Isobel Harrison

The Relationship Between IQ, Memory, Executive Function, and Processing Speed in Recent-Onset Psychosis: 1-Year Stability and Clinical Outcome

Studies commonly report poor performance in psychotic patients compared with controls on tasks testing a range of cognitive functions, but, because current IQ is often not matched between these groups, it is difficult to determine whether this represents a generalized deficit or specific abnormalities. Fifty-three first-episode psychosis patients and 53 healthy controls, one-to-one matched for sex, age, and full-scale current IQ, were compared on Wechsler Adult Intelligence Scale (WAIS) subtests representing indices of perceptual organization, verbal comprehension, processing speed, and working memory as well as other tests of executive function and episodic memory. The groups showed an equivalent pattern of performance on all WAIS subtests except digit symbol processing speed, on which the patients were significantly worse. Patients were also worse on measures where performance correlated with digit symbol score, namely working and verbal memory tasks. Standardized residual scores for each subtest were calculated for each patient using the difference between their actual subtest score and a predicted subtest score based on their full-scale IQ and the performance of controls. Scaled scores and residual scores were examined for relationships with clinical measures. Digit symbol-scaled score was significantly correlated with concurrent negative syndrome score at baseline, and digit symbol residual score significantly predicted residual negative symptoms at 1-year follow-up. In summary, our comparison of patients and controls precisely matched for IQ revealed that processing speed was attenuated in recent-onset schizophrenia, contributed significantly to working and episodic memory deficits, and was a prognostic factor for poor outcome at 1 year.

Naturalistic follow-up of co-morbid substance use in schizophrenia: the West London first-episode study

Background The impact of co-morbid substance use in first-episode schizophrenia has not been fully explored. Method This naturalistic follow-up of a cohort of 152 people with first-episode schizophrenia examined substance use and clinical outcome in terms of symptoms and social and neuropsychological function. Results Data were collected on 85 (56%) of the patient cohort after a median period of 14 months. Over the follow-up period, the proportion of smokers rose from 60% at baseline to 64%. While 30% reported lifetime problem drinking of alcohol at baseline, only 15% had problem drinking at follow-up. Furthermore, while at baseline 63% reported lifetime cannabis use and 32% were currently using the drug, by the follow-up assessment the latter figure had fallen to 18.5%. At follow-up, persistent substance users had significantly more severe positive and depressive symptoms and greater overall severity of illness. A report of no lifetime substance use at baseline was associated with greater improvement in spatial working memory (SWM) at follow-up. Conclusions Past substance use may impede recovery of SWM performance in people with schizophrenia in the year or so following first presentation to psychiatric services. The prevalence of substance use other than tobacco tends to diminish over this period, in the absence of specific interventions. Persistent substance use in first-episode schizophrenia is associated with more severe positive and depressive symptoms but not negative symptoms, and should be a target for specific treatment intervention.

The Effect of Cannabis Use and Cognitive Reserve on Age at Onset and Psychosis Outcomes in First-Episode Schizophrenia

Objective: Cannabis use is associated with a younger age at onset of psychosis, an indicator of poor prognosis, but better cognitive function, a positive prognostic indicator. We aimed to clarify the role of age at onset and cognition on outcomes in cannabis users with first-episode schizophrenia as well as the effect of cannabis dose and cessation of use. Methods: Ninety-nine patients without alcohol or substance abuse other than cannabis were divided into lifetime users and never-users of cannabis and compared on measures of premorbid function, cognition, and clinical outcome. Results: Cannabis users demonstrated better cognition at psychosis onset, which was explained by higher premorbid IQ. They also showed better social function and neither measure changed over the subsequent 15 months. Cannabis users had an earlier age at onset of psychosis, and there was a strong linear relationship between age at first cannabis use and age at onset of both prodromal and psychotic symptoms. Cannabis use spontaneously declined over time with 3-quarters of users giving up altogether. Later age at first cannabis use predicted earlier cessation of use and this in turn was linked to fewer positive psychotic symptoms and days in hospital during the first 2 years. Conclusions: Cannabis use brings forward the onset of psychosis in people who otherwise have good prognostic features indicating that an early age at onset can be due to a toxic action of cannabis rather than an intrinsically more severe illness. Many patients abstain over time, but in those who persist, psychosis is more difficult to treat.

Dissociation of long-term verbal memory and fronto-executive impairment in first-episode psychosis

Background Verbal memory is frequently and severely affected in schizophrenia and has been implicated as a mediator of poor clinical outcome. Whereas encoding deficits are well demonstrated, it is unclear whether retention is impaired. This distinction is important because accelerated forgetting implies impaired consolidation attributable to medial temporal lobe (MTL) dysfunction whereas impaired encoding and retrieval implicates involvement of prefrontal cortex. Method We assessed a group of healthy volunteers (n=97) and pre-morbid IQ- and sex-matched first-episode psychosis patients (n=97), the majority of whom developed schizophrenia. We compared performance of verbal learning and recall with measures of visuospatial working memory, planning and attentional set-shifting, and also current IQ. Results All measures of performance, including verbal memory retention, a memory savings score that accounted for learning impairments, were significantly impaired in the schizophrenia group. The difference between groups for delayed recall remained even after the influence of learning and recall was accounted for. Factor analyses showed that, in patients, all variables except verbal memory retention loaded on a single factor, whereas in controls verbal memory and fronto-executive measures were separable. Conclusions The results suggest that IQ, executive function and verbal learning deficits in schizophrenia may reflect a common abnormality of information processing in prefrontal cortex rather than specific impairments in different cognitive domains. Verbal memory retention impairments, however, may have a different aetiology.

Gaze strategies during planning in first-episode psychosis.

Eye movements were measured during the performance of a computerized Tower of London task to specify the source of planning abnormalities in patients with 1st-episode schizophrenia or schizoaffective disorder. Subjects viewed 2 arrays of colored balls in the upper and lower parts of the screen. They were asked to plan the shortest sequence of moves required to rearrange the balls in the lower screen to match the upper arrangement. Compared with healthy controls, patients made more planning errors, and decision times were longer. However, the patients showed the same gaze biases as controls prior to making a response, indicating that they understood the requirements of the task, approached the task in a strategic manner by identifying the nature of the problem, and used appropriate fixation strategies to plan and elaborate solutions. The patients showed increased duration of long-gaze periods toward both parts of the screen. This suggests that the patients had difficulty in encoding the essential features of the stimulus array. This finding is compatible with slowing of working memory consolidation.