Combination of magneto- and electroencephalography in studies of monoamine modulation on attention

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. This component can be modulated with drugs affecting dopamine transmission in the brain, such as haloperidol and droperidol, whereas no effects seem to be caused by acute tryptophan depletion (ATD), decreasing serotonin synthesis in the brain. Distinct responses are associated with "involuntary attention". Responses reflecting sound-change detection and initiation of involuntary attention, the mismatch negativity and its magnetic counterpart, appear to be modulated by ATD, but not with haloperidol. Subsequent P3a elicited by actual attention shifting, as well as reorienting negativity reflecting orienting back to a relevant task, are in turn decreased by haloperidol, but not affected by ATD or other serotonin modulators. Serotonin may affect the earliest "preattentive" phases on auditory processing, indexed by mid-latency magnetic responses and NIm, but haloperidol's effects on these parameters are insignificant. Taken together, serotonin and dopamine may have differential effects on attentional processing depending on time after stimulus presentation.