Neurobiology Curriculum, University of North Carolina, Chapel Hill, NC, USA
Eur J Neurosci. 2013 Aug;38(4):2637-48. doi: 10.1111/ejn.12271. Epub 2013 Jun 13.
The development of alcoholism may involve a shift from goal-directed to habitual drinking. These action control systems are distinct in the dorsal striatum, with the dorsomedial striatum (DMS) important for goal-directed behavior and the dorsolateral striatum (DLS) required for habit formation. Goal-directed behavior can be modeled in rats with a fixed ratio (FR) reinforcement schedule, while a variable interval (VI) schedule promotes habitual behavior (e.g. insensitivity to contingency degradation). Using extracellular recordings from chronically implanted electrodes, we investigated how DMS and DLS neurons encoded lever-press responses and conditioned cues during operant alcohol self-administration in these two models. In rats self-administering 10% alcohol on an FR schedule, the DMS neuronal population showed increased firing at the onset of start-of-session stimuli. During self-administration, the most prominent phasic firing patterns in the DMS occurred at the time of reinforcement and reinforcement-associated cues, while the most prominent phasic activity in the DLS surrounded the lever response. Neural recordings from an additional cohort of rats trained on a VI schedule revealed a similar pattern of results; however, phasic changes in firing were smaller and differences between the medial and lateral dorsal striatum were less marked. In summary, the DMS and DLS exhibited overlapping but specialized phasic firing patterns: DMS excitations were typically time-locked to reinforcement, while DLS excitations were generally associated with lever responses. Furthermore, the regional specificities and magnitudes of phasic firing differed between reinforcement schedules, which may reflect differences in behavioral flexibility, reward expectancy and the action sequences required to procure reinforcement.
酗酒的发展可能涉及从目标导向到习惯性饮酒的转变。这些行动控制系统在背侧纹状体中是不同的，背侧纹状体的背内侧（DMS）对目标导向行为很重要，背外侧纹状体（DLS）对习惯形成很重要。通过固定比率（FR）强化方案，可以在大鼠中模拟目标导向行为，而可变间隔（VI）方案则促进习惯性行为（例如对偶然性降低不敏感）。使用慢性植入电极的细胞外记录，我们研究了在这两种模型中，DMS 和 DLS 神经元如何在操作酒精自我给药期间编码杠杆按压反应和条件线索。在以 FR 方案自我给予 10%酒精的大鼠中，DMS 神经元群体在开始会话刺激时表现出更高的放电率。在自我给药期间，DMS 中最突出的相位放电模式发生在强化和强化相关线索的时候，而 DLS 中最突出的相位活动则围绕着杠杆反应。在另一批接受 VI 方案训练的大鼠的神经记录中发现了类似的结果模式；然而，放电的相位变化较小，内侧和外侧背侧纹状体之间的差异不明显。总之，DMS 和 DLS 表现出重叠但专门的相位放电模式：DMS 的兴奋通常与强化相关联，而 DLS 的兴奋通常与杠杆反应相关联。此外，相位放电的区域特异性和幅度在强化方案之间存在差异，这可能反映了行为灵活性、奖励预期以及获得强化所需的动作序列的差异。
