Suzuki W A, Miller E K, Desimone R
Laboratory of Neuropsychology, National Institute of Mental Health, Bethesda, Maryland 20892-4415, USA.
J Neurophysiol. 1997 Aug;78(2):1062-81. doi: 10.1152/jn.1997.78.2.1062.
Lesions of the entorhinal cortex in humans, monkeys, and rats impair memory for a variety of kinds of information, including memory for objects and places. To begin to understand the contribution of entorhinal cells to different forms of memory, responses of entorhinal cells were recorded as monkeys performed either an object or place memory task. The object memory task was a variation of delayed matching to sample. A sample picture was presented at the start of the trial, followed by a variable sequence of zero to four test pictures, ending with a repetition of the sample (i.e., a match). The place memory task was a variation of delayed matching to place. In this task, a cue stimulus was presented at a variable sequence of one to four "places" on a computer screen, ending with a repetition of one of the previously shown places (i.e., a match). For both tasks, the animals were rewarded for releasing a bar to the match. To solve these tasks, the monkey must 1) discriminate the stimuli, 2) maintain a memory of the appropriate stimuli during the course of the trial, and 3) evaluate whether a test stimulus matches previously presented stimuli. The responses of entorhinal cortex neurons were consistent with a role in all three of these processes in both tasks. We found that 47% and 55% of the visually responsive entorhinal cells responded selectively to the different objects or places presented during the object or place task, respectively. Similar to previous findings in prefrontal but not perirhinal cortex on the object task, some entorhinal cells had sample-specific delay activity that was maintained throughout all of the delay intervals in the sequence. For the place task, some cells had location-specific maintained activity in the delay immediately following a specific cue location. In addition, 59% and 22% of the visually responsive cells recorded during the object and place task, respectively, responded differently to the test stimuli according to whether they were matching or non-matching to the stimuli held in memory. Responses of some cells were enhanced to matching stimuli, whereas others were suppressed. This suppression or enhancement typically occurred well before the animals' behavioral response, suggesting that this information could be used to perform the task. These results indicate that entorhinal cells receive sensory information about both objects and spatial locations and that their activity carries information about objects and locations held in short-term memory.
人类、猴子和大鼠的内嗅皮质损伤会损害对各种信息的记忆，包括对物体和地点的记忆。为了初步了解内嗅皮质细胞对不同形式记忆的作用，在猴子执行物体或地点记忆任务时记录了内嗅皮质细胞的反应。物体记忆任务是延迟匹配样本的一种变体。在试验开始时呈现一个样本图片，随后是零到四张测试图片的可变序列，最后重复样本（即匹配）。地点记忆任务是延迟匹配地点的一种变体。在这个任务中，一个提示刺激在电脑屏幕上一到四个“地点”的可变序列中呈现，最后重复之前显示的地点之一（即匹配）。对于这两个任务，动物因向匹配项释放横杆而获得奖励。为了解决这些任务，猴子必须：1）区分刺激；2）在试验过程中保持对适当刺激的记忆；3）评估测试刺激是否与先前呈现的刺激匹配。内嗅皮质神经元的反应与这两个任务中所有这三个过程中的作用一致。我们发现，47%和55%的视觉反应性内嗅细胞分别对物体或地点任务期间呈现的不同物体或地点有选择性反应。与之前在额叶前部而非鼻周皮质关于物体任务的发现类似，一些内嗅细胞具有样本特异性延迟活动，在序列中的所有延迟间隔内都保持这种活动。对于地点任务，一些细胞在特定提示位置之后的延迟中具有位置特异性的持续活动。此外，在物体和地点任务期间记录的视觉反应性细胞中，分别有59%和22%根据测试刺激与记忆中保存的刺激是否匹配而对测试刺激有不同反应。一些细胞对匹配刺激的反应增强，而另一些则受到抑制。这种抑制或增强通常在动物行为反应之前就发生了，这表明这些信息可用于执行任务。这些结果表明，内嗅细胞接收有关物体和空间位置的感觉信息，并且它们的活动携带有关短期记忆中保存的物体和位置的信息。
