Department of Psychiatry, Charité-Universitätsmedizin Berlin, Campus Charité Mitte, Charitéplatz 1, D-10117 Berlin, Germany.
Neuroimage. 2012 Sep;62(3):1717-25. doi: 10.1016/j.neuroimage.2012.06.016. Epub 2012 Jun 19.
Recent studies have shown that motivational stimulus information is represented in the brain even in situations where the individual is not actively engaged in stimulus evaluation. However, it has remained unclear whether neural representations of such implicit motivational information reflect the motivational value or motivational salience of stimuli. While motivational values correspond to the desirability of stimuli, motivational salience is related to the arousal elicited by the stimulus. Here we aimed at disentangling the neural representation of both motivational dimensions. In the first part, participants learned the association of face stimuli with monetary reward and punishment. The same face stimuli were presented in a subsequent fMRI experiment, during which participants either performed a gender discrimination task on the faces or an orientation discrimination task on two simultaneously presented bars. Importantly, faces only differed regarding their implicit motivational information as acquired in the previous learning task, as participants neither received monetary reinforcement during the fMRI experiment nor were they asked to explicitly judge their face preferences. We found that neural responses in lateral OFC were modulated by implicit motivational value, whereas the faces' implicit motivational salience was coded in medial OFC. While the value-related responses in lateral OFC decreased over time, the salience-related modulation of medial OFC activity remained stable over the duration of the fMRI experiment. Neural responses to both motivational dimensions were observed independent of whether participants' attention was directed to the faces or to the surrounding bars, suggesting an automatic processing of implicit motivational value and salience. The functional dissociation within the OFC suggests that this region is critically involved in distinct motivation-related processes: In medial OFC, a representation of salient items may be maintained in order to facilitate responses towards behaviourally relevant stimuli in the future; in contrast the temporary value effect in lateral OFC might reflect decreasing stimulus valuation in the absence of explicit motivational stimulus differences.
最近的研究表明，即使在个体没有主动参与刺激评估的情况下，动机刺激信息也会在大脑中得到体现。然而，人们仍然不清楚这种隐含动机信息的神经表示是否反映了刺激的动机价值或动机显著性。虽然动机价值对应于刺激的吸引力，但动机显著性与刺激引起的唤醒有关。在这里，我们旨在分离这两个动机维度的神经表示。在第一部分，参与者学习了面孔刺激与金钱奖励和惩罚之间的关联。在随后的 fMRI 实验中呈现相同的面孔刺激，在此期间，参与者要么对面孔执行性别判别任务，要么对面孔执行两个同时呈现的条形图的方向判别任务。重要的是，面孔只在其隐含的动机信息上有所不同，因为在 fMRI 实验中，参与者既没有收到金钱奖励，也没有被要求明确判断他们对面孔的偏好。我们发现，外侧眶额皮层的神经反应受到隐含动机价值的调节，而面孔的隐含动机显著性则在内侧眶额皮层中编码。虽然外侧眶额皮层的价值相关反应随着时间的推移而降低，但内侧眶额皮层活动的显著性相关调节在 fMRI 实验的持续时间内保持稳定。对这两个动机维度的神经反应是在参与者的注意力是否指向面孔或周围的条形图的情况下观察到的，这表明隐含动机价值和显著性是自动处理的。眶额皮层内的功能分离表明，该区域与不同的与动机相关的过程密切相关：在内侧眶额皮层中，可能会保持显著项目的表示，以促进未来对行为相关刺激的反应；相比之下，外侧眶额皮层中的临时价值效应可能反映了在没有明确的动机刺激差异的情况下，刺激评估的降低。
