Psychology Department and Volen Center for Complex Systems, Brandeis University, Waltham, Massachusetts 02453.
J Neurosci. 2014 Jan 22;34(4):1248-57. doi: 10.1523/JNEUROSCI.3331-13.2014.
Neural responses in many cortical regions encode information relevant to behavior: information that necessarily changes as that behavior changes with learning. Although such responses are reasonably theorized to be related to behavior causation, the true nature of that relationship cannot be clarified by simple learning studies, which show primarily that responses change with experience. Neural activity that truly tracks behavior (as opposed to simply changing with experience) will not only change with learning but also change back when that learning is extinguished. Here, we directly probed for this pattern, recording the activity of ensembles of gustatory cortical single neurons as rats that normally consumed sucrose avidly were trained first to reject it (i.e., conditioned taste aversion learning) and then to enjoy it again (i.e., extinction), all within 49 h. Both learning and extinction altered cortical responses, consistent with the suggestion (based on indirect evidence) that extinction is a novel form of learning. But despite the fact that, as expected, postextinction single-neuron responses did not resemble "naive responses," ensemble response dynamics changed with learning and reverted with extinction: both the speed of stimulus processing and the relationships among ensemble responses to the different stimuli tracked behavioral relevance. These data suggest that population coding is linked to behavior with a fidelity that single-neuron coding is not.
这些信息随着学习而变化。尽管这些反应很合理地被认为与行为的因果关系有关，但单纯的学习研究并不能阐明这种关系的本质，因为这些研究主要表明反应随经验而变化。真正与行为相关（而不仅仅是随经验变化）的神经活动不仅会随学习而变化，而且在学习消退时也会恢复。在这里，我们直接探测了这种模式，记录了味觉皮层神经元集合的活动，这些大鼠原本非常喜欢蔗糖，但首先被训练拒绝它（即条件性味觉厌恶学习），然后再次喜欢它（即消退），所有这些都在 49 小时内完成。学习和消退都改变了皮层反应，这与（基于间接证据）的假设一致，即消退是一种新的学习形式。但是，尽管正如预期的那样，消退后的单个神经元反应并不像“幼稚反应”，集合反应动力学随学习而变化，并随消退而恢复：刺激处理的速度以及对不同刺激的集合反应之间的关系都与行为的相关性有关。这些数据表明，群体编码与行为的联系比单个神经元编码更紧密。
