Reggente Nicco, Cohen Michael S, Zheng Zhong S, Castel Alan D, Knowlton Barbara J, Rissman Jesse
Department of Psychology, University of California, Los Angeles, Los Angeles, CA, United States.
Department of Psychology, Northwestern University, Evanston, IL, United States.
Front Hum Neurosci. 2018 Jun 15;12:241. doi: 10.3389/fnhum.2018.00241. eCollection 2018.
When given a long list of items to remember, people typically prioritize the memorization of the most valuable items. Prior neuroimaging studies have found that cues denoting the presence of high value items can lead to increased activation of the mesolimbic dopaminergic reward circuit, including the nucleus accumbens (NAcc) and ventral tegmental area (VTA), which in turn results in up-regulation of medial temporal lobe encoding processes and better memory for the high value items. Value cues may also trigger the use of elaborative semantic encoding strategies which depend on interactions between frontal and temporal lobe structures. We used diffusion tensor imaging (DTI) to examine whether individual differences in anatomical connectivity within these circuits are associated with value-induced modulation of memory. DTI data were collected from 19 adults who also participated in an functional magnetic resonanceimaging (fMRI) study involving a value-directed memory task. In this task, subjects encoded words with arbitrarily assigned point values and completed free recall tests after each list, showing improved recall performance for high value items. Motivated by our prior fMRI finding of increased recruitment of left-lateralized semantic network regions during the encoding of high value words (Cohen et al., 2014), we predicted that the robustness of the white matter pathways connecting the ventrolateral prefrontal cortex (VLPFC) with the temporal lobe might be a determinant of recall performance for high value items. We found that the mean fractional anisotropy (FA) of each subject's left uncinate fasciculus (UF), a fronto-temporal fiber bundle thought to play a critical role in semantic processing, correlated with the mean number of high value, but not low value, words that subjects recalled. Given prior findings on reward-induced modulation of memory, we also used probabilistic tractography to examine the white matter pathway that links the NAcc to the VTA. We found that the number of fibers projecting from left NAcc to VTA was reliably correlated with subjects' selectivity index, a behavioral measure reflecting the degree to which recall performance was impacted by item value. Together, these findings help to elucidate the neuroanatomical pathways that support verbal memory encoding and its modulation by value.
当面对一长串需要记忆的项目时，人们通常会优先记住最有价值的项目。先前的神经影像学研究发现，表示高价值项目存在的线索会导致中脑边缘多巴胺能奖赏回路的激活增加，包括伏隔核（NAcc）和腹侧被盖区（VTA），这反过来又会导致内侧颞叶编码过程的上调以及对高价值项目的更好记忆。价值线索还可能触发精细语义编码策略的使用，这取决于额叶和颞叶结构之间的相互作用。我们使用扩散张量成像（DTI）来研究这些回路内解剖连接的个体差异是否与价值诱导的记忆调制相关。DTI数据来自19名成年人，他们还参与了一项功能磁共振成像（fMRI）研究，该研究涉及价值导向记忆任务。在这项任务中，受试者对具有任意分配分值的单词进行编码，并在每个列表后完成自由回忆测试，结果显示对高价值项目的回忆表现有所提高。基于我们先前fMRI研究的发现，即在高价值单词编码过程中左侧语义网络区域的招募增加（Cohen等人，2014年），我们预测连接腹外侧前额叶皮层（VLPFC）和颞叶的白质通路的稳健性可能是高价值项目回忆表现的一个决定因素。我们发现，每个受试者左侧钩束（UF）的平均分数各向异性（FA），一种被认为在语义处理中起关键作用的额颞纤维束，与受试者回忆的高价值单词的平均数量相关，而与低价值单词的平均数量无关。鉴于先前关于奖赏诱导的记忆调制的研究结果，我们还使用概率纤维束成像来检查连接NAcc和VTA的白质通路。我们发现，从左侧NAcc投射到VTA的纤维数量与受试者的选择性指数可靠相关，选择性指数是一种行为指标，反映回忆表现受项目价值影响的程度。总之，这些发现有助于阐明支持言语记忆编码及其价值调制的神经解剖通路。
