客体工作记忆任务中大脑皮层活动的记忆负荷效应

利用128导事件相关电位技术,采用延迟匹配任务的实验范式,测查了20名正常被试完成不同负荷客体任务时的皮层慢电位（slow cortical potentials,简称sp成分）,实验发现：背侧前额叶在刺激呈现后的700ms到1400ms出现记忆负荷效应,高负荷任务诱发的sp成分显著负于低负荷任务;低负荷任务诱发的sp成分在左前额区（500~1800ms）、左前额-中央区（700~1800ms）、左中央-顶叶区（1000~1400s和1800~4800ms）、右前额区（1800~4800ms）和右前额-中央区（1400~4800ms）显著负于高负荷任务,出现记忆负荷效应,但这种负荷效应在左右大脑半球所反映的心理意义可能不同     

工作记忆与情景记忆中脑区的重合与分离——从脑区定位看两者关系

尽管近期的研究结果认为前额叶在工作记忆和情景记忆任务中均被激活,但是仍然不清楚是否有特定的区域对两种记忆起着不同作用。对于工作记忆和情景记忆在脑区上的重合,研究者们做出了不同的解释。某些研究者认为脑区的重合反映了包含于情景记忆中的工作记忆的作用,另一些研究者则认为这种重合反映的是与工作记忆和情景记忆都有关的反省过程的性质。对此,作者提出了相应的讨论意见。     

视觉工作记忆中注意模板的表征—来自EROS的证据

采用事件相关光信号技术,分析再认任务和搜索任务下脑区的动态激活,探讨视觉工作记忆中注意模板的表征机制。实验要求被试在记忆项目后,分别完成再认任务和搜索任务。结果发现,与再认任务相比,视觉搜索任务下记忆项诱发前额叶、枕叶更高程度的激活,且前额叶的激活增强早于枕叶。研究表明,与用于再认任务的普通记忆项相比,用于视觉搜索任务的注意模板的潜在表征机制可能是：先激活前额叶以增强注意控制,并对枕叶的活动加以调节,增强注意模板表征的复述。     

视觉空间工作记忆组间差异的神经机制

为考察视觉空间工作记忆（working memory, WM）维持和操作的组间差异及其神经机制,本研究记录了高、低WM组完成延迟再认（维持）任务和心理旋转（操作）任务时的行为和事件相关电位数据。结果发现,在操作任务中,高WM组比低WM组的反应时显著更短;高WM组的中前额叶慢波显著更正、双侧后顶区慢波显著更负,并且两者的波幅显著负相关。在维持任务中,两组被试的反应时无显著差异;高WM组的中前额叶慢波显著更正。结果表明,高WM组的执行注意能力可能更强,能通过有效调节和分配加工资源来表征视觉信息。     

双特征空间客体捆绑关系的存储机制——来自ERP的证据

利用事件相关电位技术(ERPs),采用延迟匹配任务的实验范式,测查了16名正常被试完成位置客体、方向客体和位置—方向捆绑客体的工作记忆诱发的皮层慢电位。实验发现:在第1个客体呈现后的300ms到600ms之间,在顶叶皮层(CP5、P7、P3),位置客体、方向客体比捆绑客体诱发了一个更负的成分; 在右额(F4、FC6、FC2、F8)、右后颞(TP10)、左颞(T7)、左后颞(TP9)等脑区,捆绑客体比单一特征客体诱发出了一个更正的成分; 在800至1400ms的慢波成分上,位置和方向捆绑客体在F4、FC6和F8三个记录点诱发的波形比单一特征客体的波形波幅更正。右侧前额叶参与了客体整合表征的存储,该结果支持了情景缓冲器的假设。     

工作记忆的保持与操控：腹侧和背侧额叶皮层的特异性功能磁共振成像活动

为了进行大样本的老化与记忆的功能磁共振成像(fMRI)研究, 研究者设计了言语工作记忆的方案, 并且对一组健康青年人进行了施测。字母的呈现方式主要为两种条件: (i) 保持, 要求被试记住呈现的字母并且能够在4秒的间隔后保持; (ii) 操控, 被试需要将呈现的字母按字母表的顺序进行转换, 并且记住新的顺序。不管是用全脑分析, 还是用预先定义的感兴趣区域的分析方法, 对fMRI数据的分析表明本方案诱发了可靠的额叶皮层的激活, 且操控条件则引发了更为广泛的激活。背外侧和腹内侧前额叶的激活也表现出了不同特点, 操控引发了更多的背外侧前额叶激活。一些皮下区域也得到了激活, 特别是以前发现与工作记忆任务相关的一些区域。这说明该工作记忆研究方案适合探索额叶功能的与年龄相关的改变。     

两维特征图形的客体和空间工作记忆存储研究

研究采用单探测变化检测范式,考察了两维特征图形在视觉客体和视觉空间工作记忆中的存储机制,并对其容量进行测定。40名被试(平均年龄20.56±1.73岁)随机分为两个等组,分别完成实验一和实验二。实验一的刺激图形由颜色和形状两基本特征组成,实验二的刺激为由不同颜色和开口朝向组成的兰道环。两个实验结果均显示:(1)特征交换变化条件下的记忆成绩与单特征变化条件下最差的记忆成绩差异不显著;(2)空间工作记忆任务的成绩显著优于客体工作记忆任务;(3)被试在视觉工作记忆中能存储2~3个客体和3~4个空间位置。这表明,由两种不同维度特征组成的图形在视觉客体和视觉空间工作记忆中均以整合方式进行存储,空间工作记忆的容量大于客体工作记忆。     

三维图形的客体和空间工作记忆存储时程研究

研究采用单探测变化检测范式,探讨了三维图形在视觉客体和空间工作记忆中的存储时程。实验一的三维图形由不同颜色、形状组成,实验二的图形由不同颜色、图案组成。两个实验的结果均发现:被试的正确率随刺激间隔时间的延长而显著下降; 空间工作记忆任务的正确率显著高于客体工作记忆任务。研究结果表明,视觉刺激消失后,不论是客体信息还是空间信息,均随间隔时间的延长而逐渐衰退,且客体信息衰退的速度比空间信息快。总体来看,三维图形的客体和空间信息在视觉工作记忆满负荷条件下能保持大约3～5秒的时间。     

言语次级干扰任务对客体与空间信息保持的影响

通过3个行为实验,以44名大学生或研究生为被试,考察了言语次级干扰任务是否对不同言语命名难度的客体与空间工作记忆信息的保持产生选择性干扰。研究发现:无论记忆对象是言语命名困难的客体信息,还是言语命名容易的客体信息,无论探测刺激是图形形式,还是词语形式,言语次级干扰任务都对客体信息的保持产生选择性干扰;但言语次级干扰任务对空间信息保持的影响,在不同条件下则表现出不同的特点。实验结果表明客体工作记忆自动、强制性地使用言语编码和保持机制,而空间工作记忆信息的保持是否由言语编码参与则受到其他因素的影响。     

注意次级任务对客体与空间工作记忆信息保持的选择性干扰

通过两个行为实验,考察两种选择性注意干扰任务是否分别对客体与空间信息的保持产生选择性干扰,及干扰效应是否受记忆对象言语命名和编码难易程度的影响.实验1采用言语命名和编码容易的记忆任务,没有发现任何显著的干扰效应.实验2采用了言语命名和编码困难的记忆任务,结果分析发现:空间选择性注意次级干扰任务对空间工作记忆成绩存在显著的干扰效应,而基于客体的选择性注意次级干扰任务则对客体工作记忆成绩产生了显著的干扰.实验结果说明,基于客体的选择性注意和空间选择性注意分别在言语命名和编码困难客体与空间信息的保持加工中发挥作用,但当面对言语命名和编码容易的客体与空间记忆目标时,不再发生作用.     

An fMRI study of working memory for schematic facial expressions

Functional magnetic resonance imaging (fMRI) was used to examine neuronal activation in relation to increasing working memory load in an n-back task, using schematic drawings of facial expressions and scrambled drawings of the same facial features as stimuli. The main objective was to investigate whether working memory for drawings of facial features would yield specific activations compared to memory for scrambled drawings based on the same visual features as those making up the face drawings. fMRI-BOLD responses were acquired with a 1.5 T Siemens MR scanner while subjects watched the facial drawings alternated with the scrambled drawings, in a block-design. Subjects had to hold either 1 or 2 items in working memory. We found that the main effect of increasing memory load from one to two items yielded significant activations in a bilaterally distributed cortical network consisting of regions in the occipitotemporal cortex, the inferior parietal lobule, the dorsolateral prefrontal cortex, supplementary motor area and the cerebellum. In addition, we found a memory load x drawings interaction in the right inferior frontal gyrus in favor of the facial drawings. These findings show that working memory is specific for facial features which interact with a general cognitive load component to produce significant activations in prefrontal regions of the brain.     

Functional asymmetry of human prefrontal cortex: encoding and retrieval of verbally and nonverbally coded information

There are several views about the organization of memory functions in the human prefrontal cortex. One view assumes a process-specific brain lateralization according to different memory subprocesses, that is, encoding and retrieval. An alternative view emphasizes content-specific lateralization of brain systems involved in memory processes. This study addresses this apparent inconsistency between process- and content-specific lateralization of brain activity by investigating the effects of verbal and nonverbal encoding on prefrontal activations during encoding and retrieval of environmental novel sounds using fMRI. An intentional memory task was applied in which subjects were required either to judge the sounds' loudness (nonverbal encoding task) or to indicate whether or not a sound can be verbally described (verbal encoding task). Retrieval processes were examined in a subsequent yes/no recognition test. In the study phase the right posterior dorsolateral prefrontal cortex (PFC) was activated in both tasks. During verbal encoding additional activation of the left dorsolateral PFC was obtained. Retrieval-related fMRI activity varied as a function of encoding task: For the nonverbal task we detected an activation focus in the right posterior dorsolateral PFC whereas an activation in the left dorsolateral PFC was observed for the verbal task. These findings indicate that the right dorsolateral PFC is engaged in encoding of auditory information irrespective of encoding task. The lateralization of PFC activity during retrieval was shown to depend on the availability of verbal codes, with left hemispheric involvement for verbally and right hemispheric activation for nonverbally coded information.     

The neural basis of updating: Distinguishing substitution processes from other concurrent processes

Sörqvist, P. & Sætrevik, B. (2010). The neural basis of updating: Distinguishing substitution processes from other concurrent processes. Scandinavian Journal of Psychology, 51, 357–362. Most previous studies of updating processes have not been able to contrast processes of substituting items in memory with other concurrent processes. In the present investigation, we used a new task called “number updating” and an fMRI protocol to contrast the activation of trials that require item substitution (adding a new item to the working memory representation and suppressing an old item) with trials that involve no substitution (discarding the new item). Trials that require item substitution activated the dorsolateral prefrontal cortex, the posterior medial frontal cortex and the parietal lobes, areas typically seen activated for working memory tasks in general. Trials that do not require substitution activated the anterior medial frontal cortex. Studies examining executive functions have associated this area with cognitive conflict, and may represent suppression of the substitution processes.     

Investigating virtual reality navigation in amnestic mild cognitive impairment using fMRI

Spatial navigation requires a well-established network of brain regions, including the hippocampus, caudate nucleus, and retrosplenial cortex. Amnestic Mild Cognitive Impairment (aMCI) is a condition with predominantly memory impairment, conferring a high predictive risk factor for dementia. aMCI is associated with hippocampal atrophy and subtle deficits in spatial navigation. We present the first use of a functional Magnetic Resonance Imaging (fMRI) navigation task in aMCI, using a virtual reality analog of the Radial Arm Maze. Compared with controls, aMCI patients showed reduced activity in the hippocampus bilaterally, retrosplenial cortex, and left dorsolateral prefrontal cortex. Reduced activation in key areas for successful navigation, as well as additional regions, was found alongside relatively normal task performance. Results also revealed increased activity in the right dorsolateral prefrontal cortex in aMCI patients, which may reflect compensation for reduced activations elsewhere. These data support suggestions that fMRI spatial navigation tasks may be useful for staging of progression in MCI.     

Neural Bases of Human Working Memory

Working memory is the memory system that allows us to briefly keep information active, often so we can operate on it. Studies with rhesus monkeys first established that this system is partly mediated by neural mechanisms in the prefrontal cortex. Recently, there has been a substantial effort to study the neural bases of working memory in humans, using neuroimaging techniques such as positron emission tomography and functional magnetic resonance imaging. Some of the initial neuroimaging studies with humans focused on the neural mechanisms that mediate our ability to keep spatial information active. These results indicated that human spatial working memory is partly mediated by regions in parietal and prefrontal cortex. Subsequent research has shown that a different neural system is involved when people store object (rather than spatial) information, a difference similar to that found in monkeys.     

Working and long-term memory deficits in schizophrenia: is there a common prefrontal mechanism?

This study tested the hypothesis that dorsolateral prefrontal cortex deficits contribute to both working memory and long-term memory disturbances in schizophrenia. It also examined whether such deficits were more severe for verbal than nonverbal stimuli. Functional magnetic resonance imaging was used to assess cortical activation during performance of verbal and nonverbal versions of a working memory task and both encoding and recognition tasks in 38 individuals with schizophrenia and 48 healthy controls. Performance of both working memory and long-term memory tasks revealed disturbed dorsolateral prefrontal cortex activation in schizophrenia, although medial temporal deficits were also present. Some evidence was found for more severe cognitive and functional deficits with verbal than nonverbal stimuli, although these results were mixed.     

Neurocognitive Contributions to Motor Skill Learning: The Role of Working Memory

ABSTRACT

Researchers have begun to delineate the precise nature and neural correlates of the cognitive processes that contribute to motor skill learning. The authors review recent work from their laboratory designed to further understand the neurocognitive mechanisms of skill acquisition. The authors have demonstrated an important role for spatial working memory in 2 different types of motor skill learning, sensorimotor adaptation and motor sequence learning. They have shown that individual differences in spatial working memory capacity predict the rate of motor learning for sensorimotor adaptation and motor sequence learning, and have also reported neural overlap between a spatial working memory task and the early, but not late, stages of adaptation, particularly in the right dorsolateral prefrontal cortex and bilateral inferior parietal lobules. The authors propose that spatial working memory is relied on for processing motor error information to update motor control for subsequent actions. Further, they suggest that working memory is relied on during learning new action sequences for chunking individual action elements together.