Funahashi S, Inoue M, Kubota K
Department of Cognitive Sciences, Graduate School of Human and Environmental Studies, Kyoto University, Sakyo-ku, Japan.
Behav Brain Res. 1997 Mar;84(1-2):203-23. doi: 10.1016/s0166-4328(96)00151-9.
To investigate whether prefrontal neurons temporarily retain information regarding multiple spatial positions, single-neuron activity was recorded while monkeys performed a delayed sequential reaching task, in which they needed to remember two cue positions out of three and their temporal order of presentation. Most neurons were also tested on a conventional delayed reaching task, in which they needed to remember one cue position during the delay. Among 72 neurons that exhibited significant delay-period activity, one group of neurons (n = 19) exhibited delay-period activity only when a visual cue was presented at one of the three positions (position-dependent). Of these, 6 neurons exhibited this activity when a cue was presented at that position independent of the temporal order, whereas 13 neurons exhibited this activity only when a cue was presented at that position in a particular temporal order (e.g., as the first cue or the second cue). Another group of neurons (n = 39) exhibited delay-period activity only when visual cues were presented at two positions out of three (pair-dependent). Of these, 7 neurons exhibited pair-dependent activity independent of the temporal order of cue presentation. However, 32 neurons exhibited this activity only when two cues were presented in a particular temporal order. The remaining 11 neurons exhibited non-differential activity during the delay period and 3 neurons exhibited miscellaneous activity. These results show that a single prefrontal neuron can retain information regarding two spatial positions, and that, to retain two spatial positions and the temporal order of cue presentation, new types of delay-period activity emerged; i.e., pair-dependent activity and temporal order-dependent activity. Both types of activity could be a mechanism for simultaneously retaining two items of spatial information and for effectively combining multiple spatial information by a single neuron. In addition, the presence of delay-period activity with position-dependency, pair-dependency and temporal order-dependency suggests that the dorsolateral prefrontal cortex plays an important role in planning sequential behaviors.
为了研究前额叶神经元是否会暂时保留有关多个空间位置的信息，研究人员在猴子执行延迟顺序伸手任务时记录了单神经元活动，在该任务中，猴子需要记住三个提示位置中的两个以及它们的呈现时间顺序。大多数神经元也在传统的延迟伸手任务中进行了测试，在该任务中，它们需要在延迟期间记住一个提示位置。在72个表现出显著延迟期活动的神经元中，一组神经元（n = 19）仅在视觉提示出现在三个位置之一时（位置依赖性）才表现出延迟期活动。其中，6个神经元在提示出现在该位置时表现出这种活动，与时间顺序无关，而13个神经元仅在提示以特定时间顺序出现在该位置时（例如，作为第一个提示或第二个提示）才表现出这种活动。另一组神经元（n = 39）仅在视觉提示出现在三个位置中的两个时（对依赖性）才表现出延迟期活动。其中，7个神经元表现出与提示呈现时间顺序无关的对依赖性活动。然而，32个神经元仅在两个提示以特定时间顺序呈现时才表现出这种活动。其余11个神经元在延迟期表现出非差异性活动，3个神经元表现出其他活动。这些结果表明，单个前额叶神经元可以保留有关两个空间位置的信息，并且为了保留两个空间位置和提示呈现的时间顺序，出现了新型的延迟期活动；即对依赖性活动和时间顺序依赖性活动。这两种活动都可能是单个神经元同时保留两项空间信息并有效组合多个空间信息的机制。此外，存在具有位置依赖性、对依赖性和时间顺序依赖性的延迟期活动表明背外侧前额叶皮质在规划顺序行为中起重要作用。
