Kasties Nils, Starosta Sarah, Güntürkün Onur, Stüttgen Maik C
Department of Biopsychology, Faculty of Psychology, Ruhr University, 44780 Bochum, Germany.
Institute of Pathophysiology, University Medical Center of the Johannes Gutenberg University, 55128 Mainz, Germany.
Sci Rep. 2016 Oct 20;6:35469. doi: 10.1038/srep35469.
Animals exploit visual information to identify objects, form stimulus-reward associations, and prepare appropriate behavioral responses. The nidopallium caudolaterale (NCL), an associative region of the avian endbrain, contains neurons exhibiting prominent response modulation during presentation of reward-predicting visual stimuli, but it is unclear whether neural activity represents valuation signals, stimulus properties, or sensorimotor contingencies. To test the hypothesis that NCL neurons represent stimulus value, we subjected pigeons to a Pavlovian sign-tracking paradigm in which visual cues predicted rewards differing in magnitude (large vs. small) and delay to presentation (short vs. long). Subjects' strength of conditioned responding to visual cues reliably differentiated between predicted reward types and thus indexed valuation. The majority of NCL neurons discriminated between visual cues, with discriminability peaking shortly after stimulus onset and being maintained at lower levels throughout the stimulus presentation period. However, while some cells' firing rates correlated with reward value, such neurons were not more frequent than expected by chance. Instead, neurons formed discernible clusters which differed in their preferred visual cue. We propose that this activity pattern constitutes a prerequisite for using visual information in more complex situations e.g. requiring value-based choices.
动物利用视觉信息来识别物体、形成刺激-奖励关联并准备适当的行为反应。尾外侧巢皮质（NCL）是鸟类端脑的一个联合区域，其中的神经元在呈现预测奖励的视觉刺激时表现出显著的反应调节，但目前尚不清楚神经活动是代表价值信号、刺激属性还是感觉运动偶发事件。为了检验NCL神经元代表刺激价值这一假设，我们让鸽子接受巴甫洛夫符号追踪范式，其中视觉线索预测了大小（大与小）和呈现延迟（短与长）不同的奖励。受试者对视觉线索的条件反应强度可靠地区分了预测的奖励类型，从而为价值评估提供了指标。大多数NCL神经元能区分视觉线索，辨别能力在刺激开始后不久达到峰值，并在整个刺激呈现期保持在较低水平。然而，虽然一些细胞的放电率与奖励价值相关，但这类神经元的出现频率并不比随机预期的更高。相反，神经元形成了可辨别的簇，它们偏好的视觉线索各不相同。我们认为，这种活动模式是在更复杂的情况下（例如需要基于价值的选择）使用视觉信息的先决条件。
