The effect of word concreteness on recognition memory

Concrete words that are readily imagined are better remembered than abstract words. Theoretical explanations for this effect either claim a dual coding of concrete words in the form of both a verbal and a sensory code (dual-coding theory), or a more accessible semantic network for concrete words than for abstract words (context-availability theory). However, the neural mechanisms of improved memory for concrete versus abstract words are poorly understood. Here, we investigated the processing of concrete and abstract words during encoding and retrieval in a recognition memory task using event-related functional magnetic resonance imaging (fMRI). As predicted, memory performance was significantly better for concrete words than for abstract words. Abstract words elicited stronger activations of the left inferior frontal cortex both during encoding and recognition than did concrete words. Stronger activation of this area was also associated with successful encoding for both abstract and concrete words. Concrete words elicited stronger activations bilaterally in the posterior inferior parietal lobe during recognition. The left parietal activation was associated with correct identification of old stimuli. The anterior precuneus, left cerebellar hemisphere and the posterior and anterior cingulate cortex showed activations both for successful recognition of concrete words and for online processing of concrete words during encoding. Additionally, we observed a correlation across subjects between brain activity in the left anterior fusiform gyrus and hippocampus during recognition of learned words and the strength of the concreteness effect. These findings support the idea of specific brain processes for concrete words, which are reactivated during successful recognition.     

Involvement of the cerebellar cortex and nuclei in verbal and visuospatial working memory: a 7 T fMRI study

The first aim of the present study was to extend previous findings of similar cerebellar cortical areas being involved in verbal and spatial n-back working memory to the level of the cerebellar nuclei. The second aim was to investigate whether different areas of the cerebellar cortex and nuclei contribute to different working memory tasks (n-back vs. Sternberg tasks). Young and healthy subjects participated in two functional magnetic resonance imaging (fMRI) studies using a 7 T MR scanner with its increased signal-to-noise ratio. One group of subjects (n=21) performed an abstract and a verbal version of an n-back task contrasting a 2-back and 0-back condition. Another group of subjects (n=23) performed an abstract and a verbal version of a Sternberg task contrasting a high load and a low load condition. A block design was used. For image processing of the dentate nuclei, a recently developed region of interest (ROI) driven normalization method of the dentate nuclei was applied (Diedrichsen et al., 2011). Whereas activated areas of the cerebellar cortex and dentate nuclei were not significantly different comparing the abstract and verbal versions of the n-back task, activation in the abstract and verbal Sternberg tasks was significantly different. In both n-back tasks activation was most prominent at the border of lobules VI and Crus I, within lobule VII, and within the more caudal parts of the dentate nucleus bilaterally. In Sternberg tasks the most prominent activations were found in lobule VI extending into Crus I on the right. In the verbal Sternberg task activation was significantly larger within right lobule VI compared to the abstract Sternberg task and compared to the verbal n-back task. Activations of rostral parts of the dentate were most prominent in the verbal Sternberg task, whereas activation of caudal parts predominated in the abstract Sternberg task. On the one hand, the lack of difference between abstract and verbal n-back tasks and the lack of significant lateralization suggest a more general contribution of the cerebellum to working memory regardless of the modality. On the other hand, the focus of activation in right lobule VI in the verbal Sternberg task suggests specific cerebellar contributions to verbal working memory. The verbal Sternberg task emphasizes maintenance of stimuli via phonological rehearsal, whereas central executive demands prevail in n-back tasks. Based on the model of working memory by Baddeley and Hitch (1974), the present results show that different regions of the cerebellum support functions of the central executive system and one of the subsidiary systems, the phonological loop.     

Hippocampal activations during encoding and retrieval in a verbal working memory paradigm

Though the hippocampus has been associated with encoding and retrieval processes in episodic memory, the precise nature of its involvement in working memory has yet to be determined. This functional magnetic resonance imaging (fMRI) study employed a verbal working memory paradigm that allows for the within-subject comparison of functional activations during encoding, maintenance, and retrieval. In each trial, participants were shown 5 target words and, after an 8 s delay, a series of probe words. Probe words consisted of target matches, phonetically or semantically related foils, or foils unrelated to the target words. Both the left and right hippocampi showed higher mean activation amplitudes during encoding than maintenance. In contrast, the right dorsolateral prefrontal cortex (DLPFC) showed greater activation during maintenance than encoding. Both hippocampal and DLPFC regions were more active during retrieval than maintenance. Furthermore, an analysis of retrieval activation separated by probe type showed a trend toward greater bilateral hippocampal activation for probes related (both semantically and phonetically) to the target than for unrelated probes and still greater activation for target matches. This pattern suggests that there may be roles for the hippocampus and DLPFC in working memory that change as function of information processing stage. Additionally, the trend towards increased involvement of the hippocampus with the increase in relatedness of the probe stimuli to the information maintained is interpreted to be consistent with the role of the hippocampus in recollection-based retrieval in long-term memory and may indicate that this role extends to working memory processes.     

Material-specific memory processing is related to language dominance

Neuropsychological and neuroimaging data have shown a functional lateralization of the medial temporal lobes for verbal and non-verbal memory material respectively. We hypothesized that this lateralization is related to language lateralization. Using fMRI we conducted three memory tasks with different memory material (words, faces, landscape images) alongside with a paradigm for the determination of language dominance in 44 healthy subjects. We included left as well as right-handed subjects because persons with atypical language dominance are known to be overrepresented in the group of left-handers. Lateralization indices for the BOLD activation in the medial temporal lobes from the memory tasks were correlated with those for the language task. We show that the material-specific lateralization is related to language dominance such that verbal encoding shows strong positive relation to language dominance whereas face encoding shows the opposite effect. Our data provide first fMRI evidence for a relation between language dominance and material specificity of the medial temporal lobes for memory functions. We suggest that the language-dominant hemisphere is more strongly engaged in memory processing of verbal material. These data provide grounds for the investigation of pathological changes in this relationship due to cortical dysfunctions.     

Cerebellar contributions to episodic memory encoding as revealed by fMRI

Event-related functional Magnetic Resonance Imaging (fMRI) allows for the comparison of hemodynamic responses evoked by items that are remembered in a subsequent memory task vs. items that are forgotten. In this way, brain regions that assumingly contribute to successful memory encoding have been identified, including the left inferior prefrontal cortex (LIPC) and the medial temporal lobe. Although a cerebellar involvement in verbal working memory is well-established, a contribution of the cerebellum to episodic long-term encoding has only sporadically been described, and mechanisms underlying cerebellar memory effects are unclear. We conducted a typical incidental verbal memory fMRI experiment with three different encoding tasks varying the depth of semantic processing. Slice positioning allowed for the coverage of the entire cerebellum. We observed a significant subsequent memory effect within the superior and posterior right cerebellar hemisphere that was task independent. Additionally, we found a different area within the superior right cerebellum displaying a memory effect specifically for semantically processed words and a bilateral cerebellar activation specifically associated with encoding success only for a non-semantic task. Our results suggest that besides its known role in verbal working memory, the cerebellum contributes to episodic long-term encoding and should therefore be considered in future fMRI studies dealing with episodic memory.     

Parahippocampal Activation during Successful Recognition of Words: A Self-Paced Event-Related fMRI Study

In this study, we investigated retrieval from verbal episodic memory using a self-paced event-related fMRI paradigm, similar to the designs typically used in behavioral studies of memory function. We tested the hypothesis that the medial temporal lobe (MTL) is involved in the actual recovery of verbal information (retrieval success) rather than in the attempt to retrieve information (retrieval attempt). To this end, we used a verbal recognition task, distinguishing correctly recognized words, correctly rejected words, and a low-level baseline condition. Directly contrasting correct recognition with correct rejection of words, we found activation in the left fusiform/parahippocampal gyrus, indicating that this region has a distinct role in the successful retrieval of verbal information. Furthermore, our results were in agreement with those of previous imaging studies that compared a fixed-paced verbal recognition task to a baseline condition, showing activation in bilateral inferior frontal cortex, left dorsolateral prefrontal cortex, left anterior insular cortex, and anterior cingulate. This demonstrates the applicability of a self-paced event-related design within imaging studies of memory function.     

Males and females differ in brain activation during cognitive tasks

To examine the effect of gender on regional brain activity, we utilized functional magnetic resonance imaging (fMRI) during a motor task and three cognitive tasks; a word generation task, a spatial attention task, and a working memory task in healthy male (n = 23) and female (n = 10) volunteers. Functional data were examined for group differences both in the number of pixels activated, and the blood-oxygen-level-dependent (BOLD) magnitude during each task. Males had a significantly greater mean activation than females in the working memory task with a greater number of pixels being activated in the right superior parietal gyrus and right inferior occipital gyrus, and a greater BOLD magnitude occurring in the left inferior parietal lobe. However, despite these fMRI changes, there were no significant differences between males and females on cognitive performance of the task. In contrast, in the spatial attention task, men performed better at this task than women, but there were no significant functional differences between the two groups. In the word generation task, there were no external measures of performance, but in the functional measurements, males had a significantly greater mean activation than females, where males had a significantly greater BOLD signal magnitude in the left and right dorsolateral prefrontal cortex, the right inferior parietal lobe, and the cingulate. In neither of the motor tasks (right or left hand) did males and females perform differently. Our fMRI findings during the motor tasks were a greater mean BOLD signal magnitude in males in the right hand motor task, compared to females where males had an increased BOLD signal magnitude in the right inferior parietal gyrus and in the left inferior frontal gyrus. In conclusion, these results demonstrate differential patterns of activation in males and females during a variety of cognitive tasks, even though performance in these tasks may not vary, and also that variability in performance may not be reflected in differences in brain activation. These results suggest that in functional imaging studies in clinical populations it may be sensible to examine each sex independently until this effect is more fully understood.     

功能磁共振成像观察2型糖尿病患者工作记忆

目的 通过功能磁共振成像技术对2型糖尿病患者的工作记忆进行研究,探讨2型糖尿病患者工作记忆的受损状况.方法 采用1-back组块设计,对16例2型糖尿病患者及13名正常对照受试者,进行词语及客体工作记忆任务的fMRI检查,对反应时间、正确率及脑激活图进行分析.结果 2型糖尿病组患者的正确反应时间、正确率与对照组相比差异无统计学意义(P>0.05).与对照组相比,2型糖尿病组在词语工作记忆时,左侧额叶、左侧顶叶及海马旁回等脑区激活显著减弱(P<0.05),客体工作记忆时,右侧额叶、左侧顶叶及双侧枕叶等脑区激活减弱(P<0.05).结论 2型糖尿病患者存在词语及客体工作记忆损害,经典激活脑区存在损害.     

Preserved verbal memory function in left medial temporal pathology involves reorganisation of function to right medial temporal lobe

The left hippocampus and related structures mediate verbal memory function. The mechanism underlying preserved verbal memory function in patients with left hippocampal damage is unknown. Temporal lobe epilepsy, a common disease, is frequently the consequence of a characteristic hippocampal pathology termed hippocampal sclerosis, which may also affect the amygdala. In this setting, mapping the sites of memory function is a vital component of planning for surgical treatment for epilepsy. Using event-related functional magnetic resonance imaging, we studied 24 right-handed nonamnesic patients with left hippocampal sclerosis and 12 normal controls, performing a verbal encoding task. The patients were subdivided into two groups according to presence or absence of additional left amygdala pathology. Analysis of the data employed a two-level random-effects design, examining the main effects of subsequent memory in each group, as well as the differences between the groups. Additional effects of emotionality of the remembered words were also examined. Verbal memory encoding involved activation of left hippocampus in normals, but was associated with reorganisation to right hippocampus and parahippocampal gyrus in the patients. The additional presence of left amygdala sclerosis resulted in reorganisation for encoding of emotional verbal material to right amygdala. Retained verbal memory function in the presence of left medial temporal lobe pathology is mediated by recruitment of a parallel system in the right hemisphere consistent with adaptive functional reorganisation. The findings indicate a high degree of plasticity in medial temporal lobe structures.     

Hippocampal gray matter reduction associates with memory deficits in adolescents with history of prematurity

Using optimized voxel-based morphometry (VBM), we compared the relationship between hippocampal and thalamic gray matter loss and memory impairment in 22 adolescents with history of prematurity (HP) and 22 normal controls. We observed significant differences between groups in verbal learning and verbal recognition, but not in visual memory. VBM analysis showed significant left hippocampal and bilateral thalamic reductions in HP subjects. Using stereological methods, we also observed a reduction in hippocampal volume, with left posterior predominance. We found correlations between left hippocampal gray matter reductions (assessed by VBM) and verbal memory (learning and percentage of memory loss) in the premature group. The stereological analysis showed a correlation between verbal learning and the left posterior hippocampus. Our results suggest that left hippocampal tissue loss may be responsible for memory impairment and is probably related to the learning disabilities that HP subjects present during schooling.     

Hemispheric Activation of Anterior and Inferior Prefrontal Cortex during Verbal Encoding and Recognition: A PET Study of Healthy Volunteers

Evidence of bilateral prefrontal activation during memory encoding and retrieval has increased attention given to anatomical subdivisions within the prefrontal cortex. The current study examined anterior and inferior aspects of the prefrontal cortex to determine their degree of functional and hemispheric overlap during encoding and recognition. Cerebral blood flow of 25 healthy volunteers was measured using PET ¹⁵O-water methods during four conditions: resting baseline, sequential finger movement, word encoding, and word recognition. Resting and motor images were averaged to provide a single reference that was subtracted from encoding and recognition using statistical parametric mapping (SPM96). Memory conditions were also subtracted from each other to identify differences in regional activity. Subjects performed well (86% correct) and had a slightly conservative response bias. Baseline subtraction from encoding revealed focal activation of left inferior prefrontal cortex (area 45) without significant contralateral activation. Recognition minus baseline subtraction produced a focal right anterior prefrontal activation (areas 9 and 10) that was not present in the left hemisphere. Bilateral effects were seen in area 45 during recognition. Subtraction of memory tasks from each other did not reveal any areas of greater activity during encoding. However, the recognition task produced greater activation in right area 9 extending into the anterior cingulate. Greater activity during recognition was also observed in left insula and bilateral visual integration areas. These results are discussed in relation to the prevailing model of prefrontal hemispheric asymmetry during episodic memory.     

Material-specific lateralization of memory encoding in the medial temporal lobe: blocked versus event-related design

Lesion-deficit studies have provided evidence for a functional dissociation between the left medial temporal lobe (MTL) mediating verbal memory encoding and right MTL mediating non-verbal memory encoding. While a small number of functional MRI studies have demonstrated similar findings, none has looked specifically for material-specific lateralization using subsequent memory effects. In addition, in many fMRI studies, encoding activity has been located in posterior MTL structures, at odds with lesion-deficit and positron emission tomography (PET) evidence. In this study, we used an event-related fMRI memory encoding paradigm to demonstrate a material-specific lateralization of encoding in the medial temporal lobes of ten healthy control subjects. Activation was left-lateralized for word encoding, bilateral for picture encoding, and right-lateralized for face encoding. Secondly, we demonstrated the locations of activations revealed using an event-related analysis to be more anterior than those revealed using a blocked analysis of the same data. This suggests that anterior MTL structures underlie memory encoding as judged by subsequent memory effects, and that more posterior activity detected in other fMRI studies is related to deficiencies of blocked designs in the analysis of memory encoding.     

Sex influences on material-sensitive functional lateralization in working and episodic memory: men and women are not all that different

Research investigating the effects of sex on the lateralization of language functions has produced mixed results to date, with some studies finding sex differences and others not [Shaywitz, B.A., Shaywitz, S.E., Pugh, K.R., Constable, R.T., Skudlarski, P., Fulbright, R.K., Bronen, R.A., Fletcher, J.M., Shankweiler, D.P., Katz, L., et al., 1995. Sex differences in the functional organization of the brain for language. Nature 373 607-609.; Frost, J.A., Binder, J.R., Springer, J.A., Hammeke, T.A., Bellgowan, P.S., Rao, S.M., Cox, R.W., 1999. Language processing is strongly left lateralized in both sexes. Evidence from functional MRI. Brain 122 (Pt 2) 199-208.]. Further, few studies have evaluated how any such sex effects extend to tasks involving cognitive functions that may utilize language processes such as working and episodic memory. This study examined sex difference in material-sensitive functional activation (using fMRI) in working memory and episodic memory that included either words and faces. We performed these analyses on two large groups of healthy subjects with the goal of attempting to replicate results across two independent data sets. The results indicated that both males and females showed strong and consistent evidence for material-sensitive lateralization for both working and episodic memory, such that word tasks resulted in greater left-sided activation and face tasks resulted in greater right-sided activation. Further, few of the sex differences in regions showing material specificity effects in at least one gender replicated across studies, providing little evidence for any differences in lateralization patterns between the sexes. In conclusion, our data suggest that males and females show a similar pattern of lateralized activation to material type during working memory and recognition tasks.     

Boys do it the right way: sex-dependent amygdala lateralization during face processing in adolescents

Previous studies have observed a sex-dependent lateralization of amygdala activation related to emotional memory. Specifically, it was shown that the activity of the right amygdala correlates significantly stronger with memory for images judged as arousing in men than in women, and that there is a significantly stronger relationship in women than in men between activity of the left amygdala and memory for arousing images. Using a large sample of 235 male adolescents and 235 females matched for age and handedness, we investigated the sex-specific lateralization of amygdala activation during an emotional face perception fMRI task. Performing a formal sex by hemisphere analysis, we observed in males a significantly stronger right amygdala activation as compared to females. Our results indicate that adolescents display a sex-dependent lateralization of amygdala activation that is also present in basic processes of emotional perception. This finding suggests a sex-dependent development of human emotion processing and may further implicate possible etiological pathways for mental disorders most frequent in adolescent males (i.e., conduct disorder).     

Prefrontal and hippocampal contributions to the generation and binding of semantic associations during successful encoding

The ability to form and bind associations between items is an important aspect of successful memory formation. We hypothesize that, during encoding, the left inferior frontal gyrus (IFG) supports generation of associations between items and the hippocampus then binds these associations. This study examined the parametric responses of these regions to varying amounts of generative and relational processing during successful encoding (i.e., for subsequently recognized items). Encoding involved presentation of word triads varying in the number of semantic associations among them (none, one or all); participants judged how many associations were present in each triad. Thus, triads with fewer associations had higher generative load while triads with more associations had higher relational load. Participants later completed a forced-choice recognition test for encoding triads. Successful encoding relative to a control task resulted in activation of bilateral IFG and left hippocampus, and the hippocampus also exhibited a significant subsequent memory effect (hits>misses). Linear parametric analyses revealed that generative load modulated activity in bilateral IFG while relational load correlated with activity in left hippocampus. Although univariate analyses distinguished IFG and hippocampal contributions to the generative and relational stages of encoding, respectively, effective connectivity between these regions did not differ according to condition. Furthermore, this analysis revealed that the left IFG played a pivotal role in coordinating associative encoding processes. Our findings illustrate that modulation of components in a memory network can be independent of patterns of mutual connectivity among those components in mediating successful encoding.     

Parietal activation during retrieval of abstract and concrete auditory information

Successful memory retrieval has been associated with a neural circuit that involves prefrontal, precuneus, and posterior parietal regions. Specifically, these regions are active during recognition memory tests when items correctly identified as "old" are compared with items correctly identified as "new." Yet, as nearly all previous fMRI studies have used visual stimuli, it is unclear whether activations in posterior regions are specifically associated with memory retrieval or if they reflect visuospatial processing. We focus on the status of parietal activations during recognition performance by testing memory for abstract and concrete nouns presented in the auditory modality with eyes closed. Successful retrieval of both concrete and abstract words was associated with increased activation in left inferior parietal regions (BA 40), similar to those observed with visual stimuli. These results demonstrate that activations in the posterior parietal cortex during retrieval cannot be attributed to bottom-up visuospatial processes but instead have a more direct relationship to memory retrieval processes.     

Fornix damage limits verbal memory functional compensation in multiple sclerosis

Selective atrophy of the hippocampus, in particular the left CA1 subregion, is detectable in relapsing-remitting MS (RRMS) and is correlated with verbal memory performance. We used novel high-resolution imaging techniques to assess the role that functional compensation and/or white matter integrity of mesial temporal lobe (MTL) structures may play in mediating verbal memory performance in RRMS. High-resolution cortical unfolding of structural MRI in conjunction with functional magnetic resonance imaging (fMRI) was used to localize MTL activity in 18 early RRMS patients and 16 healthy controls during an unrelated word-pairs memory task. Diffusion tensor imaging (DTI) and Tract-Based Spatial Statistics (TBSS) were used to assess the integrity of the fornix and the parahippocampal white matter (PHWM), the major efferents and afferents of the hippocampus. RRMS patients showed greater activity in hippocampal and extra-hippocampal areas during unrelated word-pair learning and recall. Increased hippocampal activity, particularly in the right anterior hippocampus and left anterior CA1 was associated with higher verbal memory scores. Furthermore, increased fractional anisotropy (FA) in the fornix was correlated with both greater fMRI activity in this region and better memory performance. Altered hippocampal fMRI activity in RRMS patients during verbal learning may result from both structural damage and compensatory mechanisms. Successful functional compensation for hippocampal involvement in RRMS may be limited in part by white matter damage to the fornix, consistent with the critical role of this pathway in the clinical expression of memory impairment in MS.     

Interindividual differences of medial temporal lobe activation during encoding in an elderly population studied by fMRI

Functional MRI (fMRI) is used to study medial temporal lobe (MTL) activation during encoding of new information into memory. In most studies, fMRI data of different subjects are averaged in standard coordinate space. However, interindividual differences in activation can be extensive, reflecting functional heterogeneity. Further, anatomical differences in brain structure cause additional variance and loss of registration accuracy. Such differences in structural and functional MTL characteristics may interfere with the efficiency of averaging data across subjects, and may become more significant with aging and dementia. The current study concerns the analysis of individual differences in MTL activation associated with episodic encoding.Twenty-nine healthy elderly men between 60 and 70 years old performed a simple face encoding task during fMRI scanning. Individual data were analyzed in native space, and compared to the group average in standard space (Talairach and Tournoux).MTL volumes between subjects varied between 6.34 and 11.27 cm(3), and had considerable variation when mapped to standard space. Eighteen of the 29 subjects showed MTL activity and activation patterns varied both in location and size (ranging from 0.11 to 1.78 cm(3)), with the strongest activation in the left posterior part of the MTL. In standard space, no region was significantly activated on a group level at a comparable alpha level. We conclude that while the majority of elderly subjects show MTL activation during episodic encoding of faces, there is considerable structural and functional variability between subjects. Group analysis in standard space may not be appropriate for studies of a complex structure such as the MTL, particularly not in aging and dementia.     

正常老年人无意义图形记忆任务的fMRI研究

目的探讨正常老年人进行记忆任务的实验可行性及激活脑区.方法对11例正常老年志愿者进行无意义图形记忆任务的fMRI实验,实验以组块方式设计,包括第一次记忆组、重复记忆组和再认组.实验数据以SPM99作后处理显示激活脑区.结果 10例受试者的记忆任务完成较好,记忆和再认的激活区域主要集中双侧前额叶、双侧海马旁回(左侧为主)、右侧海马、双侧顶叶(主要为顶上小叶和楔前叶).记忆编码时海马的激活集中在海马头部,而提取时海马的激活则集中在海马的体部及尾部.结论老年人进行fMRI认知实验具有可行性,记忆的编码和提取时需要内侧颞叶海马系统的参与,但所倚重的脑区有微小的差别.     

Does egocentric mental rotation elicit sex differences?

Mental rotation tests traditionally show a male performance advantage. Some neuroimaging studies have reported sex-specific cortical activation patterns during mental rotation. However, these experiments used abstract stimuli and some studies did not systematically exclude performance as a confounding variable. The mental rotation of hands and hand-related objects, compared to abstract objects, is known to evoke an egocentric motor strategy. In this study, we used fMRI to explore potential gender-specific cortical activation patterns for the mental rotation of hands and tools in a sample with an adequate and equal performance for men and women. We found a common neural substrate for men and women comprising superior parietal lobe, dorsolateral premotor cortex, and extrastriate occipital areas, compatible with an egocentric motor strategy for the mental rotation of hands and tools. Sex differences were modest and limited to the mental rotation of hands. Women recruited more left ventral premotor cortex, which could imply that women rely more on imitation or use more perceptual comparisons. Men, on the other hand, drafted more the lingual gyrus, possibly referring to more extensive semantic or early visual processing. We conclude that men and women use a very similar motor strategy during egocentric mental rotation with a potential gender-specific accent.