Temporal modeling demonstrates preserved overlearning processes in schizophrenia: an fMRI study

Working memory (WM) deficits are a core feature of schizophrenia. However, it has not been examined whether these deficits are related to altered temporal dynamics of information acquisition and changes in executive cognitive control. Therefore, the present study intended to quantify and model the dynamic process of information acquisition during continuous overlearning of WM information. It also aimed at investigating the relation between overlearning-associated change in behavioral performance and brain activity. Thirteen schizophrenic patients and 13 healthy volunteers were studied with functional magnetic resonance imaging (fMRI) while performing a recently developed overlearning paradigm [Koch K, Wagner G, von Consbruch K, Nenadic I, Schultz C, Ehle C, Reichenbach J, Sauer H, Schlösser R (2006) Temporal changes in neural activation during practice of information retrieval from short-term memory: An fMRI study. Brain Res 1107:140–150]. Consistent with the earlier study, short-term learning of stimulus material was associated with significant performance improvements and exponential signal decreases in a fronto-parieto-cerebellar network both in schizophrenic patients and in healthy volunteers. Against expectation patients exhibited stronger signal decreases relative to controls in anterior cingulate (Brodmann area (BA) 32), middle and superior temporal (BA 37, BA 22), superior frontal (BA 8/9, BA 6) and posterior parietal regions (BA 40). Furthermore, the individually modeled exponential decay rate of the blood oxygenation level-dependent signal in the right dorsolateral prefrontal cortex was significantly correlated with exponential decrease in mean behavioral response times in healthy controls while a statistical trend emerged in patients. A relative hyperactivation in the patient group was observable only at the start of the learning process and diminished with continued overlearning. This effect might indicate a gradual reduction of recruited neuronal resources and a practice-associated activation normalization in patients with schizophrenia. Our data suggest that in subacute patients learning and associated decreases in cerebral activation brought about by short-term practice are left unimpaired.     

Attribution of intentions and context processing in psychometric schizotypy

ABSTRACT

Introduction: Impairment in Theory of mind (TOM) has frequently been associated with schizophrenia and with schizotypy. Studies have found that a tendency to over-attribute intentions and special meaning to events and to people is related to positive psychotic symptoms. Further, it has been suggested that this intentionality bias may be due to a broader deficit in context processing (CP). The aim of the present study was thus to investigate the relationship between positive schizotypy and both over-attribution of intentions and contextual processing.

Methods: One-hundred and nineteen healthy individuals completed the Schizotypal Personality Questionnaire and were assessed with tasks measuring contextual treatment and ToM.

Results: Results revealed that positive schizotypy was significantly related to an over-attribution of intentions on the ToM task and with a faster processing of implicit context. Partial correlational analyses indicated that the association between the attribution of intentions and positive schizotypy was not explained by a deficit of CP. In contrast, stepwise multiple regression analyses showed that both an over-attribution of intentions and a faster processing of implicit context significantly predicted positive schizotypy.

Conclusions: These results show that an over-attribution of intention is independent from a broader deficit in context information processing and that they both possibly contribute to the development and maintenance of positive psychotic symptoms.     

Working memory performance of older adults with insomnia

Older individuals suffering insomnia typically report declines in their cognitive performance beyond what they consider to be normal changes due to the aging process. Recent neuro‐imaging studies have demonstrated frontal lobe hypo‐activation among insomniac populations when compared with healthy, good sleepers. However, research is yet to confirm whether frontal lobe hypo‐activation translates into objective declines when performing tasks hypothesized to draw upon this brain region. This study aimed to investigate whether older insomnia sufferers demonstrate significantly impaired performance on a challenging working memory task when compared with age‐matched good sleepers. Forty‐nine older individuals (mean age = 69.43 years, SD = 4.83) suffering from sleep maintenance insomnia were compared with 49 age‐matched good sleepers. Cognitive performance was assessed using the Double Span Memory Task, a computer‐based working memory task that requires participants to indicate the names and/or spatial locations of increasingly longer sequences of visually presented objects. After controlling for general intelligence, the individuals suffering from insomnia did not perform differently when compared with the good sleepers on either the simpler or more cognitively demanding components of the task. Older individuals with insomnia did not display an observable impairment of working memory in this study relative to good sleepers. Despite the mixed results from previous research, this study adds weight to the absence of objective impairment in insomniacs, at least while performing short‐term demanding cognitive tasks.     

Figural memory performance and functional magnetic resonance imaging activity across the adult lifespan

We examined performance and functional magnetic resonance imaging activity in participants (n = 235) aged 17–81 years on a nonverbal recognition memory task, figural memory. Reaction time, error rate, and response bias measures indicated that the youngest and oldest participants were faster, made fewer errors, and showed a more conservative response bias than participants in the median age ranges. Encoding and Recognition phases activated a distributed bilateral network encompassing prefrontal, subcortical, lateral, and medial temporal and occipital regions. Activation during Encoding phase did not correlate with age. During Recognition, task-related activation for correctly identified targets (Hit-Targets) correlated linearly positively with age; nontask related activity correlated negative quadratically with age. During correctly identified distractors (Hit-Distractors) activity in task-related regions correlated positive linearly with age, nontask activity showed positive and negative quadratic relationships with age. Missed-Targets activity did not correlate with age. We concluded that figural memory performance and functional magnetic resonance imaging activity during Recognition but not Encoding was affected both by continued maturation of the brain in the early 20s and compensatory recruitment of additional brain regions during recognition memory in old age.     

Effects of mnemonic load on cortical activity during visual working memory: Linking ongoing brain activity with evoked responses

The mechanisms generating task-locked changes in cortical potentials remain poorly understood, despite a wealth of research. It has recently been proposed that ongoing brain oscillations are not symmetric, so that task-related amplitude modulations generate a baseline shift that does not average out, leading to slow event-related potentials. We test this hypothesis using multivariate methods to formally assess the co-variation between task-related evoked potentials and spectral changes in scalp EEG during a visual working memory task, which is known to elicit both evoked and sustained cortical activities across broadly distributed cortical regions. 64-channel EEG data were acquired from eight healthy human subjects who completed a visuo-spatial associative working memory task as memory load was parametrically increased from easy to hard. As anticipated, evoked activity showed a complex but robust spatio-temporal waveform maximally expressed bilaterally in the parieto-occipital and anterior midline regions, showing robust effects of memory load that were specific to the stage of the working memory trial. Similarly, memory load was associated with robust spectral changes in the theta and alpha range, throughout encoding in posterior regions and through maintenance and retrieval in anterior regions, consistent with the additional resources required for decision making in prefrontal cortex. Analysis of the relationship between event-related changes in slow potentials and cortical rhythms, using partial least squares, is indeed consistent with the notion that the former make a causal contribution to the latter.     

年龄相关的认知损害

老年人群中认知损害是非常普遍的现象 ,其中与增龄老化有关的称为年龄相关的认知损害 /下降(ｉｍｐａｉｒｍｅｎｔ/ｄｅｃｌｉｎｅ)。这种认知损害中常常以记忆受损最早或最突出 ,所以又将早期病例称为年龄相关的记忆损害 /下降 ,损害发展到严重时就是痴呆。一般来说 ,所谓年龄相关的认知损害是指介于正常认知和痴呆之间的轻度认知损害而无痴呆者。其中 ,绝大多数患者的特点是认知损害轻微 ,对日常生活影响不大 ,有自知力 ,且进展缓慢 ,呈现相对稳定状态而不会迅速加重发展为痴呆 ,被认为是正常老化[1] 。少数患者除了有记忆受损外 ,还有认…     

认知闭合需要对个体前瞻记忆的影响

目的:探讨认知闭合需要对个体的事件性和时间性前瞻记忆的影响.方法:对30名高认知闭合需要个体和30名低认知闭合需要个体进行事件性和时间性前瞻记忆差异的实验研究.事件性前瞻记忆实验任务是看到目标线索,执行目标任务;时间性前瞻记忆任务是采用双任务实验研究范式,即执行背景任务(图形任务)的同时记住某个时间点执行目标任务.结果:高、低认知闭合需要组被试在时间性前瞻记忆任务的反应时和正确率上不存在显著差异(P＞0.05),但在事件性前瞻记忆任务的反应时上存在显著差异(P＜0.05),高认知闭合需要组的事件性前瞻记忆反应时显著短于低认知闭合需要组.结论:认知闭合需要对个体的前瞻记忆有一定影响,高认知闭合需要被试的事件性前瞻性记忆反应时短于低认知闭合需要组.     

Basal and hypercapnia-altered cerebrovascular perfusion predict mild cognitive impairment in aging rodents

With increasing age, a subset of otherwise healthy individuals undergoes impairments in learning and memory that have been termed mild cognitive impairment (MCI). The enhanced neuronal activity associated with learning and memory requires increased cerebral blood flow (CBF) to specific brain regions. However, the interactions between cerebral blood flow and MCI remain unclear. In this study, we address whether baseline or hypercapnia-induced (increased blood CO₂ levels) changes in CBF are modified with age, and whether these measures are predictive of cognitive status in rodents. Adult and aged rats were evaluated using a hippocampally-dependent task in a water maze. Aged rats were classified as memory-impaired or memory-intact based on performance comparisons with adult rats. Cerebral blood flow was assessed using flow-alternating inversion recovery (FAIR) magnetic resonance imaging (MRI), before and after breathing 10% CO₂. The transition period between CO₂ concentrations was examined with blood oxygen level dependent (BOLD) MRI. Separation of aged animals into memory-intact and impaired categories revealed increased basal perfusion in the dorsal hippocampus of memory-impaired versus memory-intact aged animals. Linear regression revealed that higher hippocampal perfusion was correlated with impaired memory in aged animals, and a logistic regression indicated that hippocampal perfusion predicted spatial memory ability. Several brain regions of aged rats demonstrated an attenuation of the perfusion increase normally observed in adult rats under hypercapnia. Memory-impaired animals were the primary contributor to this effect, as their perfusion response to hypercapnia was significantly reduced compared to adult animals. Aged, memory-intact animals were not significantly different from adults. BOLD MRI demonstrated a reduced response in aged animals to hypercapnia, with impaired animals being the primary contributor to the effect. A logistic regression model based on basal and hypercapnia perfusion correctly predicted cognitive status in 83.3% of animals tested. Our results indicate that age-related changes in vascular reactivity and perfusion are important contributing factors in memory impairment.     

Cognitive Inhibition in Dissociative Identity Disorder (DID): Developing an Understanding of Working Memory Function in DID

ABSTRACT

The current study examined cognitive inhibition, a mechanism of working memory, in dissociative identity disorder (DID). A negative priming procedure was used to assess inhibitory functioning in DID patients, as well as in a general population sample and a psychiatric comparison sample. Results from the first study show a significant interaction between group and experimental condition; the general population sample showed an independently non-significant trend towards negative priming while the two psychiatric groups showed no evidence of negative priming. Using different stimuli and a new priming procedure, Study 2 essentially replicated the findings of Study 1 with the control sample displaying significant negative priming and the two psychiatric samples producing no negative priming. High dissociativity was significantly related to reduced negative priming in Study 2. Findings suggest a relationship between DID and weakened inhibitory functioning and are discussed with reference to the negative priming and dissociation literatures.