusoidal component. The results obtained demonstrated that the phase of the sinusoidal component was quite stable in normal subjects, but was predictably altered as a consequence of thalamic or midbrain lesions. Lesions of the temporal lobe did not alter the phase of the sinusoidal component. These results were interpreted as being consistent with the model developed and suggesting a midbrain or thalamic origin for the 40 Hz sinusoid.