Magnetoencephalography (MEG)

Feature-specific stimulus discrimination related to short-term auditory sensory memory can be studied electrophysiologically using a specific event-related potential (ERP) component termed mismatch negativity (MMN), which is generated in the auditory cortex, indexing automatic comparison of the existing memory trace to incoming novel stimuli.

Slowing of spontaneous alpha oscillations and an anterior shift of a source of alpha activity (8-13 Hz) have been consistently reported in the EEG studies of Alzheimer's disease (AD). It is unknown whether these changes are associated with a gradual shift in location and frequency of existing sources or rather with the involvement of a new set of oscillators.

Auditory event-related potential (ERP) components P50 and N100 are thought to index preattentive auditory processing underlying stimulus detection, whereas a subsequent component termed mismatch negativity (MMN) has been proposed to reflect comparison of incoming stimuli to a short-lived sensory memory trace of preceding sounds. Existing evidence suggests impairment of preattentive auditory processing in aging, which appears to be accompanied by decline of cholinergic activity.

The present study explored effects of background noise on the cerebral functional asymmetry of speech perception. The magnetic equivalent (MMNm) of mismatch negativity (MMN) elicited by consonant-vowel syllable change presented in silence and during background white noise was measured with a whole-head magnetometer. It was found that in silence MMNm to speech stimuli, registered from the auditory cortex, was stronger in the left than in the right hemisphere.

OBJECTIVE: Previous studies have reported abnormalities in both spontaneous and evoked electromagnetic brain activity in Alzheimer's disease (AD). We studied the auditory steady-state response (SSR) which represents the net effect of entrained background activity and superimposed cortical evoked responses, in AD patients and healthy controls.

BACKGROUND: Patients with major depressive disorder (MDD) show impairments in cognitive functions. However, neural mechanisms underlying these disturbances are poorly understood. We investigated whether MDD affects neural mechanisms of involuntary attention studied by auditory evoked potentials (AEPs) and auditory evoked magnetic fields (AEFs).

We studied the effects of acute tryptophan depletion (ATD) on early cortical auditory processing. Middle-latency auditory evoked fields (MAEF) were investigated in 14 healthy subjects after 5 h of ATD or control mixture ingestion in a randomized, double-blinded, controlled cross-over design study. MAEFs to monaural click stimuli (0.1-ms duration) were recorded with a 122-channel neuromagnetometer. Total plasma tryptophan (Trp), free Trp, and large neutral amino acid (LNAA) concentrations were determined by using high-performance liquid chromatography.

Auditory P50 and N100 responses reflect preattentive processing, whereas subsequent mismatch negativity (MMN) response indexes memory-based comparison process. Divergent ERP responses have been found in schizophrenia and in Parkinson's disease (PD), which have abnormalities in cerebral dopamine activity. We used simultaneously magnetoencephalography and electroencephalography to investigate, whether a single dose of haloperidol, a dopamine D2-receptor antagonist, modulates preattentive auditory processing using a randomized, double-blind, placebo-controlled crossover design.

OBJECTIVE: Dopaminergic function has been closely associated with attentional performance, but its precise role has remained elusive.

We used 122-channel magnetoencephalography (MEG) and 64-channel electroencephalogrphy (EEG) simultaneously to study the effects of dopaminergic transmission on human selective attention in a randomized, double-blind placebo-controlled cross-over design. A single dose of dopamine D2 receptor antagonist haloperidol (2 mg) or placebo was given orally to 12 right-handed healthy volunteers 3 hours before measurement.