The neuroscience of pleasure. Focus on "Ventral pallidum firing codes hedonic reward: when a bad taste turns good".
The neuroscience of pleasure. Focus on "Ventral pallidum firing codes hedonic reward: when a bad taste turns good".
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快乐的神经科学。
DOI：
10.1152/jn.00727.2006
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发表时间：
2006
影响因子：
2.5
通讯作者：
Carelli,ReginaM
中科院分区：
文献类型：
--
作者：
Wheeler,RobertA;Carelli,ReginaM
两千多年来，哲学家们一直在努力定义快乐或享乐，更不用说解释了。借助现代动物模型和技术，科学家现在能够通过检查其神经基础来全面描述这种情感状态。在本期《神经生理学杂志》（第 2399-2409 页）中，Tindell 及其同事使用一种优雅的还原论方法在定义这些神经基础方面迈出了意义深远的一步（Tindell 2006）。作者控制了各种奖励因素，这些因素在历史上曾让那些雄心勃勃、试图研究这样一个无形主题的研究人员感到困惑。具体来说，Tindell 及其同事确定了腹侧苍白球 (VP) 神经元在编码享乐方面的作用。作者将浓度难以接受的盐水注入大鼠口腔，同时记录单个 VP 神经元的细胞外电生理活动。同时测量口面部对难吃味道的厌恶反应。三天后，对大鼠进行低钠测试并重新进行测试。在钠耗尽的状态下，这些大鼠现在表现出从厌恶味觉反应性到食欲性味觉反应性的行为转变，这与输注盐水后 VP 活性增加相一致（类似于可口的蔗糖溶液的反应）。巧妙的隐式控制表明，改变的电生理活动编码了享乐转变，而不是动机行为或感觉编码的改变。尽管一个多世纪前就有人提出情感状态可以通过行为表达来决定（Darwin 1898），但这个概念仍然存在争议。也许当前研究中最有趣的方面是使用反映享乐的味觉反应，或者用作者的话说，“喜欢”。尽管有人认为这种解释不够有力（Panksepp 2005），但它确实推进了味觉反应作为摄取和排斥反应（即完成反应的反映）的原始研究的结论，这些反应由尾部脑干充分介导（Grill 和 Norgren 1978c）。最近的药理学操作表明，味觉反应性似乎与完成行为无关，并且受到吻端神经结构的分层调节（Berridge 2000；Kelley 和 Berridge 2002）。味觉反应也不同于动机行为。大鼠对口腔内输注溶液的浓度更适口时会增加食欲味觉反应性，同时对令人不快的促味剂浓度不断升高会增加厌恶性味觉反应性（Grill 和 Norgren 1978b）。同样，味觉反应也不是反射性感觉的简单表达。当老鼠得知甜味预示着疾病时，它不仅会避开促味剂，还会表现出排斥反应，就好像甜味现在变得难吃了一样（Grill and Norgren 1978a）。类似地，如果可口的味道与胃内葡萄糖输注相结合，食欲味觉反应就会增加（Myers and Sclafani 2001）。因此，味觉反应性似乎反映了大鼠对味觉刺激的情感反应，因此是非人类享乐的一个令人信服的衡量标准（Berridge 2000）。
For more than 2,000 years, philosophers have struggled to define, let alone explain, pleasure or hedonics. With contemporary animal models and techniques, scientists now have the ability to provide a comprehensive description of this affective state by examining its neural underpinnings. In this issue of the Journal of Neurophysiology (p. 2399–2409), Tindell and colleagues use an elegant, reductionist approach to take a profound step in defining these neural foundations (Tindell 2006). The authors control for various elements of reward that historically have confounded researchers ambitious enough to attempt to study such an intangible topic. Specifically, Tindell and colleagues establish a role for ventral pallidum (VP) neurons in encoding hedonics. The authors infused an unpalatable concentration of saline into the oral cavities of rats while recording the extracellular electrophysiological activity of single VP neurons. Aversive orofacial reactions to the unpalatable taste were simultaneously measured. Three days later, rats were made sodium deplete and retested. In a sodium-depleted state, these rats now exhibited a behavioral switch from aversive taste reactivity to appetitive taste reactivity coincident with increased VP activity to the infusion of saline (similar to responses for a palatable sucrose solution). The clever implicit controls indicate that the altered electrophysiological activity encodes a hedonic shift rather than alterations in motivated behavior or sensory coding. Despite the proposal over a century ago that affective state can be determined by behavioral expression (Darwin 1898), this notion remains controversial. Perhaps the most intriguing aspect of the current study is the use of taste reactivity reflecting hedonics, or in the author’s words,“liking.” Although it has been argued that this interpretation is not strong enough (Panksepp 2005), it certainly advances the conclusions of the original studies of taste reactivity as ingestion and rejection responses,(ie, a reflection of consummatory responses) that are sufficiently mediated by the caudal brain stem (Grill and Norgren 1978c). Recent pharamacological manipulations have shown that taste reactivity appears to be dissociable from consummatory behavior and is hierarchically modulated by rostral neural structures (Berridge 2000; Kelley and Berridge 2002). Taste reactivity also is distinct from motivated behavior. Rats increase appetitive taste reactivity for more palatable concentrations of intraorally infused solutions while increasing aversive taste reactivity to escalating concentrations of unpalatable tastants (Grill and Norgren 1978b). Likewise, taste reactivity is not a simple expression of reflexive sensation. When a rat learns that a sweet taste predicts illness, it doesn’t just avoid the tastant, it exhibits rejection responses as if the sweet taste is now unpalatable (Grill and Norgren 1978a).Similarly, if a palatable taste is paired with an intragastric glucose infusion, appetitive taste reactivity increases (Myers and Sclafani 2001). Thus taste reactivity appears to be reflective of the rat’s affective reaction to taste stimuli and therefore is a compelling measure of hedonics in non-humans (Berridge 2000).