Scopolamine enhances middle-latency auditory evoked magnetic fields

To study the influence of central cholinergic muscarinic transmission on hu man cortical middle-latency auditory evoked magnetic fields (MAEF), central ly acting antagonist scopolamine hydrobromide (0.3 mg, i.v.), and periphera l muscarinic receptor antagonist glycopyrrolate (0.2 mg, i.v.),were adminis tered to 13 healthy subjects in a double-blind randomized cross-over design . MAEF, measured with whole-head magnetoencephalography (MEG), were elicite d with clicks applied at 10-Hz rate to the left ear. The amplitudes of N(b) m and P(a)m responses were augmented by scopolamine (P < 0.01 and P < 0.08) . These effects were about equally strong for responses from ipsi- and cont ralateral auditory cortices. Thus, the present MEG findings revealed specif ic modulation of cortical generators of middle-latency auditory evoked resp onses by muscarinic transmission. These findings might be associated with a uditory processing deficits observed in dementias with cholinergic disturba nces. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.