Different types of working memory binding in epilepsy patients with unilateral anterior temporal lobectomy

The medial temporal lobe is an important structure for long-term memory formation, but its role in working memory is less clear. Recent studies have shown hippocampal involvement during working memory tasks requiring binding of information. It is yet unclear whether this is limited to tasks containing spatial features. The present study contrasted three binding conditions and one single-item condition in patients with unilateral anterior temporal lobectomy.A group of 43 patients with temporal lobectomy (23 left; 20 right) and 20 matched controls were examined with a working memory task assessing spatial relational binding (object–location), non-spatial relational binding (object–object), conjunctive binding (object–colour) and working memory for single items. We varied the delay period (3 or 6 s), as there is evidence showing that delay length may modulate working memory performance.The results indicate that performance was worse for patients than for controls in both relational binding conditions, whereas patients were unimpaired in conjunctive binding. Single-item memory was found to be marginally impaired, due to a deficit on long-delay trials only.In conclusion, working memory binding deficits are found in patients with unilateral anterior temporal lobectomy. The role of the medial temporal lobe in working memory is not limited to tasks containing spatial features. Rather, it seems to be involved in relational binding, but not in conjunctive binding. The medial temporal lobe gets involved when working memory capacity does not suffice, for example when relations have to be maintained or when the delay period is long.     

Visual search is slowed when visuospatial working memory is occupied

Visual working memory plays a central role in most models of visual search. However, a recent study showed that search efficiency was not impaired when working memory was filled to capacity by a concurrent object memory task (Woodman, Vogel, & Luck, 2001). Objects and locations may be stored in separate working memory subsystems, and it is plausible that visual search relies on the spatial subsystem, but not on the object subsystem. In the present study, we sought to determine whether maintaining spatial information in visual working memory impairs the efficiency of a concurrent visual search task. Visual search efficiency and spatial memory accuracy were both impaired when the search and the memory tasks were performed concurrently, as compared with when the tasks were performed separately. These findings suggest that common mechanisms are used to process information during difficult visual search tasks and to maintain spatial information in working memory.     

Parallel working memory for spatial location and food-related object cues in foraging pigeons: binocular and lateralized monocular performance

During foraging, animals can increase their success by both remembering feeding sites and remembering food-related object cues. Because earlier studies have tested either the site or object memory in isolation, the aim of the present study was to evaluate how efficiently birds can utilize both memories simultaneously. Furthermore, the idea was tested that lateralization might be the principle of brain organization that allows for efficient parallel processing. Pigeons learned to search for food in a complex maze with 16 baited sites. To obtain the maximum reward they had to perform two tasks in parallel, a spatial working memory task and an object-specific working memory task. Birds performed well on this dual task but, compared with spatial working memory alone, they were impaired during the first choices of a trial (Experiment 1). When the left and the right brain hemispheres were tested separately by means of monocular occlusion (Experiment 2), object discrimination was better when birds used their right eye/left hemisphere. This was most pronounced during the first choices of a trial. On the spatial component of the task, performance on binocular trials was better than on monocular trials, but monocularly both hemispheres performed at the same level. Results show that on this dual task, discrimination of food-related object cues predominantly involved the left brain hemisphere whereas both hemispheres contributed equally to spatial performance.     

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。     

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。     

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.     

Context Memory in Korsakoff’s Syndrome

Memory for contextual information and target-context integration are crucial for successful episodic memory formation and are impaired in patients with Korsakoff's syndrome. In this paper we review the evidence for the notion that a context memory deficit makes an important contribution to the amnesia in these patients. First, we focus on anterograde memory for contextual (spatial and temporal) information. Next, the use of contextual cues in memory retrieval is examined and their role in retrograde amnesia and confabulation. Evidence on the role of contextual cues and associations in working memory is discussed in relation to the underlying neurocognitive mechanisms and their dissociation from long-term encoding. Finally, we focus on implicit learning of contextual information in Korsakoff patients. It can be concluded that Korsakoff patients are impaired in the explicit processing of contextual information and in target-context binding, both in long-term (retrograde and anterograde) memory and in working memory. These results extend the context memory deficit hypothesis. In contrast, implicit contextual learning is relatively preserved in these patients. These findings are discussed in relation to evidence of dysfunction of the extended diencephalic-hippocampal memory circuit in Korsakoff's syndrome.     

客体相似性对不同认知方式个体视觉工作记忆表征的影响

采用整体检测的变化察觉范式,探讨客体的相似性对客体—空间型认知方式个体视觉工作记忆表征的影响。行为结果显示,在不相似客体的视觉工作记忆表征任务中,客体型者在长延时条件的成绩优于空间型者,而在相似客体的视觉工作记忆表征任务中,两者无差异;ERP结果显示,在不相似客体视觉工作记忆表征任务中,与客体型者相比,空间型者在大脑皮层诱发出更大的负SP。以上结果表明,客体型者比空间型者对不相似客体视觉工作记忆加工具有优势,其潜在机制可能在于,客体型者对不相似客体视觉工作记忆表征时的神经活动效能更高。     

Hippocampal involvement in spatial and working memory: a structural MRI analysis of patients with unilateral mesial temporal lobe sclerosis.

Forty-seven patients with unilateral temporal lobe epilepsy (TLE) were investigated on the Nine-Box Maze. The task was designed to compare working memory and spatial mapping theories of the functions of the hippocampus and provide measures of spatial, object, working, and reference memory. The results extended our previous findings in a larger group of patients. Spatial memory deficits across both working and reference memory conditions were found in patients with a right epileptogenic focus. There was no evidence of an object working memory deficit, but a nonlateralized impairment in object reference memory was revealed, which is consistent with our previous findings. The pattern of results was confirmed in a subgroup of 33 patients with unilateral atrophy localized to the hippocampus and parahippocampal gyrus, as verified by volumetric analysis of magnetic resonance images. In addition spatial memory errors significantly correlated with volumetric measures of mesial temporal lobe structures and not with measures of the remaining temporal cortex. In contrast, object reference memory errors correlated with volumetric measures of the temporal cortex and not with mesial temporal lobe structures. These findings support a specialized role for the right hippocampal region in spatial memory.     

Oculomotor delayed response abnormalities in young offspring and siblings at risk for schizophrenia

Individuals with schizophrenia are know to demonstrate cognitive and behavioral difficulties, particularly alterations in executive functions, including working memory. It is unclear whether these deficits reflect trait-related vulnerability to schizophrenia indicators and can be assessed by studying nonpsychotic relatives of patients with schizophrenia. In this study, we used an oculomotor delayed response (ODR) paradigm to examine spatial working memory in 37 "high-risk" child and adolescent offspring and siblings (age range=6-25 years) of patients with schizophrenia or schizoaffective disorder. Compared with 37 age- and sex-matched healthy controls (age range=6-23 years), high-risk subjects showed nonsignificantly greater errors in the ODR task at longer delay intervals. Statistical analyses suggested that performance improved with age in healthy control subjects, whereas it worsened with age in high-risk subjects. In both groups, the ODR errors were generally associated with poorer sustained attention (Continuous Performance Test: visuospatial d prime), somewhat poorer executive function (Wisconsin Card Sorting Test), and elevated Heinrichs-Buchanan neurological soft signs scores. These findings indicate the presence of spatial working memory abnormalities in individuals at risk for schizophrenia. Furthermore, these abnormalities may be progressive in nature. The ODR task is a valuable indicator of prefrontal cortical function and spatial working memory and may be a potentially valuable marker for familial risk of schizophrenia.     

客体相似性对不同认知方式个体视觉工作记忆表征的影响

采用整体检测的变化察觉范式,探讨客体的相似性对客体—空间型认知方式个体视觉工作记忆表征的影响。行为结果显示,在不相似客体的视觉工作记忆表征任务中,客体型者在长延时条件的成绩优于空间型者,而在相似客体的视觉工作记忆表征任务中,两者无差异;ERP结果显示,在不相似客体视觉工作记忆表征任务中,与客体型者相比,空间型者在大脑皮层诱发出更大的负SP。以上结果表明,客体型者比空间型者对不相似客体视觉工作记忆加工具有优势,其潜在机制可能在于,客体型者对不相似客体视觉工作记忆表征时的神经活动效能更高。     

Neuropsychological profile in patients with schizotypal personality disorder or schizophrenia

Neuropsychological impairments have been consistently reported in patients with schizophrenia. As little is known whether subjects with schizotypal personality disorder exhibit neurocognitive dysfunction similar to that in schizophrenia, we assessed the neuropsychological profile of 15 subjects with schizotypal personality disorder and compared it with that for 15 patients with schizophrenia and for 15 psychiatrically normal volunteers. All participants were administered a standard neuropsychological battery assessing language ability, spatial ability, visuomotor function, verbal memory, visual memory, auditory attention, visual attention, and executive function. Performance on most of the cognitive domains was impaired in patients with schizotypal personality disorder but less than patients with schizophrenia. Specifically, impairment in verbal memory and visuomotor ability in patients with schizotypal personality disorder and patients with schizophrenia were comparable, while patients with schizophrenia performed worse on the test of executive function than did patients with schizotypal personality disorder. As a whole, cognitive deficits in patients with schizotypal personality disorder were qualitatively similar to, but quantitatively milder than, those for patients with schizophrenia. The results suggest that cognitive abilities related to frontotemporal lobe function are disturbed across these schizophrenia-spectrum disorders.     

Ensemble coding remains accurate under object and spatial visual working memory load

A number of studies have provided evidence that the visual system statistically summarizes large amounts of information that would exceed the limitations of attention and working memory (ensemble coding). However the necessity of working memory resources for ensemble coding has not yet been tested directly. In the current study, we used a dual task design to test the effect of object and spatial visual working memory load on size averaging accuracy. In Experiment 1, we tested participants’ accuracy in comparing the mean size of two sets under various levels of object visual working memory load. Although the accuracy of average size judgments depended on the difference in mean size between the two sets, we found no effect of working memory load. In Experiment 2, we tested the same average size judgment while participants were under spatial visual working memory load, again finding no effect of load on averaging accuracy. Overall our results reveal that ensemble coding can proceed unimpeded and highly accurately under both object and spatial visual working memory load, providing further evidence that ensemble coding reflects a basic perceptual process distinct from that of individual object processing.     

客体和空间工作记忆中三维图形的特征加工时程

采用单探测变化觉察范式，对三维图形的特征在客体和空间工作记忆中的加工时程进行了探讨。实验一的材料是由不同颜色和形状组成的规则立体图形。实验二的材料是由不同颜色和图案组成的六棱柱。实验结果显示：（1）客体和空间工作记忆绩效均随识记项目数的增加而显著下降；（2）随着刺激呈现时间的延长，客体工作记忆绩效显著提高，空间工作记忆绩效无明显增加；且在三种呈现时间条件下，空间工作记忆绩效均高于客体工作记忆；（3）三维图形中颜色特征的检测绩效优于形状、图案和特征捆绑。这些结果表明，视觉工作记忆中三维图形的特征加工存在显著的时程效应，空间位置加工最早完成，其次是颜色加工，然后是形状与颜色-形状的捆绑，最后是图案与颜色-图案的捆绑。     

A male advantage for spatial and object but not verbal working memory using the n-back task

Sex-related differences have been reported for performance and neural substrates on some working memory measures that carry a high cognitive load, including the popular n-back neuroimaging paradigm. Despite some evidence of a sex effect on the task, the influence of sex on performance represents a potential confound in neuroimaging research. The present study investigated sex-related differences in verbal, spatial, and common object versions of the high cognitive load "n-back" working memory task. Eighteen male and 18 female undergraduates completed all 3 versions of the task. A mixed ANOVA, with Sex (male and female) as the between-subjects factor and Condition (verbal, spatial, and object) as the within-subjects repeated measure revealed that males were significantly more accurate than females on the spatial and object versions of the n-back task and performed equivalently to females on the verbal version of the task. Although the expected female advantage for verbal working memory was not found using this effortful n-back task, these results support a male advantage for high cognitive load spatial and object working memory. Future research should take into account the influence of sex on performance of the n-back task, and examine sex-related differences in working memory using other paradigms.     

Role of the dorsal hippocampus in object memory load

The dorsal hippocampus is crucial for mammalian spatial memory, but its exact role in item memory is still hotly debated. Recent evidence in humans suggested that the hippocampus might be selectively involved in item short-term memory to deal with an increasing memory load. In this study, we sought to test this hypothesis. To this aim we developed a novel behavioral procedure to study object memory load in mice by progressively increasing the stimulus set size in the spontaneous object recognition task. Using this procedure, we demonstrated that naive mice have a memory span, which is the number of elements they can remember for a short-time interval, of about six objects. Then, we showed that excitotoxic selective lesions of the dorsal hippocampus did not impair novel object discrimination in the condition of low memory load. In contrast, the same lesion impaired novel object discrimination in the high memory load condition, and reduced the object memory span to four objects. These results have important heuristic and clinical implications because they open new perspective toward the understanding of the role of the hippocampus in item memory and in memory span deficits occurring in human pathologies, such as Alzheimer's disease and schizophrenia.     

Cognitive decline and human (Homo sapiens) aging: an investigation using a comparative neuropsychological approach

Using a comparative neuropsychological approach, the authors compared performance of younger and healthy older adults ages 65 and over on tasks originally developed to measure cognition in animals. A battery of 6 tasks was used to evaluate object discrimination, egocentric spatial abilities, visual and spatial working memory, and response shifting. Older adults performed more poorly than younger adults on tasks that evaluate egocentric spatial abilities, response shifting, and to a lesser extent object recognition. The two groups did not differ for tasks that evaluate spatial working memory and object discrimination. The impairments the authors observed in tasks that evaluate response shifting and object recognition are consistent with those found in canines and primates as well as those found in Alzheimer's disease. The results are consistent with the notion that cognitive processes supported by the amygdala and the orbitofrontal cortex are among the first to decline with increasing age in both humans and animals.     

三维图形的视空间工作记忆容量研究

采用三维几何图形为材料,通过单探测变化觉察范式来测定视觉工作记忆的存储容量,并比较客体工作记忆和空间工作记忆容量的差异。实验1、2的材料分别为由颜色和形状两个基本特征组成的三维图形和由一个基本特征和一个细节特征组成的三维图形。两个实验结果显示,被试能在视觉工作记忆中存储约2-3个客体和4个空间位置,空间工作记忆容量显著大于客体工作记忆容量。进一步的比较发现,被试对由两个基本特征组成的三维图形的存储容量大于由一个基本特征和一个细节特征组成的三维图形。这表明,组成三维图形的特征类型对视空间工作记忆的存储容量有显著影响。     

Effects of Domain,Retention Interval,and Information Load on Young and Older Adults’ Visuospatial Working Memory

Age-related differences in visuospatial working memory were examined in 69 young adults and 49 older adults exposed to three pairs of tasks. Each pair consisted of one task involving information about the form or appearance of items and another task involving information about item locations. The first pair of tasks manipulated retention interval and required maintaining information about one item. The second pair also manipulated retention interval and required maintaining information about multiple items presented simultaneously. The third pair manipulated the number of sequentially presented items. Analyses of the first two pairs of tasks revealed significant age deficits in working memory for spatial locations but not in working memory for visual features. Notably, there were no age differences in the effect of retention interval on any of the four tasks, suggesting that visuospatial information is lost at similar rates in older and young adults. Analyses of the third pair of tasks revealed that, regardless of domain, increasing the amount of information impaired older adults’ memory performance to a greater extent than young adults’ performance. Thus, the present results suggest differences in basic working memory capacity in both domains, but a lack of age differences in rates of forgetting from working memory, and greater age-related deficits in the spatial domain than in the object domain.     

Emotion-induced amnesia in rats: working memory-specific impairment, corticosterone-memory correlation, and fear versus arousal effects on memory

We have shown previously that psychological stress (predator exposure) impairs spatial memory in rats. We have extended that finding here to show that predator stress selectively impaired recently acquired (hippocampal-dependent) spatial working memory without affecting long-term (hippocampal-independent) spatial reference memory. We also investigated why predator exposure impairs memory. Was spatial memory impaired because of the fear-provoking aspects of predator exposure or only because the cat was a novel and arousing stimulus? If the latter possibility was correct, then any novel and arousing stimulus, independent of its emotional valence (i.e., aversive or appetitive), would impair memory. We found that spatial working memory was not impaired when the male rats were exposed to a sexually receptive female rat, a stimulus that was novel and arousing to them, but not aversive. We also found that there was an equivalent increase in serum corticosterone levels in male rats exposed to either a cat or a female rat, but only the cat-exposed rats exhibited a significant correlation between corticosterone levels and impaired memory. Overall, this series of experiments demonstrates that (1). predator stress selectively impaired working (hippocampal-dependent), but not reference (hippocampal-independent), memory; (2). a fear-provoking stimulus, and not merely novelty and increased arousal, impaired spatial memory; and (3). increased corticosterone levels correlated with impaired spatial working memory only under predator exposure, that is, fear-provoking conditions.