Connectome signatures of neurocognitive abnormalities in euthymic bipolar I disorder

ObjectivesConnectomics have allowed researchers to study integrative patterns of neural connectivity in humans. Yet, it is unclear how connectomics may elucidate structure–function relationships in bipolar I disorder (BPI). Expanding on our previous structural connectome study, here we used an overlapping sample with additional psychometric and fMRI data to relate structural connectome properties to both fMRI signals and cognitive performance.Methods42 subjects completed a neuropsychological (NP) battery covering domains of processing speed, verbal memory, working memory, and cognitive flexibility. 32 subjects also had fMRI data performing a Go/NoGo task.ResultsBipolar participants had lower NP performance across all domains, but only working memory reached statistical significance. In BPI participants, processing speed was significantly associated with both white matter integrity (WMI) in the corpus callosum and interhemispheric network integration. Mediation models further revealed that the relationship between interhemispheric integration and processing speed was mediated by WMI, and processing speed mediated the relationship between WMI and working memory. Bipolar subjects had significantly decreased BA47 activation during NoGo vs. Go. Significant predictors of BA47 fMRI activations during the Go/NoGo task were its nodal path length (left hemisphere) and its nodal clustering coefficient (right hemisphere).ConclusionsThis study suggests that structural connectome changes underlie abnormalities in fMRI activation and cognitive performance in euthymic BPI subjects. Results support that BA47 structural connectome changes may be a trait marker for BPI. Future studies are needed to determine if these “connectome signatures” may also confer a biological risk and/or serve as predictors of relapse.     

Brain activation during working memory 1 month after mild traumatic brain injury: a functional MRI study.

OBJECTIVE: To assess patterns of regional brain activation in response to varying working memory loads shortly after mild traumatic brain injury (MTBI). BACKGROUND: Many individuals complain of memory difficulty shortly after MTBI. Memory performance in these individuals can be normal despite these complaints. METHODS: Brain activation patterns in response to a working memory task (auditory n-back) were assessed with functional MRI in 12 MTBI patients within 1 month of their injury and in 11 healthy control subjects. RESULTS: Brain activation patterns differed between MTBI patients and control subjects in response to increasing working memory processing loads. Maximum intensity projections of statistical parametric maps in control subjects showed bifrontal and biparietal activation in response to a low processing load, with little additional increase in activation associated with the high load task. MTBI patients showed some activation during the low processing load task but significantly increased activation during the high load condition, particularly in the right parietal and right dorsolateral frontal regions. Task performance did not differ significantly between groups. CONCLUSION: MTBI patients differed from control subjects in activation pattern of working memory circuitry in response to different processing loads, despite similar task performance. This suggests that injury-related changes in ability to activate or to modulate working memory processing resources may underlie some of the memory complaints after MTBI.     

Relationships between time estimation,memory, attention,and processing speed in patients with severe traumatic brain injury

The present experiment was aimed at investigating the effects of memory and attention deficits and of information processing slowing on time estimation in patients with severe traumatic brain injury (TBI). Patients with TBI and normal control subjects reproduced and produced durations (5, 14, 38s) in both a control counting condition and in a concurrent reading condition. They also performed finger-tapping tasks at a free rate and at a 1s rate. Both groups were assessed on processing speed using a reaction-time task, and on memory and attention using a battery of neuropsychological tests. The results showed that time estimation was not less accurate in patients with TBI than in control subjects on the reproduction task or on the production task performed either in the control counting condition or in the concurrent reading condition. Conversely, duration judgments were more variable in patients with TBI than in control subjects on both tasks in both conditions. The results also showed that TBI patients exhibited slower reaction-times, and poorer working and episodic memory scores than control subjects. Most importantly, the variability index in the duration reproduction task was related to both working memory scores and processing speed measures, whereas the variability index in the duration production task was only related with the processing speed measures. The temporal performance pattern in TBI patients does not appear to reflect specific deficits in timing, but rather overall problems in attention, working memory, and processing speed mechanisms.     

Precision and accuracy of subjective time estimation in different memory disorders

The aim of this study was to evaluate how different memory disorders affect subjective time durations. For this purpose we studied prospective time estimations in 4 amnesic (A) and in 15 Alzheimer's disease (AD) patients, and compared their performance with that of 5 matched young normal controls (YC) and 15 elderly subjects (EC). For the short-time durations we asked the subject to repeatedly reproduce a standard interval of 1 s. To test how subjects evaluated longer time durations, we choose a verbal estimation procedure. The subjects' task was to read either 5, 10, 20, or 40 digits appearing one at a time, while concurrently keeping the rhythm of 1 key press per second. At the end of each sequence, subjects had to judge the elapsed time from the beginning of the trial. Results showed that amnesics can correctly reproduce 1-s intervals. However, their accuracy of verbal estimates of longer durations was severely impaired. AD patients showed increased variability on repeated reproduction of 1-s intervals and were both inaccurate and imprecise in their verbal estimate of longer durations. Using the framework of the Scalar Timing Model, we conclude that amnesic patients exhibit a deficit in encoding and storing the current time for intervals that exceed their short-term memory range, while AD patients show a pattern of deficit that is explained by a more widespread involvement of both the clock, the memory, and the decisional mechanisms.     

Episodic odor memory: influences of handedness, sex, and side of nose

It is not known whether, or to what degree, odor memory is influenced by lateralized brain processes. In this study, we administered a 12-item match-to-sample odor memory test separately to the left and right sides of the nose of 30 left- and 30 right-handed subjects of equivalent age, sex distribution, and overall general smell ability. For each test item, one of three delay intervals (10-, 30-, and 60-s) was interspersed between smelling the target stimulus and smelling the first of four response alternatives. Women, but not men, performed significantly better on the left than on the right side of the nose, conceivably reflecting greater reliance upon left-hemisphere semantic processes. Subjects who received the first test on the right side of the nose outperformed those who received the first test on the left side of the nose. As in previous work, an age-related decrement in odor memory test scores was present. These data contribute to the debate on the role of lateralized brain processes in episodic odor memory, and suggest that performance on a standardized match-to-sample odor memory task is influenced by a number of interacting factors.     

Verbal cognition and attention deficits do not explain the verbal memory decline associated with pharmacoresistant partial epilepsy

The aim of this study was to explore whether change in verbal memory with time in patients with epilepsy is influenced by performance on tasks assessing verbal cognition or attention/processing speed. Thirty-six patients and twenty-five healthy controls were tested twice with median retest intervals of 4.8 and 3.1 years, respectively. Aspects of verbal memory, verbal cognition, and attention/processing speed were assessed. Decline in one verbal memory variable (Cronholm-Molander Memory Test Paired Associates -- Delayed Recall) was the strongest correlate of epilepsy. The second strongest correlate was a decrease in one attention/processing speed variable (Digit Symbol). The relationship between decline in verbal memory and epilepsy was not influenced by the decline in attention/processing speed, and the results did not support the notion that limited mental reserves as reflected in impaired verbal cognition or attention/processing speed can explain the relationship between verbal memory and epilepsy.     

Age-related changes in fronto-parietal networks during spatial memory: an ERP study

Spatial attention and memory were compared in young and old subjects using non-delayed and delayed matching-to-sample tests. Both young and older subjects revealed a right hemisphere superiority for spatial processing. Older subjects were as accurate as young controls in the non-delay task supporting preserved attention ability in this spatial task. However, older subjects were impaired at 3 s retention intervals supporting an encoding and/or retrieval deficit in spatial memory. Stimulus evaluation demands were highest in the non-delay task and younger subjects generated the largest posterior P3 in this condition plus an additional frontal P3. The frontal P3 was reduced in amplitude in the delay tasks in the young subjects. Retention of spatial information during the delay period was characterized by a negative slow wave maximal over Pz that predicted later memory performance and was enhanced in those subjects with high memory performance. Conversely, older subjects generated a frontal P3 in both delay and non-delay conditions and a reduced sustained posterior scalp negativity in some delay conditions. The results support age-related alterations in frontal-parietal networks during spatial memory.     

Prefrontal cortical involvement in visual working memory.

Studies of human amnesia provide evidence for a short-term memory store with information transfer to long term memory occurring within 60 s of sensory encoding. Human and nonhuman primate research has shown that maintenance of this short-term or working memory store is dependent upon frontal cortical activation, although the critical temporal parameters of frontal involvement throughout this 60-s window are undetermined. We examined prefrontal contributions to rapid (under 2 s) and sustained (over 4 s) visual working memory by recording behavioral performance and event-related potentials (ERPs) in patients with lesions in dorsolateral frontal cortex and age-matched control subjects. Prefrontal lesioned patients generated a reduced sustained frontal positivity at all delays. At short delays, patients generated reduced performance to stimuli presented in the contralesional field. Patients generated a negative potential (N400), greatest to contralesionally presented stimuli, that was observed in the control subjects only at long delays. The results indicate that prefrontal lesions impair the frontal component of an anterior-posterior working memory network activated during rapid and sustained visual memory processing. Frontal patients may require activation of limbic cortex, indexed by N400, for maintenance of both rapid and sustained working memory.     

The Palau Early Psychosis Study: neurocognitive functioning in high-risk adolescents

ObjectiveThe purpose of the present study was to evaluate both the independent and joint effects of genetic risk and clinical status on neurocognitive functioning in adolescents from a population isolate with an elevated risk for schizophrenia and strong familial aggregation of cases.MethodThe subjects were 310 non-help seeking, drug-naïve adolescents 14–19 years of age from the Republic of Palau. The sample comprised 98 Genetically High Risk (GHR) adolescents, 54 of whom were symptomatic, and 212 Genetically Low Risk (GLR) adolescents, including 113 Clinically High Risk (CHR) subjects who were symptomatic and 99 normal controls who were non-symptomatic. Neurocognitive testing was conducted after the clinical assessment and included Wechsler Memory Scale tests of logical, visual and working memory, the perceptual organization and processing speed subtests of the WISC-III, CPT-IP measures of sustained attention, and tests of fine and gross neuromotor function.ResultsGHR adolescents showed impairments in immediate logical memory, verbal working memory, CPT-IP performance, and fine motor skills. The only two cognitive components influenced by the presence of early psychosis symptoms were WISC-III perceptual organization and spatial working memory. Neurocognitive deficits did not increase with increasing levels of psychopathology. We found no significant interactive effects of genetic risk and clinical status on neurocognitive functioning.ConclusionsGenetic risk and clinical status exert independent effects on neurocognitive function in HR adolescents, and genetic risk has a broader impact than clinical status. Our results suggest that many of the neurocognitive impairments associated with early psychosis are genetically mediated and can occur in genetically vulnerable individuals regardless of their clinical status. However, visuospatial processing appears to be uniquely disrupted by emerging symptomatology.     

The time course of temporal discrimination: An ERP study

ObjectiveThe question of how temporal information is processed by the brain is still a matter of debate. This study aimed to elucidate the brain electrical activity associated with a visual temporal discrimination task.MethodsFor this purpose, 44 participants were required to compare pairs of sequentially presented time intervals: a fixed standard interval (1000 ms), and an equal-to-standard, longer (1200 ms) or shorter (800 ms) comparison interval. Behavioural data and event-related potentials (ERPs) were analyzed.ResultsLong intervals were more rapidly identified than short intervals. The amplitude of the contingent negative variation (CNV) found at frontocentral sites before the end of the comparison interval was significantly affected by the difference between its duration and the standard one. The amplitude and the scalp distribution of ERPs registered after the offset of the comparison interval were linearly modulated by its absolute duration.ConclusionsERP components associated with the offset of the comparison intervals clarified the involvement of working memory processes and different brain structures in temporal discrimination.SignificanceThis study further improves our understanding of the cognitive processes and neural substrates underlying temporal discrimination in healthy subjects and lays the ground for the investigation of clinical samples with time processing deficits.     

Brain activity in cigarette smokers performing a working memory task: effect of smoking abstinence.

BACKGROUND: When nicotine-dependent human subjects abstain from cigarette smoking, they exhibit deficits in working memory. An understanding of the neural substrates of such impairments may help to understand how nicotine affects cognition. Our aim, therefore, was to identify abnormalities in the circuitry that mediates working memory in nicotine-dependent subjects after they initiate abstinence from smoking. METHODS: We used blood oxygen level-dependent (BOLD) functional magnetic resonance imaging (fMRI) to study eight smokers while they performed a letter version of the N-Back working memory task under satiety (< or = 1.5 hours abstinence) and abstinence (> or = 14 hours abstinence) conditions. RESULTS: Task-related activity in the left dorsal lateral prefrontal cortex (DLPFC) showed a significant interaction between test session (satiety, abstinence) and task load (1-back, 2-back, and 3-back). This interaction reflected the fact that task-related activity in the satiety condition was relatively low during performance of the 1-back task but greater at the more difficult task levels, whereas task-related activity in the abstinence condition was relatively high at the 1-back level and did not increase at the more difficult task levels. CONCLUSIONS: We conclude that neural processing related to working memory in the left DLPFC is less efficient during acute abstinence from smoking than at smoking satiety.     

Visual perceptual and working memory impairments in schizophrenia

BACKGROUND: Impairments in working memory have been proposed to underlie a broad range of cognitive deficits seen in schizophrenia. Visual working memory impairments are frequently reported in schizophrenia. Investigations of visual working memory generally assume intact visual information processing, despite evidence of visual perceptual impairments in schizophrenia. In this study, we evaluated the integrity of the perceptual system for object and spatial visual information and the relevant working memory system, after adjusting for individual perceptual performance differences. METHODS: Thirty patients with schizophrenia and 20 healthy control subjects underwent testing using a task of perceptual discrimination of spatial and object visual stimuli. For testing visual working memory, a delay was introduced to the perceptual discrimination task. A thresholding procedure was used so that each subject adequately perceived the information during the working memory test. RESULTS: Subjects with schizophrenia exhibited impaired performance relative to controls for object and spatial visual perceptual discrimination. The extent of impairment was greater for the object than for the spatial test. After controlling for perceptual impairments, the subjects with schizophrenia exhibited impaired performance relative to controls for the spatial working memory test but not the object working memory test. CONCLUSIONS: Findings implicate dysfunction of posterior brain areas that mediate visual perceptual processing and the prefrontal areas involved in the active maintenance of information during delay intervals. However, the systems that govern object and spatial visual perception and working memory appear to be affected differentially by schizophrenia.     

Verbal and spatial working memory performance among HIV-infected adults.

Subtypes of working memory performance were examined in a cohort of 50 HIV-infected adults and 23 uninfected controls using an n-back paradigm (2-back) in which alphabetic stimuli were quasi-randomly presented to a quadrant of a computer monitor. In the verbal working memory condition, participants determined whether each successive letter matched the letter that appeared two previously in the series, regardless of spatial location. In the spatial working memory condition, participants determined whether each letter matched the spatial location of the letter that had appeared two previously, regardless of letter identity. The dependent variable was percent accuracy in each condition. Results of mixed model ANOVA revealed that the HIV-infected participants performed significantly worse than controls on both the verbal and spatial working memory tasks. A significant main effect for working memory condition was also present with both participant groups performing better on the spatial working memory task. These results, the first study of HIV-infected adults to directly compare verbal versus spatial working memory performance using the identical test stimuli across task conditions, suggests that HIV infection is associated with a decrement in working memory efficiency that is equally apparent for both verbal and spatial processing. These findings implicate central executive dysfunction as a likely substrate and provide the basis for hypothesizing that decline in working memory may contribute to other HIV-associated neuropsychological deficits.     

Time estimation by patients with frontal lesions and by Korsakoff amnesics.

We studied time estimation in patients with frontal damage (F) and alcoholic Korsakoff (K) patients in order to differentiate between the contributions of working memory and episodic memory to temporal cognition. In Experiment 1, F and K patients estimated time intervals between 10 and 120 s less accurately than matched normal and alcoholic control subjects. F patients were less accurate than K patients at short (< 1 min) time intervals whereas K patients increasingly underestimated durations as intervals grew longer. F patients overestimated short intervals in inverse proportion to their performance on the Wisconsin Card Sorting Test. As intervals grew longer, overestimation yielded to underestimation for F patients. Experiment 2 involved time estimation while counting at a subjective 1/s rate. F patients' subjective tempo, though relatively rapid, did not fully explain their overestimation of short intervals. In Experiment 3, participants produced predetermined time intervals by depressing a mouse key. K patients underproduced longer intervals. F patients produced comparably to normal participants, but were extremely variable. Findings suggest that both working memory and episodic memory play an individual role in temporal cognition. Turnover within a short-term working memory buffer provides a metric for temporal decisions. The depleted working memory that typically attends frontal dysfunction may result in quicker turnover, and this may inflate subjective duration. On the other hand, temporal estimation beyond 30 s requires episodic remembering, and this puts K patients at a disadvantage.     

Correlation between special brain area and blood perfusion in patients with cerebral infarction at convalescent period

BACKGROUND: Presently, clinic memory scale is used to evaluate learning memory ability in most studies, and the influence of difference in measurement condition of individuals exists. OBJECTIVE: To study the correlation between regional cerebral blood flow (rCBF) perfusion and learning memory function in special brain regions of patients with cerebral infarction at convalescent period, and to try to find out a method which can quantitatively evaluate learning ability. DESIGN: Case observation, and correlation analysis. SETTINGS: Shandong Institute for Behavioral Medicine; the Affiliated Hospital of Jining Medical College. PARTICIPANTS: Totally 70 patients with cerebral infarction admitted to Department of Neurology, Jining Medical College between January 2004 and December 2005 were involved. The involved patients, 58 male and 12 female, were averaged （52±3）years, and they were all right handed. They all met the diagnosis criteria instituted by the Fourth National Conference on Cerebrovascular Disease, and were confirmed as cerebral infarction by skull CT or MRI. Informed consents of detected items were obtained from all the patients and relatives. METHODS: When the patients were at convalescent period, their learning and memory ability were measured with " clinic memory scale (set A)". The 18 patients whose total mark over 100 were regarded as good learning memory function group; The 23 cases whose total mark less than 70 were regarded as poor learning memory function group. RCBF of hippocampus, nucleus amygdalae, temporal cortex and prefrontal lobe of patients between two groups were measured and compared by single photon emission computed tomography (SPECT). The total scores of the 18 good learning memory patients and 23 poor learning memory patients were taken as dependent variable Y, and their rCBFs of hippocampus, nucleus amygdale, temporal cortex and prefrontal lobe respectively as independent variable X for linear correlation analysis. MAIN OUTCOME MEASURES: Correlation of rCBF in different brain regions and learning memory ability in patients with cerebral infarction. RESULTS: ① The rCBF of hippocampus, nucleus amygdale, temportal cortex and prefrontal cortex of good learning memory function group were significantly higher than those of poor learning memory function group (P < 0.05). ②In the good learning memory function group, rCBF of hippocampus, nucleus amygdale, temportal cortex and prefrontal cortex were significantly positively correlated with memory scale scores（r = 0.961, 0.926, 0.954, 0.907, P < 0.05）, and also in the poor learning memory function group （r = 0.979, 0.976, 0.991, 0.953, P < 0.05）. CONCLUSION: The rCBF of hippocampus, nucleus amygdale, temportal cortex and prefrontal cortex of patients with cerebral infarction are significantly positively correlated with memory scale scores. Predicting learning memory ability of patients by quantitative determination of rCBF provides a quantitative and objective method for evaluating learning memory ability.     

Executive function and cognitive subprocesses in first-episode, drug-naive schizophrenia: an analysis of N-back performance

OBJECTIVE: This study investigated changes in the cognitive architecture of N-back performance in schizophrenia. METHOD: N-back performance of 12 patients with first-episode, drug-naive schizophrenia and matched healthy comparison subjects was studied in a reaction-time decomposition paradigm. RESULTS: Imposition of a working memory load led to a significant drop in response accuracy in patients. Reaction-time decomposition suggested slowing of visuomotor and choice reaction processing as well as an inability of parallel processing directed by working memory. DISCUSSION: Although N-back tasks validly access working memory function as a neurocognitive trait in the illness, several additional subprocesses and the ability for cognitive parallel processing are altered and require further study in schizophrenia.     

Diagnosis threat and underperformance: The threat must be relevant and implicit

Introduction: The diagnosis threat (DT) phenomenon shows that, in some cases, reminding people with mild traumatic brain injury (mTBI) about their past neurological history diminishes subsequent cognitive performance. The aim of the present study was to investigate the role of personal relevance (i.e., domain identification) and type of threat (i.e., implicit vs. explicit) as moderating variables. We investigated intrusive thoughts as a potential mediator.

Method: Control (non-mTBI) and mTBI participants were recruited and completed a domain identification questionnaire. Under either an implicit or an explicit DT condition, they completed neuropsychological tasks assessing working memory, episodic memory, and executive processing, as well as measures of intrusive thoughts.

Results: As expected, the main results showed that, for working memory and episodic memory, high identifier mTBI participants scored worse in the implicit DT condition than in the explicit condition. The implicit DT condition also led high identifier mTBI participants to score worse than low identifiers for working memory. Conversely, the explicit DT condition led high identifier mTBI participants to perform better than low identifiers for both working and episodic memory. Unexpectedly, low identifier mTBI participants scored better on working memory tasks in the implicit DT condition than in the explicit condition. We found no evidence of mediation by intrusive thoughts.

Conclusions: Domain identification and the explicit or implicit nature of the DT must be taken into account, as they can impact mTBI participants’ cognitive performance. This study suggests the influence of DT as a factor biasing neuropsychological assessment.     

A detailed analysis of rats' spatial memory in a probe trial of a Morris task

In the present study, we evaluated the search behavior of rats during a probe trial of a Morris water escape task. More specifically, the spatial memory during different stages of a 2 min probe trial in different zones was examined. After rats were trained for 4 days with four trials per day, their spatial memory was tested in a first probe trial. The rats showed a preference for the target quadrant during each of four 30-s intervals. The time in the annulus decreased across the four 30-s intervals. The preference for the previous target quadrant was also observed in a second probe trial, when the rats had received additional training for 4 days with four trials per day. However, the time spent in the annulus was highest during the first 30-s of the probe trial, and was lower and similar during the next three 30-s intervals. Therefore, probe trials of 60s seem to underestimate the spatial ability of rats. It appears that using a quadrant for assessing the performance may overestimate the spatial ability of a rat. Our findings suggest that the evaluation of the spatial memory of rats in a probe trial in the Morris water escape task requires a more detailed analysis.     

Dysfunctional prefrontal regional specialization and compensation in schizophrenia

OBJECTIVE: It has been suggested that in healthy persons higher-order cognitive processing engaged by incremental working memory load hierarchically employs more dorsal than ventral prefrontal resources in healthy individuals. Given that working memory performance is impaired in schizophrenia, especially at higher executive loads, the authors investigated how this prefrontal functional organization might be altered in disease, independent of performance deficits. METHOD: Using N-back working memory functional magnetic resonance imaging (fMRI) data, the authors studied 15 patients with schizophrenia and 26 healthy comparison subjects. Subgroups based on median performance accuracy at 2-back were analyzed; high performers included eight schizophrenia patients and 14 comparison subjects, and low performers included seven patients and 12 comparison subjects. RESULTS: High-performing but not low-performing comparison subjects responded to incremental working memory executive load with disproportionately greater dorsal but not ventral prefrontal cortex activation, which also predicted performance accuracy. In the high- and low-performing patient groups, incremental working memory load caused a disproportionate increase in ventral but not dorsal prefrontal cortex activation relative to the respective comparison group, which also correlated with accuracy. Functional connectivity between the ventral prefrontal cortex and posterior parietal cortex was relatively greater in patients, whereas comparison subjects had greater functional connectivity between the dorsal prefrontal cortex and posterior parietal cortex. CONCLUSIONS: The hierarchical organization of the prefrontal cortex may be compromised in schizophrenia, resulting in loss of functional specialization and integration at the dorsal prefrontal cortex and in compensatory activation from the ventral prefrontal cortex, which may ultimately affect working memory and executive cognition.     

No Effects of Slow Oscillatory Transcranial Direct Current Stimulation (tDCS) on Sleep-Dependent Memory Consolidation in Healthy Elderly Subjects

BackgroundStudies in young healthy volunteers provided evidence of a beneficial impact of an anodal time-varied transcranial direct current stimulation (tDCS) during early slow wave rich sleep on declarative memory but not on procedural memory.Objective/hypothesisThe present study investigated whether sleep-dependent memory consolidation can also be affected by slow oscillating tDCS in a population of elderly subjects.Methods26 subjects (69.1 years ± 7.7 years) received bi-frontal anodal stimulation (max. current density: 0.331 mA/cm²) during early NREM sleep in a double-blind placebo-controlled randomized crossover study. Stimulation effects on offline consolidation were tested by using a declarative and a procedural memory task. Furthermore, sleep stages were scored, EEG power was analyzed and spindle densities were assessed.ResultsIndependently from stimulation condition, performance in both memory tasks significantly decreased overnight. Stimulation revealed no significant effect on sleep-dependent memory consolidation. Verum tDCS was accompanied by significantly more time awake and significantly less NREM stage 3 sleep during five 1-min stimulation free intervals.ConclusionsThe results of the present study are in line with other studies showing that offline consolidation during sleep varies with age and is less pronounced in the elderly than in young or middle-aged subjects. Contrary to an almost identical positive study in young adults, slow oscillatory tDCS applied to the elderly failed to show a beneficial effect on memory consolidation in the present study.