Schizophrenics know more than they can tell: probabilistic classification learning in schizophrenia

BACKGROUND: Previous studies have demonstrated impaired explicit and preserved implicit memory functions in schizophrenia. However, it is less clear whether schizophrenics can learn complex information (e.g. probabilistic stimulus response associations) with or without access for conscious recollection. In this study we applied a classification learning task to assess explicit and implicit processes concurrently. METHODS: Two test procedures were administered to 40 schizophrenic subjects and 20 healthy volunteers: a probabilistic classification learning (PCL) task to evaluate implicit memory functions; and a category cue recognition test to investigate the explicit memory system. The PCL task included feedback guided category learning of geometrical shapes. These shapes were called category cues, predicting class membership with certain probabilities. The gradual increase of categorization performance during the feedback learning was a potentially implicit process, whereas the subsequent recognition of category cues required explicit memory functions. RESULTS: The schizophrenic patients improved their categorization performance to a similar extent to the controls, but they failed to recognize the category cues. Memory performances were independent of the positive and negative symptoms. CONCLUSIONS: Patients with schizophrenia were able to establish representations of complex categories, but these remained unconscious. This is consistent with earlier reports, suggesting damaged explicit and spared implicit memory in schizophrenia.     

Implicit memory for music in Alzheimer's disease

Short, unfamiliar melodies were presented to young and older adults and to Alzheimer's disease (AD) patients in an implicit and an explicit memory task. The explicit task was yes-no recognition, and the implicit task was pleasantness ratings, in which memory was shown by higher ratings for old versus new melodies (the mere exposure effect). Young adults showed retention of the melodies in both tasks. Older adults showed little explicit memory but did show the mere exposure effect. The AD patients showed neither. The authors considered and rejected several artifactual reasons for this null effect in the context of the many studies that have shown implicit memory among AD patients. As the previous studies have almost always used the visual modality for presentation, they speculate that auditory presentation, especially of nonverbal material, may be compromised in AD because of neural degeneration in auditory areas in the temporal lobes.     

Impaired conditioned taste aversion learning in APP transgenic mice

Cognition in transgenic mouse models of Alzheimer's disease (AD) has been predominantly characterized in explicit spatial orientation tasks. However, dementia in AD encompasses also implicit memory systems. In the present study a line of transgenic mice (TgCRND8) encoding a double mutated allele of the human amyloid precursor protein (APP) genes was evaluated in an implicit associative learning task of conditioned taste aversion (CTA). CTA is a form of Pavlovian classical conditioning, in which a mouse learns to avoid a novel taste of saccharine (conditioned stimulus) paired with an experimentally induced (systemic injection of lithium chloride) nausea (unconditioned stimulus). In contrast to conditioned non-Tg mice, TgCRND8 APP mice developed weaker aversion against saccharine and quickly increased its consumption in repeated tests. These results indicate that TgCRND8 mice show a significant impairment not only in explicit spatial memory, as has been previously shown [Nature 408 (2000) 979], but also in implicit memory. Control experiments confirmed that TgCRND8 and non-Tg mice had comparable taste sensitivities in response to appetitive as well as aversive tastes. The study suggests that the CTA paradigm can be a sensitive tool to evaluate deficits in implicit associative learning in APP transgenic mouse models of AD.     

Amnestic mild cognitive impairment: difference of memory profile in subjects who converted or did not convert to Alzheimer's disease

Episodic long-term, short-term, and implicit memory were investigated in 79 elderly subjects who fulfilled criteria for the amnestic form of mild cognitive impairment (a-MCI; i.e., by having an idiopathic amnestic disorder with absence of impairment in cognitive areas other than memory and without confounding medical or psychiatric conditions) and who developed Alzheimer's disease (AD) after 2 years as well as in 111 subjects affected by a-MCI who did not develop dementia. Results document a memory profile in a-MCI subjects characterized by preserved short-term and implicit memory and extensive impairment of episodic long-term memory. In virtually all episodic memory indexes examined (learning, forgetting, recognition abilities), a-MCI subjects who converted to AD were more severely impaired than were subjects who did not become demented. This memory profile, which closely resembles that exhibited by amnestic patients with bilateral mesial-temporal lobe lesions, confirms a precocious phase in preclinical AD characterized by selective involvement of mesial-temporal areas and worsening of the memory impairment as atrophic changes progress in hippocampal structures. In this context of pervasive episodic memory impairment, tests assessing the free recall of verbal material following a delay interval demonstrated the greater sensitivity to memory deficits of a-MCI subjects who developed AD.     

Impaired implicit learning in schizophrenia

Schizophrenia patients consistently show deficits on tasks of explicit learning and memory. In contrast, their performance on implicit processing tasks often appears to be relatively intact, although most studies have focused on implicit learning of motor skills. This study evaluated implicit learning in 59 medicated schizophrenia outpatients and 43 controls using 2 different cognitive skill tasks. Participants completed a probabilistic classification task to assess procedural habit learning and an artificial grammar task to assess incidental learning of complex rule-based knowledge, as well as an explicit verbal learning and memory task. In addition to performing worse than controls on the explicit learning task, patients showed worse overall performance on the probabilistic classification task, which involves gradual learning through trial-by-trial performance feedback. However, patients and controls showed similar levels of learning on the artificial grammar task, suggesting a preserved ability to acquire complex rule-based knowledge in the absence of performance feedback. Discussion focuses on possible explanations for schizophrenia patients' poor probabilistic classification task performance.     

Spatial and nonspatial implicit motor learning in Korsakoff's amnesia: evidence for selective deficits

Patients with amnesia have deficits in declarative memory but intact memory for motor and perceptual skills, which suggests that explicit memory and implicit memory are distinct. However, the evidence that implicit motor learning is intact in amnesic patients is contradictory. This study investigated implicit sequence learning in amnesic patients with Korsakoff’s syndrome (N = 20) and matched controls (N = 14), using the classical Serial Reaction Time Task and a newly developed Pattern Learning Task in which the planning and execution of the responses are more spatially demanding. Results showed that implicit motor learning occurred in both groups of participants; however, on the Pattern Learning Task, the percentage of errors did not increase in the Korsakoff group in the random test phase, which is indicative of less implicit learning. Thus, our findings show that the performance of patients with Korsakoff’s syndrome is compromised on an implicit learning task with a strong spatial response component.     

Implicit motor-sequence learning in humans following unilateral stroke: the impact of practice and explicit knowledge

Learning and memory are sub-served by two interrelated systems - explicit and implicit. Explicit memory involves facts, while one form of implicit memory involves perceptual-motor processes. The purpose of this series of experiments was to investigate the ability of individuals with stroke-related brain damage to demonstrate implicit motor-sequence learning and the relative impacts of (1) extended practice, or (2) explicit knowledge prior to practice. Implicit learning was severely impaired without explicit knowledge and even under conditions of extended practice. However, when explicit knowledge was provided prior to practice, participants with stroke demonstrated implicit motor-sequence learning. These data suggest that following unilateral stroke, providing explicit information about the task and sequence can attenuate implicit motor learning deficits.     

Alzheimer病与Parkinson病患者记忆损害的比较研究

目的：测查Alzheimer病、Parkinson病患者的记忆功能，了解这两种疾病病人记忆损伤的特征。方法：采用多维记忆评估量表中的12个分测验对30例原发性Parkinson病患者、30例临床诊断可能的Alzhdmer病患者及年龄、性别和教育程度与2个病人组相匹配的2个正常对照组进行外显记忆、内隐记忆及日常生活记忆等记忆功能的评定。结果：AD组在所有的分测验和记忆因子上均差于对照组；PD组在图画再认、数字广度、汉词回忆、图形再生、经历定向等分测验和记忆广度、再认记忆、自由回忆、日常记忆、外显记忆等记忆因子上均显著低于对照组：经以教育年限为协变量校正后发现。除自由组词、残图命名、数字广度、空间广度、汉词回忆、常识记忆、记忆广度、内隐记忆外，AD组在其余各分测验和记忆因子上均存显著差于PD病人组。结论：AD病人存在着广泛的记忆功能障碍：PD病人存在着工作记忆和策略记忆的障碍：两者的记忆功能障碍存在着明显的不同。     

Somatostatin and cognitive dysfunction in Alzheimer's disease

Multiple research groups have documented reductions in cortical somatostatin‐like immunoreactivity (SRIF) in Alzheimer's disease (AD). This study investigated the relationship between cerebral cortical SRIF levels and concurrent measures of specific neuropsychological functions in early‐to‐middle‐stage AD patients. Biopsy samples obtained from nondominant frontal cortex of 5 patients with histopathologically confirmed AD were assayed for SRIF. Concurrent measures of intelligence, memory, language, visuoperception, visuoconstruction, attention, concentration, reaction time, and overall dementia severity were obtained. Close associations were observed between SRIF and dementia severity, four‐choice visual reaction time, and visuoperceptual and visuoconstructional abilities. No relationship was observed between SRIF and the remaining neuropsychological measures. Results are consistent with the hypothesis that the functional deficits in AD are caused, in large part, by a loss of cortico‐cortical projection neurons and a subsequent dissociation of specific cortical functional areas from one another.     

内隐记忆的研究证据及临床意义

内隐记忆 (ｉｍｐｌｉｃｉｔｍｅｍｏｒｙ)一词最初由Ｇｒａｆ与Ｓｃｈａｃｔｅｒ于 1985年提出 ,指对特定的过去经验进行有意识或外显的回忆测验中表现出来的对先前获得信息的无意识提取 ,也就是说 ,在有意或无意间获得的信息、技能或习惯 ,虽不能有意识地回忆和再认 ,但会影响类似作业的成效和行为的有效性。这一概念的提出扩大了记忆研究的内涵 ,因此迅速成为记忆研究的热点之一。目前内隐记忆的研究在测量方法与理论解释方面都取得了一些进展 ,大量证据表明它与外显记忆存在质的不同 ,是一个相对独立的记忆系统。不过现存的问题也很多 ,…     

The transition from implicit to explicit representations in incidental learning situations: more evidence from high-frequency EEG coupling

Implicit learning, i.e. knowledge acquisition in incidental learning situations, is a fundamental feature of the human mind. The extraction of (and subsequent adaptation to) regular patterns in the environment facilitates everyday actions. The cognitive and neural processes accompanying the transition from subconscious (implicit) to verbally reportable (explicit) knowledge about task contingencies are of high interest to the cognitive neurosciences, since they indicate a process that generates awareness for learned associations. Previous studies indicated an important role of high-frequency coupling (gamma-band) for the process that initiates the emergence of awareness for an implicitly learned task-underlying structure. It is unclear, however, whether this EEG coupling is indicative of a general, task-independent process accompanying the shift between implicit and explicit knowledge. To test the general role of this synchrony effect, we investigated EEG gamma-band coherence in the time period where this transition takes place using a serial reaction time paradigm. As expected, we find increased coupling in the gamma-band EEG between right prefrontal and occipital electrode sites just before the behavioural manifestation of emerging explicit sequence representation. These results support both the notion of general involvement of widespread cortical associative couplings in the generation of conscious knowledge and the necessity to study emerging consciously available memory representations using fine-grained properties of behavioural data.     

Ontogeny is different for explicit and implicit memory in humans

This study was aimed to clarify in how far ontogenetic development is different for declarative/explicit compared to procedural/implicit learning. These two memory subsystems are differentially affected in a number of pathological conditions. Sixty-one children between the age of 5 and 10 years were tested on a verbal story recall and non-verbal pictorial recall task, representing explicit memory. To test for implicit memory, a motor mirror tracking task and a non-motor tower-of-hanoi puzzle were used. Both explicit memory tasks showed a clear developmental profile with an increase in the number of recalled items for immediate, late and delayed recall with adult values not reached before the age of 9–10 years. In contrast, there were no age differences for both implicit memory tasks. The study demonstrates that explicit and implicit memory follow different maturational trends and further corroborate the notion of two different memory systems.     

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.     

The mere exposure effect in patients with Alzheimer's disease

The mere exposure effect was examined in patients with mild to moderate Alzheimer's disease (AD). Twenty patients and 20 elderly controls judged the physical characteristics of faces. Implicit memory was tested later by presenting pairs of faces (old and new) and asking participants which faces they liked better. Patients and controls exhibited above chance preference for previously exposed faces. Experiment 2 evaluated whether the preserved implicit memory of patients was mediated by explicit memory. Patients and controls again judged faces but then later chose which faces they had seen before. Patients exhibited impaired recognition memory compared to controls. These findings suggest that a mere exposure effect for unfamiliar faces is present in mild to moderate AD. The results are discussed in terms of perceptual and conceptual priming and relatively spared occipital lobe functioning in early AD.     

The role of color in the implicit memory performance of healthy older adults and individuals with Alzheimer's disease

Although the Alzheimer's disease (AD) patients in this study were severely impaired in recognition performance, their naming performance demonstrated normal priming across transformations in object color. This is evidence for preserved implicit shape-based memory performance in AD patients. For colored-object decision, healthy older adult control participants but not AD patients showed priming for new associations between previously encountered object shapes and colors. The author argues, on the basis of this colored object decision performance, that the deficits present in AD do not allow shape and color to be integrated to form a novel unitized representation that can be used to benefit cognitive performance.     

Age differences in explicit and implicit memory for pictures

In the present study, the authors examined age effects in memory for nonverbal material. A picture fragment completion task was used to test explicit and implicit memory in a younger and an older group. Explicit memory was indexed by free recall of pictures, whereas implicit memory was indexed by perceptual learning (priming). Both free recall and perceptual learning performance were found to be impaired in the older group. A measure of executive functioning was found to be predictive of both explicit and implicit memory.     

Conceptual implicit memory performance in Alzheimer's disease.

Alzheimer's disease (AD) patients often exhibit deficits on conceptual implicit memory tests such as category exemplar generation and word association. However, these tests rely on word production abilities, which are known to be disrupted by AD. The current study assessed conceptual implicit memory performance in AD patients and elderly control participants using a conceptual priming task that did not require word production (i.e., semantic decision). Memory performance was also examined using a category exemplar generation test (i.e., a conceptual priming task that required word production) and a recognition memory test. AD patients exhibited deficits on the semantic decision task, the category exemplar generation task, and the recognition memory task. The results indicate that the conceptual memory deficits observed in AD patients cannot be attributed completely to word production difficulties.     

酒依赖病人内隐和外显记忆的综合研究

记忆测量与记忆形式的研究足认知神经心理学的一个重要课题。本文以直接测量和间接测量评价法。综合研究了中老年酒依赖病人的记忆功能。结果表明:(1)病人内隐记忆无损害,而外显记忆有损害,表现出内隐与外显记忆间的不一致性;(2)项日性与联想性内隐记忆各有不同特点,前者在机械识读的条件下产生效应,而后者表现了语义学习的特点。     

内隐情感记忆实验研究 Ⅱ: 遗忘及其情感特征

目的：在概念加工水平上考察内隐情感记忆的特征及其遗忘规律。方法：用再认法测量外显记忆，用残字补全法测量内隐记忆。８３名被试分成七组分别在学习后即时、１９＇、６３＇、１天、２天、６天、３１天进行再认和补笔测验。结果：（１）测验距离学习时间越短，积极事件启动值保持量越大，时间越长，积极事件启动值保持量越少。消极事件启动值相对恒定，不受时间条件的影响。两者之间在学习后即时－２天差异显著。６天、３１天无差异；（２）外显情感记忆存在明显遗忘，两种意义的事件其保持量和遗忘率受时间条件影响，模式相似，无显著差异；（３）内隐和外显情感记忆出现实验性分离。结论：内隐情感记忆存在明显遗忘，其保持和遗忘规律不同于外显记忆，表明内隐和外显记忆属于两个独立的记忆系统。     

Changes of procedural learning in Chinese patients with non-demented Parkinson disease

To study procedural learning changes in patients with non-demented Parkinson disease (PD) but without depression. The Nissen serial reaction time task (SRTT) software version II (as a task of procedural learning), the Wechsler Memory Scale-Chinese version (WMS-CR), and two tasks of implicit memory were applied to 20 PD patients with a Hoehn-Yahr score at I-II degrees and 20 matched healthy controls were enrolled for the Nissen Version test. In the explicit WMS-CR and the implicit (word stem completion and degraded picture naming) tasks, the patients' scores fell within normal limits. In the SRTT, healthy controls displayed significantly reduced response times and error rates across the blocks of repeated sequence trials. In contrast, PD patients only showed a reduction in error rates but no change in response times. Impairment of nigrostriatal pathways selectively affects the performance in visuo-motor learning tasks such as the SRTT, but not in both the explicit tasks of WMS-CR and the implicit tasks.