Memory impairment in schizophrenia: its extent, affiliations and neuropsychological character

A deficit profile of executive, memory, and motor functions in schizophrenia

This study examined the neuropsychological deficits associated with schizophrenia and the interrelationships among multiple dissociable cognitive and motor functions. The tests were selected for their previously demonstrated sensitivity to circumscribed brain pathology and included four functional domains: executive functions, short-term memory and production, motor ability, and declarative memory. Each test composite was divided according to verbal versus nonverbal material or left- versus right-hand performance; this distinction permitted functions principally subserved by the left or right cerebral hemispheres to be tested separately. Data reduction was theoretically driven by the test selection and was achieved first by standardizing the scores of each test for age-related differences observed in the normal control group, and then by calculating test composite scores as an average of the age-corrected Z-scores of the tests comprising a functional composite. The schizophrenic group was impaired equivalently on all composites for both cerebral hemispheres; on average, the Z-scores of the patients were 1 standard deviation below those of the control group. The cognitive test composite scores were highly intercorrelated but showed only weak associations with motor ability. Multiple regression analyses suggested that symptom severity was a significant predictor of the Declarative Memory and Short-Term Memory/Production composite scores after accounting for disease duration, whereas disease duration uniquely contributed to the Executive Functions composite scores after controlling for symptom severity. Even though the schizophrenics as a group showed an equivalent level of deficit across all test composites, 1) the deficits were associated with different aspects of psychiatric symptomatology, 2) the motor deficit was independent of the cognitive deficits, and 3) each neuropsychological domain contributed independently to the deficit pattern. Thus, what appears to be a generalized functional deficit in schizophrenia may actually be, at least in part, combinations of multiple specific deficits.

Memory function in schizophrenia

Memory impairment in schizophrenia has been reported in several studies during the last decades. Issues related to the interpretation of such deficits are discussed. Research strongly suggests specific memory dysfunction in schizophrenia that may be neither drug induced nor secondary consequences of attentional disorders. Our own longitudinal data indicate that these deficits deviate from normal function in a relatively stable way. Although medial temporal lobe structures seems to be of special importance, memory function may be vulnerable to a variety of neurobiological abnormalities.

A neural network model of cortical information processing in schizophrenia. I: Interaction between biological and social factors in symptom formation

Exploiting the biological and psychological plausibility of parallel distributed processing, a neural network model of cortical processing is proposed in order to provide a framework for understanding pathological processes in schizophrenia. Major psychosocial and neurobiological factors are assigned to appropriate parameters in the model. Behaviour of the network is explored through simulation, in particular interaction between the temperature and memory loading parameters is studied. The emergent network behaviour provides a model for complex interaction between dopaminergic activity, cortical and hippocampal pathology, and psychosocial factors in the production of psychotic symptoms. This integrative model provides an account of a wide range of observations in schizophrenia. It also produces testable predictions concerning cognitive performance and the course of schizophrenia.

Effect of NE-100, a novel sigma receptor ligand, on phencyclidine-induced cognitive dysfunction

N,N-Dipropyl-2-[4-methoxy-3-(2-phenylethoxy)phenyl]-ethylamine monohydrochloride (NE-100) is a selective and potent sigma receptor ligand. We investigated the effects of NE-100 on phencyclidine (PCP)-induced cognitive dysfunction in rats in a water maze task. NE-100 significantly shortened the PCP-induced prolonged swimming latency as did 1-(cyclopropylmethyl)-4-[2'(4"-fluorophenyl)-2'-oxoethyl]- piperidine monohydrobromide (Dup 734), 4-[2'-(4"-cyanophenyl)-2'-oxoethyl]-1-(cyclopropyl-methyl)pi peridine (XJ 448), alpha-(4-fluorophenyl)-4-(5-fluoro-2-pyrimidinyl)-1-piperazine butanol (BMY 14802) and rimcazole, all of which are sigma receptor ligands and possibly antagonists. Ritanserin, a 5-HT2 receptor antagonist, also showed a tendency to shorten swimming latencies. Latencies of haloperidol-, cis-N-(1-benzyl-2-methyl-pyrrolidin-3-yl)-2-methoxy-5-chloro-4-met hyl- aminobenzamide (YM-09151-2)- and sulpiride-, dopamine D2 receptor antagonists, treated groups did not differ from that seen in the PCP-treated group. Thus, PCP-induced cognitive dysfunction may be improved by sigma receptor ligands.

Childhood autism: An appeal for an integrative and psychobiological approach

The difficulty that a person with autism has in establishing relationships, maintaining them (communicating and responding appropriately) is a common experience of those close to them., That impaired perceptual and cognitive processing can underlie this difficulty and the interactions of people with autism with the material environment has been established in the laboratory. The consequences at a psychological level of analysis may converge in the inadequacy of second-order representations of the world. An attenuation of such endogenous monitoring processes could also indirectly account for features of withdrawal and the stereotypies often observed. At another level of analysis there are delays in neurotransmission, in the CNS and a lack of flexibility of physiological response shown by evoked potential recordings. Tomographic studies of blood flow and metabolism illustrate a lack of correlation between information processing centres in the brain that may sometimes arise from diffuse gray matter atrophy. A "stop-go" form of modulation of central processing is mediated by anomalous ascending serotonergic and dopaminergic function (transmitters with inhibitory and switching functions). On these bases it is no wonder that representations are not formed and inappropriate and repetitive behaviors follow, although the link remains somewhat speculative. Both levels of analysis are useful for an explanation. As behavioral and pharmacotherapy, though helpful, are severely limited in their efficacy, more effort is required to synthesize the different levels of analysis into a psycho-biological approach, to remedial programs and new forms of therapy.

The Autobiographical Memory Interview (AMI) in organic and psychogenic amnesia

The Autobiographical Memory Interview (AMI) is a semi-structured interview, sampling a subject's recollections across three broad time-periods. In patients with organic amnesia or dementia, there is an impairment in recalling both autobiographical facts and incidents, and there is a temporal gradient such that early memories are relatively spared. Correlations with measures of anterograde memory are relatively low, and lesions affecting the frontal lobes, anterior temporal poles, the posterior-medial temporal lobes, or even projections from the occipital lobes, can impair retrieval of autobiographical memories. In schizophrenia, an impairment in retrieving autobiographical incidents, comparable with organic amnesia, has been reported in some patients. However a patient with delusional memories secondary to schizophrenia is cited, in whom AMI performance was normal. Finally, patients with psychogenic amnesia show a variable pattern of performance, but, in general, there is a disproportionate impairment of autobiographical memory, and often an anomalous temporal gradient, which can recover subsequently.

Psychosis-proneness and verbal memory in a college student population

Previous research has revealed numerous neuropsychological deficits in schizophrenics. Research on individuals with schizotypal personality features has also demonstrated similar neuropsychological deficits. However, the latter literature is limited in scope. This study examined verbal memory function in psychometrically identified (Chapman Scales) psychosis-prone college students (n = 409). Subjects were administered a standard verbal memory procedure (Logical Memory; Wechsler Memory Scale-Revised) as well as measures of verbal intelligence (Shipley Scale) and depression (Beck Depression Inventory). Results reveal no relationship between degree of schizotypic features and recall measures (immediate recall, delayed recall, and retention rate). Moreover, comparisons between low schizotypic subjects and those scoring at the extreme (greater than 2 standard deviations above the mean) also failed to reveal significant differences in recall. These results raise the possibility that memory deficits may be specific to schizophrenia and not the schizophrenia spectrum or that they are restricted to only those with the familial form of the disorder (i.e., those with family histories of schizophrenia).

An experimental phenomenological approach to delusional memory in schizophrenia and late paraphrenia

A preliminary model is described to account for the 'reality testing' of memories (after Johnson & Raye, 1981) in an attempt to explain delusional memory. Two routes are proposed: route one involves evaluation of the factual content of the memories against stored general knowledge. Route two relies on the evaluation of the perceptual and narrative characteristics of memories with the assumption that the stronger these characteristics, the more likely the memory is to be real. The integrity of these routes is examined in four patients with delusional memories, using standardized tests. The results suggest that in these cases, general knowledge is essentially intact while the perceptual characteristics of delusional memories are stronger than real memories which in turn, are stronger than fantasies. This could lead the evaluation system to accept delusional memories as true memories despite their implausibility. The roles of rehearsal and affect are probably important in this and require further study.

Regional cerebral blood flow (rCBF) in schizophrenia during verbal memory activation: a 99mTc-HMPAO single photon emission tomography (SPET) study

Regional cerebral blood flow (rCBF) was investigated in a group of medicated DSM-III-R schizophrenic patients and age, sex and handedness matched normal volunteers using a split-dose 99mTc-HMPAO Single Photon Emission Tomography (SPET) protocol. Measures were taken during the performance of a verbal memory task aimed at activating the left medial temporal lobe, a region repeatedly suggested to be structurally abnormal in schizophrenia. In normal subjects, the performance of the task was associated with significant rCBF increases in the left medial temporal, left inferior frontal and anterior cingulate cortices, and right cerebellum. Despite their significantly poorer performance on the memory task, the degree of medial temporal activation measured in the schizophrenic patients was not significantly different from that found in the control group. This finding suggests that memory deficits in schizophrenia do not necessarily imply failure to activate the left medial temporal lobe as assessed by 99mTc-HMPAO SPET.

Memory impairment in schizophrenia--a comparison with that observed in the Alcoholic Korsakoff syndrome

Until very recently, memory impairment was not considered to be a central feature of schizophrenia, except in chronic, deteriorated patients. In this study of a heterogeneous sample of 40 patients with DSM-III-R schizophrenia, episodic memory impairment was found to be prevalent, and in some cases, severe. The degree of memory impairment was not attributable to neuroleptic or anticholinergic medication, or to poor motivation or cooperation. These results, therefore, replicate those reported by McKenna et al. (1990) and Tamlyn et al. (1992), who suggested that the pattern of memory impairment in schizophrenia may conform in important respects to that of the classic amnesic syndrome. However, in a direct comparison of the schizophrenic sample with 18 patients suffering from the Alcoholic Korsakoff Syndrome (AKS), both quantitative and qualitative differences were found to exist between the two groups of patients. In particular, the level of long-term episodic memory impairment was found in the AKS sample to be far greater than that in the schizophrenic group. An interesting possible double-dissociation emerged between the two groups; although demonstrating superior episodic memory functioning, the schizophrenic sample were found to perform significantly more poorly than the AKS sample on a test of semantic memory.

Semantic memory is both impaired and anomalous in schizophrenia

The integrity of semantic memory in schizophrenia was examined in a reaction time task requiring subjects to verify words as members or non-members of a conceptual category, where the words differed in their degree of semantic relationship to the category. Compared to matched normal controls, 28 schizophrenic patients were impaired on the task, showing slower responses in all conditions. In addition, their performance was anomalous in that they took longest to respond to items that were outside the category but semantically related to it, in contrast to the controls who took the longest to respond to ambiguous words at the borderline of the category. The pattern of 'yes' and 'no' responses of the patients was anomalous in a similar way. In both speed and accuracy of responding, the findings indicate that there is an outward shift of semantic category boundaries in schizophrenia.

Memory in schizophrenia: what is impaired and what is preserved?

This study assesses the pattern of long-term memory performance in a sample of 12 schizophrenic patients who were selected on the basis of showing a memory deficit in the absence of gross overall intellectual impairment. When compared with 12 control subjects matched for age, sex and estimated premorbid IQ, presence of an episodic memory deficit was confirmed for both prose recall and forced-choice word and face recognition. Semantic memory was assessed using the sentence verification task developed by Collins and Quillian, an unpaced category judgement task, and the Mill Hill Vocabulary Scale. The schizophrenic patients were slower on sentence verification and they made significantly more errors in all three tasks. Procedural tasks included pursuit rotor performance, speed of repeatedly assembling a jigsaw puzzle and rate of improvement in reading transformed script. Here, while the schizophrenic patients showed poor overall performance on the pursuit rotor and jigsaw learning, their rate of learning on all three procedural tasks was comparable with that of the controls. When examined on two implicit memory tasks involving biasing of spelling of homophones and word stem completion, the patients showed a normal degree of priming in both. Implications for the nature of the memory deficit in schizophrenia are discussed.

A topographical study of senile plaques and neurofibrillary tangles in the hippocampi of patients with Alzheimer's disease and cognitively impaired patients with schizophrenia

Neuropsychological testing of elderly schizophrenic patients reveals that a significant portion of this population exhibit varying degrees of cognitive impairment. Since Alzheimer's disease is the most common cause of dementia in geriatric patients, we investigated whether the cognitive decline observed in schizophrenia is the result of degenerative changes analogous to those characteristic of Alzheimer's disease. For this purpose, the number and distribution of senile plaques and neurofibrillary tangles were mapped in the hippocampi of 10 cognitively impaired schizophrenic patients, 10 patients with Alzheimer's disease, and 10 patients with dementia not attributed to either schizophrenia or Alzheimer's disease. In Alzheimer's disease, degenerative changes invariably predominated in the CA1 subfield, subiculum, and proisocortex. By contrast, findings characteristic of Alzheimer's disease were virtually never observed in the hippocampi of schizophrenic and other cognitively impaired patients. In some patients with Alzheimer's disease, the presence of senile plaques in the molecular layer of the dentate gyrus suggested the existence of an underlying entorhinal cortex lesion. Similar dentate gyrus pathology was never found in any of the other patients. The authors conclude that cognitive impairment in schizophrenia is not the result of degenerative changes analogous to those found in Alzheimer's disease.

Severe cognitive impairment in elderly schizophrenic patients: a clinicopathological study

The severe cognitive impairment that affects many of the elderly schizophrenic patients could represent the outcome of schizophrenia in old age for the very severe and chronically ill patients or may be the result of lengthy institutionalization and somatic treatment. Alternatively, it could be due to the presence of concurrent dementing disorders, such as Alzheimer's disease (AD) or multi-infarct dementia. Using an identical neuropathological protocol, brain specimens from schizophrenic patients who showed evidence of severe cognitive impairment were compared with 12 age-matched control cases and the same number of age-matched cases of neuropathologically confirmed patients with AD. Despite their relatively advanced age (mean age 77.1 years +/- 2.8), none of the schizophrenia cases showed sufficient degree of senile plaques and neurofibrillary tangle formations to confirm a diagnosis of AD. Other neurodegenerative disorders associated with dementia were also not identified. These studies suggest that alternative explanations need to be sought for the severe cognitive impairment commonly encountered in elderly schizophrenic patients.

Visual imagery and visual semantics in the cerebral hemispheres in schizophrenia

Divided visual field tasks were given to normal subjects, and patients with schizophrenia and affective disorder, to investigate hemisphere differences in the visual processing of standardised pictorial stimuli. There were two conditions: in the first, subjects were asked to decide whether a common entity represented by a picture was living or non-living, a task involving a categorical judgement based on semantic information; a left hemisphere task. In the second condition, subjects judged whether these depictions represented entities which were bigger or smaller than a cat; a right hemisphere task requiring visual imagery to compare spatial dimensions. It was found that the patient groups, while showing slower reaction time (RT) overall, both displayed a right hemisphere (RH) advantage on the imagery task. Furthermore, the schizophrenics' RHs showed the normal relationship between closeness of size comparison and RT, additional evidence that the visual imagery mechanism is intact. However, these patients failed to show the expected left hemisphere advantage on the visual-semantic task. There was a suggestion that performance on the semantic task was related to the experience of vivid imagery in normals and visual hallucinations in the schizophrenics. The possible contribution of hemispheric imbalance in the production of visual hallucinations from a disordered semantic system is discussed.

Phenomenology. Its place in schizophrenia research

In some quarters schizophrenia has gained the reputation of a graveyard of research. Few findings stand the test of time, most of the pieces of this particular jigsaw seem to be missing, and it is not easy to make sense of those that are available. Even ‘hard’ scientific findings fail to be replicated, an example being the status of D2receptors in drug-naive schizophrenics (Wonget al, 1986; Fardeet al, 1987).