Neuropathological Dynamics of Magnetic, Auditory Steady-State Responses in Alzheimer’s Disease

The steady-state auditory mid-latency response in humans is maximal in amplitude and sinusoidal in form in response to repetitive auditory stimulation between 35 and 45 Hz (Galambos et al., 1981). This has been reported in both, EEG and MEG studies. MEG data reported single dipoles in the temporal lobe of cortex in humans after an auditory 40Hz stimulation (Maekelae and Hari, 1987), which were believed to be a part of a thalamo-cortical loop becoming resonant at 40 Hz (Weinberg et al., 1988). Recently, our EEG/MEG studies suggested two dipoles in thalamo-cortical areas, indicating that more than one generator must be involved in the 40Hz response (Ribary et al., 1989a and 1989b). Moreover, these dipoles seemed to be more rigerously in phase in controls than those observed in psychiatric patients.