Naya Yuji, Yoshida Masatoshi, Miyashita Yasushi
Department of Physiology, The University of Tokyo School of Medicine, Hongo, Tokyo 113-0033, Japan.
J Neurosci. 2003 Apr 1;23(7):2861-71. doi: 10.1523/JNEUROSCI.23-07-02861.2003.
The macaque inferotemporal (IT) cortex, which serves as the storehouse of visual long-term memory, consists of two distinct but mutually interconnected areas: area TE (TE) and area 36 (A36). In the present study, we tested whether memory encoding is put forward at this stage, i.e., whether association between the representations of different but semantically linked objects proceeds forward from TE to A36. To address this question, we trained monkeys in a pair-association (PA) memory task, after which single-unit activities were recorded from TE and A36 during PA trials. Neurons in both areas showed stimulus-selective cue responses (347 in TE, 76 in A36; "cue-selective neurons") that provided, at the population level, mnemonic linkage between the paired associates. The percentage of neurons in which responses to the paired associates were significantly (p < 0.01) correlated at the single-neuron level ("pair-coding neuron") dramatically increased from TE (4.9% of the cue-selective neurons) to A36 (33%). The pair-coding neurons in A36 were further separable into Type1 (68%) and Type2 (32%) on the basis of their initial transient responses after cue stimulus presentation. Type1 neurons, but not Type2 neurons, began to encode association between paired stimuli as soon as they exhibited stimulus selectivity. Thus, the representation of long-term memory encoded by Type1 neurons in A36 is likely substantiated without feedback input from other higher centers. Therefore, we conclude that association between the representations of the paired associates proceeds forward at this critical step within IT cortex, suggesting selective convergence onto a single A36 neuron from two TE neurons that encode separate visual objects.
猕猴颞下（IT）皮质是视觉长期记忆的储存库，由两个不同但相互连接的区域组成：TE区（TE）和36区（A36）。在本研究中，我们测试了记忆编码是否在这个阶段提出，即不同但语义相关的物体表征之间的关联是否从TE区向前传递到A36区。为了解决这个问题，我们训练猴子进行配对联想（PA）记忆任务，之后在PA试验期间记录TE区和A36区的单神经元活动。两个区域的神经元都表现出刺激选择性线索反应（TE区347个，A36区76个；“线索选择性神经元”），在群体水平上提供了配对联想之间的记忆联系。在单神经元水平上，对配对联想的反应显著（p < 0.01）相关的神经元百分比（“配对编码神经元”）从TE区（线索选择性神经元的4.9%）到A36区（33%）急剧增加。A36区的配对编码神经元根据线索刺激呈现后的初始瞬态反应进一步分为1型（68%）和2型（32%）。1型神经元，而不是2型神经元，一旦表现出刺激选择性就开始编码配对刺激之间的关联。因此，A36区1型神经元编码的长期记忆表征可能在没有来自其他高级中枢的反馈输入的情况下得到证实。因此，我们得出结论，配对联想的表征之间的关联在IT皮质内的这个关键步骤向前进行，这表明从两个编码单独视觉物体的TE神经元选择性汇聚到单个A36神经元上。
