Ahveninen Jyrki, Kähkönen Seppo, Pennanen Sirpa, Liesivuori Jyrki, Ilmoniemi Risto J, Jääskeläinen Iiro P
Cognitive Brain Research Unit, Department of Psychology, P.O. Box 13, University of Helsinki, Helsinki, FIN-00014, Finland.
Neuroimage. 2002 Aug;16(4):1052-61. doi: 10.1006/nimg.2002.1142.
Involuntary attention shifting, i.e., detecting and orienting to unexpected stimulus changes, may be altered at low brain serotonin (5-hydroxytryptamine; 5-HT) levels. This was studied in 13 healthy subjects (21-30 years old; 6 females) by using a dietary challenge, acute tryptophan depletion (ATD), which decreases 5-HT synthesis in the brain. Five hours after ingestion of either ATD or control mixture (randomized, double-blinded, crossover design), brain responses indexing involuntary attention were measured with simultaneous 64-channel electroencephalography (EEG) and 122-channel magnetoencephalography (MEG). During the measurement, the subjects were instructed to discriminate equiprobable 200- and 400-ms tones by pressing one of two buttons rapidly. Occasionally, the frequency of the tones changed (10% increase/decrease), causing involuntary attention shifting. ATD significantly lowered plasma tryptophan concentrations (total tryptophan decreased by 75%, free tryptophan decreased by 35%). As compared to the control condition, ATD reduced the amplitude of the deviant-tone N2 wave, including the overlapping mismatch negativity (MMN) and N2b subcomponents, which are suggested to reflect change detection in the brain. The EEG results were accompanied by a significant increase in the peak latency of the magnetic counterpart of MMN. However, no ATD effects were observed in P3 to task-irrelevant frequency change. Reaction time (RT) to deviants per se was not significantly affected, but RT in trials succeeding the deviant-frequency tones was increased by ATD, which suggested impaired reorienting to the task-relevant activity. In conclusion, the results suggest that decreased level of central 5-HT function after ATD may decrease involuntary attention shifting to task-irrelevant sound changes and thus modulate resource allocation to the task-relevant activity.
非自愿性注意力转移，即检测并转向意外的刺激变化，可能在脑血清素（5-羟色胺；5-HT）水平较低时发生改变。本研究以13名健康受试者（年龄21 - 30岁；6名女性）为对象，采用饮食激发试验——急性色氨酸耗竭（ATD），该试验可减少大脑中5-HT的合成。在摄入ATD或对照混合物（随机、双盲、交叉设计）5小时后，通过同步64导脑电图（EEG）和122导脑磁图（MEG）测量指示非自愿性注意力的脑反应。测量期间，受试者被要求通过快速按下两个按钮之一来辨别等概率出现的200毫秒和400毫秒音调。偶尔，音调频率会改变（增加/减少10%），从而引起非自愿性注意力转移。ATD显著降低了血浆色氨酸浓度（总色氨酸降低75%，游离色氨酸降低35%）。与对照条件相比，ATD降低了异常音调N2波的幅度，包括重叠的失配负波（MMN）和N2b子成分，这些被认为反映了大脑中的变化检测。EEG结果伴随着MMN磁对应物的峰值潜伏期显著增加。然而，在对与任务无关的频率变化的P3中未观察到ATD效应。对异常刺激本身的反应时间（RT）没有受到显著影响，但在异常频率音调之后的试验中，ATD使RT增加，这表明重新定向到与任务相关活动的能力受损。总之，结果表明ATD后中枢5-HT功能水平降低可能会减少对与任务无关的声音变化的非自愿性注意力转移，从而调节对与任务相关活动的资源分配。
