Working memory performance and thalamus microstructure in healthy subjects

Research on the neural basis of working memory (WM) has generally focused on cortical regions, specifically frontal and parietal areas. Comparatively, evidence of a possible involvement of deep gray matter structures, that are parts of cortico-cortical circuits linking anterior and posterior cortical areas, is far less clear. The goal of the present study is to test the hypothesis that individual structural variations within deep gray matter structures may affect the cortical networks involved in WM. To this aim, a large sample (n=181) of healthy subjects underwent a high-resolution structural magnetic resonance imaging (MRI) and a diffusion tensor imaging (DTI) scan protocol. Data of micro- (mean diffusivity, MD) and macro- (volume) structural variations of six bilateral deep gray matter structures (thalamus, caudate nucleus, putamen, hippocampus, amygdala and pallidum) and lateral ventriculi volume were analyzed in association with score in a WM (the so-called n-back task) and other neuropsychological tasks. Results showed that increased MD of bilateral thalami was the only structural parameter that significantly correlated with reduced WM performance. In particular, a voxel-by-voxel analysis revealed that the greater percentage of voxels showing significant anticorrelation between WM score and MD values were localized in those thalamic nuclei projecting to prefrontal and posterior parietal cortices. Results highlight the specific involvement of thalamus microstructure, not volume, in modulating WM performance, possibly by regulating the connections among cortical areas that are recruited during WM tasks.     

Direct and indirect semantic priming with neutral and emotional words in schizophrenia: Relationship to delusions

Introduction. Evidence is accumulating that suggests that semantic networks are abnormal in schizophrenia. Methods. To investigate this further, we examined priming in 42 schizophrenics and 28 normal controls on a lexical decision task involving three different prime-target conditions all at 700 ms stimulus onset asynchrony (SOA): directly semantically related, indirectly semantically related, and unrelated; and three types of emotional pairings: positive, negative, and neutral. Two schizophrenic groups were compared: nondeluded (no current delusions) and deluded. Results. Schizophrenic patients did not demonstrate significant direct priming overall, whereas controls did. However, when material was examined according to emotional pairing, the controls and deluded subjects demonstrated significant priming to neutral word pairs. Neither schizophrenic group showed direct priming with positive and negative word pairings, the deluded subjects showing inhibition of priming with negative stimuli. Controls failed to show direct priming with negative stimuli. Indirect priming was obtained in all groups. The absence of direct priming and indirect priming with negative material in deluded subjects was particularly striking. The results point to quantitative and qualitative abnormalities in semantic networks in schizophrenia. Conclusions. We propose that delusions may be the result of intact, unusual (indirect) associations in contrast to poorer normal (semantic) associations; a particular bias being shown toward material of a negative valence.     

Working memory for visual objects: complementary roles of inferior temporal, medial temporal, and prefrontal cortex

Humans have an extraordinary ability to maintain and manipulate visual image information in the absence of perceptual stimulation. The neural substrates of visual working memory have been extensively researched, but there have been few attempts to integrate these findings into a model of how different cortical areas interact to form and maintain visual memories. In this paper, I review findings from neurophysiological, neuropsychological, and neuroimaging studies of visual working memory in human and nonhuman primates. These data support a model in which visual working memory operations rely on activation of object representations in inferior temporal cortex, via top-down feedback from neocortical areas in the prefrontal and medial temporal cortex, and also from the hippocampus.     

Age-related prefrontal over-recruitment in semantic memory retrieval: Evidence from successful face naming and the tip-of-the-tongue state

Studies that have attempted to determine the effects of aging on the brain neural sources of memory retrieval have reported two contrasting age effects: under-recruitment and over-recruitment of several prefrontal areas. However, the causes for these effects are still a matter of debate. In order to study the underlying factors that cause the effects, we compared brain activation in young and older adults, in a successful word retrieval condition, and a failed word retrieval condition: the tip-of-the-tongue state. For this, we used the event-related potentials technique and neural source estimation with low-resolution tomographies. The results showed that the older adults did not display under-recruitment in any brain area in comparison with the young adults. However, they displayed additional prefrontal activation that varied depending on the processing stage and the condition, which supports the hypothesis of selective over-recruitment in older adults.     

Conceptual priming in semantic dementia: A window into the cognitive and neural basis of conceptual implicit memory

The present study examined the impact of impairment in semantic memory on conceptual repetition priming by means of the longitudinal study of a patient with semantic dementia. ST was tested in four consecutive years, during which his semantic memory progressively deteriorated. On each occasion, he performed an abstract/concrete verification task and a verb generation task. In both of these tasks, performance during a test phase was compared for stimuli previously processed in a study phase and stimuli first seen in the test phase. Control subjects showed priming, as indicated by faster responses to studied than to baseline stimuli. ST showed intact priming that was of normal magnitude in the first two years of testing, but failed to show priming in the subsequent two years of testing. This pattern of results is interpreted with reference to the differential decline of item-specific and superordinate knowledge. The implications of these findings for the neural basis of conceptual priming are also discussed.     

Working memory capacity,intelligence, and the magnitude of the attentional blink revisited

The attentional blink (AB) is a well-established phenomenon in the study of attention. This deficit in reporting the second of two targets presented in rapid serial visual presentation when it occurs 200–500 ms after the first is considered to reflect a fundamental limitation in attentional processing. However, we recently reported that some individuals do not show an AB, and presented psychophysiological evidence that target processing differs between blinkers and non-blinkers. One possibility is that non-blinkers may have a larger WM capacity, allowing better attentional control. Here we explore the relation between the magnitude of the AB, general intelligence, and different measures of working memory (WM) and short-term memory (STM) capacity. Surprisingly, no correlation was found between memory capacity measures and AB magnitude, raising doubts about the generalizability of earlier findings of such a relationship.

Conceptual priming in semantic dementia: A window into the cognitive and neural basis of conceptual implicit memory

The present study examined the impact of impairment in semantic memory on conceptual repetition priming by means of the longitudinal study of a patient with semantic dementia. ST was tested in four consecutive years, during which his semantic memory progressively deteriorated. On each occasion, he performed an abstract/concrete verification task and a verb generation task. In both of these tasks, performance during a test phase was compared for stimuli previously processed in a study phase and stimuli first seen in the test phase. Control subjects showed priming, as indicated by faster responses to studied than to baseline stimuli. ST showed intact priming that was of normal magnitude in the first two years of testing, but failed to show priming in the subsequent two years of testing. This pattern of results is interpreted with reference to the differential decline of item-specific and superordinate knowledge. The implications of these findings for the neural basis of conceptual priming are also discussed.     

Repetition priming and recognition memory in younger and older persons: temporal stability and performance

The dissociation between intact priming and reduced explicit memory in aging has been called into question on the basis of limited information that suggests that priming measures are less reliable than explicit memory measures. No aging study to date, however, has offered a comprehensive examination of the reliability of these measures. Age-related performance and test-retest stability coefficients for multiple priming and explicit memory tasks were compared. Age effects were found on some tasks but not others, and stability was not related to task performance. Stability was similar for implicit versus explicit task instructions, younger versus older persons, and studied versus unstudied items. Results indicate that dissociations between priming and explicit memory performances cannot be accounted for by differential reliability of the measures.     

Working memory impairment and reduced hippocampal and prefrontal cortex c-Fos expression in a rat model of cirrhosis

Hepatic encephalopathy (HE) is a frequent neurological complication observed in patients with liver malfunction. Previous studies have shown memory impairment in these patients. In order to investigate brain substrates of spatial working memory impairment in chronic HE, neuronal expression of c-Fos protein was studied in an experimental model of cirrhosis. Control and cirrhotic rats were trained on a spatial working memory task in the Morris water maze (MWM). Differences between groups were found in the working memory task. Cirrhotic rats were unable to locate the platform in the retention trial. Neuronal activation, measured by c-Fos protein, was compared between groups. No differences were found in c-Fos expression of control and cirrhotic rats that were not tested in the MWM. Working memory task produced increase in c-Fos positive cells in dorsal hippocampus, CA1 and CA3, and prefrontal cortex in control group compared to thioacetamide group or naïve, which only swam in the maze during a similar time. These findings suggest that cirrhotic rats show spatial working memory impairment that could be linked to dysfunction in neuronal activity in prefrontal cortex and hippocampus.     

Hyperventilation and attention: effects of hypocapnia on performance in a stroop task

This study aimed to investigate the effect of hypocapnia on attentional performance. Hyperventilation, producing hypocapnia, is associated with physiological changes in the brain and with subjective symptoms of dizziness, concentration problems and derealization. In this study (N=42), we examined cognitive performance on a Stroop-like task, following either 3 min of hypocapnic or normocapnic overbreathing. Both overbreathing trials were run on separate days, each preceded by a baseline trial with the same task during normal breathing. More and other symptoms were reported after hypocapnia compared to normocapnia. Also, more errors were made and progressively slower reaction times (RT's) were observed during recovery from hypocapnia. These performance deficits were only found in participants characterized by apneas. The number of symptoms did not correlate with RT's or errors. The pattern of data suggested that hypoxia, as a result of apneas during recovery from hypocapnia, caused the cognitive performance deficit.     

Working memory and acquisition of implicit knowledge by imagery training, without actual task performance

This study investigated acquisition of a mirror-reading skill via imagery training, without the actual performance of a mirror-reading task. In experiment I, healthy volunteers simulated writing on an imaginary, transparent screen placed at eye level, which could be read by an experimenter facing the subject. Performance of this irrelevant motor task required the subject to imagine the letters inverted, as if seen in a mirror from their own point of view (imagery training). A second group performed the same imagery training interspersed with a complex, secondary spelling and counting task. A third, control, group simply wrote the words as they would normally appear from their own point of view. After training with 300 words, all subjects were tested in a mirror-reading task using 60 non-words, constructed according to acceptable letter combinations of the Portuguese language. Compared with control subjects, those exposed to imagery training, including those who switched between imagery and the complex task, exhibited shorter reading times in the mirror-reading task. Experiment II employed a 2 x 3 design, including two training conditions (imagery and actual mirror-reading) and three competing task conditions (a spelling and counting switching task, a visual working memory concurrent task, and no concurrent task). Training sessions were interspersed with mirror-reading testing sessions for non-words, allowing evaluation of the mirror-reading acquisition process during training. The subjects exposed to imagery training acquired the mirror-reading skill as quickly as those exposed to the actual mirror-reading task. Further, performance of concurrent tasks together with actual mirror-reading training severely disrupted mirror-reading skill acquisition; this interference effect was not seen in subjects exposed to imagery training and performance of the switching and the concurrent tasks. These results unequivocally show that acquisition of implicit skills by top-down imagery training is at least as efficient as bottom-up acquisition.     

Verbal learning in schizopsychotic outpatients and healthy volunteers as a function of cognitive performance levels

OBJECTIVEThe aim was to analyze and compare neurocognitive test profiles related to different levels of verbal learning performance among schizopsychotic patients and healthy volunteers.METHODA single-center patient cohort of 196 participants was compared with an equal-sized volunteer group to form three cognitive subgroups based on the shared verbal learning performance.RESULTS43.9% of the patients had normal learning ability. Despite this, all patients underperformed the volunteers on all subtests with the exception of working memory, and, for those with high learning ability, even verbal facility. All patients also presented equally poor visuomotor processing speed/efficacy.CONCLUSIONA global neurocognitive retardation of speed-related processing in schizophrenia is suggested.     

Working memory performance in typically developing children and adolescents: behavioral evidence of protracted frontal lobe development

Post-mortem histological and in vivo neuroimaging findings both reveal frontal lobe development that extends beyond the adolescent years. Few studies have examined whether this protracted neurodevelopment coincides with improvements in adolescent performance on putative frontal lobe tasks. An instrumental function supported by the frontal lobes is working memory, the ability to maintain and manipulate information online. This study investigated the performance of typically developing children and adolescents on a battery of working memory tasks. Findings revealed an improvement in performance on most working memory tasks across the adolescent years. In contrast, no improvement was observed on tasks largely supported by more posterior neural substrates. Current findings indicate a similar unfolding of the executive aspects of verbal working memory as previously demonstrated with spatial working memory. Factor analysis revealed a grouping of working memory tasks based largely on task demands, irrespective of working memory domain, adding support for process-specific models of prefrontal organization. Important implications for typical and atypical frontal lobe development are discussed.     

Separating input and output phonology: semantic,phonological, and orthographic effects in short-term memory impairment

Recent research with both normal and brain-damaged people shows that linguistic representations are important sources of information in short-term memory tasks. This paper addresses the role of semantic and phonological information in the performance of two individuals with severely impaired short-term memory span (HB and MMG). The performance of these individuals is investigated on span tasks manipulating, for example, lexicality, imageability, word length, and phonological similar as well as on their ability to perform other tasks involving the judgment and/or manipulation of phonology (e.g., rhyme judgments, phonological lexical decision, segmentation tasks, and minimal pairs). The subjects' performance across these tasks provides strong evidence for separate but linked language and short-term memory systems, with lexical and semantic representations contributing to immediate serial recall. There is also evidence for separate phonological and semantic short-term stores (buffers), each of which are supported by the corresponding representations in the language system. Furthermore, the results support separate phonological stores at input and output. Finally a cautionary note is cast regarding the significant role of orthography in many tasks previously assumed to reflect manipulation of phonology.     

Separating input and output phonology: semantic, phonological, and orthographic effects in short-term memory impairment

Recent research with both normal and brain-damaged people shows that linguistic representations are important sources of information in short-term memory tasks. This paper addresses the role of semantic and phonological information in the performance of two individuals with severely impaired short-term memory span (HB and MMG). The performance of these individuals is investigated on span tasks manipulating, for example, lexicality, imageability, word length, and phonological similar as well as on their ability to perform other tasks involving the judgment and/or manipulation of phonology (e.g., rhyme judgments, phonological lexical decision, segmentation tasks, and minimal pairs). The subjects' performance across these tasks provides strong evidence for separate but linked language and short-term memory systems, with lexical and semantic representations contributing to immediate serial recall. There is also evidence for separate phonological and semantic short-term stores (buffers), each of which are supported by the corresponding representations in the language system. Furthermore, the results support separate phonological stores at input and output. Finally a cautionary note is cast regarding the significant role of orthography in many tasks previously assumed to reflect manipulation of phonology.     

They know the words, but not the music: affective and semantic priming in individuals with psychopathy

Previous work has indicated dysfunctional affect-language interactions in individuals with psychopathy through use of the lexical decision task. However, it has been uncertain as to whether these deficits actually reflect impaired affect-language interactions or a more fundamental deficit in general semantic processing. In this study, we examined affective priming and semantic priming (dependent measures were reaction times and error rates) in individuals with psychopathy and comparison individuals, classified according to the psychopathy checklist revised (PCL-R) [Hare, R.D., 1991. The Hare Psychopathy Checklist-Revised. Multi-Health Systems, Toronto, Ont] Individuals with psychopathy showed significantly less affective priming relative to comparison individuals. In contrast, the two groups showed comparable levels of semantic priming. The results are discussed with reference to current models of psychopathy.     

健康人大脑和小脑空间记忆认知功能的fMRI研究

本研究应用功能磁共振成像(functional magnetic resonance imaging,fMRI)技术,检测了健康人大脑和小脑参与空间记忆的认知过程。通过对10名右利手健康志愿者进行一项短时空间记忆任务作业的同时进行脑功能磁共振扫描,实验采用组块设计,任务与对照任务交替进行,数据采用SPM99软件进行数据分析和脑功能区定位。结果显示:当统计阈值设定为P<0.0001时,大脑皮层和右侧小脑一起被显著激活;大脑皮层所激活的脑区有双侧顶叶的楔前叶、顶上小叶、缘上回(BA7/40,BA:Brodma-nn Area),双侧前额上、中、下回(BA6/9/47),双侧枕叶和枕颞交界处(BA18/19/37),右侧海马回;左侧中脑黑质及被盖部也被激活。上述结果提示:小脑和大脑皮层一起参与了空间记忆的认知过程。     

Age differences in control beliefs regarding health: Control,strategy and capacity

Objectives. A new model of perceived control has been proposed ( Skinner, 1995 ) in which 3 types of control‐related beliefs were distinguished: control, strategy and capacity. This model has not yet been applied to health issues. Hence, the main purpose of this study was to apply it to the health domain, exploring age differences in the way children and teenagers conceptualize control‐related beliefs. Design and setting. A prospective age cohort study was carried out with older children and teenagers attending public schools in Lisbon's metropolitan area. Method. A newly developed instrument (HPCQ) was administered to 188 healthy participants (91 6th graders and 97 11th graders). Results. Analyses of variance showed no age differences in individuals' strategy beliefs. Generally, children showed stronger capacity beliefs and a higher perceived control over their own health than teenagers. Hierarchical regression analyses showed that the belief in being a lucky person was a central predictor of control in later childhood. In adolescence, chance‐related factors lost their predictive power, and effort and attributes‐related beliefs remained controls' primary predictors. Conclusions. These results emphasize the heuristic value of this recent conceptualization of control‐related beliefs. Moreover, they contribute to the development of more effective and reliable health‐related school‐based prevention/intervention programmes aiming at these particular age cohorts.