RATIONALE: Intensity dependence of the N1/P2 components may be regulated by serotonergic neurons in the primary auditory cortex, where low activity leads to a high intensity dependence and vice versa. Depletion of tryptophan (TRP), a precursor for serotonin has been described to reduce serotonin content in brain of animals and humans.
The brain monoamines serotonin and dopamine have an important role in the regulation of human cognitive functions. Neural correlates of attention can be studied in millisecond resolution with magnetoencephalography (MEG) and electroencephalography (EEG), which provide complementary views on attentional processing. During "selective attention", a processing negativity (PN) overlaps EEG response to the attended tones.
Neurochemical mechanisms mediating the interaction between emotional and cognitive processing are not yet fully understood. Here, we utilized acute tryptophan depletion (ATD) to reduce the brain synthesis of serotonin (5-HT), which is thought to have a central role in regulation of emotions and mood in humans. ATD effects on event-related potentials and magnetic fields were studied using a passive odd-ball paradigm in a randomized, double-blinded, controlled, cross-over design.
Magnetoencephalography (MEG) was used to determine the effect of neuroleptic challenge on brain responses in healthy subjects. In a double-blind, randomized, placebo-controlled, cross-over design study, the dopamine D(2) receptor antagonist haloperidol (2 mg) was given orally to 12 healthy volunteers. The middle-latency auditory evoked magnetic fields (MAEF) were recorded 3 h after administration of haloperidol or placebo with a whole-head 122-channel MEG. Haloperidol did not significantly affect MAEF responses.
RATIONALE: Serotonin is shown to regulate the activity of primary auditory cortex, but little is known about serotonin modulation of other sensory cortices.
Cognitive processes including selective attention may depend on synchronous activity of neurons at the gamma-band (around 40Hz). To determine the effect of neuroleptic challenge on transient auditory evoked 40-Hz response, simultaneous measurement of 122-channel magnetoencephalogram (MEG) and 64-channel electroencephalogram (EEG) was used. Either 2mg of dopamine D(2)-receptor antagonist haloperidol or a placebo was administered orally to 11healthy subjects in a double-blind randomized crossover design in two separate sessions.
Spontaneous magnetoencephalographic activity was recorded with a 24-SQUID gradiometer over the lateral aspects of the head in 3 healthy adults. All subjects displayed 8-10 Hz rhythmic activity which was not affected by opening of the eyes but was occasionally dampened by auditory stimuli. The equivalent sources of the rhythm were in the supratemporal auditory cortex, and the activity may therefore represent 'idling' of the auditory cortex. Obviously each sensory projection cortex has its own local spontaneous rhythm.
The signal-to-noise ratio (SNR) in averaged evoked responses is proportional to the signal amplitude and to the square root of the stimulation frequency. If the SNR-stimulation-rate dependence is known for some specified component or feature of the response it is possible to select a rate that maximizes the SNR of that component within a given measurement time. The same stimulation rate also minimizes the acquisition time for a given SNR.
Spatially focal source estimates for magnetoencephalography (MEG) and electroencephalography (EEG) data can be obtained by imposing a minimum ℓ(1) -norm constraint on the distribution of the source currents. Anatomical information about the expected locations and orientations of the sources can be included in the source models. In particular, the sources can be assumed to be oriented perpendicular to the cortical surface.
Evidence from functional neuroimaging indicates that visual perception of human faces and bodies is carried out by distributed networks of face and body-sensitive areas in the occipito-temporal cortex. However, the dynamics of activity in these areas, needed to understand their respective functional roles, are still largely unknown. We monitored brain activity with millisecond time resolution by recording magnetoencephalographic (MEG) responses while participants viewed photographs of faces, bodies, and control stimuli.
