Are cholinergic enhancers beneficial for memory in schizophrenia? An event-related potentials (ERPs) study of rivastigmine add-on therapy in a crossover trial

The Neuro Patterns Prior to Error Responses in Long-Lasting Working Memory Task: An Event-Related Potential Study

Few studies exist regarding the mechanism prior to response by which cognitive impairment may induce error in a single long-lasting task. The present study intends to clarify the changes in cognition at the electrophysiological level. Changes in amplitude and latency of N1, P2, N2, and P3 components of event-related potentials (ERPs) were analyzed for error and correct trials during normal and fatigue. Twenty-nine participants had to perform a 2-back working memory (WM) task for 100 min. The first 10 min and the last 10 min of the task were used as the normal state and fatigue state of the participant, respectively. EEG data were obtained from the first 10-min period and the final 10-min period. The results revealed smaller P3 and P2 amplitudes and longer P2 and N2 latency in the final 10-min which was after a long-lasting time task. Moreover, smaller P3 and P2 amplitudes but larger N2 amplitudes were observed in error trials for both states. Our results indicated that: (1) long lasting involvement in a cognitive task had a detrimental effect on attention, memory updating and cognitive control; and (2) impaired attention, impairments in memory updating and cognitive control were related to task errors. Our results imply that several impaired cognitive processes were consistently associated with the error and the altered ERP represents the neural patterns prior to error response in mental fatigue state.

Cognition Impairment Prior to Errors of Working Memory Based on Event-Related Potential

Cognitive impairment contributes to errors in different tasks. Poor attention and poor cognitive control are the two neural mechanisms for performance errors. A few studies have been conducted on the error mechanism of working memory. It is unclear whether the changes in memory updating, attention, and cognitive control can cause errors and, if so, whether they can be probed at the same time in one single task. Therefore, this study analyzed event-related potentials in a two-back working memory task. A total of 40 male participants finished the task. The differences between the error and the correct trials in amplitudes and latencies of N1, P2, N2, and P3 were analyzed. The P2 and P3 amplitudes decreased significantly in the error trials, while the N2 amplitude increased. The results showed that impaired attention, poor memory updating, and impaired cognitive control were consistently associated with the error in working memory. Furthermore, the results suggested that monitoring the neurophysiological characteristics associated with attention and cognitive control was important for studying the error mechanism and error prediction. The results also suggested that the P3 and N2 amplitudes could be used as indexes for error foreshadowing.

Electrophysiological repetition effects in persons with mild cognitive impairment depend upon working memory demand

Forms of implicit memory, including repetition effects, are preserved relative to explicit memory in clinical Alzheimer's disease. Consequently, cognitive interventions for persons with Alzheimer's disease have been developed that leverage this fact. However, despite the clinical robustness of behavioral repetition effects, altered neural mechanisms of repetition effects are studied as biomarkers of both clinical Alzheimer's disease and pre-morbid Alzheimer's changes in the brain. We hypothesized that the clinical preservation of behavioral repetition effects results in part from concurrent operation of discrete memory systems. We developed two experiments that included probes of emotional repetition effects differing in that one included an embedded working memory task. We found that neural repetition effects manifested in patients with amnestic mild cognitive impairment, the earliest form of clinical Alzheimer's disease, during emotional working memory tasks, but they did not manifest during the task that lacked the embedded working memory manipulation. Specifically, the working memory task evoked neural repetition effects in the P600 time-window, but the same neural mechanism was only minimally implicated in the task without a working memory component. We also found that group differences in behavioral repetition effects were smaller in the experiment with a working memory task. We suggest that cross-domain cognitive challenge can expose "defunct" neural capabilities of individuals with amnestic mild cognitive impairment.

Low Arousal Positive Emotional Stimuli Attenuate Aberrant Working Memory Processing in Persons with Mild Cognitive Impairment

Emotional enhancement effects on memory have been reported to mitigate the pathophysiology of Alzheimer's disease (AD). However, relative to their manifestation in persons without pathologic aging, these effects may be reduced in magnitude or even deleterious, especially in tasks that more closely model ecologic memory performance. Based upon a synthesis of such reports, we hypothesized that in persons with AD low arousal positive stimuli would evoke relatively intact emotional enhancement effects, but that high arousal negative stimuli would evoke disordered emotional enhancement effects. To assess this, participants with and without mild cognitive impairment (MCI) presumed to be due to AD performed an emotionally-valenced short-term memory task while encephalography was recorded. Results indicated that for persons with MCI, high arousal negative stimuli led to working memory processing patterns previously associated with MCI presumed due to AD and dementia of the Alzheimer-type. In contrast, low arousal positive stimuli evoked a processing pattern similar to MCI participants' unaffected spouses. Our current findings suggest that low arousal positive stimuli attenuate working memory deficits of MCI due to AD.

Cognitive effects with rivastigmine augmentation of risperidone: A 12-month, randomized, double-blind, placebo-controlled study in schizophrenia

OBJECTIVE

An important challenge in schizophrenia therapeutics is to develop an efficacious treatment for cognitive impairment. Acetylcholinesterase inhibitors, such as rivastigmine, have been studied for improving cognitive performance in these patients.

MATERIALS AND METHODS

Rivastigmine (uptitrated to 6 mg/day) was given as an add-on therapy to risperidone-treated stable schizophrenia patients in a randomized, double-blind, placebo-controlled design. Of 67 patients who met eligibility criteria, 55 were recruited into the study. Twenty-eight were assigned to rivastigmine and 27 to placebo. These patients completed tests of attention, executive functioning, verbal skills, verbal and visuospatial working memory, and psychomotor speed on five occasions: at baseline, and at the end of the 1^st, 3^rd, 6^th, and 12^th months.

RESULTS

The groups were similar in terms of sociodemographic profile and baseline clinical characteristics (Positive and Negative Syndrome Scale and Clinical Global Impression-Severity). Contrary to expectations, rivastigmine patients showed poorer outcomes on several cognitive measures. Rivastigmine patients experienced also more psychological as well as neurological side effects. Core psychopathology ratings, however, did not differ between rivastigmine and placebo groups.

CONCLUSIONS

Our study does not support the long-term use of rivastigmine as an augmentation agent in schizophrenia. Rivastigmine may be associated with higher incidence of psychological and neurological side effects in patients with schizophrenia.

Acetylcholinesterase inhibitors for schizophrenia

BACKGROUND

Antipsychotic medication remains the mainstay of treatment for schizophrenia and has been in use for a long time. As evidenced by ongoing research and partial effectiveness of the antipsychotics on cognitive and negative symptoms, the search is on for drugs that may improve these domains of functioning for someone suffering from schizophrenia. Acetylcholinesterase inhibitors have long been in use for treating cognitive symptoms of dementia.

OBJECTIVES

The aim of the review was to evaluate the clinical effects, safety and cost effectiveness of acetylcholinesterase inhibitors for treating people with schizophrenia

SEARCH METHODS

We searched the Cochrane Schizophrenia Group's Register (February 2009), and inspected the references of all identified studies for further trials.

SELECTION CRITERIA

We included all clinical randomised trials comparing acetylcholinesterase inhibitors with antipsychotics or placebo either alone, or in combination, for schizophrenia and schizophrenia-like psychoses.

DATA COLLECTION AND ANALYSIS

We extracted data independently. For dichotomous data, we calculated risk ratios (RR) and their 95% confidence intervals (CI) on an intention-to-treat (ITT) basis based on a random-effects model. For continuous data, we calculated mean differences (MD), again based on a random-effects model.

MAIN RESULTS

The acetylcholinesterase inhibitor plus antipsychotic showed benefit over antipsychotic and placebo in the following outcomes.1. Mental state - PANSS negative symptoms average end point score (2 RCTs, n = 31, MD -1.69 95% CI -2.80 to -0.57), PANSS General Psychopathology average end point score (2 RCTs, n = 31, MD -3.86 95% CI -5.40 to -2.32), and improvement in depressive symptoms showed at least by one short-term study as measured by CDSS scale (data skewed).2. Cognitive domains - attention, (1 RCT, n = 73, MD 1.20 95% CI 0.14 to 2.26), visual memory (2 RCTs, n = 48 , MD 1.90 95% CI 0.52 to 3.28), verbal memory and language (3 RCTs, n = 42, MD 3.46 95% CI 0.67 to 6.26) and executive functioning (1 RCT, n = 24, MD 17.10 95% CI 0.70 to 33.50).3. Tolerability - EPSE: AIMS, (1 RCT, n = 35, MD 1.50 95% CI 1.04 to 1.96).No difference was noted between the two arms in other outcomes. The overall rate of participants leaving studies early was low (13.6 %) and showed no clear difference between the two groups.

AUTHORS' CONCLUSIONS

The results seem to favour the use of acetylcholinesterase inhibitors in combination with antipsychotics on a few domains of mental state and cognition, but because of the various limitations in the studies as mentioned in the main text, the evidence is weak. This review highlights the need for large, independent, well designed, conducted and reported pragmatic randomised studies.

Cholinesterase inhibitors as adjunctive therapy in patients with schizophrenia and schizoaffective disorder: a review and meta-analysis of the literature

BACKGROUND

Cognitive deficits have been described in patients with schizophrenia from the first descriptions of dementia praecox to current concepts of cognitive dysmetria. Nevertheless, little is known about how to deal with them. In Alzheimer disease, cholinergic deficit is found and cholinesterase inhibitors have been used to delay the progression of memory and cognitive dysfunction. Several lines of evidence suggest that the cholinergic system may be disrupted in schizophrenia.

OBJECTIVE

To evaluate cognitive and clinical effects of adjunctive cholinesterase inhibitors in patients with schizophrenia and schizoaffective disorder.

METHOD

We conducted a literature search on PubMed and EMBASE (up to December 2008) for articles that investigated adjunctive cholinesterase inhibitors in patients with schizophrenia. The terms 'schizophrenia', 'acetylcholinesterase inhibitors', 'rivastigmine', 'donepezil', 'galantamine' and 'cognitive deficit' were searched with restriction for English language and without a year limit. All articles that presented original data from randomized, double-blind, placebo-controlled trials with donepezil, rivastigmine or galantamine in patients with schizophrenia or schizoaffective disorder were included in the meta-analysis. Studies were excluded for the following reasons: (i) case study/letter/correspondence/review; (ii) animal study; (iii) molecular/genetic investigation; and (iv) inclusion of patients with schizophrenia and co-morbid dementia. Few appropriate data for meta-analysis were found because of the large heterogeneity of the assessment instruments used. Nevertheless, effects of cholinesterase inhibitors in some cognitive domains (executive function, memory and language), psychopathology (using the Positive and Negative Syndrome Scale) and extrapyramidal symptoms could be analysed.

RESULTS

Six open-label and 24 double-blind studies were found. In five open-label studies there was an improvement in memory, attention and executive functions. Thirteen double-blind studies (four with rivastigmine, six with donepezil and three with galantamine) contributed to the meta-analysis. Significant improvement was found in this analysis for memory and the Trail Making test part A.

CONCLUSIONS

The reviewed studies suggest that specific cognitive deficits (memory, and the motor speed and attention part of executive function) of patients with schizophrenia and schizoaffective disorder are responsive to rivastigmine, donepezil and galantamine as adjunctive therapy. Confirmatory studies are needed to determine the clinical utility of this treatment strategy.

Pharmacological strategies for enhancing cognition in schizophrenia

Researchers have long recognized that individuals with schizophrenia experience challenges in a wide range of cognitive domains, and research on cognitive impairment in schizophrenia is not a recent phenomena. However, the past 10-20 years have seen an increasing recognition of the central importance of cognition to understanding function and outcome in this illness (Green et al. in Schizophr Bull 26:119-136, 2000), an awareness that has shifted the emphasis of at least some work on schizophrenia. More specifically, there has been a rapidly growing body of work on methods of enhancing cognition in schizophrenia, as a means to potentially facilitate improved outcome and quality of life for individuals with this debilitating illness. The current chapter reviews the results of a range of studies examining adjunctive pharmacological treatments to enhance cognition in schizophrenia using a range of designs, including single-dose studies, open-label repeated dosing studies, and double-blind parallel group and crossover designs with repeated dosing. Although many of the single-dose and open-label studies have suggested positive cognitive effects from a range of agents, few of the larger-scale double-blind studies have generated positive results. The current state of results may reflect the need to identify alternative molecular mechanisms for enhancing cognition in schizophrenia or the need to reconceptualize the ways in which pharmacological agents may improve cognition in this illness, with a concomitant change in the traditional clinical trial study design used in prior studies of cognitive enhancement in schizophrenia.

REM sleep EEG spectral analysis in patients with first-episode schizophrenia

The pathophysiology of schizophrenia includes abnormalities in subcortical-cortical transfer of information that can be studied using REM sleep EEG spectral analysis, a measure that reflects spontaneous and endogenous thalamocortical activity. We recorded 10 patients with first-episode schizophrenia and 30 healthy controls for two consecutive nights in a sleep laboratory, using a 10-electrode EEG montage. Sixty seconds of REM sleep EEG without artifact were analyzed using FFT spectral analysis. Absolute and relative spectral amplitudes of five frequency bands (delta, theta, alpha, beta1 and beta2) were extracted and compared between the two groups. Frequency bands with significant differences were correlated with BPRS positive and negative symptoms scores. Patients with schizophrenia showed lower relative alpha and higher relative beta2 spectral amplitudes compared to healthy controls over the averaged total scalp. Analysis using cortical regions showed lower relative alpha over frontal, central and temporal regions and higher relative beta2 over the occipital region. Absolute spectral amplitude was not different between groups for any given EEG band. However, absolute alpha activity correlated negatively with BPRS positive symptoms scores and correlated positively with negative symptoms scores. Since similar results have been reported following EEG spectral analysis during the waking state, we conclude that abnormalities of subcortical-cortical transfer of information in schizophrenia could be generated by mechanisms common to REM sleep and waking.

Add-on therapy with acetylcholinesterase inhibitors for memory dysfunction in schizophrenia: a systematic quantitative review, part 2

RATIONALE

Memory impairment is frequent in schizophrenia and remains difficult to treat. Improved memory function is associated with a better functional outcome. Some clinical trials have used add-on therapy with acetylcholinesterase inhibitors (AChEIs) to test the cognitive enhancement effect of this kind of medication, which is usually prescribed for other indications than schizophrenia.

OBJECTIVE

To perform a systematic review with meta-analysis.

METHODS

Studies were identified using electronic search engines, hand searches, cross-referencing of studies, and contacts with investigators. Eligible studies were those comparing cognitive performance in patients with schizophrenia before and after AChEI treatment, randomized controlled trials, and crossover and open trials of AChEI in people with schizophrenia, with trial duration of more than 2 weeks. Validated neurocognitive measures and computerized batteries were used to corroborate the effect.

RESULTS

Our findings reveal a small to medium improvement in short-term memory and long-term memory (LTM) performance when patients are compared with the baseline performance, but when compared with controls (placebo treatment) at the end of the trial, they performed worse on both short-term memory and on LTM. However, the effects were nonsignificant. The LTM magnitude estimate demonstrating a treatment effect between the start and end points of the trial consisted of 8 studies (before treatment, n = 209; overall attrition rate, 8%). The effect estimate was significant and close to heterogeneous. Duration of trial increases the effect estimate slightly. The analysis was broken down by AChEI: 5 studies of donepezil (effect size [ES], -0.352), 2 studies of rivastigmine (ES, 0.383), and 1 study of galantamine. There were 6 studies of AChEI added to second-generation antipsychotics (ES, 0.424) and 2 studies of first-generation antipsychotics (ES, 0.207).

CONCLUSIONS

Notwithstanding an extensive investigation, eligible data for the meta-analysis were nominal. To date, and overall, our quantitative systematic review provides no clear evidence on whether AChEIs should be prescribed for memory enhancement in patients with schizophrenia.