Implicit and explicit memory following anterior communicating artery aneurysm rupture

Understanding anterior communicating artery aneurysms: A bibliometric analysis of top 100 most cited articles

Bibliometric analysis is of paramount importance in assessing the research impact wherein studies are ranked on the basis of citations received. It also brings out the excellent contribution of authors and journals in adding evidence for future research. This study aimed at evaluating the top 100 most cited articles on anterior communicating artery (ACoA) Aneurysms. Scopus database was searched using title specific search for the aneurysm of ACoA and top 100 most cited articles along with their authors, author IDs, affiliated institutions, countries and funding bodies were identified. Search yielded 841 articles and top 100 articles were identified to include in this analysis which secured 5615 citations. Citations per year was also calculated to minimize the risk of bias. Maximum citations by any article were 242. The United States was the major contributor to the number of articles while Kessler Institute for Rehabilitation became the highest contributing institution. DeLuca J proved to be a pioneer in this specialized area as he penned 6 studies being first author in 4 of them, making him the most frequent author. National Institutes of Health and the U.S. Department of Health and Human Services were the main funding bodies. Subcategory analysis revealed, 50% studies provided evidence for the treatment and the surgical outcome of the aneurysm. Studies like these can aid in better neurological and neurosurgical management in decision making of ACoA aneurysm.

On the Complexity of Brain Disorders: A Symptom-Based Approach

Mounting evidence shows that brain disorders involve multiple and different neural dysfunctions, including regional brain damage, change to cell structure, chemical imbalance, and/or connectivity loss among different brain regions. Understanding the complexity of brain disorders can help us map these neural dysfunctions to different symptom clusters as well as understand subcategories of different brain disorders. Here, we discuss data on the mapping of symptom clusters to different neural dysfunctions using examples from brain disorders such as major depressive disorder (MDD), Parkinson’s disease (PD), schizophrenia, posttraumatic stress disorder (PTSD) and Alzheimer’s disease (AD). In addition, we discuss data on the similarities of symptoms in different disorders. Importantly, computational modeling work may be able to shed light on plausible links between various symptoms and neural damage in brain disorders.

The association between saliva control, silent saliva penetration, aspiration, and videofluoroscopic findings in Parkinson's disease patients

Background:

Dysphagia is a common disorder among patients with Parkinson's disease (PD). It occurs in up to 80% of all (PD) patients during the early stages of the disease and up to 95% in the advanced stages; but professionals may not hear from the patients about dysphagia symptoms until these symptoms reach an advanced stage and lead to medical complications.

Materials and Methods:

Thirty-three PD patients (mean age 66.09 ± 9.4 years; 24 men, nine women) participated in this study at our Neurology Institute, between April 20, 2013, and October 26, 2013. They were asked two questions; one about saliva control and the other about silent saliva penetration and aspiration. Next, they underwent the videofluoroscopic swallowing study (VFSS).

Results:

The Pearson Correlation coefficient between the Penetration–Aspiration Scale (PAS) scores and question 1 scores was 0.48 (P < 0.05, =0.25), and there was a significant correlation between the PAS scores and question 2 scores, and also question 1 scores + question 2 scores (r = 0.589, P < 0.05, =0 and r = 0589, P < 0.05, =0).

Conclusions:

This study showed a significant correlation between the questions about saliva control, silent saliva penetration, and aspiration, and laryngeal penetration and aspiration during VFSS. Therefore, by using these two questions, the potential silent laryngeal penetration and aspiration during meals could be detected before it led to aspiration pneumonia. Taking the benefit of these questions, as a part of the swallowing assessment of PD patients, is recommended.

Repetition priming and cortical arousal in healthy aging and Alzheimer's disease

Repetition priming refers to a form of implicit memory in which prior exposure to a stimulus facilitates the subsequent processing of the same or a related stimulus. One frequently used repetition priming task is word-stem completion priming. In this task, participants complete a series of beginning word stems with the first word that comes to mind after having viewed, in an unrelated context, words that can complete some of the stems. Patients with Alzheimer's disease (AD) exhibit a significant deficit in word-stem completion priming, but the neural mechanisms underlying this deficit have yet to be identified. The present study examined the possibility that the word-stem completion priming deficit in AD is due to disruption of ascending neuromodulatory systems that mediate cortical arousal by comparing word-stem completion priming and behavioral measures of spatial orienting and phasic alerting. Results showed that in healthy elderly controls higher levels of phasic alerting were associated with a sharpening of the temporal dynamics of priming across two delay intervals: those with higher levels of alerting showed more immediate priming but less delayed priming than those with lesser levels of alerting. In patients with AD, priming was impaired despite intact levels of phasic alerting and spatial orienting, and group status rather than individual levels of alerting or orienting predicted the magnitude of their stem-completion priming. Furthermore, the change in priming across delays they displayed was not related to level of alerting or orienting. These findings support the role of the noradrenergic projection system in modulating the level of steady-state cortical activation (or "cortical tonus") underlying both phasic alerting and the temporal dynamics of repetition priming. However, impaired priming in patients with AD does not appear to be due to disruption of this neuromodulatory system.

Lexical-semantic processing in the semantic priming paradigm in aphasic patients

There is evidence that the explicit lexical-semantic processing deficits which characterize aphasia may be observed in the absence of implicit semantic impairment. The aim of this article was to critically review the international literature on lexical-semantic processing in aphasia, as tested through the semantic priming paradigm. Specifically, this review focused on aphasia and lexical-semantic processing, the methodological strengths and weaknesses of the semantic paradigms used, and recent evidence from neuroimaging studies on lexical-semantic processing. Furthermore, evidence on dissociations between implicit and explicit lexical-semantic processing reported in the literature will be discussed and interpreted by referring to functional neuroimaging evidence from healthy populations. There is evidence that semantic priming effects can be found both in fluent and in non-fluent aphasias, and that these effects are related to an extensive network which includes the temporal lobe, the pre-frontal cortex, the left frontal gyrus, the left temporal gyrus and the cingulated cortex.

A neural model of hippocampal-striatal interactions in associative learning and transfer generalization in various neurological and psychiatric patients

Building on our previous neurocomputational models of basal ganglia and hippocampal region function (and their modulation by dopamine and acetylcholine, respectively), we show here how an integration of these models can inform our understanding of the interaction between the basal ganglia and hippocampal region in associative learning and transfer generalization across various patient populations. As a common test bed for exploring interactions between these brain regions and neuromodulators, we focus on the acquired equivalence task, an associative learning paradigm in which stimuli that have been associated with the same outcome acquire a functional similarity such that subsequent generalization between these stimuli increases. This task has been used to test cognitive dysfunction in various patient populations with damages to the hippocampal region and basal ganglia, including studies of patients with Parkinson's disease (PD), schizophrenia, basal forebrain amnesia, and hippocampal atrophy. Simulation results show that damage to the hippocampal region-as in patients with hippocampal atrophy (HA), hypoxia, mild Alzheimer's (AD), or schizophrenia-leads to intact associative learning but impaired transfer generalization performance. Moreover, the model demonstrates how PD and anterior communicating artery (ACoA) aneurysm-two very different brain disorders that affect different neural mechanisms-can have similar effects on acquired equivalence performance. In particular, the model shows that simulating a loss of dopamine function in the basal ganglia module (as in PD) leads to slow acquisition learning but intact transfer generalization. Similarly, the model shows that simulating the loss of acetylcholine in the hippocampal region (as in ACoA aneurysm) also results in slower acquisition learning. We argue from this that changes in associative learning of stimulus-action pathways (in the basal ganglia) or changes in the learning of stimulus representations (in the hippocampal region) can have similar functional effects.

Task-specific contribution of the human striatum to perceptual-motor skill learning

Acquisition of new perceptual-motor skills depends on multiple brain areas, including the striatum. However, the specific contribution of each structure to this type of learning is still poorly understood. Focusing on the striatum, we proposed (a) to replicate the finding of impaired rotary pursuit (RP) and preserved mirror tracing (MT) in Huntington's disease (HD); and (b) to further explore this putative learning dissociation with other human models of striatal dysfunction (i.e., Parkinson's disease and focal vascular damage) and two new paradigms (i.e., Geometric Figures, GF, and Control Stick, CS) of skill learning. Regardless of the etiology, participants with damage to the striatum showed impaired learning of visuomotor tracking skills (i.e., RP and GF), whereas the ability to learn skills that require motor adaptation (i.e., MT and CS) was not affected. These results suggest a task-specific involvement of the striatum in the early stages of skill learning.

Impaired acquisition of a mirror-reading skill in Alzheimer's disease

Several studies using the mirror-reading paradigm have shown that procedural learning and repetition priming may be preserved in the early stages of Alzheimer's disease (AD) (e.g., Deweer et al., 1994). According to the classical interpretation, improved reading time for repeated words is sustained by a repetition priming effect, while procedural learning is demonstrated when this improvement is also observed for new words. Following Masson (1986), the hypothesis tested in the present study was that improved reading of new words could also be due to a repetition priming effect rather than to the acquisition of a mirror-reading skill. Indeed, because the same letters are presented throughout the task, a repetition priming effect for the letters could suffice to explain the improvement in performance. To test this hypothesis, we administered to 30 healthy young and elderly subjects and to 30 AD patients a new mirror-reading task in two phases: an acquisition phase comprising pseudo-words constructed with one part of the alphabet, and a test phase in which both pseudo-words constructed with the same part of the alphabet and pseudo-words constructed with another part of the alphabet were presented. If the new pseudo-words composed with repeated letters were read faster, it would reflect a repetition priming effect; if pseudo-words composed of 'new' letters were read faster, it would reflect a procedural learning effect. The results show comparable repetition priming effects in AD patients and in healthy elderly subjects, whereas only healthy subjects showed a procedural learning effect. These results suggest, contrary to previous studies, that the learning of a new perceptual skill may not always be preserved in AD.

Validation of a swallowing disturbance questionnaire for detecting dysphagia in patients with Parkinson's disease

Underreporting of swallowing disturbances by Parkinson's disease (PD) patients may lead to delay in diagnosis and treatment, alerting the physician to an existing dysphagia only after the first episode of aspiration pneumonia. We developed and validated a swallowing disturbance questionnaire (SDQ) for PD patients and compared its findings to an objective assessment. Fifty-seven PD patients (mean age 69 +/- 10 years) participated in this study. Each patient was queried about experiencing swallowing disturbances and asked to complete a self-reported 15-item "yes/no" questionnaire on swallowing disturbances (24 replied "no"). All study patients underwent a physical/clinical swallowing evaluation by a speech pathologist and an otolaryngologist. The 33 patients who complained of swallowing disturbances also underwent fiberoptic endoscopyic evaluation of swallowing (FEES). According to the ROC test, the "optimal" score (where the sensitivity and specificity curves cross) is 11 (sensitivity 80.5%, specificity 81.3%). Using the SDQ questionnaire substantially reduced Type I errors (specifically, an existing swallowing problem missed by the selected cutoff point). On the basis of the SDQ assessment alone, 12 of the 24 (50%) noncomplaining patients would have been referred to further evaluation that they otherwise would not have undergone. The SDQ emerged as a validated tool to detect early dysphagia in PD patients.

Knowing "what" and knowing "when"

The ability to situate autobiographical memories accurately in the "time-line" of one's own life is a particular aspect of retrograde memory that has received little attention in well-controlled, systematic studies. Here, we addressed this issue by testing the hypothesis that patients with basal forebrain damage would be impaired in their ability to place various autobiographical memories accurately on a 'time-line' of their life. Seven such subjects were contrasted with 11 medial temporal lobe subjects, 8 brain-damaged comparison subjects, and 18 normal comparison subjects, using a procedure in which subjects placed autobiographical events on a time-line of their life. The basal forebrain group was very impaired in this task, relative to the other groups, and on average, misplaced events by more than five years. Although the basal forebrain group was also impaired in retrieving the contents of autobiographical memory, they did not differ statistically from the medial temporal lobe group in this regard (and the medial temporal lobe group did not have impaired time placement of memories). The results indicate an intriguing dissociation between "knowing what" and "knowing when," and suggest that the basal forebrain contains structures that are especially important for "knowing when." Our findings are compatible with the view that the basal forebrain participates critically in retrieval strategies important for memory chronology, which contrasts with the medial temporal lobe's critical role in relational memory per se.

Implicit and Explicit Memory in Children With Congenital and Acquired Brain Disorder

Implicit and explicit memory were examined in 8- to 15-year-old children with myelomeningocele and shunted hydrocephalus, severe traumatic brain injuries, or orthopedic injuries. Each group included between 22 and 29 children. Children completed a fragmented picture identification task to assess perceptual priming and a semantic decision-making task to assess conceptual priming. Each task also assessed procedural learning as well as explicit recall and recognition. All 3 groups showed significant perceptual and semantic priming of similar magnitude. In contrast, both brain-disordered groups displayed poorer explicit memory than did the comparison group. No group showed significant procedural learning on either task. Age and IQ were stronger predictors of explicit recall than of implicit memory. The findings indicate that implicit memory is relatively intact in many children with congenital and acquired brain disorders, despite deficits in explicit memory, and support the existence of separate memory systems in children.

Dynamic cortical and subcortical networks in learning and delayed recall of timed motor sequences

We used positron emission tomography to examine learning and retention of timed motor sequences. Subjects were scanned during learning (LRN) and baseline (ISO) on 3 d: day 1, after 5 d of practice (day 5) and after a 4 week delay (recall). Blood flow was compared across days of learning and between the LRN and ISO conditions. Overall, significant changes in activity were seen across days for the LRN condition, but not the ISO baseline. Day 1 results revealed extensive activation in the cerebellar cortex, particularly lobules III/IV and VI. Day 5 results showed increased activity in the basal ganglia (BG) and frontal lobe, with no significant cerebellar activity. At recall, significantly greater activity was seen in M1, premotor, and parietal cortex. Blood flow in the cerebellum decreased significantly between day 1 and recall. These results reveal a dynamic network of motor structures that are differentially active during different phases of learning and delayed recall. For the first time our findings show that recall of motor sequences in humans is mediated by a predominantly cortical network. Based on these results, we suggest that during early learning cerebellar mechanisms are involved in adjusting movement kinematics according to sensory input to produce accurate motor output. Thereafter, the cerebellar mechanisms required for early learning are no longer called into play. During late learning, the BG may be involved in automatization. At delayed recall, movement parameters appear to be encoded in a distributed representation mediated by M1, premotor, and parietal cortex.

The impact of semantic impairment on word stem completion in Alzheimer's disease

Both the extent of semantic memory impairment and the level of processing attained during encoding might constitute critical factors in determining the amount of word-stem completion (WSC) priming encountered in Alzheimer's disease (AD) subjects. We investigated the impact of varying encoding level in AD and elderly normal subjects, using a set of stimuli ranked as "intact" or "degraded" in terms of each subject's semantic knowledge on probe questions. For both shallow and deep encoding conditions, overall priming in the two subject groups was equivalent. However, for the deep encoding condition, consisting of a semantic judgment task performed on each target word, the priming effect noted in AD subjects was significantly smaller for semantically degraded items than for semantically intact items. Results indicate that the degree of semantic impairment represents one important variable affecting the amount of WSC priming which results when deep encoding procedures are used at study.

Visuomotor skill learning on serial reaction time task in patients with early Parkinson's disease

This study tested the role of basal ganglia in visuomotor skill learning. Thirty-nine patients early in the course of Parkinson's disease (PD) and 30 patients after operation for an aneurysm of the anterior communicating artery (ACoA) were compared with 31 matched control subjects on a Serial Reaction Time test (SRTt). The patients with PD showed impaired visuomotor skill learning across the repeating blocks, in the presence of preserved declarative knowledge of embedded sequences, in contrast to the ACoA group in whom the reverse pattern was observed. The significant correlation in patients with PD between the standard neuropsychological and motor measures and the performance observed in the skill acquisition test, in the ACoA group and control subjects was not observed. The suggestion that this learning impairment could not be attributed to a motor deficit per se was also confirmed more directly for patients with PD. Accuracy of performance after the initial learning phase on the SRTt in patients with PD was associated predominantly with visual span capacity measures. Declarative knowledge of the embedded sequence of the SRTt was correlated to general cognitive and verbal span abilities in the PD group. The impairment observed in the PD group was not the result of a general decline in cognitive functioning, mood disturbances, or the severity of the motor symptoms.

Basal forebrain amnesia: does the nucleus accumbens contribute to human memory?

OBJECTIVE

To analyse amnesia caused by basal forebrain lesions.

METHODS

A single case study of a patient with amnesia after bleeding into the anterior portion of the left basal ganglia. Neuropsychological examination included tests of attention, executive function, working memory, recall, and recognition of verbal and non-verbal material, and recall from remote semantic and autobiographical memory. The patient's MRI and those of other published cases of basal forebrain amnesia were reviewed to specify which structures within the basal forebrain are crucial for amnesia.

RESULTS

Attention and executive function were largely intact. There was anterograde amnesia for verbal material which affected free recall and recognition. With both modes of testing the patient produced many false positive responses and intrusions when lists of unrelated words had been memorised. However, he confabulated neither on story recall nor in day to day memory, nor in recall from remote memory. The lesion affected mainly the nucleus accumbens, but encroached on the inferior limb of the capsula interna and the most ventral portion of the nucleus caudatus and globus pallidus, and there was evidence of some atrophy of the head of the caudate nucleus. The lesion spared the nucleus basalis Meynert, the diagnonal band, and the septum, which are the sites of cholinergic cell concentrations.

CONCLUSIONS

It seems unlikely that false positive responses were caused by insufficient strategic control of memory retrieval. This speaks against a major role of the capsular lesion which might disconnect the prefrontal cortex from the thalamus. It is proposed that the lesion of the nucleus accumbens caused amnesia.

Time-dependent motor memory processes in amnesic subjects

Functional properties of motor memory change with the passage of time. The time-dependent nature of memories in humans has also been demonstrated for certain "declarative" memories. When the declarative memory system is damaged, are the time-dependent properties associated with motor memories intact? To approach this question, we examined five subjects with global amnesia (AMN), including subject H.M., and a group of age-matched control subjects. The task was to make reaching movements to visually presented targets. We found that H.M. (but not the other subjects) was significantly impaired in the ability to perform the visuomotor kinematic transformations required in this task, to accurately move the hand in the direction specified by a target. With extensive practice, H.M.'s performance improved significantly. At this point, a force field was imposed on the hand. With practice in field A, H.M. and other AMN subjects developed aftereffects and maintained these aftereffects for 24 h. To quantify postpractice properties associated with motor memories, subjects learned field B on day 2 and at 5 min were retested in field A. In both subject groups, performance in field A was significantly worse than their own naive performance a day earlier. The aftereffects indicated persistence of the just-learned but now inappropriate motor memory. After 4 h of rest, subjects were retested in B. Performance was now at naive levels. The aftereffects at 4 h indicated a reduced influence of the memory of field A. The time-dependent patterns of motor memory perseveration, as measured at 5 min and 4 h, were not different in the AMN and normal control groups.

Neurobehavioural disturbances, rehabilitation outcome, and lesion site in patients after rupture and repair of anterior communicating artery aneurysm

OBJECTIVE

To determine: (1) patterns of cognitive and psychiatric dysfunction; (2) those neurobehavioural parameters which mostly influence disability in activities of daily living (ADL) and handicap in occupational and psychosocial activities, and (3) underlying neuroanatomical pathology in patients after rupture and repair of anterior communicating artery (ACoA) aneurysm.

METHODS

30 patients were extensively examined by means of a comprehensive battery of neuropsychological tests, by rating of psychopathological symptoms, and by use of the functional independence measure (FIM), Glasgow outcome scale (GOS), and MRI.

RESULTS AND CONCLUSIONS

(1) Three main groups were characterised by primary impairment of memory, executive functions, or of attentional performance. Within these main groups, specific patterns were identified relating to extent of primary dysfunction and associated disorders. The variety of neuropsychological disturbances is in contradiction to the existence of an "ACoA syndrome" as an entity. (2) Rehabilitation outcome proved to be mostly associated with both memory and attentional performance. (3) In neuropathological terms, lesions of the medial septum and nucleus of the diagonal band of Broca (MS/ndbB) were closely associated with memory deficits and prefrontal lesions were associated with attentional, executive, and psychopathological dysfunctions. At the same time, bilateral lesions were associated with severe disturbances. The type and severity of the above mentioned deficits were independent of the side of lesion in unilateral cases, of rectus gyrus resection, and of the Hunt and Hess grading system.

Non-associative lexical priming is impaired in Alzheimer's disease

A word-fragment completion task was used to assess long-term, non-associative lexical priming in patients with probable Alzheimer's disease (AD) and age- and education-matched elderly normal control (NC) subjects. Despite equivalent baseline performance, the AD patients exhibited less facilitation in their ability to complete word fragments from having previously read the intact words than did the NC subjects. The AD patients were also impaired relative to NC subjects on an explicit recognition memory task, but there was no relationship between explicit memory performance and priming for either group. These results are consistent with previous demonstrations of impaired semantically-based priming in patients with AD and extend the domain of their impairment to priming that is predominantly based on lexical activation.

The nucleus accumbens and learning and memory

Recent research on the nucleus accumbens (NA) indicates that this brain region is involved in learning and memory processes in a way that is separable from its other well-known roles in behavior, such as motivation, reward, and locomotor activity. These findings have suggested that 1) the NA may be involved in declarative, or hippocampal formation-dependent learning and memory, and not in several other non-declarative forms of learning and memory, and 2) the NA may be selectively involved in certain stages of learning and memory. These characteristics suggest that the NA may be part of a larger striatal system which subserves acquisition and consolidation, but is not a site of long-term storage, of different forms of learning and memory.

Memory disorders in Alzheimer's disease and the organization of human memory

The Squire and Zola-Morgan parallel organization model of the memory and the Tulving hierarchical model were developed mainly through the study of amnesic patients. The predictions of these two models are different, the first being more open to double dissociations and less restrictive than the second. Alzheimer's Disease is characterized by a differential impairment of the memory systems and by an interindividual variability which may take the form of dissociations between preserved and disturbed abilities in some patients. The objective of this study was to use the memory dysfunctions of patients with AD to test the validity of the two models. Analysis of the group data provided an average profile of memory disturbance consistent both with much of the data given in AD literature and with the two models. Using a multiple single-case strategy, we demonstrated several simple dissociations which are for the greater part compatible with the two models. Two of the dissociations underline the limits of the Tulving model, which otherwise accounts for a lot of results. The study supports the relevance of AD for the understanding of the cognitive architecture of the human memory.

Stem-completion priming in Alzheimer's disease: the importance of target word articulation

Stem-completion priming performance in patients with Alzheimer's type dementia (DAT) was explored in three experiments in which both the standard repetition priming effect and a novel indirect form of priming, cohort priming, were measured. In the first experiment, in which study stimuli were words, both priming effects were found to be markedly attenuated in the DAT group. In the second experiment, the study stimuli were specially constructed nonwords, and it was found that cohort priming was present at normal levels in the DAT group. In a third experiment we tested the specific hypothesis that the requirement to overtly articulate target stimuli during the study phase was critical for the appearance of normal cohort priming in the DAT group in Experiment 2, and also for the normal levels of repetition priming which have been reported in some published studies. Two encoding conditions were compared, one in which subjects simply had to read aloud the target words and a second in which subjects were required to make evaluative (pleasantness) ratings for each of the target words (identical to that used in Experiment 1). Stem-completion priming performance following the latter condition was significantly attenuated in the DAT group relative to a healthy control group, but following the "read aloud" encoding condition, normal levels of repetition and cohort priming were observed. It is suggested that the most fruitful approach to understanding the performance of DAT subjects on lexical repetition priming tasks will involve a detailed analysis of language functions and how they interact with other, possibly mnemonic, processes in the generation of primed responses.

Neurobiology of skill and habit learning

Recent evidence indicates that the basal ganglia are critical brain structures for motor-skill and habit learning, and may be important for the acquisition of some perceptual and cognitive skills. The cerebellum appears to contribute importantly only to motor-skill learning. Transitory cortical changes occur during motor-skill learning, but perceptual-skill learning may involve a semi-permanent change in neuronal sensitivity in the primary sensory cortex.

Aneurysm of the anterior communicating artery: a review of neuroanatomical and neuropsychological sequelae

For over 100 years, the study of amnesia in humans has been limited primarily to subjects with either diencephalic or mesial temporal lobe lesions. However, over the last 30 years, it has been reported that individuals who survived aneurysms of the anterior communicating artery (ACoA) often displayed an amnestic syndrome, despite the fact that diencephalic and mesial temporal structures were intact. This article presents a comprehensive review of the ACoA literature concerning the neurobehavioral and neuroanatomical substrates of what has been termed the "ACoA syndrome". Various theoretical models regarding the neural substrates of amnesia are discussed. Possible directions for future research are outlined.